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CHIMNEY INSPECTION DIAGNOSIS REPAIR
BACKDRAFTING HEATING EQUIPMENT
CARBON MONOXIDE - CO
CHIMNEY COMPONENT DEFINITIONS
CHIMNEY FIRE ACTION / PREVENTION
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
FLAME COLOR, BLUE vs YELLOW COMBUSTION
HEATING SYSTEM INSPECTION
HOME HEATING SAFETY
ODORS GASES SMELLS, DIAGNOSIS & CURE
SAFETY RECALLS CHIMNEYS VENTS HEATERS
STAIN DIAGNOSIS on BUILDING EXTERIORS
WOOD, COAL STOVES & FIREPLACES
WOOD STOVE SAFETY
This article describes side wall vent systems for conventional & mid-range-efficiency heating boilers, furnaces & water heaters. We include for comparison, low temperature side wall vent systems used by high efficiency or condensing boilers, furnaces & water heaters. We explain the difference between side wall or direct venting for conventional/mid-range efficiency oil or gas burning heaters and side wall vented high efficiency condensing heating appliances. Contact Us by email if you are having trouble finding the information you need.
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Direct-venting or side wall vent chimney and flue systems are a method of venting the exhaust gases from a heating appliance directly out through the side wall of a building while eliminating the need for a vertical chimney of any sort. Gas or oil fired side wall power venters are provided by several manufacturers listed at the end of this article.
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Side Wall Vent Equipment for Oil Fired Boilers, Furnaces, Water Heaters
For safe and clean sidewall venting of oil fired heating equipment the vent system incorporates a power vent fan to assure that gases leave the building side wall with sufficient velocity to avoid sooting or otherwise harming the wall.
The system, such as Tjernlund's SIDESHOT® series of power vents draws outdoor air thorough the outer passage(s) of a multi-walled vent plenum, cooling the exhaust gases as they pass through the vent.
Risk of fire and heater malfunction with improperly installed or site-built side wall vent systems
One look at the "do-it-yourself" attempt at side wall venting (photo at left) makes clear why the proper equipment is needed to vent an oil fired appliance directly though the building wall. Avoid a building fire with do-it-yourself though-wall chimneys & flues
Our soot stained wall photo (photo at left ) shows what happens at a direct-vented oil-fired heating system when there are multiple errors and unsafe conditions including:
The heater is not working properly and needs immediate service as it is blowing thick dense sooty smoke
The through-wall metal flue vent and "chimney" appears to be a home-made adaptation rather than a listed and approved direct-vent device.
The effects of this home made direct-vent "chimney" are quite visible: the siding on the building has been thickly coated with soot. If you (click to) enlarge the photo you will also see some interesting reverse thermal tracking effects marking the wall studs. This is an unsafe installation that needs immediate repair.
Watch out: the photograph above illustrates an unsafe thorough-wall vent for an oil fired heating appliance. See SOOT on OIL FIRED HEATING EQUIPMENT for more information. We have received or read building owner complaints that sidewall venting has "ruined the building siding" or "stained the siding" but in our OPINION such problems occur because of an improper installation or improper heating equipment maintenance.
Side Wall Power Vent Equipment for Gas Fired Boilers, Furnaces, Water Heaters
Our photo at below left shows an Energy Kinetcs oil fired heating boiler vented using an OEM direct vent system. At below right is the exterior wall of the same installation. The stained wall photo (photo at left ) shows what can happen at a direct-vented high-efficiency heating boiler if the vent is not properly sloped through the wall. Condensate accumulates in the vent pipe, dissolves flue gas deposits, and ultimately leaks both outside and back into the equipment.
To repair this mistake the installer will have to disassemble the entire vent system, and either remove a bit of masonry block from the bottom of the present wall opening or change the interior flue vent connector piping to slightly raise the inside end of the through wall vent - one or the other - to obtain proper condensate slope and condensate handling on this equipment.
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Direct or Sidewall Vent Conventional Oil or Gas Fired Heater Exhaust compared with a High Efficiency Condensing Furnace or Boiler
Exhaust or venting of heating appliances may be horizontal, direct through a building side wall, or vertical, up through the building roof. But what is the difference between Direct Exhaust and Direct Venting ? Weil-McLain makes the following important distinctions: 
Definitions of Sidewall or Vertical Direct Venting compared with Direct Exhaust
Direct Venting uses a power ventilating blower or fan (and in some models a heat exchanger plenum to cool outgoing gases passing through the building wall (sidewall direct exhaust) or roof or through an existing unused chimney through which a vent pipe is passed (vertical direct exhaust). Combustion air for heating boilers or furnaces is drawn from outdoors through a dedicated air intake pipe or duct (the small diameter pipe in the pair at left of our photo below).
Definitions of Sidewall or Vertical Direct exhaust:
Direct exhaust venting draws combustion air from the utility room or boiler room around the heating appliance and vents appliance exhaust out through a building sidewall or through the roof using an approved or listed B-vent, metal chimney, or similar materials. Combustion air is provided to the heating appliance from the space surrounding the equipment.
Sidewall direct exhaust heating appliances
Sidewall direct exhaust uses a B-vent or other listed or approved metal or even plastic flue vent connector and metal chimney materials to vent outgoing combustion gases through a building side wall (sidewall direct vent).
A blower or power vent draws combustion air in to the heater and a power vent pushes exhaust gases out through a separate or dedicated exhaust flue.
The heating appliance vents directly out through a building side wall, powered by natural draft provided by the heating equipment, typically using a single wall metal flue or chimney or a B-vent. This venting method, typically for gas fired boilers, can be used only by certain heating appliance models such as Weil-McLain's CGs boilers excluding the CGs-4E model.
Vertical direct exhaust-vented heating appliances
Vertical direct exhaust is a similar installation to the sidewall direct exhaust vented vertically, typically up through the building roof. This heater venting system, typically for gas fired boilers, is used only by certain heating appliance models such as Weil-McLain's CGs boilers.
Safety Controls at side wall power venters include
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Safety controls and power vents for gas fired heating appliances are certified by the AGA, the American Gas Association.
Image at left courtesy of Carson Dunlop Associates. [Click to enlarge any image]
What's the Difference Between Venting a High Efficiency Condensing Boiler or Furnace or Water Heater with a Mid-range or Conventional Heating Boiler, Furnace, or Water Heater?
In comparing the venting of exhaust gases from a high efficiency furnace, boiler or water heater with the venting of exhaust gases from a conventional heating system it will be immediately obvious that the high efficiency equipment exhaust is produced at a low-enough temperature that it is vented through comparably small-diameter plastic piping rather than a cooled, fire-protected metal heating vent.
What can be confusing is that some mid-range efficiency heating equipment may vent through a (larger diameter, say 4") plastic heater vent referred to as HTPV (high temperature plastic vent) chimneys.
We illustrate an HTPV system at below left and a high efficiency plastic direct vent system at below right (Image courtesy of Carson Dunlop Associates). More details about HTPV and a product safety recall are at PLASTIC Plexvent / Ultravent RECALL.
Exhaust Vent Termination Clearance Requirements
In a table below we provide a complete list of required clearance distances between the air intake or combustion gas exhaust vents for direct vented heating appliances. Illustration adapted from Thermo Products installation instructions - click to enlarge this or any other image or photo at InspectAPedia. 
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Some highlights include:
Importance of Proper Slope on Heating Equipment Exhaust Vent Piping & Protection from Blockage by Snow, Ice, Shrubs or Wind
We can tell from the height above ground that the heaters are most likely located in the building basement.
The pair of plastic lines in the left of the photo are an air intake (the shorter protruding plastic pipe) and exhaust vent outlet (the longer plastic outlet pipe). The wider single round plastic vent at the right side of our photo is venting a second appliance, perhaps a water heater.
Watch out: We cal also see that as with the gas appliance power vent shown in the previous section, this high efficiency heating system condensate is also not being properly drained from the left hand condensing heater - instead of condensate running back into the building and into a building drain, this pipe is sloped so that condensate runs out of the end of the plastic vent line.
The problem with this arrangement becomes evident in cold weather as condensate freezes and the ice formed can actually block the safe venting of exhaust gases.
Watch out: Ice formation at sidewall vents is not the only cold weather hazard for this equipment. Our photo at left shows that the vents are less than 24 inches from the ground. In climates where snowfall may occur at depths capable of covering the air intake or sidewall vent outlet, Vermont Gas and Thermo Products both warn that it is critical to keep sidewall vents clear of snow-cover. Blocking the combustion air intake or exhaust outlet by accumulated snow, ice, or even shrubs or piled leaves can result in dangerous. potentially fatal carbon monoxide gas poisoning of the building occupants.
You should inspect the exhaust vent and combustion air intake vent for blockage at least annually, and we recommend further inspection in winter for blockage by snow or ice:
Protect direct vented appliance vents from becoming blocked by snowfall
As you can read in our citation of direct vent and sidewall vent clearance distance requirements in the FAQs below,
For at least some heating appliances and manufacturers, and to solve vent clearance difficulties when your installation cannot meet the specifications in the Gas Code, manufacturers' specifications, or local building codes, roof vent termination kits are available. Notice that the illustration (left) of roof-vent termination of direct-vent appliance air intake and exhaust does not show the necessary flashing & sealing to avoid roof leaks. Illustration adapted from Thermo Products installation instructions. 
Watch out: when chimneys or vents pass through building floors and roofs above, additional fires stopping may be required.
Protect direct vent appliances from wind:
Comment: Keep hedges, fencing, or other wind barriers far enough away from the air intake vent to avoid obstructing air intake, and keep hedges far enough away to avoid plant injury from the heat of exhaust gases.
Illustration adapted from Thermo Products installation instructions. 
Comment: OPINION: an exhaust vent that is dripping condensate to the outdoors in freezing climates risks dangerous blockage by ice formation.
Weil Mc-Lain , Thermo Products  and other manufacturers warn that if the heating appliance is in an area where local indoor-area-supplied combustion air is likely to be contaminated the installer must pipe an outdoor combustion air supply to the heating boiler (or other heating appliance) combustion air intake port.
Watch out: There are critical concerns with combustion air contamination for heating appliances:
Combustion air that is contaminated with corrosives can damage the boiler by corroding the heat exchanger or other components. The result can be worse than damage to the equipment. Corrosion that leads to flue gas leaks can leak potentially fatal carbon monoxide or other gases into the occupied space of the building.
Other combustion air contaminants that are flammable or themselves combustible could lead to an actual fire or explosion.
Examples of corrosive contaminants include
If your building contains any of these or other corrosive or explosive products and if you cannot remove them from the locale, an outside combustion air supply must be piped to the heating appliance air intake.
Watch out: also make sure that the combustion air supply outdoors is not itself close to a source of corrosive or explosive materials.
Direct sidewall vent heating appliance manufacturers & products can be listed here at no fee. CONTACT US to provide information or technical comment.
Listed special gas vent systems that comply with UL-1738 & UL S636 and in Canada, certified by CSA are the only vent systems that can be used with Weil Mc-Clain's CGs heating boilers. Depending on the brand and model, your heating appliance may have similar restrictions so be sure to read the installation instructions with care.
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Frequently Asked Questions (FAQs) about Sidewall Vent Equipment for Heating Boilers, Furnaces, Water Heaters & Fireplaces
Question: is it ok to install an elbow on the outside plastic direct-vent exhaust to avoid ice problems?
I see by the photo of ice on the exhaust pipe, 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
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?
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. [www.bclaws.ca/EPLibraries/bclaws_new/document/ID/freeside/00_03038_01]
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]
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:
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
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
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
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.
Thanks to Alan Carson, Carson Dunlop Associates, Toronto, for assistance with this topic.
Question: spalling brick wall damage from gas fired heater exhaust
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
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. (CARBON MONOXIDE WARNING )
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.
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