How to integrate ERV with bathroom direct venting if needed.
mhenson
| Posted in General Questions on
I am building a home in Colorado at 8500ft zone 5a and am about to install rigid ducts for a Zehnder Q600 ERV. Zehnder’s analysis and a drawing of my layout are attached, ductwork is rigid metal.
I have read the articles and posts on avoiding using the ERV for bathroom exhaust. However, in trying to limit roof penetrations, reduce costs, and simplify the system, it would be very beneficial if the system, as I have drawn it, would work.
As drawn, the system will run on medium 195 CFMish, boost at 353CFM, and there are multiple exhaust vents in the bathroom where needed the most.
Do I have to add any direct venting to any of the bathrooms? If so, will they unbalance and hurt the ERV? I have assumed the blower door at ACH 2.0, but hope it will be better than that because all the taping/air sealing is being done by myself and a helper, and the detailing is very good, maybe excellent.
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Replies
Since your boost flow is about 2x steady state, you are looking at 40CFM per bath. I have a 30CFM ERV pickup plus an exhaust fan but never need to run the exhaust fan for a shower.
I think you'll be fine as is, maybe add an adjustable damper to the less used bathrooms in case you want a bit more flow in the main suite down the road.
Great news, thank you.
mhenson,
The situation is a bit more nuanced when it's an ERV, rather than an HRV.
From: https://www.greenbuildingadvisor.com/article/does-a-home-with-an-hrv-also-need-bath-fans
"What about ERVs?
A final note of caution comes from Max Sherman, a senior scientist at Lawrence Berkeley National Laboratory and former chairman of the ASHRAE 62.2 committee. “From the [ASHRAE] 62.2 compliance point of view, 20 cfm continuous extract complies, which should be easy for a ducted HRV to meet,” Sherman pointed out. “So for an HRV, I think there are plenty of reasonable designs without having a separate exhaust. The situation for an ERV, though, needs a bit more thought. Since an ERV recovers moisture (and maybe formaldehyde), you are not really exhausting moisture from the bathroom, you are redistributing it. There may be times of the year where that is just fine, but there will be times when you really just want to exhaust it. So I have more sympathy for adding the extra exhaust (e.g. instead of a booster fan) when the system is an ERV.”
I am in a high desert, but there are times when clouds are on the ground at 8500ft. Our humidity averages 35-45% and this house is hydronically heated rather than forced air. We won't need air conditioning in the summer even though we do get a couple of days that reach 100 degrees F. The nights are cool, and a couple of open windows at night will keep things pleasant. If you have looked at the drawing I have placed multiple exhaust vents in the primary bathroom, which has the steam room.
What would you recommend?
mhenson,
I think you will be fine with the ERV on its own.
Malcolm Taylor