Venting
So now I’ve built a super tight, super insulated house. (well, I haven’t yet, but it’s in process). Seems crazy to now put in vents for the dryer and the exhaust fans that are not every bit as high tech as the wraps/barriers/HVAC/etc. My old house has just a simple roof mounted vent with no flapper. It relied on the flapper in the exhaust fan itself, which I could hear flapping every time the wind picked up a little bit. If I get on my roof on a cold day, I can feel the heat coming out of the vent when the fan is off. I don’t want to make that mistake on this new structure.
I’m thinking that eave mounted vents might save me a roof penetration and be slightly less susceptible to wind (yes?/no?). Are there particular styles/types that’ll maintain my building envelope when off, but permit free flowing air when on?
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Rszimm, if you have a tight house you won't be happy with a conventional dryer, because it will quickly depressurize your house unless you include a makeup air system. Condensing dryers cost more but are a better choice in a tight house.
If you are using exhausting bath fans instead of using your ventilation system, you should use wall caps with dampers. Soffit-mounted caps usually have spring-controlled dampers, and the springs will eventually fail.
For additional control, cape dampers can help: https://www.tamtech.com/product-category/cape-backdraft-dampers/.
Many (if not all) of the Panasonic WhisperGreen units have built-in back draft dampers. They are located on the unit (so outside air can still infiltrate the ducting) and they aren't the most effective because they are pretty light weight, but it's better than nothing if a soffit/in-line damper is not practical.
I'm not as familiar with other brands, but looking quickly at the Broan offerings some seem to have a damper in this location (like the QT series) and some do not (like the Economy series).
Still, as Michael notes, eliminating penetrations or moving to a dedicated horizontally mounted damper would be preferred.
Two good choices: The Lambro seals a bit better, but the Seiho looks nicer.
https://www.lambro.net/product/4-dryer-vent-seal/
https://seiho.com/product/sfbp/sfbp.html
Edit: Disregard Seiho's wildly impractical diagram of how it could be mounted through a roof.
You could use a HRV to do your bathroom ventillation. Relevant article:
https://www.greenbuildingadvisor.com/article/does-a-home-with-an-hrv-also-need-bath-fans
I don't subscribe, so I can't read it. But I think I've read elsewhere that around 20CFM continuous ventilation in a bathroom is usually sufficient rather than a bathroom fan that's used when needed. In my own experience I have a Panasonic fan with a 20CFM or 110CFM setting, and 20CFM is almost adequate to keep up with bathroom humidity during a shower in my small bathroom, and if I leave it running for a while afterwards it is certainly sufficient.
Interesting. I didn't spec in an HRV or ERV. I'm in Tucson, so the delta temp between inside and outside isn't ever more than 40 deg F on the coldest nights, but within 20 degrees almost all the time. By my calcs an ERV would take forever to pay for itself. Plus I've got a flat roof and no mechanical room (all mini-split), so I didn't really have a place to put one. The plans now call for the bath fan to be on low with a timer and an inlet grille somewhere in the living room. Do you guys think I made the wrong call here?
With a tight house and no distributed mechanical ventilation, you are going to have to rely on opening windows in the bedrooms year round, or the air quality will be very poor.
Ok. So maybe I'll go back and revisit. Just an FYI, this place is pretty small. 900 square feet. It's a guest house. It's got 2 bedrooms, a bath and a "common room". It's a bit like a large hotel room suite. There's not even a kitchen. I have mini-split units in each of the bedrooms and one for the common area. I've spoken with 3 HVAC guys here and all three told me that putting the bathroom fan on all the time (or on a timer) along with a vent to bring in outside air somewhere should be sufficient, but I don't think that they're familiar with super tight houses (no one builds them down here. For instance, there's a single supplier of zip system in Phoenix and they told me they've never sold any of it to anyone outside of the Flagstaff area. I had to call 5 different insulation companies before I found one that would do spray foam...)
All that said, I don't want my new house to smell like an old shoe, and it's a zillion times easier to make changes now rather than later.
rszimm,
It's the night-time CO2 build-up in bedrooms with closed doors that is the primary problem. Cracking a window does work.
Since the building is not always occupied, I think you made the right call. The weather there is pretty dry, ventillting with outside air even in the summer is not that big of an energy penalty.
The only change I would make to your plan is to have a fresh air inlet in each bedroom instead of a single one in the living space. Have the fresh air inlet near the mini split intake so that the air will get conditioned by it.
A properly sized single bath fan on low/timer should be all you need. Might be good to have a way to bump up the ventilation rate when the guest house is occupied.
If you have a small, tightly air-sealed house and no mechanical ventilation system (yet) or space to run Zender ductwork, you might consider a pair of Lunos fans for your ventilation needs.
IMO, I'd rather have separate, simple systems for ventilation and bathroom exhaust. So you still need to sort out your exhaust, whether thru the roof or thru the wall.