Erv vs hrv: Dallas texas – GreenBuildingAdvisor

Replies

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   matthew25 | Sep 16, 2025 08:43pm | #1

   65-70% RH is when mold growth occurs, so you are close to that limit and should be extra careful. If the outdoor air is usually more humid than the indoor air, then yes an HRV will get you your desired outcome. But I doubt that is always the case. In the winter, for example, the indoor air would be more humid since you as occupants are producing moisture and using showers, etc. So in the wintertime an ERV would be more ideal so that you retain some of the moisture from the air you are expelling out of the house. Some companies make interchangeable cores so that you could swap between HRV and ERV depending on the season.

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   big__o | Sep 17, 2025 06:37pm | #3

   Thank you Matthew25.

   It does get above 60% for several hours a day but also does below 60 percent for several hours a day. I read on here they as long as it gets around 50% for a couple of hours a day then mold growth is not a problem

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   walta100 | Sep 17, 2025 05:44pm | #2

   “In winter when the indoor rh can get to 16%, it seems we would need supplemental humidification whether we use an erv or hrv.”

   Your low winter time humidity indicates that your home is already over ventilated and you need to work on air sealing the leaks.

   In my opinion the people that need ERVs or HRVs have problems with high winter humidity.
   
   Note I do not believe ERVs or HRVs transfer any heat when the differential is under 20°F. I am pretty sure the 90% transfer claims only happen when the differential is -40° outside and 80° inside. Let’s hope you never see a 120° differential in TX.

   In zone 1,2 and 3 if you need ventilation open a window the amount of energy to be recovered is too small most of the time recouping the high cost of this equipment is impossible in warm climates. .

   Walta

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   big__o | Sep 17, 2025 06:41pm | #4

   Hi walta, thanks for your input. The home might be over ventilated but we do what it takes to keep CO2 below 800 ppm.

   Right now my strategy is keeping windows open and even then CO2 still rises. I have a window wide open in my bedroom and without fans CO2 would still climb over 1000 ppm.

   I was thinking of self installing an erv. The Panasonic for example is $1000. I figure I could be all in for $2000. Do you think it would still be wasted money if I’m only spending $2000?

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   Trevor_Lambert | Sep 18, 2025 02:06pm | #5

   I don’t think your beliefs about ERV and HRV efficiency are correct. There are published data showing the test conditions, and while I can’t recall the exact numbers I’d probably bet my house it isn’t -40F outside and 80F inside. I also can’t imagine why there would be no energy transfer happening at a differential of 20deg.

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   big__o | Sep 19, 2025 01:04pm | #6

   @trevor_lambert. I have seen date at 32f and that’s pretty much it. do you have any reports showing efficiency at a higher outdoor temp?