HRV as sole means of controlling interior humidity – fail!
I’ve got one year of data in my new house, and I’m not pleased with the HRV’s ability to lower interior relative humidity. I’m hoping folks with more experience can clarify which is more flawed: my mechanicals or my expectations.
Here is the context. CZ 5, northern Ohio. Brand new SIP construction, blower door tests coming in well under 1.0 ACH50. Volume of house approximately 10,500 cubic feet on three levels, including full poured concrete basement. Heating/cooling are two 9kBtu/hr minisplit heat pumps. One sump well in conditioned space, sealed. No combustion appliances. No dehumidifier. Full-time residents are 2 middle-aged humans, a medium dog, and a cat. Here is the ventilation setup: Venmar Kubix HRV Plus Model 44102. Exhausts two small bathrooms, supplies fresh air to two upstairs bedrooms. Unit claims 40-80 cfm depending on speed and static pressures. Trying to get someone with the right equipment to confirm airflow, but it seems strong at all ports.
So far this winter, I have NEVER been able to get any of my seven hygrometers to drop below 47%. They typically hover around 60%. All my plumbing traps are good. We hardly take any showers. We cook some, not a lot. No dishwasher. No aquarium. No dryer–we dry clothes offsite. I figure all the entrained construction moisture is long gone.
Even in a worst case scenario of compromised or short-circuiting airflow, say 25 cfm, shouldn’t this unit be capable of doing several total air changes per day? It was a damp December, but we had some cold, dry days that didn’t move the needles much.
In such a tiny tight house, does the humidity produced by just the two of us require a dehumidifier IN ADDITION to the HRV? Is there some moisture source we’re overlooking? Or is there typically a long lag in getting the house’s contents–tons of drywall and flooring and interior framing and everything–to dry out so it’s no longer the source?
Edit – hygrometers show RH varies little from upstairs ceiling to basement floor, so I haven’t been able to identify any wet zones.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part