Consolidating multiple exhaust vents
r_wiley
| Posted in Expert Exchange Q&A on
We’re preparing to begin our mechanical rough in on a new construction home in climate zone 6a.
Between make-up air and exhaust, we will need 7 penetrations, and this is with consolidating two bath exhaust fans into one with a remote fan.
It is my hope that I can avoid having this many penetrations through the sidewall, mainly for aesthetic purposes. Is there any recommendations to potentially consoidate some of these behind, say, a gable vent (with provisions made for insulation and air sealing)?
I am curious if there are other clever ways to achieve reducing the number of penetrations. Many thanks!
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Replies
7 Penetrations does sound like quite a few. Can you name them all off so that we can take a closer look at how you can possibly combine them? Often what I do on commercial jobs is to combine all the supply and exhaust. For example I'll have one ERV that will have two penetrations one for the intake and one for the exhaust and that will supply fresh air to the entire building. The exhaust from that ERV will also be the exhaust for the entire building, except for the kitchen hood (grease laden exhaust). Those 3 penetrations would be the only penetrations for the air systems (on commercial jobs there's usually a 4th for kitchen exhaust makeup air but for residential it's not usually a high enough airflow to warrant a separate intake).
There could be many others of course though depending on your setup and what systems we're including. Supply and exhaust for a natural gas water heater, furnace, or other appliance. Are we counting plumbing vents? I usually try to combine all the plumbing vents into one vent so that there is only one penetration for that vent. Radon vents. Wood stove chimney. Wood stove combustion air.
Of course, and yes that approach makes sense. I did not consider bringing bath exhaust and HRV exhaust together. The range hood will be independent, though it will have its own MAU. Could I consolidate that with HRV fresh air intake? Here’s what we have (excluding boiler exhaust and intake). Dryer exhaust with inline fan;
Bath exhaust, remote for multiple baths;
Rangehood exhaust, remote w/ MAU;
HRV;
General exhaust fan for attic
The dryer exhaust will have to be its own separate exhaust.
The Range hood exhaust will have to be its own separate exhaust.
Instead of having restroom exhaust fans, you can duct the HRV exhaust from the restroom.
Does the range hood need it's own MAU or is it small enough the space can accommodate the exhaust flow rate? Typically most residences don't have a MAU for the range hood. The only problem with combining the makeup air for the range hood with the HRV is that it will create an imbalance, unlike if you use the HRV to both exhaust from the RR and provide outside air to the house balancing out that exhaust. But you could combine the two with ductwork if it is sized properly and then you would have just one penetration, yes, that could work.
If you can duct all of your restroom exhausts to the HRV that will reduce those exhausts to just one.
I don't really see how to eliminate any more of these penetrations. You could possibly combine the HRV and kitchen hood exhausts into one duct and have backdraft dampers on both but that may not work too well so I don't think I'd go that route.
1-HRV & Kitchen intake
2-HRV exhaust
3-Kitchen exhaust
4-Attic fan
5-Dryer exhaust
Deleted
Thank you!
I'm wondering about the attic exhaust fan - haven't those been shown to be totally useless? If you use a condensing dryer, you don't need a dryer vent (but check with code - we had to provide the inspector with a documentation from a specific condensing dryer showing it did not use an external vent). Ditto for the range hood - we have a large, mostly unfinished basement and are venting our range hood thru a large particulate and charcoal filter into that space. We did this for both air flow and to avoid venting the hood out through the ceiling of our ranch-style front porch (again, run this by the inspector - I had to provide the IRC section allowing this and the range hood documentation). We're also using the ERV to vent the bathrooms, with a booster switch. We haven't moved in yet so I can't yet tell you how well all this will work.
These are some good ideas. If the roof were changed to a naturally ventilated attic with soffit vents and a ridge vent and the appliances changed slightly this could get down to just two penetrations for the HRV.