Questions & Answers about fixing back-draft & wind problems at direct vent chimneys.

This article series explains how to diagnose and fix complaints of loss of heat blamed on wind blowing at direct-vent or side-wall vent chimneys or exhaust systems for gas or oil fired boilers and furnaces. The article includes both manufacturer's advice regarding wind problems at direct vent systems and a ten-point checklist of things to explore when diagnosing an repairing wind-related loss of heat at a building.

Q&A on Wind Problems at Direct Vent or Side-Wall Vent Chimneys & Flues

Question: Strong winds may overcome exposed direct vent chimneys or flues for heating appliances?

Concerning sidewall power vent to one of my residential gas furnaces.

It is a proper code compliant side vent sloped properly with condensate drain etc. However, it is on a wall exposed to a wide open area - thus winds can be strong against the house.

Do I need to install something like an open vent collar to reduce the back pressure variations caused when winds are heavy? - Sack from VA 12/2/12

Reply:

Sack

Interesting question, I don't know but if you can tell us equipment brand and model we will research the question - or you can all the the manufacturer who can tell us.

I've never seen a power vent with wind protection installed, and we have presumed that the blower fan that provides positive draft for the direct-vented heating appliance is designed & tested by the manufacturer to provide more than adequate draft provided that you have followed the manufacturer's installation instructions. Those instructions typically state that

The combustion air intake shall be installed upwind of the vent outlet when exposed to prevailing winds.

Avoid locating the vent terminal on a wall facing prevailing winds and wide-open areas. When impractical, choose a location that protects the vent from strong winds, such as behind a fence or hedge. [15]

Do you have a copy of the installation instructions and can you give the brand and model of your heating appliance?

Question: what is the required clearance between adjacent houses & a neighboring direct vent fireplace?

Is there a minimum distance between brick houses in Toronto for venting termination of a fireplace using direct vent? - A.W., 12/30/2012

Reply:

I have not found building code citations that refer to nearby or adjacent buildings when specifying clearances for direct vent fireplaces, but it seems likely that your local building code inspector would agree that the clearance requirements for the building in which the fireplace is installed would set the minimum acceptable clearances that would then apply also to a nearby or adjacent building.

In other words, if the fireplace vent distances and position relative to your own building windows or doors were LESS THAN those to the windows & doors on the building where the fireplace is installed, and presuming for a moment that the fireplace was installed properly, meeting local building permit and code requirements, then a violation probably exists.

If the fireplace vent distances and position relative to your own building windows and doors is GREATER THAN those to the windows and doors where the fireplace is installed, and presuming for a moment that the fireplace was installed properly, meeting local building permit and code requirements, then a violation probably does not exist.

Take some some sharp photos of the installation that concerns you, or make a sketch and send those along and we may be able to comment further.

Thanks to Alan Carson, Carson Dunlop Associates, Toronto, for assistance with this topic.

Question: neighbor's power vent 18" from power line

(Mar 8, 2014) James S said:

My neighbor just installed a power vent for his furnace on the outside of his house.

The house is 18" from the property line (this is a grandfathered non-conforming setback), but the new very loud power vent extends a further 10" into the space, so stops 8" from the property line. Is it ok to extend into the non-conforming set back like this when the code says they can't build 3' from the property line?

Reply:

James,

Good question, for which I don't have a sure answer; this is a question for your building department.

Most communities indeed have restrictions on just what can be close to the property line, with variations depending on whether you're considering a front, side, or rear property boundary. Keep me posted.

Question: clearance distance from direct vent furnace exhaust to clothes dryer exhaust vent

(Apr 8, 2014) Paul T said:

what is the clearance for a direct vent furnace to a dryer exhaust vent?

Reply:

Paul I'm not aware of a clearance specification between the furnace and a dryer exhaust vent, and I'm not sure if your question is distance to the vent pipe or distance from the direct vent furnace combustion air intake or distance from its exhaust, or distance from the heating appliance itself.

But I'd say that ANY dust emitting source close to any fuel burning appliance is a concern if the dryer lint can enter or clog combustion air inlets (very dangerous where carbon monoxide may be produced) or other air vents such as cooling vents on equipment.

I can suggest two approaches to getting past speculative arm-waving:

1. if you see dryer lint in or on the appliance that's a potential safety concern that needs to be addressed

2. Check with the appliance manufacturer directly, for the particular brand and model of heater, starting with a review of its installation instructions and if needed a call to the manufacturer.

Watch out: if your clothes dryer were a model whose air intake were at risk of drawin in combustion products that would be a dangerous situation.

Question: repairs for Sears Homart® direct vent gas fired wall-mount furnace

(May 18, 2014) Anonymous said:

I have an old Sears Homart Direct Vent Gas Fired wall furnace model #867.72542
It has worked well for 29 years with only the fan being replaced 3 times.

As of late, it has been getting so hot behind the front panel that the wires going to the 2 limit switches are melting causing smoke. I'm not sure how to fix this or what the problem is. Any suggestions would be greatly appreciated. I can't seem to find anybody that knows anything about these old Homart furnaces. Anteup711@aol.com
Lawrence Markowski

Reply:

Lawrence

The overheating you describe is dangerous and suggests backpressure in the combustion chamber. I'd expect that to happen if the system has not been properly serviced or adjusted and/or in particular if the exhaust venting is blocked or not working properly.

Shut off the system and ask your heating service technician to diagnose and repair the cause for overheating. Any overheated switches and wiring should be replaced as well, as if they're damaged the system is unsafe and risks a fire.

The problem is not one likely to be unique to the Homart Furnace.

Finally, if the total proposed cost of repairs is a significant portion of the cost of a new furnace, I'd give that option consideration.

Question: direct vent Weil McLain gas boiler may be too close to neighbor's windows

(July 17, 2014) Concerned said:

A neighboring house has a Weil-McLain gas-fired boiler with a sidewall direct vent that is directly across from the window of my 3' x 4' powder room. There is less than 9 feet between our houses- 7 feet on his side and 2 feet on my side of the property line. If I open my window, you can see the condensation come in through the window. You can smell and taste it.

I put a carbon monoxide meter on the windowsill and got a reading of 15. I called the company and they originally told me that there is no specification as far as a required distance from the vent to a window and that exhaust is being emitted and that the city should follow code.

I called the inspector and he told me that it should be 10 feet and that it had to be corrected, but it was a "sensitive issue" because they passed the inspection.

After about a year and various phone calls he told me that according to the 2009 International Residential Code the manufacturer's instructions needed to be followed which requires 6 feet from an adjacent wall- no mention of a window- which brings this around to the beginning again.

I read a copy of the instructions and on the very first page it has a warning saying "Perform steps in the order given. Failure to comply could result in severe personal injury, death or substantial property damage." There is a section which comes before any clearances are given which says,

"Consider the surroundings when terminating the vent: Position the vent where vapors will not... be objectionable. Avoid possibility of accidental exposure of flue products with people or pets."

These are just 2 of the 7 considerations that should be given before proceeding to the clearance distances.

Again I called the company and they told me that they would not guarantee the safety of this exposure and that I should keep my window closed. I met with a lawyer and he told me that it was a trespass on my property and that I would have to take my neighbor to court and not the installer. I talked to my neighbor about it, but no response. What to do?

Reply:

Concerned,

If the neighbor is not interested in addressing this concern, and before launching a costly lawsuit that will upset everyone for some time, I'd try speaking with your local building department. If your local code officials agree that the installation you describe is improper and violates local building ordinances that alone may be enough to encourage the neighbor to change the installation as needed.

Question: clearance distance between direct vent propane fireplace exhaust and oil storage tank

(Aug 26, 2014) Elsbeth said:

Is there a required clearance for a direct vent from a propane fireplace and an outside oil tank? Thanks

Reply:

Elsbeth

I'd respect the same distance for oil storage tanks as that required for clearance from the oil burner, since like an oil burner, a propane fireplace will involve flame - that's ten feet from the burner - which is not the same as 10 feet from the vent.

Propane tanks also have clearance requirements, typically ten feet

Reader follow-up:

Thanks for your response- Are there any requirements preventing an oil tank being in close proximity to a propane tank? We're moving and want to install a propane fireplace and the oil tank is outside near the living room wall which is where we want the fireplace.

Question: venting new gas boiler through old chimney?

(Sept 7, 2014) Pam said:

We had a natural gas boiler installed in our house to replace a diesel burning unit.

We asked that the new boiler be vented through the old chimney but the installer said that the new gas water heater was vented through there and that only one appliance could be vented through the chimney.

We live in Alberta and from everything i have read my understanding is that 2 gas appliances through one flue is no problem so long as they don't exceed the max BTU output....please confirm or correct.

Also, I have been reading here on testing new systems for leaks....please let me know how that test is performed as I don't think it was done here. Yesterday I noticed an exhaust leak where the pvc didn't meet the outside wall vent cover and liquid was leaking down the siding of the house.

That and other issues with the installation has made me lose confidence in the installer and now want to make sure all was done correctly. Thanks so much. Have a great day!

Reply:

Really? 

two appliance through one flue .... "is no problem " may or may not really be the case. In addition to total BTUs vs. chimney venting capacity there are guidelines for how appliances are connected and how their draft hoods are arranged. If done wrong, for example, a higher BTU appliance can back-vent out through the smaller appliance flue vent connector, particularly when the smaller one is OFF,

Also venting a small appliance into a large chimney can cause it to fail to vent properly when it's running alone - the chimney may be too big and too cold to develop proper draft.

In sum, you want a qualified chimney or gas appliance technician to be sure that the installatin is correct and safe If not the CO risk can be fatal.

Furnace leak testing procedures are found at

HEAT EXCHANGER LEAK TEST

and furnace leak standards are found at

HEAT EXCHANGER LEAK ALLOWED

(Sept 11, 2014) Pam said:

Thanks for the information Dan, we have a different gas fitter coming out to have a look at our system to ensure all was installed properly.

As for the venting, after a big hole was cut through my wall for the intake and exhaust pipes, they now say it is ok to vent through the chimney and will come out when they get a chance.

We had asked for chimney venting before the hole was cut .... deep sigh!! Is there a government agency out there concerned with installers who don't seem to know or care about what they are doing? LADD Plumbing and Heating out of High Prairie AB definitely need to be investigated....in my opinion.

Reply:

You can complain to your local better business bureau if you are not happy with a contractor - it's like whipping the fellows with a piece of wet spaghetti, but maybe more effective than doing nothing. Before complaining to the BBB be sure you've given the company a calm telephone call to ask for satisfaction - give them a chance to respond to you.

Question: convert from masonry flue to direct side-wall vent?

(Oct 3, 2014) warren Keyes said:

I now have a stack concrete flue for a oil fired boiler can i use just a direct sidewall vent

Reply:

Usually Yes, Warren - you need to check the location of the boiler, the distance to a sidewall, and the suitability of that wall for a direct vent location - to meet ground and other clearance distances and clearances from combustibles. For example, a too-long horizontal run can give trouble.

Question: what's the difference between direct-vent and non-direct-vent heating systems?

(Oct 13, 2014) Anonymous said:

Hi Dan, Can you please explain the difference between a direct-vent and a non-direct-vent system?

I understand the differences in the code clearances; but I'm confused about how to determine whether I am or need to be working with a direct or non-direct system. Thanks in advance!

Reply:

Anon: a direct vent heating appliance vents exhaust gases without requiring a chimney. Typically a direct vent system vents horizontally through a building wall and often incorporates positive exhaust of flue gases as well as obtaining combustion air for the appliance by adding an appropriate fan or blower system.

Question: too-hot side-wall vent

(Oct 22, 2014) Dave said:

We have a side wall vent that appears to work well. The amount of heat that leaves the vent, to the outside, is very significant.

It seems that enough heat escapes the vent to "heat a house". Is this the normal behavior for a side vent? If so, can any of the heat be recovered in any way?

Reply:

Dave you don't name the fuel nor type of appliance being vented.

But a properly selected and installed sidewall vent can still be quite hot - enough to burn one's fingers. The manufacturer specifies necessary fire clearances from the vent as well as details for how the vent should pass through the building wall. Give us some product name and model number details and we can comment further.

Question: air flow problems with Benjamin direct vent oil fired furnace

(Oct 28, 2014) Barry said:

We have an oil burning furnace (Benjamin) with a direct-vent. We often have problems with the air flow, when it is either very windy out (seems to blow out the furnace) and no wind (seems there's not enough air flow). Is this a common problem and is there a solution (i.e.: Build a wind fence around it)?

Reply:

Barry wind should not be able to blow out an oil-fired furnace. Something is wrong, perhaps with combustion air supply. I'd give your heating service company a call, discuss the problem with the service manager, and ask for help from an experienced heating service technician.

Question: heat delivery problems

(Nov 16, 2014) mihir said:

One of my room on 2nd floor does not get heat via the vent. How do I detect where the blockage is ?

Reply:

Mihir this sounds like a heating air deliver duct system problem.

Please see DUCT SYSTEM DESIGN SIZE & DEFECTS for help in finding out what's wrong.

Question: gas furnace direct-vent exhaust close to ground

(Nov 16, 2014) Anonymous said:

Our exhaust to our gas furnace is located at the front of our home very low to the ground..

Our unit is part of a 6 unit building and the front is the only location for this to be installed. Our problem is during the winter months we have to be very careful snow does not cover the opening.

Is there some kind of an extension we can use to raise it higher from the ground?

11/28/2014 kevin said:

i have a gas boiler with side wall vents outside the home ,where they are located it happens to be where snow drifts occur and must be cleared frequently, since my inlaws are elderly and cannot get out to clear this, is there a way i can build a box around these vents with vent holes cut out ?

Reply:

Kevin

Indeed manufacturers want the side wall vent to be installed above the likely snow height - else the system could be unsafe, even fatal for building occupants.

You might be able to improve conditions by installing a roof of adequate size and height to minimize the snow accumulation. I would FIRST check with the vent manufacturer for their own recommendations. I'd be very wary of building any sort of an enclosure that might constrict vent, air intake, cause system malfunction, etc.

Question: why would exhaust pipe from older vented lp floor heater all of the sudden be cool to the touch as if the exhaust is not escaping?

(Dec 29, 2014) Anonymous said:
why would exhaust pipe from older vented lp floor heater all of the sudden be cool to the touch as if the exhaust is not escaping.

The pipe is generally very hot to touch. Now today exaust pipe is cold when heater runs. bottom line is there a mechanical mechanism that opens and closes or does the exaust just leave the gas fire by gravity?

It is not blocked by animal or debris. Is there most likely a mechanical problem? Heater does not have a fan for pushing exhaust. Only for blowing hot air once heater gets up to certain temp

Reply:

Anon

If the heater is running the flue vent connector would indeed be hot. IF you are discussing a direct-vent heating appliance it would normally use a blower fan for proper exhaust and possibly to obtain combustion air. Older "gravity" vented appliances are not "direct-vent" and require a chimney but typically don't use a blower fan.

Bottom line: I can't quite make out what equipment you have installed nor what it's doing. But gas fired equipment, if not properly vented, can be fatally dangerous - as carbon monxide could be produced. If in doubt, shut off the equipment immediately and call for emergency heat service from your service company.

(Dec 31, 2014) Anonymous said:
its a Seigler furnace that sits on the floor. The fan pushes hot air out of the bottom. The exhaust is fine now after warming up. It is a very old heater. The pipe is hot enough to almost burn you. Not very efficient, half the heat leaves out of exhaust. I do not hear a fan running to push out exhaust but maybe there is one.

Thank you very much for comment. I appreciate it. Rick

Question: the intake vents for my furnace and hot water heater are less than the 12 inch requirement. Is it possible to raise them by adding additional elbows/piping

(Jan 1, 2015) Asker said:
Hello, the intake vents for my furnace and hot water heater are less than the 12 inch requirement. Is it possible to raise them by adding additional elbows/piping on the outside? There is very minimal distance from my furnace to the sidewall vents and I have not used the maximum number of 90 degree elbows permitted in the manual.

Reply:

Ask

I'm not sure what 12-inch you refer-to. If you mean above-ground clearance for combustion air supply, sure you can duct the vents upwards, but more important is locating intake or exhaust vents sufficiently high to also avoid being blocked by snow - if you live in snow country.

Question: vent clearance distances to propane tank fill valve

(Jan 11, 2015) Dave said:
Please advise, what is the code distance between exhaust outlet for direct vent propane and inlet valve and/or fill valve for fuel tank (distance to tank)? Thanks much.

Reply:

Dave

We give clearance distances for LP tanks at

LP / PROPANE GAS TANKS

Question: Improper direct vent installation?

(Jan 15, 2015) Carole Rowley said:
I have had a new gas system put in that vents out to the side of the building on to the garden and street, It's a private home.

I travel a lot. My neighbors have sent me concerned emails about the fact that all around the exhaust pipe there are icicles forming. obviously attaching themselves to the siding (not wood siding.

I suppose it's some kind of plastic) Usually I only have icicles hanging from the eves. Can this corode the siding?

Has the vent been improperly installed? It sticks out about 3 or 4 inches from the siding. I did have other problems with the companies installation. I wish I had chosen to go through the chimney but the company suggested it would be more expensive . true? Then venting system is very noisy - both inside and outside the house.
Thank you for your help.

Reply:

Carole

Watch out: the dangers are more than ice damage to siding. Ice formation at a direct vent gas appliance can ultimately block the vent causing formation of dangerous, even fatal carbon monoxide gas in the building, or loss of heat and concomitant freeze damage to the building.

it's possible that your venting is not sloped properly or not handling condensate properly.

Use our email found at CONTACT at page top or bottom to send me some photos and I can comment further.

Question: I only have two (2) feet 9 inches from an old Exhaust Power Vent (oil fired furnace) to a 90 degree corner of the building

3 Feb 2-15 Rev. Odie said:
I only have two (2) feet 9 inches from an old Exhaust Power Vent (oil fired furnace) to a 90 degree corner of the building (outside). The power Vent needs to be replaced with the installation of a new oil furnace. Town codes will approve depending on the distance requirements of the manufacturer.

Are their any current Power Vent manufacturers that would allow installation of the power vent at that distance from the corner? If it is "recommended" three (3) feet but not "required", is it a danger to install at the distance I have?
Thank you

Reply:

Odie, my reading of the direct vent clearance distances in the table in our article above shows that two feet (or more) from an outside corner is acceptable.

Question:

(Feb 3, 2015) Rev. Odie said:
I only have two (2) feet 9 inches from an old Exhaust Power Vent (oil fired furnace) to a 90 degree corner of the building (outside). The power Vent needs to be replaced with the installation of a new oil furnace. Town codes will approve depending on the distance requirements of the manufacturer.

Are their any current Power Vent manufacturers that would allow installation of the power vent at that distance from the corner? If it is "recommended" three (3) feet but not "required", is it a danger to install at the distance I have?

Reply:

Odie, the specs in the article above point out that two feet from the corner is in-spec.

Question:

(Feb 4, 2015) Luke said:
I did a roof for a guy and totally reflashed properly around the chimney and put in new counter flashing. Hes still getting leaks inside on two corners on the same side of the chimney. He has a high efficient boiler and it just vents into the brick chimney. There is tons of steam and in the attic the bricks are soaked. I'm sure its the boiler that is causing the bricks to get wet and causing the leak. My question is shouldn't there be a b vent or a plastic pipe that runs right from the boiler all the way up the chimney past the roof line?

Reply:

Luke:

You raise a common and troubling issue I agree.

First, double check that there is a good chimney cap and crown and top seal so we know that we're not getting rain blowing down the flue interior.

Then take a very close look, from in the attic, at the juncture of chimney to roof deck: you should be able to see if water is entering at that point - if not I suspect the flashing is not leaking.

In comparison, if moisture is condensing in the chimney flue interior and leaking through the chimney, it's likely to leak out at several points along the run of the chimney inside the building.

Next, if this is a single-thickness (single wythe) brick chimney that is un-lined, in my opinion it's unsafe and needs a liner.

Finally, if this is not a single thickness of brick and if you don't see obvious leaks coming out of the chimney but originating below the roofline, to protect both the occupants and yourself, call for a careful inspection of the chimney interior flue safety and condition by a certified chimney sweep, using a Chimscan or similar camera.

See this article

inspectapedia.com/chimneys/Un-Lined_Chimney_Flues.htm

Keep me posted. Use our CONTACT link to send me photos for further comment

Question: snow covers direct vent chimney outlet

Apr 28, 2015) Jack said:
I have read this information with great interest. I have the two pipes in question and each winter these pipes get covered with very heavy snow.
I was wondering if there is a recommended covering that I can use instead of continually having to shovel the snow away. Any information would be helpful. Jack Walsh at jfwalsh01@comcast.net.

Reply:

Jack

The installation instructions I've read suggest that the vent needs to be located above the snow line. You may be able to build a shed roof at a safe (fire cleareance) height above the vent but I would not make such a modification without first checking with the manufacturer of your particular equipment. Or tell us the brand and model and we'll check into it as well.

Question:

(Apr 29, 2015) Randy said:
In a two-pipe "direct-vent" system, is it possible to draw combustion air through a wall and vent the exhaust out the roof? This would place the hot air exhaust away from people, plants, etc., but farther than 24" from the intake. Is this inadvisable? If so, why?
Thank you.

Reply:

There may be such a system - I'm not familiar with it. There are complete direct vent systems that operate vertically however. Did you check with the manufacturers about vertical venting models of their equipment?

...

Continue reading at DIRECT VENT WIND PROBLEMS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• DIRECT VENTS / SIDE WALL VENTS
  • CONDENSING BOILERS/FURNACES
  • DIRECT VENT GAS APPLIANCE CLEARANCES
  • DIRECT VENT INSTALLATION, SNAFUS & SPECS
  • DIRECT VENT WIND PROBLEMS

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DIRECT VENT WIND PROBLEM FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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