Automatic or manual HVAC air duct airflow zone control FAQs:

Questions & answers about diagnosing & repairing both manual and automatic heating and air conditioning ductwork zone dampers & airflow controls used to control airflow through heating or cooling ductwork.

These zone damper questions and replies help diagnose & repair problems with both automatic duct dampers and manually operated duct air flow controls as well as the use of individual airflow booster fans in the ductwork.

Ductwork Zone Dampers & Airflow Control FAQs

These questions and answers about zone dampers or ductwork dampers and heating or cooling air flow control were posted originally at ZONE DAMPER CONTROLS - be sure to review that article.

On 2020-12-17 by (mod) - when is a damper used on return air duts? Is it ever correct ?

Bruce

Thank you for an interesting question about reasons to use a motorized Zone damper on the return duct in an HP AC system.

Some HVAC technicians argue for using a damper in the return of warm air to an air handler unit to "keep the input energy to the cooling system low".

In my OPINION, if I see such a duct installed I suspect that the duct system or air handler are not the best design for the building. For example if an air handler or A/C or heating system is over-sized for the building, then in cooling mode it may cool the building too fast, resulting in inadequate dehumidification in warm weather.

Someone might then "slow down" the cooling system with a return damper.

Actually for most HVAC systems I can't think of a good reason and I can think of a lot of bad reasons for having Any obstruction in the return air of an air handling system. Most common problem and unbalanced heating and air conditioning systems is inadequate return air.

It's such a common problem that frequent topic we discuss with homeowners and mechanical systems installers is how to increase return air and where to add return air inlets and ducts in buildings. So it seems unlikely to me that you would want to place an obstruction in the return air.

If you can contact or give me the contact information for your Source I would be glad to pursue the question because perhaps they know something that we don't.

See details

at RETURN AIR, INCREASE

In general if there is an air flow problem such as imbalance between building areas, that is indeed an inefficient way to operate an heating or cooling system. But IMO the proper "fix" is to usually install balancing dampers in the supply ducts and at supply registers, not in the return system.

Where a control damper does make sense in the "return" system is when there is an outside air supply to the HVAC system. In that case we may indeed need to make seasonal adjustments to the supply of outdoor air. In humid weather you may want to close down that outside air supply.

We might also find additional duct damper controls when there are both high and low RETURN air registers in a room or building area.

In heating mode we prefer to draw cool air into the return duct system from low in the room near the floor where the air is coolest.

In cooling mode we prefer to draw return air into the return duct system from high in the room where the air is wamest.

So if a room had both types of return registers we might adjust them depending on the season: heating vs cooling. But IMO those are simplest and usually should be placed right on the air registers, not in a less-accessible return duct.

Finally, we might also find control dampers on return air ducts in buildings that use separate air handlers for cooling vs. heating. In that design we might need to swap the return air between two destinations: sending return air into the A/C air handler during the cooling season and the heating furnace air handler during the heating season.

Bottom line:

Watch out: do not block or obstruct return air to the air handler in any heating or cooling system or you may simply be increasing the system operating cost and lowering its efficiency as well as reducing the comfort of building occupants.

See details at UNDERSIZED RETURN DUCTS

Did your webinar speaker discuss making static pressure measurements in the duct system to determine if it is properly balanced and sized?

On 2020-12-17 by Bruce - webinar recommends a motorized damper on the return duct

During a recent webinar I took, they mentioned when, in a zoned air system, that a motorized damper on the return was suggested. If I remember correctly, it had something to do with when you have fossil fuel equipment. Can you explain?

On 2020-11-26 - by (mod) -

Noor

In the Recommended Articles or in our ARTICLE INDEX see the live links for

ZONE DAMPER CONTROLS - home

ZONE DAMPER ACTUATOR MOTOR REPLACEMENT

On 2020-11-26 by Noorsharmash

we are looking for automatic air dampaners motorized

On 2020-09-21 by Becky

Shown above: EWC Controls 16 CLBD Ultrla-Zone Zone damper / bypass damper control showing position of the damper between "open" and "closed".

Excerpting from product literature from EWC:

The model CLBD Bypass Damper is an easy and economical way to manage system static pressure, in a zoned HVAC system. Damper adjustment is easily achieved by increasing or decreasing the force applied to the bypass damper blade, until the desired static pressure is achieved. ....

Due to the constant load applied to the damper blade and the unique magnetic latch, the CLBD Bypass Damper can be installed in any position on your bypass duct-work, to manage the HVAC system’s static pressure during zoned operations.

The CLBD minimizes bypass volume, while still preventing the HVAC system static pressure from rising above the selected Static Pressure set-point.

The CLBD is a basic, cost effective Bypass Solution for Constant Speed or Variable Speed “zoned” HVAC systems.

On 2020-07-08 - by (mod) -

Brian

If you're sure the vents and dampers are fully open but the air flow is weak, there are some diagnostic suggestions to follow at

AIR FLOW IMPROVEMENT, HVAC https://inspectapedia.com/aircond/Duct_Air_Flow.php

On 2020-07-08 by Brian

My dampers are all open but at my vents there is burly any air flow coming out of my vents what could be problem? It seem like my unit is running on 50% usually you can hear it coming out the vents but now I can burly tell my unit is on. My line going to my unit just froze up as well any help would be appreciated on what case of this

On 2020-02-26 - by (mod) -

Jim

Thank you for the interesting sticking zone damper question.

From the work that you've already done, it appears to me that you're pretty Savvy about diagnosing a poor Zone damper operation.

I have to suspect that there's a bent shaft or a damaged bearing surface in the problem damper or perhaps a blade that's askew and is catching inside of the duct.

If close inspection shows scrape marks for example we might know that it's misaligned.

I would be inclined to replace the damper itself.

To address your specific question more directly, I haven't found failure rate data for Zone damper bearings and I suspect that there hasn't been an organized study. That's why my first thoughts were focused on careful Visual and mechanical inspection to see what evidence we could find.

I'll take a look to see if I can find any failure study reports and we'll post those here.

Meanwhile I'd be interested in the additional detailed observations that you can make and photos that you can post about your particular damper failure.

On 2020-02-26 by JimT

One of the zones in my home is sticking, usually open, but sometimes closed. That zone uses a Honeywell ARD10 damper. I've pulled the actuator from the damper, and it worked fine on the bench. There is quite a bit of friction when I try to operate the damper by hand. I switched the actuator with another damper, and it operates that damper fine, but neither actuator will reliably open and close the first damper.
I'm familiar with the actuators having problems with return springs breaking or the nylon gear getting stripped, but neither issue is at play here. The damper just appears to have too much friction for the actuator to reliably operate it. How common is it for the ARD10 damper bearings to wear out or get gummed up after 12 years of use?

On 2020-02-16 - by (mod) -

If the noise continues when you remove all power from the zone damper then we can suspect there is a mechanical issue - loose components, thermal expansion/contraction, air movement.

If the noise stops then there's a problem in the controller or zone damper motor or actuator or its wiring.

On 2020-02-16 by Dan

My damper actuators make a non-stop, high speed clicking noise even when the zone is turned off.

On 2020-02-02 by (mod) - find those "almost -hidden" ductwork zone dampers

Thanks for the sharper photo, Jim,

Yes I agree with you that the white object in the center of the photo is probably a ceiling pot light (fed by a white electrical wire),

and that the air duct does carry a motorized duct damper activated by a signal along that gray wire.

It's possible that the damper is stuck closed due to a motor or control failure.

Unfortunately it doesn't look easy to reach (not a great installation in that regard);

If you can get to it AND if you already know that you're not getting conditioned air out of the supply register fed by this air duct, AND you are getting good airflow from other supply registers, THEN I'd figure the damper is closed (or there is another obstruction somewhere in that duct line)
...
Anyway all those ifs and ands and thens, with those arm-waving reclamas,

if you can get to the duct damper, remove the operating motor, note the position of the duct-turning axle or lever, and then try rotating it 90 degrees to see what happens.

The fact that we see goo around the rectangular cutout for the duct damper suggests that there has been work on this particular device before so it'd be no surprise if it's giving trouble.

On 2020-02-02 by Anonymous

Thanks. Here’s the high res photo [shown above]. The white box is a can light, but thinking good the silver box on duct plus white cord coming out of it might be a damper

. What do you think? Appreciate the help.

On 2020-02-02 by (mod) -

Jim I clicked to try to see an enlarged version of your image but it's a bit small and not quite sharp so I'm uncertain but the combination of that white device sticking through what looks like a wall and wires from it to a device on the duct sure looks like it could be a duct damper.

On 2020-02-02 by Jim - no air flow in some zones - is this a zone damper that might be stuck shut?

I do not have air flow to 2 rooms in my home. I’ve been through all of the lines and all of the manual dampers that I can find are open. Before I call my HVAC person, wondering if anyone can tell me if this is an electric damper on this line? Found it during my search and am not aware of what it is.

On 2020-01-26 by (mod) - Half of the vents in my house is not getting any air flowing through them.

Neil:

If you start at the air handler and follow the supply duct, looking carefully on all accessible sides of the ductwork, including following each branch, if there's a manual or automatic duct damper installed you will most-likely find it.

It would be unusual (not impossible) for an installer to place a duct damper where nobody could find it.

That said, you should also be looking for other causes of poor air flow in the duct system such as collapsed or crimped ductwork or ducts inside with interior insulation has collapsed.

You will find an extensive series of articles starting at AIR FLOW IMPROVEMENT, HVAC

On 2020-01-26 by Neil

Half of the vents in my house is not getting any air flowing through them. I believed it was either a clog or a closed damper but I cannot seem to find a control for a damper on the unit, thermostat, or the duct work underneath the house. What’s could I find this at?

On 2019-08-27 by (mod) -

Anna

Most motorized zone dampers or ductwork dampers can be installed in any position.

In the article above, after you clear your browser cache and re-load our updated version, you'll find installation instructions for zone dampers and zone damper motors.

On 2019-08-24 by Anna

Does it make a difference if dampers are installed upside down with the motor on the bottom? For some reason they were installed this way. Thank you.

On 2019-07-04 by Bill

How do you tell if the damper is a normally open or closed to buy a replacement. I have a three story townhome with a damper for each floor.

Twice now on the first floor damper I have noticed the AC on and noisier than usual with no air coming out of the damper. I tapped on the exposed motor and it started working correctly.

I think I need to replace this but don’t know which one I need. Common sense would tell me it’s a closed model and mine failed to open. When I tapped on the motor housing it opened. I am just not sure.

On 2019-03-25 by (mod) - Automatic zone dampers are operated by the room thermostat,

Paul

Automatic zone dampers are operated by the room thermostat, opening on a call for heat and closing at the end of the call for heat as well as ceasing the call for heat at the furnace too.

On 2019-03-25 by paul - how do zone dampers stop or know when to stop ?

how do zone dampers stop or know when to stop. i don't see how after it has reached its limit that it doesn't just keep running.

On 2018-11-09 by (mod) -

There may be no duct dampers in your system. That is quite common.

You may make some air flow adjustment by using the supply register outlets.

On 2018-11-09 by Mike

I have a home built in 1919. It has rectangular ductwork. I am having trouble locating the dampers, I don’t see any at all !

I have a couple cold spots in my home just trying to control the airflow. Thank you for any ideas or suggestions.

On 2018-07-25 by (mod) - I would look at other duct balancing options

Dee:

I moved our discussion and photos of your stuck Dampact zone damper controller to ZONE DAMPER FAQs [now this page]

The red button made disengage the damper shaft from the drive motor and that will allow you to try turning it manual leaves in the white knob from closed at to open

I would look at other duct balancing options in the actual duct layout, diverters, and the design rather than leading a problem layout of them trying to fix it after the fact with expensive automated dampers.

On 2019-12-24 by Anonymous

Thanks. I was able to get up in the duct and see that the actuator is working and it is in the proper closed position.

I've now tested with the manual damper that actually seals the duct the most but even with the automatic and manual damper close I still get enough leakage to raise the temp in that zone by 5-6 degrees during the heating cycle to bring the other zones up to temp (for example after I set back at night when we sleep, then heat it back up right before we wake).

I was hoping the double damper setup would help but it doesn't seem to do so, wondering now if it's better with the manual damper open, allow the leakage in the automatic damper, then the system is smart enough to open the damper (I've confirmed this also) when there is no active heating happening so I get proper airlfow through the duct and around that zone.

Sure seems to me there is simply a bad design here in how my ductwork is laid out.

So you don't think it's worth spending $700 to try a new automatic damper that hopefully completely closes the zone when the actuator is in the closed position?

At this point I now have an automatic damper and a manual one, the manual one with maybe 1/8" opening at the top/bottom in a duct that is about 12" wide and I still have a 5-6 degree swing? I think the only solution here is if I can fully close it 100%?

On 2019-12-23 by (mod) - Bryant Evolution system with 5 zones

Sw

I agree that the hot air zone and damper and registers closest to the air handler get the most pressure and heat;

It's common for zone dampers to not close completely, even in the "closed" position. I'm not sure that explains the "too hot" issue; I'd be looking for improper zone damper baffle position (not closing across the duct) when the actuator is moving to what it thinks is "closed", or an actuator that's simply not working.

On 2019-12-23 by swerb

I have a Bryant Evolution system with 5 zones. I have one zone that is always too hot, I can even feel the duct work is hot to the touch even when the zone is closed.

I was suspicious the zone control inside the duct wasn't working and fortunately there was a vent about 2 feet down from the zone control so I pulled the vent off to get a look.

Turns out there is about a 1/3 inch gap on the top and bottom of the damper, and the damper just looks like even when closed it isn't totally air tight.

It looks like a louvered damper that opens/closes with the zone control electronic box.

Looks like someone before me installed a manual damper right after the automatic one to try and totally shut down the ductwork going to this zone. Problem is that it's the first one off the furnace and when calling for heat to one ore more zones that air pressure seems to push through enough to heat this zone that is off.

I had a HVAC company out today that recommended I replace it with a combo electronic/spring loaded damper which they think will be more air tight ($700!). Once I was in there I was able to close the manual damper to shut off almost all of the gap airflow. The problem is now with this off I can't get any airflow to that zone, should I worry?

I've been reading online that it's normal to have leakage through a damper system, and with this one so close to the main furnace (it's literally the first duct above the main furnace and when it blow, boy it blows...

Is it worth replacing this, can I assume I'd get the leakage to stop and better control of the zone or should I stick to trying to totally plug up the venting like I have at the source? I also have radiant heat so the basement can easily stay warm but without airflow I don't get the humidifier (I'm in MN) to run like I'd want and lose out on keeping fresh airflow in the zone (it's an underground zone, media room, no windows).

Curious on your thoughts?

On 2019-08-27 by (mod) - ductwork zone dampers can be mounted with motor in any position

Anna

Most motorized zone dampers or ductwork dampers can be installed in any position.

In the article ZONE DAMPER CONTROLS you'll find installation instructions for zone dampers and zone damper motors.

On 2019-08-24 by Anna

Does it make a difference if dampers are installed upside down with the motor on the bottom? For some reason they were installed this way. Thank you.

On 2019-07-04 by Bill

How do you tell if the damper is a normally open or closed to buy a replacement. I have a three story townhome with a damper for each floor. Twice now on the first floor damper I have noticed the AC on and noisier than usual with no air coming out of the damper.

I tapped on the exposed motor and it started working correctly. I think I need to replace this but don’t know which one I need. Common sense would tell me it’s a closed model and mine failed to open. When I tapped on the motor housing it opened. I am just not sure.

On 2019-03-25 by (mod) -

Paul

Automatic zone dampers are operated by the room thermostat, opening on a call for heat and closing at the end of the call for heat as well as ceasing the call for heat at the furnace too.

On 2019-03-25 by paul

how do zone dampers stop or know when to stop. i don't see how after it has reached its limit that it doesn't just keep running.

On 2019-01-27 by Jennifer

There is a little difference when it is in the closed positions (also when the handle is turned in the opposite direction 180°) there really isn’t a way for me to look inside the duct this is a rental and there is also a gigantic beam thats in the way of removing any duct work. If it’s normal for some heat to still blow out of the vents upstairs then I suppose we are okay. Thank you for your help.

On 2019-01-27 by (mod) - position of manual duct damper handle indicates duct damper position

Jennifer

Usually the line formed by the damper handle indicates the cross-section of the actual damper inside the ductwork;

So if the damper is set to "across" the duct then the damper would be at its most-closed position.

Even in that position it won't close the duct 100% - instead it's maybe 85% shut.

However if you see absolutely no change when closing the duct damper I suspect that the actual damper blade inside the duct has come loose from the handle that is intended to cause it to rotate, or in some designs it may have fallen off entirely.

You will want to get a look inside the actual duct interior, using an inspection camera or if necessary, a bit of disassembly.

Let me know what you see (attach a photo or two).

On 2019-01-27 by Jennifer

Hi we have a manual damper for our heat pump, the second floor dampers even though marked with closed half and open don’t seem to stop or slow the flow of heat to our second floor.

I have turned it in all directions to see if there is a better position but none seem to exist.

On 2018-10-25 by (mod) -

Geoff

I am assuming that you're talking about an HVAC (heating or cooling) air duct automatic damper such as those described in the article above.

In that case if the damper never opens the result would be that heated or cooled air from your HVAC system would not be delivered into the area served by that heating or cooling zone.

That failure would not directly explain the health complaints you cite.

There could be more subtle indirect effects on indoor air quality however such as

- reduced dehumidification by an air conditioning system unable to reach the areas whose zone isn't working

- reduced air filtration - for the same reason

**IF** - and this is VERY speculative on your part and mine - IF a section of the duct system has very limited or no air flow inside it, and IF at the same time there is some leak or moisture source that collects water or moisture in that duct system, THEN yes those conditions could produce mold growth in the duct system.

It's easy enough to check for that problem by having the entire duct system scoped with a duct inspection camera.

"Toxins" venting is not a normal feature of home HVAC systems and their ductwork, though in tight homes your HVAC engineer might include a fresh-air makeup system to improve indoor air quality - a feature not common in residential structures.

New building materials can indeed off-gas various compounds, some of which can be irritating and on occasion harmful.

On 2018-10-25 by Geoff - Honeywell Duct Damper Not Working

We have a newer home (just over a year old). We are concerned our new home is making us sick (eye irritation, ear and sinus infections, respiratory problems; now on our fifth round of antibiotics). A

fter some investigating, we found that our automatic (Honeywell) damper was not working, and we are having it replaced under warranty. Would the fact that our damper has been broken and closed, perhaps the entire time we have been living here, cause health problems?

Could it cause mold in the ductwork?

Alternatively, is it not properly venting other possible toxins and off gassing of the new building materials?

On 2017-11-10 by Anonymous - zone damper leakage

I have a new construction house with zoning damper. We have 15-20% zoning leakage. We tested by switching on fan on one zone and then testing air flow on other zone. Other zone was having 15-20% leakage of air. I understand that it will not be full shut off, but what is acceptable leakage?

I mentioned this to builder and HVAC contractor and they state that there is no code to regulate this. If this is the case, I'm not getting benefits of zoning. Do you know of any codes here too?

On 2017-05-05 by (mod) -

Glen, probably yes, provided you can match the motor size, voltage, drive shaft, capacity, and mounting arrangements. Figure that the company that makes the automatic vent dampener probably did not have a motor designed specifically for their product; rather their engineers chose an off-the-shelf motor that fit their needs (and was much less costly than a custom-motor).

Before replacing the motor check that the mechanical parts of the zone dampener will move freely when disconnected from the motor.

On 2017-05-05 by Glen

Motor on automatic dampener went out. Can it be replaced with another brand? I have duel zone and the zone for downstairs was staying closed not allowing heat for the lower floor. The motor was making a non-stop clicking noise and not moving the dampener.

On 2016-12-12 by Art - trouble shoot a zoning issue.

Hello, attempting to trouble shoot a zoning issue. We have a Lennox LZP-2 zone control system installed. The control panel looks good. Self diagnostics are good. When I call for heat in zone 1 (bedroom) I see heat1 + Zone 1 open; when I call for heat in zone 2 (living room) I see zone 2 + zone 2 open on the control panel. (we have 2 thermostats).

From the control panel perspective (LZP-2) all is well however, the dampers are not cutting off heat to inactive zone. I get heat and cool air depending on the time of the year to both zones. absolutely no issue with the heat or air however, I would like them to be driven only to the zone required. I sort of believe that I have a damper issue ??

On 2018-11-09 by (mod) -

There may be no duct dampers in your system. That is quite common.

You may make some air flow adjustment by using the supply register outlets.

On 2018-11-09 by Mike

I have a home built in 1919. It has rectangular ductwork. I am having trouble locating the dampers, I don’t see any at all !!!
I have a couple cold spots in my home just trying to control the airflow. Thank you for any ideas or suggestions.

On 2018-07-25 by (mod) -

Dee:

I moved our discussion and photos of your stuck Dampact zone damper controller to ZONE DAMPER FAQs at https://inspectapedia.com/heat/Ductwork_Zone_Damper_FAQs.php

On 2018-07-17 by (mod) -

The red button made disengage the damper shaft from the drive motor and that will allow you to try turning it manual leaves in the white knob from closed at to open

On 2018/07/16 Fixing a Stuck or Failed Dampact® Zone Damper Controller

Dee:

If we assume (so I'm guessing) that your Dampact® zone damper was correctly installed and set-up in the first place, and that it's now not doing what you want, take a look at the position of the arrow embossed into the surface of the white knob, and compare that to the little illustrations of "Closed" and "Open" that you see printed in white on the blue case of the zone damper control module - in your photo to the left (open ) and right (closed) of the white knob.

[Click to enlarge any image]

When I enlarged your photo I saw that the knob's arrow is set to the CLOSED position.

See if by using the zone damper control switch - follow those small-diameter wires if you don't know where the switch is) - you can rotate it to the OPEN position.

The white arrow on the white knob will rotate to the "open" position as shown on the control.

That will let air flow through the bedroom air duct.

Your Dampact zone controller is an original equipment controller - the company provides replacement zone controllers that can be used to replace the one in your photo if that one does not work as it should.

Some older Dampact zone dampers included a small bolt or screw through the housing that pinned the white rotating knob (thus pinning the position of the actual shaft that rotates the damper inside the ductwork) in the proper position during installation.

I could not see such a screw in your photo though I did see what looks like a circlip holding the assembly together.

Either the set screw is present but not visible in your photo, or it's not there.

Models of the Dampact that do not use the set-screw don't need one and should be designed so that the drive mechanism cannot shift on the shaft.

But if your damper controller does have a lock or set screw, AND IF that screw has come loose then it may be possible to repair the control though I suspect you will want help from your heating service tech to do that.

I'll include a photo of the replacement Dampact zone damper control - you'll see that it uses a shaped white bushing that omits the need for a set screw.

The red button made disengage the damper shaft from the drive motor and that will allow you to try turning it manual leaves in the white knob from closed at to open

On 2018/07/16 Dee Said my bedroom on the main floor is hotter than any other room in the house

I have 3 story home and my bedroom on the main floor is hotter than any other room in the house. I was advised to adjust the dampers but not sure how to operate it. It is a dampact45def-b but I have no clue on how to open the damper.

I assume the damper was installed correctly. It is the original that came with the house was first built in 2009. What is the zone damper control switch?

The white knob with the arrow on it will not turn. Will pressing the red button do anything to assist in turning the white knob?

On 2018-05-15 by (mod) - if the Duro-Zone zone damper or its switch don't work some areas may not receive cool (or warmed) air

Amy:

RE: Duct damper control switch "failure"

The switch appears from your photo to control a electrically-operated duct damper in one of your cooling zones. A damper allows you to regulate the amount of cooling or heating air distributed to different building areas by partly opening or closing a baffle or "damper" in the ductwork.

It may be that the problem isn't the switch but in the damper itself - either could be broken.

If so,

It is quite possible that your duct damper is not working, maybe jammed or a failed motor, and that in turn that means that the cooling air is not being delivered upstairs.

[Click to enlarge any image]

On 2018-05-15 1 by Amy

I have a control in the master bedroom [photo above]. It does not seem to work.

The upstairs in the house gets so hot while the downstairs is almost cold. Does this control even do anything? I have just a regular thermostat too. No extra buttons

On 2018-04-14 by (mod) -

Eric if you can find the supply registers and move the adjusting lever so that the register is open, and find any manual duct dampers and confirm that those are in the open position, and if there's still no air flow, and if the air handler fan is running, then there are disconnected or crimped ducts or a clogged air filter or unusually dirty blower fan.

On 2018-04-14 by Eric

Pleas advise me how to open vents in 2 rooms of my house so I get air, heat in those rooms? I know there is flappers that can control the flow but all other rooms on main level work fine

On 2018-03-17 by (mod) -

I see.

On 2018-03-16 0 by Anonymous

i have two ceiling fan in it now
They just blow around the hot air
it has a a frame ceiling

On 2018-03-15 by (mod) -

Would a ceiling fan be better and less costly?

On 2018-03-15 by Frank

I am not thinking of actually cooling the screened porch to much, just need air movement during the summer as it is closed on three sides.

This duct would come off a supply register that has a damper for that zone. this duct would also be in a foam insulated attic until it reaches the porch. I am in a high humidity area so that is why i want a good seal to eliminate back draft in system. Thank you for your suggestions.

On 2018-03-15 7 by (mod) -

Frank

You could indeed install a duct damper just inside the supply register and wire it to shut off when the system is not running, or you could simply use a manual damper or manually closing register. I do think this is an expensive way to cool.

On 2018-03-14 by Frank

I would like to cool (move cooler air through my screened in porch) by adding a duct to my hvac system, a 5 ton heat pump. What type of non reversible closed damper can be used so I do not get humidity back in the system from outside?

On 2018-01-23 by GregB

I’m planning to build a new home with a bonus room over the garage. I want two HVAC units to each handle a separate “zone” in the house, and I want to assign the bonus room to one of those zones. Can I have a plenum control installed on that zone with a wall switch so that I can heat/cool the bonus room only as needed by “switching it on” with this wall control. Or must I install a separate HVAC system for a “third zone” — that being the bonus room?

On 2018-01-08 by (mod) -

You may need to work more-carefully to balance the supply register dampers. Surely we can get somewhere between not enough heat and too much heat.

You might also want to check the whole duct system to be sure that ducts are not blocked, disconnected, or shut off by manual dampers in the ductwork.

On 2018-01-08 by Anonymous

I have a very old Schill furnace, and it is supplying way too much heat to an upstairs bedroom. Most other rooms are simply warm, while the downstairs kitchen area is literally freezing. I've tried manipulating the dampers, but then the hot room barely gets heat, and the rest of the house is noticeably warmer.

The more info I find on the subject, the more confused I'm getting.
I need to know which position should I have the damper on the air return duct.

On 2018-01-03 by Anonymous

Jason

Both of those sound like a very bad duct design to me. Picking up return air from the basement rather than the occupied space is the most expensive possible way to heat a building and potentially dangerous if an open return air Inlet draws fumes from heating system or interferes with its combustion Air Supply.

Amending a heating system to blow your heating air into an attic is an expensive way to heat an unoccupied space for which you have not mentioned why there would be a need

On 2018-01-03 by Anonymous

Both of those sound like a very bad duct design to me. Picking up return air from the basement rather than the occupied space is the most expensive possible way to heat a building and potentially dangerous if an open return air Inlet draws fumes from heating system or interferes with its combustion Air Supply.

Amending a heating system to blow your heating air into an attic is an expensive way to heat an unoccupied space for which you have not mentioned why there would be a need

On 2018-01-03 by Jason

Should I remove the card board from my cold air return in the basement and open the other end in the attic during the winter? Then reverse this in the summer?

On 2017-12-31 by Rich

I am getting to much air flow on second floor and hardly any air flow on the first floor. Do they use two different blower fans?

On 2017-12-12 by (mod) -

Mike,

In principle that idea sounds workable but I'm concerned that when you reduce the return air by cutting it perhaps in half the furnace could overheat and therefore shut down or be unsafe. It would be perhaps easier to try closing the supply vents in the area where you want less Heat. Also safer.

On 2017-12-12 by Mike Eppler

I have a 2 story home and the heat is one zone. It's forced air. The registers upstairs and downstairs are both supplied air from one duct. The upstairs and downstairs are separated by a door that prevents mixing if its closed. There are 2 separate air return vents, again one upstairs and one downstairs. I wonder if I could close the returns with a motorized damper to create two zones. Is this something that is being done? Will it work?

On 2017-11-27 by (mod) -

If your zone damper is electrically operated and does not open when forced warm air heat is operating then we need to check
- power to the damper
- damper control wire connections
and if necessary, for emergency heat, you'd need to disconnect the damper door lever from the motorized mechanical operating arm and then open it manually

If you give me the brand and model of your zone damper and attach photos of it I can research more specific repair details. You can attach photos to a comment using the tiny "picture" image to the right of the "Comment" button

On 2017-11-27 16:16:12.560179 by Pete

I just turned on the electric heat.do I open the damper as well.2 story home right now it’s on shut

On 2017-08-01 by cathy

I am having problems with my damper system on my rental unit. The owner keeps saying that system is working as expected but often there is a 7-9 degree difference between the temperature in the house and the thermostat.

Several companies has come out to adjust the dampers. My electric bill was around 70 bucks during the winter months and has now jumped to around 260 during the summer months. I can hear the unit running none stop and the house is still warm. any suggestions?

On 2017-02-18 by (mod) -

Good grief.
First: is there a separate thermostat?
Next: are there registers or a duct damper that is closed?

Search InspectApedia for NO HEAT for other suggestions.

On 2017-02-16 y Cindy

The previous owner shut off all heat to the upstairs and we are unable to find out how to get heat upstairs. Help!! A company wanted $800 to do it for us.

On 2017-01-26 by Chris Yoo

I have a single furnace with 3 automatically controlled dampers via 3 thermostats. Bedroom zone splits into 2 ducts for two separate bedrooms. Bedroom 1 run is short and straight, bedroom 2 is longer with a couple turns.

Room 1 is getting blasted with high velocity air and there is no anual damper at the wall register. Usually, only one zone is running at a time. How would one best balance airflow within one zone?

Should I install manual damper to room 1 and limit flow there? Install an airflow regulator in one or both ducts to the bedrooms, like American Aldes Constant airflow regulator?

The original installer of the system (1 year ago) is not getting back to us. We've lived with it till now by taping cardboard on the inside of the wall register to room 1 effectively limiting the area of the register to about 50% but it's noisy and air still blasting out. Need a better solution.

On 2017-01-10 by (mod) -

New

You'd trace thermostat wires to see what they are controlling, and you'd perform a visual inspection of the whole duct system. Typically a duct damper, if one is in place at all, will be on the supply ducts and in an accessible location.

On 2017-01-10 by (mod) -

RE-posting
AUTHOR:New Buyer (no email)
COMMENT:How do I find dampers in my ductwork that were put in before I purchased the house?

On 2016-07-23 1 by (mod) -

Dave, even if there are no zone dampers in the ducts carrying cool air to the basement, you ought to be able to close off most of the basement air-flow by closing registers at the air supply outlets there.

My OPINION is that a very well-designed HVAC system includes return ducts that bring air to the air handler from various building areas that otherwise tend to be under-treated or that do not otherwise allow easy air movement through the building to the HVAC system. However it's rather common in newer buildings (to reduce installation cost) to provide only a single air return.

On 2016-07-22 by Dave

Basement air ducts do not have shut offs, and main floor not getting cool enough, should there be shut offs for basement ductwork? Also there is no cold air return in the basement should there be?

On 2016-07-22 by (mod) -

Usually, yes, Steve. Here's a tip: often when we rotate a damper we can actually feel a resistance or hear a little scrape when the edge of the damper blade passes the interior surface of the ductwork - compare what you feel and hear with the screw slot position. OF course one could also feel for a change in the air flow at the nearest register during the same adjustment.

On 2016-07-22 1 by Steve

Our manual dampers do not have a handle. They are controlled with a slotted screw that has a locking wing nut. Does the slot on the screw head indicate the direction of the damper?

On 2016-06-30 by (mod) -

Sounds like something is wrong with the installation but from just your e-text I don't know.
- A fan running backwards
- improper duct or supply or return air plenum construction
- improper control wiring or set-up.

The system may be unsafe to use for heat as well as not working properly for cooling.

Call the installing company, speak to the service manager, calmly, without scaring them, ask for help from their senior technical service expert who can diagnose and fix the problem. Let us know what you're told.

Daniel

On 2016-06-30 by Anonymous

I had a new furnace installed in my mobile home. I have an external AC unit. Why is there cool air blowing out the front of my furnace.

On 2015-12-27 by (mod) -

From your etext I can't say what you are looking at. Where is the home? What type of heat has it ever had? You can use the page bottom CONTACT link to send some pictures for comment if you like.

On 2015-12-27 by Smith

I have a tri level home and in the basement (south side) wall is a t shaped plastic what appears to be some sort of duct work. On either end of the "t" its open. Someone stuffed towels in there. There is a handle that has and open and close direction. It looks to go staight into the wall- but it is an exterior wall and there is no vent on the outside. Any idea what this is and if it ok to remove.

Thanks

On 2015-12-06 by davis

thank you so much.

On 2015-12-06 by (mod) -

Davis

The damper motor can be located anywhere in the duct system at the start of the duct trunk or segment that it intends to control. Start at the air handler, follow the supply duct from the supply plenum to where you see it branching off to the two trunk lines serving the two different floors.

The lower floor damper - IF THERE IS ONE - will be between that point and the first branch-off for individual first floor rooms.

On 2015-12-06 by davis

we have a 2-story house and the damper in the duct work for the downstairs thermostat is stuck in the open position because the damper motor is broken according to our AC guy.

the problem is he can't find where the damper motor is for the downstairs thermostat. In a 2-story house, where is the damper motor usually located for the downstairs zone? thanks

On 2015-11-06 by (mod) -

Look for:

a duct damper that's manually shut or an automatic one that is not opening

crimped, disconnected ductwork

a thermostat for upstairs that is not working (try jumping that thermostat's heat terminals at the furnace to see if that turns the unit on)

Search InspectApedia (using the search box just above) for NO HEAT FURNACE to read more diagnostic details.

On 2015-11-06 by Steve

Hi, my two zone system works fine for downstairs but not for upstairs. hen calling for heat (or cool) the furnace (or AC) seems to be working fine but no air blowing out the vents. How do I fix this problem? Thanks

Question: troubleshooting air leaks in a Brivis 30IN with 3 zones

(July 11, 2011) Toni said:

Just had a Brivis 30IN installed with 3 zones. All was fine until heavy winds went up the flue pipe.
In one zone there is now a hot air seepage. Been told this is normal?
Is it. It's not a lot of hot air but enough to notice it;'s there.

Been told the tape / foam contracts?
Have no idea if this is true as it worked fine before.

Unit had error 68 58 48 then stayed at 49
Also now slight hum in the machine which wasn't there before the wind.
Any help appreciated.

Reply:

Toni I don't have a quite clear image of what's going on with your system but heavy winds going up a flue pipe (a chimney??) - how did wind get into the flue pipe bottom to go up?

And in any case there should be absolutely no connection beween a flue pipe (that vents heating system combustion exhaust) and air ducts that carry building air.

In a problem installation, if return air for an air handler is being drawn right at the furnace and the furnace is running (heating mode) there is a risk of drawing flue gases and hot air into the ductwork - very dangerous.

If by hot air coming out of a cold air supply duct the system is certainly not working properly in cooling mode - you need an HVAC service tech to do some diagnosis.

Question: can I over-ride automatic duct dampers?

(July 27, 2011) fred said:

i have some room with little to no aire (hot or cool) is ti possible to manually operate the automatic dampers?

Reply:

Fred you should be able to manually operate a duct damper by disconnecting its power or the entire drive motor shaft, and manually pushing and fixing the damper in an open position. This is not however a step that I recommend before first doing some troubleshooting.

For example if your inadequate air supply in heating and cooling modes is caused by some other duct defect (leaks, disconnected sections, dirty air filter, dirty blower) you'd be better off finding and fixing that problem.

Question:

(July 29, 2011) sherry said:

I am having a sound like a fan blade hitting something. The sound is coming out of the return air register. It only happens when the air cuts off after reaching the correct temperature. It's not a lot of noise just a slight scraping sound. What can this be and how
do I correct it?

The heat has been over 100 degrees for over 30 days here in texas and
the air has run almost continuously. The hottest month is just starting. I have two ivalids in the house and cannot have the air off. Please can you tell me what I should look for or how to fix the problem. I can't afford to have the air conditioner people come out to fix and have them jack me. I would like to know they are telling me the truth. We have never had this problem before. Thanks so much. Appreciate anything you could do to help.

Reply:

Sherry, if you are hearing a mechanical sound like a fan blade hitting something I'd inspect the blower assembly fan - sound might be transmitted into ductwork in either or both directions. It's possible that a bad fan bearing, pulley, or belt (not all systems use a drive belt) can wobble or make noise only at start-up or shut down and not at full run speed.

If the sound is not regular, I tend not to suspect rotating parts as a source and might look for something else loose in the duct system.

Question: Individual zone dampers are not coordinating or responding properly

(Aug 8, 2011) Julia said:

I have 3 zone damper ducts. The dampers appear to be responding to the thermostats, each one closes, opens upon change in temp setting. However, they don't seem to be "coordinating". i.e., if upstairs thermostat kicks in, the all the other zones continue to receive air as well. Consequently, in order to keep my upstairs cool downstairs is icy cold. I've had the repairman out, he keeps telling me I need to have the whole furnace rewired, however, I don't see how this is necessary when the dampers are responding to the thermostats individually.

Reply:

Julia SOP would be that any individual duct zone damper opens and closes individually in response to just its thermostat, and any one or more of these same thermostats can call for heating or cooling (if both are provided).

If someone did not wire up your system correctly (or perhaps if there is a control board in the system that we don't know about) you'd have the symptom you describe. You need a service call to examine and fix the control wiring.

Normally individual zone dampers are each wired to an individual room or area thermostat. So I would not expect them to all open or close at the same time; rather the dampers open or close in response to the thermostat setting.

When the technician says "re-wiring" is needed, perhaps she or he means that your thermostats and zone dampers and heating and cooling equipment controls were not properly wired in the first place. But a "complete re-wire" is a bit much work - first let's determine where the problem lies: it could be one or two simple connections.

Question: humming zone damper problem

(Jan 12, 2012) Dave said:

I have an automatic air conditioning damper in my ceiling that 'hums' or vibrates when that zone is switched on. I suspect that there is a harmonic vibration in the damper or the damper control from the airflow. Is this a common thing? Should I be able to fix it by removing/inspecting and/or cleaning the damper?

Reply:

Dave, a humming zone damper first makes me think that a low voltage transformer is bad; possible other problems could be a failed zone damper motor, control, or a jammed damper mechanism.

See LOW VOLTAGE TRANSFORMER TEST

Question: effects of water on fire dampers in HVAC duct systems

(June 5, 2011) hafiz said:

what happens when water gets in contact with fire dampers?

Reply:

Hafiz:
When water, say from a plumbing leak, wets motorized dampers intended to close ductwork during a fire, I'd be worried that electrical components have been damaged, shorted, or corroded. You wouldn't notice a thing, since the fire damper is normally not doing anything. But in the event of a fire it might not work. I'd check with the manufacturer about what they recommend you do; most likely they'll want the equipment inspected and tested.

If you were asking what happens if there is a fire and water is used to extinguish it, at that point the fire dampers should have already closed the HVAC ducts to help resist fire spread through the duct system. In that case soaking HVAC controls is moot: the ducts are already closed and the fire damage repair will have to include repair and replacement of HVAC components as needed.

Question: how to add dampers on old AC system

(Aug 8, 2012) NW said:

How do I install dampers on an old AC system in a building with no visible controls on the large or small ducts and where the upstairs receives constant flow as a result and the downstairs remains static?

Reply:

NW an easy approach if there is no access to ductwork is to install supply registers that include an operable control to close the supply openings in each room.

Where ducts are accessible it's usually trivial to cut the ductwork to install a manual duct damper.

If you want to go to automatic duct damper or zone damper systems you'll need to locate an accessible portion of ductwork at the start of individual heating or cooling zones, then add an automatic zone damper, wiring it to a room-mounted thermostat in each zone.

Question: Should I use one large HVAC system with zone dampers or individual HVAC systems?

(Sept 15, 2012) Anthony said:

I'm going to be installing forced hot air and central ac in my home. I want to have a two zone system. Should I use
one larger unit with automatic dampers or two smaller units? What's more effieient?

Reply:

Anthony

There are both installation cost and operating costs to consider.

I'm not smart enough to give a sure answer to your question as the building and ductwork layout and requirements of your home are not given. It is certainly less expensive to install one heater and zone dampers than to buy two heating systems.

On the other hand, building layout and usage and size might argue for two smaller heating systems.

In hot water (not hot air) heating systems there is an argument for installing a cascade of smaller boilers to heat large buildings so that we don't run a big (less efficient) boiler unnecessarily. But I'm not sure how that theory translates to air handlers.

But often for efficiency and also effectiveness (in pushing warm or cool air) in larger and multi-story homes we see two heating/cooling systems installed, one in an attic for upper floor space and one in basement for lower building floors. You pay more for the equipment and earn that back over time in operating cost savings.

Question: how to write reports

(Nov 29, 2012) MOHAN said:

I have problem how to write the reports Is there anyway to catch it ASAP

Reply:

Mohan, for help with learning to report defects in air condtioning systems see DEFECTS LIST - AIR CONDITIONING -

or for heating systems see

DEFECTS LIST - HEAT FURNACE GAS

DEFECTS LIST - HEAT FURNACE OIL

Question: how to seal ceiling air ducts for winter

(Dec 21, 2012) cold said:

Besides paying $20 per cover, is there a more cost effective or simple way to seal my ceiling a/c ducts for the winter to prevents heat loss?

I should add that they are circular, 14", and have twist knob coming down to shut damper.
:Besides paying $20 per cover, is there a more cost effective or simple way to seal my a/c ducts for the winter to prevents heat loss?

Reply:

Cold, first try just closing the registers. But if they are leaky, there are simple magnetic covers that you can apply, or for a cheap, ugly solution, use foil or plastic wrap.

Question: damper door closing when the Lennox pulse furnace stops

(Jan 27, 2013) Lee said:

I hear what sounds like a damper door close after my Lennox pulse has run it's cycle. Is this normal?

Reply:

Lee if your system uses duct dampers for zone control it would be normal to hear the damper close at the end of a heating or cooling cycle.

Question: green lights on the zone controls - dampers open?

(Feb 1, 2014) Anonymous said:

When both thermostats are off, are all three zone lights supposed to be green (dampers open)?

Reply:

When you are not calling for heat, I'd expect heating zones to be closed.

But if you can tell me brand and model number we can look up your particular devices and comment further.

Question: warm air blowing out of cooling vents

(June 20, 2014) 3 zone airconditioning said:

We have a fairly new home with 3 zone air conditioning for the 3 levels being the upstairs with 3 rooms, the main floor, and the finished basement. Our son recently moved back in the warm weather and finds it very warm upstairs where his room is. Our bedroom on the main floor is not as warm, and comfortable with the windows opened. When the air is only on upstairs, the air conditioning comes through the vents on the main floor even though our zone is off. Is this normal, or was it installed improperly?

Reply:

Air blowing out of a cooling zone that is turned off sounds like a problem worth investigating and correcting. Certainlu im a zoned air conditioning system if you are sure that thermostats are not calling for cooling in two of the zones but that the 3rd zone is calling for cooling, then cool air should come only out of the active zone's duct system. The problem may be improper duct routing, improper damper location, or something else we've not considered.

Question: why is there no cooling in my damper-controlled room?

(Aug 16, 2014) Anonymous said:
why does is my damper controlled room not cooling?

Reply:

If you've no air flow then the damper is not opening, OR there is another failure such as the blower fan not running or ducts that have become disconnected.

Also see AIR FLOW IMPROVEMENT, HVAC

Question: when to replace a zone damper system

(Sept 10, 2014) Nancy said:
Should I replace zone damper system when I replace furnace?

Reply:

Nancy that's not necessary unless the zone damper is not working properly.

But it would make sense to inspect the state of the whole duct system when putting in a new furnace, less the investment be wasted.

Question: what is the proper lever position on a Weathermaker Furnace

(Nov 15, 2014) Anonymous said:
In what position should I have the lever on my Weathermaker8000 furnace during the winter?

Reply:

I'm not sure what lever you are asking about. But if you want heat you need the zone damper or duct damper in the heating duct to be in an open position; just how far open might vary if manual zone dampers are being used to balance air supply among different building areas.

Question: how to check duct damper operation

(Dec 26, 2014) Maurice said:
How to check if damper operates properly?

Reply:

Maurice

Heating zone dampers, discussed in the article above are manual or automatic. In either case one needs to observe that the damper blade moves to either open or close the ductwork in response to its operation.

There can be a hidden failure: if the damper blade comes loose from the rod that operates it then the operating mechanism may continue to move but the damper does not - and might be left in any position between open and closed. One might notice unexpected presence or absence of air flow out of the appropriate supply registers, or ultimately one might need to inspect the duct interior by partial disassembly.

Question: using a variable speed fan to blow heating air to a lower floor

10 Feb 2015 Dean Becker said:
I just built a new 2200 sq. ft ranch house. I had 6 runs ran downstairs and my furnace is a variable speed and I have the fan on all the time which is recommended. The only heat that goes to the downstairs is when the heat clicks on upstairs so it is always about 4-5 degrees cooler downstairs.

My friend has a second zone downstairs and it is cozy warm and makes you want to be downstairs.

My hvac guy said that if I wanted a second zone, I would have to put my furnace fan on auto and couldn't use my variable speed motor to have fan on all the time. Is that true? We are going to put a fireplace downstairs and maybe instead of putting a second zone downstairs we would put a really good put out lots of heat fireplace downstairs instead of the second zone.

But it takes for ever for the basement to heat up with the fireplace and not to mention you don't always want the fireplace on if you are gong to go down stairs for a short period of time. What is your recommendations?

Reply:

Dean

Indeed it's a bit difficult to push warm air down into a cold space (warm air we know wants to rise) - which would mean you may need to run the fan on its higher speed.

I don't understand your HVAC guy's advice (but then he may be very smart but not a good communicator), unless he is saying that the variable speed fan, when in "ON" Mode, is running at a low speed and that on AUTO it will run at a higher speed. In any event it ought to be possible to set the fan to run at its highest speed on a call for heat - which makes me think perhaps the controls are not wired or set properly.

Question: Hot air blowing out of wrong ductwork

(Mar 13, 2015) Jack G said:
I have a single air handler heating two different parts of the house. The basement and first floor. both zones have independent thermostats.

No problems in the beginning when it was installed. Now, out of the blue, when we raise the thermostat heat in the basement, hot air blows into the first floor instead of the basement.

The thermostats were set for 64 degrees in the basement and 61 degrees in the first floor. First floor temperature is 68 degrees while the temperature in the basement is 62 degrees. The Handler is Lennox and the boiler is Mclain. Thanks.

Reply:

I think I'd be looking for a control board failure or cross-connected thermostat wires.

Question: hurricane loud noises in duct work

(July 20, 2015) Bruce Savik said:
My heat pump supplies air to two zones. One of the zones is only a small room with three registers.

The heat pump is a new 5 ton Carrier Performance unit with dual stage compressor and variable air handler. The problem is when only the zone for the small room calls for air the air flow sounds like a hurricane. Each zone is controlled by a motorized damper. Any suggestions.

Reply:

I'd ask the HVAC tech to look for an air leak at a motorized damper (or however else you're controlling the two zones) and also to check the actual air velocity. It may be excessive.

...

Continue reading at ZONE DAMPER CONTROLS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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• ZONE DAMPER CONTROLS - home
• ZONE DAMPER ACTUATOR MOTOR REPLACEMENT

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