Venting challenges persist in the field  

By Gord Cooke

The flush mounted vent on the left tripped a vent-blocked sensor four times in one particularly cold winter in southern Ontario. The neighbour’s goose neck vent did not result in any shutdowns. It was possible the water vapour from the gooseneck vent was exacerbating the frosting over of the flush mounted grille. The occurrences were so infrequent and random that we weren’t able to correlate a cause and effect.

I was recently looking at a planned renovation project with a builder and their mechanical contractor. The project is for a quaint century home that has undergone many modifications over the years. Part of the plan requires removing a couple of old masonry chimneys, one of which accommodates the flue for an older, B-vented gas boiler.

As the mechanical contractor contemplated routing alternatives for a new direct vent boiler through messy crawlspaces and the 18-in. thick rubble stone foundation, the homeowner asked why venting was an issue at all. The owners had been doing some reading and noted, given that climate change action plans were calling for reducing the reliance on fossil fuels for space heating, they would be interested in switching to a heat pump heating and cooling strategy. They were happy to eliminate the hot water system and the associated old cast iron radiators in favour of a system with a variety of mini-split heat/cool heads to improve the carbon foot print of their home. This was with a full understanding that their energy bills might go up. Indeed, the federal government’s Greener Homes program provides space heating incentives only for heat pump-based systems, that is systems greater than 100 per cent efficient. When thinking about resolving difficult venting situations for combustion appliances, forward thinking contractors may want to first consider heating options that don’t require venting of combustion products at all.

With 25 or more years of industry experience with the venting of high-efficiency furnaces and water heaters, there should be few limitations left in finding reliable, safe and unobtrusive vent termination locations for even the most difficult remaining applications. However, there is an urgency now to move past the challenge of venting combustion products and to find reasons to install technologies that leap-frog both the efficiency of gas appliances and reduce carbon dioxide emissions.


New construction exacerbates the issue

Besides eliminating venting all together, consider other alternatives to ease the challenge of finding suitable venting locations for high-efficiency, direct vent combustion appliances for space and domestic water heating.

The challenge has become particularly acute in new construction, since over at least the last five years approximately 60 per cent of all new dwellings built in Canada were attached multi-family type units.

The drive to higher density, more affordable housing designs presents challenges in finding safe, practical and aesthetically acceptable locations for the venting of combustion appliances and ventilation systems due to diminished exterior wall areas. One strategy to easing venting challenges is to combine the space and water heating functions using a combination boiler or water heater, and hot water air handlers or other hot water-based heating systems such as in-floor heat or radiators. This can be useful as it eliminates one air intake and exhaust outlet for the traditional gas furnace.

The availability of appliances that are rated for both space and water heating has grown significantly over the last 10 years, primarily with a wider selection of wall-hung boilers and water heaters being introduced to the Canadian market. To ensure proper operation and efficiency it is important to choose combination systems that have been tested to the CSA P.9.11 “Test Method for Determining the Performance of Combined Space and Water Heating Systems (Combos).” There are now approximately 80 systems that have been tested to this important standard. To find systems that have been tested go to:


Manufacturers respond

To further ease venting challenges, manufacturers raced to find ways to increase the allowable lengths and reduce the diameter of venting pipes. For example, I purchased a condensing tankless water heater in 2019 and the maximum vent length at that time was 18 m (60 ft.). While writing this article, I was intrigued to learn the updated version of the same water heater now has a 23 m (75 ft.) maximum vent length. This is with a 50 mm (2 in.) pipe diameter. The same water heater can be vented up to 45 m (150 ft.) with a 75 mm (3 in.) diameter pipe.

These additional lengths allow contractors more flexibility in finding suitable venting locations. For example, in older, urban, tall townhomes going up through a roof may be the only option to avoid walkways, raised porches, decks and driveways that wouldn’t provide the required clearance above grade.

In small commercial applications, there has been progress in combination or co-venting of wall-hung boilers and tankless water heaters, such that the venting for two or more units can be combined into one penetration through an exterior wall. This is useful when upgrading the efficiency of large capacity old water heaters or boilers, and to enable staging and modulation of multiple smaller appliances rather than one larger boiler. Flexibility in vent locations is another benefit.

There is a good selection of vent terminations that allow for a single penetration for the air inlet and combustion exhaust while improving the aesthetics on the outside wall. The location of the exhaust of products of combustion is still limited by other air inlets, meters, and various architectural and hardscape elements. However, vents such as the flush mounted vent, shown on pg. 32, may help in finding an acceptable location. Similarly, there are concentric vent kits for both sidewall and roof terminations, shown here as well. It has been my experience that these terminations are more prone to ice-up in very cold and damp weather. Fortunately, the gas appliances they are connected to all have safety shut-offs that detect vent blockages. Advise homeowners of this nuisance occurrence – they must keep the vent termination clear to avoid no heat or no hot water calls if they choose these less obtrusive looking vents.