More Product Guide
Balanced ventilation systems like heat recovery ventilators (HRVs) and energy recovery ventilators (ERVs) require two openings in the building envelope. One brings in fresh outdoor air, which is filtered, tempered, and distributed throughout the building. The other exhausts stale air. The exhaust air is usually drawn from a central return or from bathrooms and laundry rooms, which have elevated levels of moisture and other pollutants.
The ventilation unit contains filters, fans to move the air, and an exchanger across which heat (HRVs) or heat plus moisture (ERVs) moves between the incoming and ongoing air streams. Ducts connect the unit to the outdoor openings and the indoor distribution system.
Previous GBA articles explain the benefits of heat- and energy-recovery ventilation, explore ducting approaches, discuss strategies for preventing frost buildup in cold climates, and describe the commissioning process. I’ll focus on two small but important details: 1. location of ventilation openings, and 2. termination fittings. There are currently hundreds of products available; here, I’ll cover the main types. The prices listed are taken from online sources and are meant to provide a general sense of cost.
What the codes say
The International Residential Code (IRC, here I’m quoting the 2021 Edition) addresses the air intake and exhaust locations in sections R303.5.1 and M1504.3. Air intakes must be at least 10 ft. “from any hazardous or noxious contaminant, such as vents, chimneys, plumbing vents, streets, alleys, parking lots and loading docks.” This provision prevents vehicle exhaust, flue gases, and sewer gas from being drawn in and circulated through the living space.
The IRC continues, “For the purpose of this section, the exhaust from dwelling unit toilet rooms, bathrooms and kitchens shall not be considered as hazardous or noxious,” though, for obvious reasons, it’s best to keep fresh air intakes away from these potential sources…
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7 Comments
Great overview. I recently had a builder switch my carefully planned ERV intake and exhaust locations to an all-in-one wall caps without my knowledge; I don't like the idea and will continue to avoid them when possible.
Thanks, Michael. The extra restriction from these is pretty significant and could lead to problems with airflow, balancing, and possibly fan energy/lifespan if it's not taken into account.
Jon,
Great article - as usual.
One thing that I wish was designed differently is the connection between vent terminations and the ducts they are connected to. When terminations need to be swapped out for any reason, the connection is often inside the wall/floor, and not accessible to be mechanically connected or re-sealed. I wish there was a standard plate that both provided a mount for attachment, and a seal to any style of termination.
Doug McEvers - are you reading this?
Thanks, Malcolm. This is a great idea. Getting a good connection with flex duct takes attention to detail when the fitting is easily accessible, and when it's in a wall or floor, it's even harder. It seems like this would be a useful and low-cost accessory.
Great article. One question I hate the 10” and 12” hoods we use for exhaust and see all the time companies selling the rectangle hoods that look a little better but never see what the conversion from round to rectangle duct should be is there a calculation that if I need a 10”round the rectangle must be size x to prevent a problem
Any recommendations for a supply / exhaust through a soffit? I.e. both point down.
User...047,
Supply doesn't matter. For exhaust I would get a directional vent termination to move the air beyond the soffit. Something similar to this:
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