ERV Without Bath Fans in Humid Climate
On recent projects in the PNW (zone 4), we have connected the interior “return” side of the ERV to bathrooms, kitchen and laundry. The interior “supply” side was ducted to bedrooms and living areas. Instead of providing separate bath fans, we installed timer “boost” switches that put the ERV into max speed for a set time (an hour or two).
Next project is in central Texas (border of climate zone 2A and 3A). Seeking opinions on whether the approached (ERV with no bath fans) described above would work well in this warmer and more humid climate. Or, should there be both an ERV + separate bath fans? There will be supplemental dehumidification plumbed into the ASHP ducting.
In searching the site, some (Martin) appear to advise against using ERVs as bath fans (see for example: https://www.greenbuildingadvisor.com/question/erv-as-a-bathroom-vent-fan).
Thanks in advance for opinions.
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Replies
There is nothing wrong with using the ERV for bath exhaust in any climate. You'll get a bit of extra moisture transfer to the fresh air stream but bathroom high humidity events are so short it just doesn't matter.
The only issue is making sure the ERV has enough capacity on the bathroom pickups.
A 120CFM ERV is only really good for clearing one bathroom and a so-so job for two. Definately not more than that. Given that most houses around are approaching 1.5bath/bed ratio, you'll probably need separate exhaust fans for some of the bathrooms.