Spalling brick below vent (C) Daniel Friedman Side Wall & Direct-Venting Heater Installation SNAFUs

  • POST a QUESTION or READ FAQs about the installation or diagnosis of sidewall vent or direct vent chimney or flue exhaust systems for heating appliances and for condensing furnace or boiler sidewall vents

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Specifications & Errors in Direct Vent, Side-Wall Vent, & Condensing Boiler or Furnace Vent installations:

This article describes common mistakes found in both side wall vent systems for conventional & mid-range-efficiency heating boilers, furnaces & water heaters and also mistakes in low temperature side wall vent systems used by high efficiency or condensing boilers, furnaces & water heaters.

We include links to example installation specifications for side wall vented hearers from manufacturers of several brands.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Direct Vent Exhaust for Heating Flues: Installation & Inspection Questions & Answers

Reader Question: is it ok to install an elbow on the outside plastic direct-vent exhaust to avoid ice problems?

Vent condensate freeze (C) Daniel Friedman

I see by the photo of ice on the exhaust pipe of what looks like a condensing boiler or furnace installation, that the installation is not sloped back into the furnace, or that it may not be high enough.

Can the pipe be best elbowed on the outside, slanted back into the house, while extensions are on the exhaust pipe well above snow levels.

And what about insulation in an unheated crawl space and a heat tape.

Then there are testing for improper gluing of the elbows and round connectors of PVC piping. How should they be tested for no leakages. - Concerned2 11/20/2012

Reply: No


I am nervous about your pipe elbowing in the exterior as I think it violated the manufacturers instructions, and increases the freeze risk too by adding more travel distance through freeze temperature piping - but I may have misunderstood.

The pipe needs to be re set to proper slope to fix the freeze problem

Tests for leaks in a PVC condensate drain can be done using pressure fittings and plugs but I doubt anyone does that, relying more on workmanship during installation and inspection for leaks afterwards.

Too I agree that a condensate drain routed through a freezing crawl space would be unsafe. I would not rely on heat tapes, rather the installation sounds off.

Reader follow-up:

Direct vent heater cleareances

I live in B.C. I do not know who was to be held accountable when the installation of my Lennox Pulse was not inspected by the gas inspector, back in 1994.

A trouble area inside the house, just before the exhaust PVC pipe was to go outside, there was placed four connectors, close together, up in the beam or joist area of the house. They did this to have the pipe on the outside 12 inches above snow level, which is not sufficient for this area.

One elbow became detached. No one in the gas industry would come to fix a Lennox Pulse G21, claiming if they did so, it would void the warranties. The installer would not inspect the pipe.

The permit was taken out, but no inspector came to investigate, and there seems to be no one investigating how pvc pipe is installed to a high efficiency gas furnace. I went from 1995-1996, after the detached pipe was noted by guests reporting they were feeling sick in the bedroom above this venting.

The problem was that no one would come because it was Lennox G21 H-EF. The other companies were declaring they did not know how to work on a Pulse, or testing piping or the heat exchanger.

that there were so many elbows in a small area, less than 15 inches, between the beam and the outside house what Code or instructions from the manufacturer were being violated, and how do you deal with those involved?

Rather than fixing the problem on May 3, 2012, another Lennox dealer, instead of my request one straight pipe, a correction of that area, he, too, put in two elbows on the inside area, up in the beams. I asked for a straight pipe and the elbows on the outside of the house.

He left the premises not pressure testing the piping system or the heat exchanger as requested.
He put in 90 percent new replacement piping, when the only area was of less than two feet. He said he did a visual inspection for the heat exchanger, knowing the exchanger was 18 years old, and the new piping could yet have a problem of leakages.
What all codes may have been violated? - Concerned 12/2/12

More from Concerned2:

In British Columbia we do have a licensing and training agency and one that gives out permits and for inspection. This is a private group, operating as a not-for-profit corporation. It is unclear under what Provincial Government Ministry, if any, they are subjected to, if they are doing their duty. It is believed they operate with government funding and fees for permits.

Who can determine if this SSA have any authority on installers, suppliers, manufacturers, and gas service providers for any brand of H-EF, and for testing of safety of a H-EF in the home and on the piping systems used for any and all H-EFs. It would take an experience trades person to understand this act, or an extremely intelligent lawyer. []

Failure to inspect on original installation of an unknown city building inspector, or gas inspector, Dec. 8, 1994, And the allowance that a requested service of pressure testing was not thought in violation of the due diligence of care owed by a Lennox dealer to a user of the Lennox product.

More from Concerned2:

Failure to inspect on original installation of an unknown city building inspector, or gas inspector, Dec. 8, 1994, And the allowance that a requested service of pressure testing was not thought in violation of the due diligence of care owed by a Lennox dealer to a user of the Lennox product. (this comment is not published until you approve it) [delete]

(Dec 1, 2012) The one site demonstrates a proper pvc venting installation, the other shows an improper system, which was similar to mine. On the inside of my house there were four connectors, or elbows, and one elbow was not properly glued and became detached.

No other firm would touch the work previously done by the Fort St. John Lennox dealer, nor of the current Dawson Creek Lennox Dealer. thermo pride installation of venting pipes - .they are close to the house, high up, and not sticking 12 inches from the house.

Figure 8, page 21 of Thermo Pride's installation instructions vs photo of ice on venting pipe, extending about 12 inches from the house, and not above expected snow levels. - [see sketch above][15]

The inside pvc pipe just before the pipe goes to the outside vent is yet having at least two connectors, a 90 degree and a 45 degree elbow, yet up in the beam area of the house, of less than twelve inches of that area. My crawl space is unheated, and the installation instructions were ignored, in 1994, and now of May 3, 2012, requiring insulation, plus an electrical heating tape, installed for winter use.

Can anyone tell me of what National or International codes were violated, and is there any discipline if the local city inspector or Provincial inspector did not inspect the installation to the directions stated by the manufacturer in printed manuals or how to test PVC piping systems, and, of course, the heat exchanger. No one is taking any responsibility. All is placed on the homeowner, and we had the least chance to know what was proper, in the past, and even now. Please help. I would think a lawyer would be required of any violations or risk to the home and people. Thank you for forwarding to those who may be concerned in Canada and the USA.


Concerned: note the with respect to clearances between the direct vent and the ground surface, the distance shown is a minimum not a maximum allowable distance. But in relocating the exhaust or intake openings, keep in mind that other safety clearances from windows etc. must still be respected. The instructions to which you refer include the following additional details that address your concerns:

The outlet/inlet of the vent and air intake terminations shall be a minimum of 12 inches above highest anticipated snow level. The vent outlet must be installed a minimum of 12 in. above the air intake inlet.

The combustion air intake shall be installed upwind of the vent outlet when exposed to prevailing winds. [15]

More Unsafe Direct Vent Chimney Details

Below: other strange and terrible driect-vent chimneys we have found:

First what looks like automobile or truck exhaust pipe extensions used as a direct vent flue tdhrough a stone masonry wall.

Second a leaky damaged, direct vent chimney at the same building.

Auto exhaust used for direct vent chimney ? (C) Daniel Friedman at Damaged leaky side wall vent chimney (C) Daniel Friedman at

Reader Question: spalling brick wall damage from gas fired heater exhaust

Spalling brick wall over gas heater vent (C) InspectAPedia RM

My propane boiler exhausts out at about 18" above grade. I have recently had some issues with it short cycling and possibly some propane has not been burning (sometimes all jets weren't firing.)

While investigating I noticed that the brick is spalling near the exhaust. I had some mortar falling out there when I moved in two years ago, but haven't gotten around to fixing the problem. Now the brick is spalling off also, I don’t think it was doing that before. Any ideas if this could be caused by improper boiler operation?

The vent is 4” type BH stainless single wall, pitched so it higher on the outside, cap does’t protrude far from the brick. However the manufacturer suggests venting so it is pitched down to the outside.

I am thinking of replacing the existing exterior cap with a 90 deg elbow pointing down 8” from wall as suggested by the manufacturer (original one installed by contractor had been broken off, this one installed by previous home owner.)

The boiler is a Smith GV100W, maximum of 84% efficiency. I've attached a picture in case that helps, Thanks. R.M. 1/21/2014


Spalling brick below vent (C) Daniel Friedman

A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. That said I offer these comments:

As both your photograph (above) and mine (at left) show, exhaust gases can cause spalling brick damage on buildings. Whether the damage appears above or below the vent depends mostly on the direction of exhaust and moisture movement.

You should absolutely follow the manufacturer's vent recommendations. The manufacturer has a great interest in the safe use of their equipment, as do you.

A back-sloped (wrong way) vent on a gas fired appliance risks condensate drain-back into the equipment where it may cause dangerous or expensive rust damage, even risking carbon monoxide leaks. (Be sure you have working CO detectors properly installed in the home).

Watch out: A second consideration is whether or not you have adequate ground clearance. If you are in  a freezing climate I'd worry that snow cover can block the exhaust vent - a dangerous condition.


Finally, I agree that gas exhaust can indeed speed up spalling on brick work, especially on an older building at which the original bricks may be of a softer composition than many modern masonry walls. Perfect combustion of LP or natural gas would produce just water vapor and CO2.

But that water vapor alone, rolling up the wall above the vent, tends to be absorbed by brickwork that then, depending on climate and brick composition, may be softened or may be frost damaged.

Reader Question: gas furnace direct-vent exhaust too close to ground or not protected from snow cover

(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 in laws 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 ?


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.

12/5/2014 Reply from reader Concerned2: lack of enforcement of recommended direct vent safety specifications

Concerned 2 said: [OPINION]

Update. Bad original installation on a Lennox Pulse G21Q3-100-3 and poor workmanship skills, thereafter. I had the outside air intake pipe cut off and this has stopped chilly air (-39 F) from coming into the furnace and shutting it down. I have a 1200 ft of unheated crawl space and this seems best to have the intake air into the HEF to be at about 50F. It prevents the water vapor from drawing into the air vent and freezing, too. No chilly air is shutting down the furnace for colder climates that can be -39 C or lower.

I yet have to change the exhaust venting to be over 12 inches above the expected accumulated snow for the Dawson Creek,BC area, the drifting can be up to 5 feet or 60 inches. Many older roof top chimneys were at least that 60 inches tall. I think the system was preparing for global warming. I yet have to have this 20 feet of venting to be insulated inside and outside.

It seems the HEF installers in this colder area have been allowed to reduce the roof top and side venting to dangerous heights (24 inches or less) and this is being ignored by the British Columbia private safety gas authorities, at present.

Few inspections. What is justice when the good of the manufacturer's furnace's installation instructions are ignored or the good in the CSA B149 Codes?

What is justice if the furnace manufacturer never really tested their HEF in the colder climates and approved the six inches close venting systems to allow re circulation of the bad air into the gas and air chamber and shut down the furnace and cause expensive repairs to the control board unit, a cost of close to $1000.00 to repair the furnace.

Others have had similar freeze up but in their city water lines. I now use RV anti-freeze if any of my exhaust venting is freezing up or in the water drip vent. It works. And so does drawing in the crawl space air at 50 F to no more than 80F back into the furnace from a 1200 square footage of crawl space. If you know of any gas codes that support that this is okay, let me know, thank you.

Reader Question: Improper direct vent gas heater installation - icicles hanging from the vent, improper sealing

Leaks and icing at direct vent through side wall (C) InspectApedia C.R.

(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 corrode 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.

Leaks and icing at direct vent through side wall (C) InspectApedia C.R. Leaks and icing at direct vent through side wall (C) InspectApedia C.R.




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.

Leaks and icing at direct vent through side wall (C) InspectApedia C.R.

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.

Reader Follow-up:

Thank you so much for replying. I’m glad to find someone to trust! I am a single woman home owner and the company that installed the new Gas heating system was negligent in many ways.

Today we had warmer weather so the icicles have mostly melted but you can see a slightly darker tint in the last 3 pictures on the siding where others were. And they went up much higher on the siding on colder days/weeks forming 1 on top of the other sometimes. There are 5 views here.

Leaks and icing at direct vent through side wall (C) InspectApedia C.R.


Leaks and icing at direct vent through side wall (C) InspectApedia C.R.


Leaks and icing at direct vent through side wall (C) InspectApedia C.R.

I have to say this looks like a rather questionable vent installation at the wall. Simply screwing a flashing atop vinyl siding is hardly weatherproof and invites rain leaks into the wall structure.

And the ice as well as what looks like moisture shadows in your photos suggests to me that equipment is actually venting into the space behind the siding - itself an unsafe condition as we don't know that it's venting with proper draft and we don't know that flue gases can't be re-admitted to the building - a potential carbon monoxide hazard.

I'd start by identifying the brand, model, serial number of the equipment installed, obtaining the installation manuals for each device including the vent systems.

Compare that to what was actually done. Or if you can't find those manuals give me the equipment information and I'll see what I can find.

And tell me the city/state/province/country of this installation.

Reader Follow-up:

My heating boiler is a Burnham ESQ with IQ control system by US Boiler company
model ESC4C (serial 65410825). I don't have the installation or operation manual for my boiler.

And I took more pictures around the intake and out take. The square box is 4 x 4.5 roughly and 2 inches deep. Other round about 2 or 3 inches deep.


Burnham's manuals are now found through

Here are the user's manual and the installation & operation manuals - these should cover your unit and include venting installation details. I am including an Install/Operate manual for earlier models as I'm not sure the date of yours.

And here is an installation sketch showing details of a proper direct-vent installation for the Burnham ESC gas boiler, excerpted from the first citation given just above.

Details of direct vent installation for a Burnham ESC gas boiler (C) Burnham US Boiler -

[Click to enlarge any image]

Watch out: other readers: be sure to follow the instructions for your specific product from its manufacturer.

Reader Questions & Comments on distance between "moisture exhaust vents" and air intake vents for heaters


(Mar 22, 2015) Jag said:
In my house, the builder installed the gas vent pipe 636, about 25 feet long to exhaust the gasses to one side of the building, where as other side of the house is only about 6 feet far from hot water heater. Why did they waste pipe in extra length or is there any requirement that we must install the exhaust vent with minimum certain length from water tank. Thanks



I don't know - perhaps there was not proper outdoor clearance at the shorter route. What did the installer say in response to this question?

Reader follow-up:

2015/12/07 concerned2 said:

Update. VENTING PROBLEMS TO HEF (the below quotes a CSA standard): gas chamber outside air intake must be further apart than 3 feet from any moisture exhaust gas vent.

The B149 gas and propane code, section 8.3.7 states no moisture exhaust vent should be closer to any air intake vent back to the furnaces air and combustion chamber. All HEF produce water vapors.

My intake air vent was on the wrong side and was five inched apart from the exhaust vent. You can see in the winter the vapors being drawn into the furnace. My crawl space was no heated where the two vents run. No insulation was on them, inside or outside.

The were not above 12 inches of accumulated snow. In this area common safety for roof top or side venting, and of informed consent, should be 50 inches. My furnaces would frequntly go in shut down and on the coldest days.

Any code to take my air into the natural gas chamber in a 1200 sq. Ft. Crawl space for the 100 BTU as it would be warmer than 50 F, but not hotter than about F. I am told this is okay, but have no gas code.

Concerned2 said:

Correction, B149 8.3.7, Jan. 2010, confirmed 2015 states: the gas chamber outside air intake must be further apart than 3 feet from any moisture exhaust gas vent.



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