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kittysmitty
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# Posted: 5 Feb 2023 09:02am
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This is more toward a house, but there are some pretty smart people here, so just think of it as a big cabin. Over the last couple of years I completely redid a house inside and out. Added 1 inch rigid insulation and house wrap under the new siding, upgraded the inside wall insulation, vapor barrier and did an excellent job to air seal, confirmed by the Door blower testing. I have a Heat exchanger to exhaust the stale are and to provide fresh air. Here's my question, lets say I have the three bathroom exhaust fans running, the kitchen Range Hood on and drying a load of wash in the dryer with all vented to the outside. Where does this air come from? Does the heat exchanger supply more air to offset? Thanks in advance for your comments
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Steve_S
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# Posted: 5 Feb 2023 02:23pm
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An HRV system needs to be sized properly for any home regardless of size. You need to add up the Maximum CFM (Cubic Feet per Minute) all your exhaust systems will push out of the house and size the HRV to be able to provide that sufficiently. Bath Fans, Range hoods and such are usually around the 100CFM Mark +/- a bit but dryers are not rated in such a way so you have to make assumptions.
In your current state as you posted, the HRV will let as much air in as it can and that will vary a lot by the nature of the type & design that it is, there is a LOT of variations in designs.
IF the HRV cannot provide sufficient "input air" it will also get drawn in through chimney pipes and anywhere else that air can infiltrate. Should there be a lack of free air to move the exhaust out, it can create other issues and even create a Cavitation where the fans move nothing at all (albeit this is pretty out there nd not usual).
A simple test:
Turn on Bath or Range hood fan and go outside and feel how much air is coming out, possibly tie a wee ribbon of plastic on the vent so you can see it. Then go and turn on all your venting apparatus and check your ribbons and vents and watch, have a Partner in Crim inside the house open a window by 1" and see if the ribbons (air flow) inproves. If they do, you do not have enough free-air coming in, if no change at all, then you are likely fine.
Also of note, being a Canadian this is a constant thing we have had to deal with... An airtight home is a good thing but also a bad thing at the same time, when all closed up in a typical winter, this can allow higher levels of moisture within the building and it will condense on cold surfaces (visible or not) and ultimately can lead to various moulds, of which Black Mould is the worse of the lot ! Generally up here when an HRV is being considered, a dehumidifier component is usually included so that the return air is managed while the outgoing is dried... Failure to do so can cause that humidity to ice up at the exterior vents and even into the pipes creating yet another set of issues.
Pro-Tip for Vent Pipes from Bath Fans, Range Hood etc... Be sure to use INSULATED pipes in order to prevent condensation occurring on the pipes and dripping into the cavities providing a "home for mould & mildew" which can have adverse effects on the health of the occupants. This is a primary step to prevent creating a "Sick House".
Hope it helps, Good luck.
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Notes
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# Posted: 6 Feb 2023 08:13am
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An HRV has intake and exhaust fans balanced to equal airflows. The only way to use the HRV as a make-up air supply would be to disable the exhaust blower.
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kittysmitty
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# Posted: 7 Feb 2023 09:22am
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Steve_S Thanks for your feedback, and I am also in Canada, Nova Scotia actually. I did your simple test. Ribbon on the bathroom fan exhaust, Bathroom fan, Range hood and dryer all on. When I opened the door from outside I did see an increase in the amount of exhaust air. Everything is working well, no moisture on the inside of windows, and we have recently have some wild swings in outside temperature. Winter time humidity levels are around 30 to 40%. Again, Thanks
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Steve_S
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# Posted: 7 Feb 2023 11:30am
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Yes, I'm near Algonquin Park Ontario... Went from -40 to +5 and back to the -30's and then 30-60cm snowfalls - oi, it's been bad ! Even got snow bound here for a week till I got dug out... Good thing I am prepped for this stuff LOL...
Seems like it's all working fine for you and the most obvious indicator is not there which is condensation on surfaces anywhere. That is the one sign to keep an eye out for. CMHC has a lot of info on sick houses and what causes it and how to remedy it properly and that info is fairly handy too.
Take care Kitty 
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NorthRick
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# Posted: 7 Feb 2023 04:27pm - Edited by: NorthRick
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Quoting: Steve_S A simple test: Turn on Bath or Range hood fan and go outside and feel how much air is coming out, possibly tie a wee ribbon of plastic on the vent so you can see it. Then go and turn on all your venting apparatus and check your ribbons and vents and watch, have a Partner in Crim inside the house open a window by 1" and see if the ribbons (air flow) inproves. If they do, you do not have enough free-air coming in, if no change at all, then you are likely fine.
There is an easier way to do that test. Take a sheet of toilet paper, with the vent fan on, stick the toilet paper up to the intake in the ceiling. If the piece of paper sticks to the vent, you have some flow going out. If it just falls back to the floor when you let go, that vent isn't venting. No climbing on the roof. All our vents come out on the roof except for the dryer which goes out the wall.
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