HVAC return air questions & answers:

Frequently asked questions (and answers) about HVAC system return air; how to improve heating or cool air output by improving the flow of return air to the air handler.

IThis article series describes problems with return air inlet size, location, and ductwork.

Watch out: as shown in our page top photo, when the return air for a heating furnace is taken right at the heater itself the system may be unsafe, causing improper burner operation. See UNSAFE DUCT OPENINGS.

Return Air Flow in Heating or Air Conditioning Ducts: FAQs

These questions & answers were posted originally

at RETURN AIR REGISTERS & DUCTS - or at UNDERSIZED RETURN DUCTS be sure to see the HVAC return air duct and air flow diagnosis and repair suggestions in those articles.

Photo: a return air inlet at the ceiling of this home may work well to cool warm air during the air conditioning system (warm air rises by convection up to the ceiling) but during the heating season this would be a poor location that increases heating costs.

How do I find the source of air noise in HVAC ducts, issues with air plenum size

We just had our A/C & Furnace replaced with a new unit that was very expensive and since the installation we are experiencing a high pitch whistling noise from the Return Air Plenum, the installers used the same plenum 12"x20" and bent a bunch of sheet metal to adapt to a larger return air grille 17"h x 30" w.

The company has sent their warranty tech out twice to no avail, they keep trying to make the return air plenum bigger by adding bent sheet metal.

Everything I have read says the return air plenum needs to be much larger. I am looking for answers and getting very frustrated. Answers anyone? - On 2017-08-18 by tsthumpr

3.5 ton Lennox A/C and Lennox variable speed Furnace (fan).

Our new A/C unit probably does have a more powerful fan, but if you could see what they have done to make the existing plenum fit the new Grille you would understand why I believe the plenum size needs to be increased

I wish there was a way to send you pictures and a video (audio) of the noise.

I am no expert but other A/C installation companies I've had come look at the problem believe it is an installation issue including too small a plenum.

Let me know via my email if there is a way I can send you pictures and videos of my noisy unit. They will be coming out for the third time Tuesday, their installation supervisor said the installers should have done it properly the first time, I am very annoyed with the whole issue.

I think there's a way to email me your contact info. - Thanks, Tim On 2017-08-26

by (mod) - how to track down air noise in HVAC return air duct or air handler or plenum system

Tim:

Indeed it sounds as if there's an air noise, perhaps disclosed if the new fan is more-powerful. I'm not sure that making the plenum or return air inlet is the fix - but of course I cannot possibly be smarter than your onsite people who know the equipment and installation.

I'd ask them if there might be an air leak or an obstruction in the air path that's causing the noise. I have seen techs address a problem like this by experimenting with small bits of aluminum tape to either close a suspected opening or change its shape.

Use the page bottom CONTACT link to find my email to send me some sharp photos of the installation.

 

Question: short circuits in air flow - supply air flows right into the return air duct

Should the return vent and the vent that the air flows out of be located side by side. It seems that the return is sucking up the cool air and the air-conditioner doesn't cut off on a hot day. - (May 19, 2014) fgh

Reply:

Fight
I agree that what you describe is a poor design. It's what is called a

Short circuit

In the airflow and it will limit the effectiveness of the system and increase operating costs.

 

Question: Debris-clogged evaporator coil reduces air flow across the coil

Can a dirty (or old) residential a/c evaporator coil effect and/or reduce the forced air flow(coming from the vents)thus effecting the units overall cooling efficiency, even if the evaporator coil is not freezing over and the vent air temperature is adequate? (June 29, 2014) john said:

Reply:

John

Certainly yes. Debris-clogged evaporator coil reduces air flow across the coil and also reduces the transfer of heat from the air to the coil even if the coil is not iced or frosted over

 

Question: ratio between air return grille size (opening) and filter size?

Is there a ratio between air return grille size (opening) and filter size? If I have "clear air" (all doors are open to all rooms being supplied by the a/c handler) provided the return and filter are the same number of square inches, is that sufficient to ensure my system is not air starved? Thank you, Ed (Aug 15, 2014) Anonymous said:

Reply:

Anon, usually the air filter length and with dimensions are matched to the size of the return air grille itself.

It is the total return air capacity, determined by the number, location, and size of return air inlets that must be matched to the air handler's blower capacity and supply duct design.

There are some crude rules of thumb and an elementary test that can give a good guess at return air adequacy:

If the return air inlet square inches is smaller than the cross section of the blower or air handler's return air inlet in cross section then there is probably not enough return air.

Also we propose a crude return air test: with the blower fan running (and if there is no door safety interlock switch in play) if we open the door and release it and it SLAMS shut with vigor I figure that the blower compartment was under high vacuum and there is probably not enough return air. (Admittedly this is crude).

Keep in mind that even if good quantity of return air inlet by location, size, and ducting are all provided, if we are considering a system with central return air and room doors are shut (or not under-cut), the ability of the air system to force conditioned air INTO the rooms will be limited.

 

Question: water in return air compartment

I had new a coil installed,getting water in return air compartment (Sept 6, 2014) lee

Reply:

Lee this is baffling but I suspect that there is so much moisture in your return air that there is condensation in the return air plenum OR *more likely* depending on the type and position of your system's air handler, there may simply be leakage from the condensate handling system (or on occasion from a poorly-located or leaky humidifier on combined heating/cooling systems).

 

Question: Thinking of changing filter size to improve air flow

I have a 4 ton, 2 speed compressor with Variable speed inside fan. It has 2 16x25x1 pleated paper, merv 4. even with filter changes I think the air flow is restricted. I am Looking at modifiying the wall filter housing to accommodate a 16x25x4. (July 25, 2015) Allen Marshall, Mobile, Al

Reply:

A larger air filter at the air return inlet makes sense up to a size equal to the cross-sectional area of the duct inlet. Larger than that? I'd look first at the air flow rates and pressure drop across the filter you're using.

 

Question: upstairs bedrooms get too hot

My warm air heating unit works quite well, however, in order to heat the downstairs open plan living areas, it means that the upstairs bedrooms become extremely hot. All the air vent throughout the house have a slider lever but none of the levers are now functional.

If I replace the air vents with slider levers that do work, will this enable me to channel the heating for example, to the downstairs parts of the house by closing the air vents in the upstairs rooms? Any advice (Dec 9, 2015) Ronnie

Reply:

Ronnie:

Yes you can try closing down the upstairs supply registers. But a better approach would be to install a manual (or automatic) zone damper at the beginning of the ductwork that sends warm air upstairs.

Also take a look at the location of return air venting. If all of the return air vents are upstairs (say in a ceiling at the top of the stairs) that, too, tends to move warm air upstairs.

 

Question: common causes of reduction in air flow in a heating or cooling system

I have a heater that is 18 years old and has not been heating well. Repairman said that my return air flow is not large enough which makes no sense for this to happen all of the sudden.

Plus, I was told that if I replace the heater I would also have to replace my AC unit (which is not that old) due to change in refrigerants used now? Wondering if this is true as it would be a very costly repair. (Dec 19, 2015) Debbie

Reply:

I agree Debbie - if the problem were one of design (ducts too small) the problem would have always been there.

There COULD be inadequate return air - that's very common and easy to demonstrate - but if your system air flow has CHANGED then I suspect

- a dirty air filter

- a collapsed or blocked air duct

- dirt on the squirrel cage blower fan assembly

- a slow or damaged blower assembly such as a slipping belt, loose pulley, or even low voltage or a bad motor.

 

Question: HVAC air duct fills under pressure and then bounces around

Our church has an adjoining A frame building.

Below the ridge there is this fabric duct which fills with air and bounces off at the sealed end. This duct runs almost as long as the building.

The effect of the duct filling then bouncing the air is like blowing into a paper bag with the sound much louder. I've never seen such duct before (obviously there are no branches from it). I believe the design is not cost effective. I'd appreciate any help that would shed light on this design. Thank you. (Dec 30, 2015) Rolando Bartolome said:

Reply:

This sounds to me as if there is an air flow restriction; and duct bouncing around sounds like excessive length of free, unsupported flex duct; bouncing ductwork also invites duct damage, leaks, higher HVAC costs.

Use the page bottom CONTACT link to send some pictures and we can comment further, Roland. I'll be glad to do what I can.

 

Question: Adding a return duct in the basement

I want to add return air ducts in the basement to improve my home's air conditioning and heating. It's cooler down there.

Reply: always ok to add more return air

A significant number of residential AC systems I've examined had insufficient return air in the first place, so adding more return air usually isn't a problem, it's an improvement; you can always adjust the balance between the return duct openings later.

Watch out: avoid taking return air where it may cause unsafe operation of heating equipment such as causing backdrafting and fatal carbon monoxide poisoning;

See UNSAFE DUCT OPENINGS

 

Question: return air inlet opening size adequacy

Will a 20 by 30 return for a 2and half ton unit work for a 1 floor cottage 1350 sq ft? (Apr 3, 2016) Bill said:

Reply:

Bill it's the right question to ask but not one I can guess-at by a one-line e-text. Factors such as duct run length, duct sizing, blower size, fan type, fan speed, and dimensions of the air handler as well as more technical considerations that an HVAC engineer would consider all need to be evaluated for a technically correct design.

I suspect that most installers use a few simple rules of thumb, starting with matching the air return dimensions to the air inlet of the air handler.

See UNDERSIZED RETURN DUCTS

 

Question: Effect of a soccer ball jamed in the ductwork

(May 24, 2016) Kathy D said:
What kind of problems will it cause to the heating and air conditioning units, to have a soccer ball logged in our main return vent? And is there any danger involved?

Reply: here are possible effects & costs of blocked or obstructed heating and air conditioning ductwork

1. Blocked air flow means:
2. Increased heating & cooling costs
3. Possible duct collapse and damage
4. Possible fire if the obstruction is drawn into the blower fan
5. Inadequate building heating and cooling, including, in freezing weather, risk of frozen water pipes, burst pipes, building flooding, costly mold or structural damage

 

Question: air conditioner doesn't remove humidity & takes too longto cool

(July 26, 2016) Jmendoza said:
NEED HELP. SUGGESTIONS. I installed a new carrier AC 2.5T for 1140 sq foot home. My problem is that it's not removing humidity and it takes forever too cool. House is a split level. Pressures and sub cooling are on point. Only got two returns one upstairs and one downstairs next to the furnace. I found I had too much air going across the coil.

I slowed down the blower. I did many tweaks to the system where I finally got the system to remove humidity. I opened up my blower motor compartment. Closed the door where the furnace is at. It's in the laundry room by the way. It's a small room. I blocked 3/4 of the return in the lower level of the house.

This is the only way the system will remove humidity and cool quickly. My question is would adding another return in the upstairs level help remove humidity better. I feel like it's not sucking any return air from the upstairs level and I feel like 90% of the return air is coming from the downstairs level which is always cooler than upstairs and less humid. Any suggestions on how to fix this?

Reply:

JM

Typically an over-sized unit will cool down the space too quickly and thus fail to dehumidify. When a unit won't cool AND is not dehumidifying I suspect a different problem, including a duct problem just as you're thinking.

As you're on-site you can best think about the air distribution: if return air is not moving hot air from the occupied space back to the A/C air handler then yes the system will not be nearly as effective.

Even a crude subjective measure (holding a tissue near an air return or air supply) can give a feel for how air is moving.

But before adding returns or supplies, review the whole duct system looking for snafus such as leaks, disconnected ducts, crimped or squashed ducts, or a dirty filter.

 

Question: clearance between top of air handler to ceiling for ductwork?

How many inches is recommended between the top of air handler to ceiling for the duct? I only have 56 inches clearance and having a tough time finding a 4ton 16 seer split system ac. (Sept 17, 2016) SL said:

Reply:

SL if your installer can't fit a supply plenum and duct connection in nearly six feet of free space over the air handler, then something is rotten in the state of affairs - call someone who knows something.

 

Question: do I need a low or high return?

I'm having different views from different hvac guys I have compares about 10 and still need to know if I need a low or high return ? I have 1206 sq 12 registers that will be in ceiling I have hardwood floors with 2 1/2 tin unit please help me (Nov 12, 2016) Theresa Phillips said:

Reply:

For air conditioning, placing the return air up high means you're pulling warm air from where it tends to collect (up near the ceiling) - a more efficient cooling air return inlet location than on the floor.

 

Question: ok for return air to go in at the ceiling?

in a manufactured home is it adequate for the return air to go in the ceiling. We had a metal roof put on and now we are having an incredible amount of dust. I have to dust every other day. Do we need make one of those vents at the eve of our home? (Nov 12, 2016) kat said:

Reply:

Kat it sounds to me as if we're mixing up some questions. It's common for homes to put a central return air inlet in a ceiling. (Though that works better for cooling than for heating).

But if you're seeing excessive indoor dust levels we need to start by finding the source of the dust. Perhaps having a forensic lab analyze a settled dust sample would help point to a source. Search InspectApedia.com for TAPE SAMPLE FOR DUST to see details.

 

When to make the return air inlet larger

We just had our A/C & Furnace replaced with a new unit that was very expensive and since the installation we are experiencing a high pitch whistling noise from the Return Air Plenum, the installers used the same plenum 12"x20" and bent a bunch of sheet metal to adapt to a larger return air grille 17"h x 30" w.

The company has sent their warranty tech out twice to no avail, they keep trying to make the return air plenum bigger by adding bent sheet metal. Everything I have read says the return air plenum needs to be much larger. I am looking for answers and getting very frustrated. Answers anyone?

3.5 ton Lennox A/C and Lennox variable speed Furnace (fan). On 2017-08-18 by tsthumpr

by (mod) -

TS am I right that you asked and we replied to this in email?

I suggested trying to track down the actual noise source, perhaps using foil tape on suspect openings or to change edges and angles in the air flow.

Just making the return inlet larger would make perfect sense if there was an air volume or flow mismatch, but if the noise is from air moving over an obstruction the size change may not help.

Bangs, Clunks and other noised from ductwork: undersized ducts or other causes?

I've installed a new 2 stage variable speed furnace in my basement, the air return is above it in one central register on the main floor about 30 x 12. I have found that when the furnace starts it sucks in the metal air return panels in the basement that lead into the back of the furnace.

I added another heating vent to the system into the basement, but have not increaased the air return yet.

I have also turned the down speed of the fan to the lowest it will go, so now it ramps up slower. those 2 items have helped a lot. however I need as well to leave the front of the furnace door open for additional air, otherwise it still sucks in the metal return.

I was told to put bracking inside the return, which is an option, another option I thought would be to add another return to the other side of the furnce with another opening and filter.

A furnace man came out and said that would work, but wanted some others ideas and opinions. Thank you in advance, email to cws56501@yahoo.com On 2016-10-25 by curt

by (mod) -

Curt,

I've seen and heard metal panel bangs, clunks, and thunks that can be a startling heating system noise easily traced to just what you observed. When the fan starts up the system is at least initially a bit air-starved creating a vacuum on the return side of the system. A powerful fan can also cause the same noise by bulging out rather than in sheet metal components on the supply side of the heating or cooling system.

If the system is truly air-starved then it makes a lot of sense to add more return air inlets since not only will you be curing the start-up or shut-down BANG noise in the duct and air handler system but you'll also improve the effectiveness and efficiency of the system.

If the problem is a powerful fan at start-up but no air-starved concerns, then I would add reinforcement U-channel to stop flexing sheet metal noises.

If the system is not air-starved, a fan control that ramps up the fan speed improves the situation but that's not a normal control.

Running the fan always on the lower speed defeats the purpose of having a multiple speed or variable speed blower fan in the first place: different speeds for varying needs.

When you have to leave the a blower compartment door open then it's a pretty good indicator that the system needs more return air. Another similar test I make is to wait until the blower has been on for 5 minutes or more, then open the air handler blower compartment door about 6" and let go. If the door SLAMS shut with a powerful BANG then the system is probably air starved.

On 2016-10-25 by (mod) - metal panel bangs, clunks, and thunks can be a startling heating system noise

Curt

Please see an expanded reply to your question now found

at BANGING NOISE at AIR HANDLERS or in DUCT SYSTEMS

Also see INCREASING RETURN AIR

and see SOUND CONTROL for AIR DUCTS, HVAC

Dual Pak HVAC unit 7 years old (Rheem) stopped supplying cold air. Duct was crushed!

My Dual Pak HVAC unit 7 years old (Rheem) stopped supplying cold air. I have coverage on my HVAC system with AHS. The first company came out and insisted that since the outside air temp was 100 degrees and i was getting 78 degree supply air it was working fine. I disagreed with him and told him.

He then went up and said there was some insulation blocking the air duct and that was the problem. We still were getting a lower volume of air (tEmp 78 degrees. He went up again and after an hour said my TXV was not working ( he was basing this on the fact that the pressures didnt equalize at the compresser.

This tech finally just went out to his truck and just left. AHS sent out another company and this teck said the shrader valve was leaking and the unit needed 3 lbs of freon 22 and he also said the compressor needed a hard start put on it along with a main contactor replaced.

After he did all this the supply air temperature dropprd to 57 degrees.He said it should work fine now. I still didnt feel the air flow the unit has had since i had it installed 7 years ago. We used the unit for 12 hours and it ran constantly and by the late afternoon the temperature got up to 89 degrees in the rooms.

I called the company back and the same tech came and checked the unit and said there was a leak somewhere and he couldnt find it so he finally left without saying anything to my wife. I called him and finally got thru and he said he was giving up and he called AHS and they would be sending out another company.

This company came out and the technican said the unit was low on freon and there was a leak somewhere. He finally located the leak in the EVAP coil and said it couldnt be repaired so they would have to order one. He also said he he thought the TXV wasnt working correctly so it would also need replaced.

The last thing he said was that my return air duct appeared to be smashed a little lile someone may have stepped on it. He said they would have to replac the return air duct work also. He left and said someone would call On 2014-09-11 by Gerry

by (mod) -

Gerry

Good going sticking to your guns in the first place. If a cooling system isn't dropping the temp below 78 something's wrong somewhere.

Low refrigerant (which means there's a leak) can cause coil icing that would then block air flow and prevent cooling.

It is certainly true that if a cooling coil is leaking and is corroded and fragile the HVAC tech is likely to advise that it's not repairable. Tossing in the TEV may be a bit like shotgunning the repair diagnosis though it is often a less expensive approach to replace several doubtful parts than to run up a bill with longer diagnosis.

Smashed AC duct is important to fix and hopefully is a minor addition.

Too-slow air flow can contribute to coil icing.

If a return duct has an elbow and connects to air handler at a smaller size than the wall intake opening, will the air flow be compromised?
We are trying to solve a problem with freezing coils and have ruled out low refrigerant, dirty coils, dirty filter, blocked ducts and non functioning blower, valve (tXV) metering refrigerant was replaced.
Thanks. On 2014-07-09 by dcr

by (mod) -

In my opinion, probably yes - as it's a restriction.

I agree that a too-slow air flow can contribute to coil icing.

Remember to check with great care the blower fan itself - a small amount of dirt on the squirrel cage blower fan blades may not look like much but I've found that dirt there can cut air flow by 40% or more.

How to Compare return air vent size with air filter size?

Is 160sq.in.of return vent adequate in a heat pump unit with a 20x20 air return filter. On 2014-06-18 by Reg

by (mod) -

400 sq.in is more than 160.

If the filter describes the air handler return plenum size there's the answer. Probably not.

Our return duct is much smaller than what the factory recommends: how much does that increase my heating cost?

The air return duct is 12"x 19", 228 sqin, about 2/3 the area of the factory recommended air filter 14"x 25", 350 sqin. How much is the under sized return air duct reducing the efficiency of my new 95% furnace? On 2014-05-08 by Greg

by (mod) -

Greg the efficiency of a furnace is indeed impacted by a constriction in the air delivery and return system, since to satisfy the thermostat while pushing air through a restriction means the system has to run longer. I'm not sure it's a trivial calculation however as in my experience there are usually multiple, overlapping efficiency reductions - so removing one does not necessarily assure that the boost in performance is exactly what you might hope or calculate.

Of all restrictions, however, a return air constraint is particularly ugly as it constrains *all* of the air movement through the air handler and on to the supply duct system. So a 33% reduction in return air is significant. But with just that single number I can't compute the actual real-world effect. An interesting technical article on the complexity of calculating the effects of changes in the air handling system is available from the US DOE: See

• Burdick, Arlan, "Advanced Strategy Guideline: Air Distribution Basics and Duct Design", U.S. DOE (2011) at Available electronically at http://www.osti.gov/bridge Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831 - 0062 phone: 865.576.8401 fax: 865.576.5728 email: mailto:reports@adonis.osti.gov Available for sale to the public, in paper, from: U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 phone: 800.553.6847 fax: 703.605.6900 email: orders@ntis.fedworld.gov online ordering: http://www.ntis.gov/ordering.htm
• Take a look at RETURN AIR, INCREASE

Question: is our heat pump return register too small? What about noisy heat pump operation?

We recently had installed an American Standard 2 ton 14 seer heat pump in an 1,100 sq ft basement. The basement is now finished but I continually questioned the installer on the size of the return.

The unit is multi-staged and when it ramps up the return is very loud. He installed a 14 by 20 inch return because it fit neatly between the studs. He used 8 ft of round flexible ducting to the air handler.

He also suggested I use the cheap thin filters for lower sound levels and better air flow. There is also a place for a 20 by 20 inch filter at the air handler which he said could be used instead of a filter at the wall return.

Could you please let me know how large the return should be and any pointers on filter use. - D.K.

Reply: Return duct eyeballing and guesstimating

A competent onsite inspection by an HVAC expert usually finds additional clues that help accurately diagnose a problem or could certainly make a more accurate statement about the needed return air inlet and duct layout. And I don't want to get too far into speculation by second guessing your installer since I don't know enough. That said, here are some things to consider:

• The size of the filter at the air handler gives a clue about the anticipated size of the air return that equipment manufacturer expected to have.
• Your 14 x 20 return air inlet = 280 sq. in. of air return;
• Your filter size at the actual air handler is 20 x 20 = 400 sq in of air return
• That means that at the air handler the design expected 120 more square inches than what you've got - or a 30% reduction in return air intake area.
• A very crude test can tell you if the system seems to be return-air-starved: if we briefly open a cover or case at the air handler by a few inches to admit free-flowing air into the air handler and then let the cover go and it "SLAMS" back with great force into place we figure the system is running with high negative pressure and may be air starved. (A door safety interlock may prevent this test on your system - don't mess with it or you risk having a finger cut off by a moving blower fan - let an expert look into this problem]
• Using a thinner filter may slightly improve air flow but in my OPINION that sounds a bit like a band aid and a bit inadequate if the system return air is 30% less than design.
• Probably an HVAC engineer expert in this would give a more accurate accounting but it sounds as if the return may be a bit small. - longer distances of flex duct also can reduce air flow - installers try to keep the duct distance from return air inlet to air handler as short and as straight as possible for best airflow If the system is return-air-starved its performance will suffer and operating costs will increase.

Noise: I'm not sure what noise you are describing; if it's airflow it could be related to the return and return duct

Question: return opening bigger than return ducts

I have a new system where the duct entering the return air plenum opening at the furnace is 16" x 25" but it is fed by a duct between the joists that is only 16" x 12". Would it be a good idea to just increase the duct size so it extends below the joists, to say, 16" x 25" for example" - (May 30, 2015) Duct size

Reply:

Possibly. First I'd check the system for inadequate return air since it's possible that the return inlet was simply larger than needed.

See UNDERSIZED RETURN DUCTS

Question: improve air conditioning by increased fan speed, cleaning blower fan, clean air filter, remove duct obstructions before changing duct size

I recently purchased a house (60 years old) with central air. 3 ton unit. The home heating was fine this winter but now that we are using the central AC the house never goes down more than 2 degrees. It just doesn't cool the house like it should. It appears from researching this it is

1.) insufficient air returns AND insufficient duct work to deliver the cool air.

I am reading central air requires larger duct work to deliver the cool air than heat does ? Is that true ?(June 15, 2015) Victoria G

Reply:

Victoria

It may be possible to improve the performance of your central air conditioning system by increasing the fan speed, changing to a variable speed fan, cleaning the blower fan assembly to improve its air movement ability, making sure that the air filter is clean, that no ducts are crimped or disconnected and similar measures.

Before even considering the costly change of duct size in a building I'd want to investigate not only those basic air flow improvements but I'd want the system examined by an expert who could tell us if the air conditioner is working properly: what is the temperature drop across the cooling coil? is there an improper refrigerant charge? is the thermostat properly set and located? etc.

 

Question: can under-sized ducts cause HVAC air conditioner or heater to short cycle?

Is it possible for an undersized duct system to cause a heater or air conditioner to short cycle (Dec 22, 2015) Emre said:

Reply:

Emre: in my view, yes, possibly so. If back-pressure causes overheating in the supply plenum a fan limit might shut down the system.

Thank you to our readers for their generous comments

31 Oct 2014 Grace De Bavay said:

This is really a great and very informative post. We normally install HVAC and don't pay attention over such small things which causes big problems. I too had ventilation system installed in my home and it is working well and good so far.
www.ventis.com.au/

Reply: Thanks for the nice note, Grace. We also welcome questions, criticism, and content suggestions and especially would appreciate noting differences in requirements, terms, or HVAC issues special to Australia.

...

...

Continue reading at RETURN AIR REGISTERS & DUCTS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

HVAC Return Air Improvement Articles

• AIR FLOW IMPROVEMENT, HVAC
  • AIR FLOW MEASUREMENT CFM
  • AIR FLOW TOO WEAK
  • AIR LEAK NOISES
  • AIR LEAKS in RETURN DUCTS
  • AIR LEAKs in SUPPLY DUCTS
  • BALANCING AIR DUCT FLOW
  • BLOWER LEAKS, RUST & MOLD
  • COOL AIR SUPPLY IMPROVEMENT
  • DIRTY A/C BLOWERS
  • DIRTY AIR FILTER PROBLEMS
  • DIRTY COOLING COIL / EVAPORATOR COIL
  • FROST BUILD-UP on AIR CONDITIONER COILS
  • FURNACE OVERSIZE PROBLEMS
  • INSULATION BLOCKED COOLING COIL
  • LEAKY DUCT CONNECTIONS
  • REGISTER & DUCT LOCATION
  • RETURN AIR, INCREASE
  • RETURN AIR REGISTERS & DUCTS - home
  • SLAB DUCTWORK
  • UNDERSIZED RETURN DUCTS
• AIR FLOW RATES in HVAC SYSTEMS

Suggested citation for this web page

RETURN AIR FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HVAC DUCT SYSTEMS

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