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I’m surprised there’s no mention here of heat recovery ventilators (HRV) or energy recovery ventilators (ERV) here. New buildings are increasingly designed to p

I’m surprised there’s no mention here of heat recovery ventilators (HRV) or energy recovery ventilators (ERV) here. New buildings are increasingly designed to provide regular air exchange (fresh air replacing indoor air) while retaining thermal energy with these devices, and, in the case of ERV, retaining humidity.

jonstewart 6y ago
Yeah, ERVs are amazing. I want to install one in my house just to provide fresh air all the time.
compumike 6y ago
Agree. HRV / ERV is a powerful concept because it allows you to design better insulated buildings, both with fewer air gaps and thicker wall insulation, while still reducing indoor CO2 and humidity levels by bringing in fresh air. On the downside, like much in the HVAC world, it requires new construction or a fairly major retrofit to take advantage of it. My guess is that it's only going to make sense for new higher-end construction where other attention is being paid to energy efficiency. (Though I'd love to see a window box HRV for renters, just like window box air conditioners.) If you haven't heard of HRV / ERV yet, this video shows how they work in an impressive but simple demo with the 4 temperature sensors in the last few minutes: https://www.youtube.com/watch?v=QOSelUK6dpQ https://www.youtube.com/watch?v=QOSelUK6dpQ (Also compares aluminum core heat exchanger vs. desiccant enthalpy wheel) For the DIYers, here's a forum full of people building their own HRVs: https://ecorenovator.org/forum/showthread.php?t=891 https://ecorenovator.org/forum/showthread.php?t=891
- amluto 6y ago
  They don’t necessarily need a major retrofit. Lunos makes clever paired half-HRVs that require two wall penetrations but no ducts. Zehnder makes single-room through-wall HRVs.
mherdeg 6y ago
Yup. Now that I'm measuring how much CO2 I have indoors and can watch what happens when I open a window and it equilibrates, it's really hard to resist 2021+ plans to retool the HVAC to put in a fresh air ventilator. There were also a few days this summer where it was 50°F and low-humidity outside, but 78°F inside, my preferred temperature was closer to 72°F, and I wished I had some better way than "open a window and stick in a Lasko box fan" to cycle in cool outdoor air.
dota_fanatic 6y ago
Having just built an addition which needed its own HVAC system, I was surprised to find the cost of an American Standard ERV to be several thousand dollars, prohibitively expensive for us given all the other costs. :/
- turtlebits 6y ago
  Not sure the size of your addition, but Panasonic makes a small ERV for around $400, I use it in my 500sf workshop. They have a larger model that is around $1000.
- johnrgrace 6y ago
  Most of the cost is install. A basement glass block window with a dryer vent (under $100 for a pro to install around me) makes self installing easy and professional a few hours of labor. I've seen new ERV units under $1,000 and some pop up used on Ebay for great prices.
turtlebits 6y ago
I would only recommend an ERV for newer houses. On older houses, an ERV running 24/7 is just going to pull all the heat out of your house and cause your energy bills to go up. Best would to get a blower door test run and see what your ACH50 rating is before considering one.
kev009 6y ago
Was looking to see if anyone had experience with ERV/HRV. I would like to put these on my new to me home when I replace the HVAC units.
- blacksmith_tb 6y ago
  I've lived for 8yr now in a home with a Zehnder HRV. It has mostly worked well, though recent wildfires were too much for its MERV-13 filters, forcing me to run it at the very slowest speed and use air purifiers.
- gwd 6y ago
  I retrofitted one on a house we bought a couple of years ago. I'm really happy with it, although it does add a constant background 'hum'. It wouldn't have been possible however if we weren't doing major renovation -- we tore out & replaced the downstairs ceiling and completely redid the second floor bathroom; that meant we could run the ducts down the corner of the bathroom and then through the joists in the first floor fairly easily. And the attic is a bit cluttered with the ducts. You definitely notice a difference when you turn it off.
- tzs 6y ago
  This report [1] suggests that HRVs only actually have a net energy savings in the US in climate zones 4-8 (and such a small amount in zone 4 that it would take several decades to break even). Is there a good reason to get them if one is in a place where they won't save energy? Here's a US climate zone map [2]. [1] https://www.osti.gov/biblio/1488935 https://www.osti.gov/biblio/1488935 [2] https://basc.pnnl.gov/images/iecc-climate-zone-map https://basc.pnnl.gov/images/iecc-climate-zone-map

jonstewart 6y ago

Yeah, ERVs are amazing. I want to install one in my house just to provide fresh air all the time.

compumike 6y ago

Agree. HRV / ERV is a powerful concept because it allows you to design better insulated buildings, both with fewer air gaps and thicker wall insulation, while still reducing indoor CO2 and humidity levels by bringing in fresh air. On the downside, like much in the HVAC world, it requires new construction or a fairly major retrofit to take advantage of it. My guess is that it's only going to make sense for new higher-end construction where other attention is being paid to energy efficiency. (Though I'd love to see a window box HRV for renters, just like window box air conditioners.) If you haven't heard of HRV / ERV yet, this video shows how they work in an impressive but simple demo with the 4 temperature sensors in the last few minutes: https://www.youtube.com/watch?v=QOSelUK6dpQ https://www.youtube.com/watch?v=QOSelUK6dpQ (Also compares aluminum core heat exchanger vs. desiccant enthalpy wheel) For the DIYers, here's a forum full of people building their own HRVs: https://ecorenovator.org/forum/showthread.php?t=891 https://ecorenovator.org/forum/showthread.php?t=891

amluto 6y ago
They don’t necessarily need a major retrofit. Lunos makes clever paired half-HRVs that require two wall penetrations but no ducts. Zehnder makes single-room through-wall HRVs.

mherdeg 6y ago

Yup. Now that I'm measuring how much CO2 I have indoors and can watch what happens when I open a window and it equilibrates, it's really hard to resist 2021+ plans to retool the HVAC to put in a fresh air ventilator. There were also a few days this summer where it was 50°F and low-humidity outside, but 78°F inside, my preferred temperature was closer to 72°F, and I wished I had some better way than "open a window and stick in a Lasko box fan" to cycle in cool outdoor air.

dota_fanatic 6y ago

Having just built an addition which needed its own HVAC system, I was surprised to find the cost of an American Standard ERV to be several thousand dollars, prohibitively expensive for us given all the other costs. :/

turtlebits 6y ago
Not sure the size of your addition, but Panasonic makes a small ERV for around $400, I use it in my 500sf workshop. They have a larger model that is around $1000.
johnrgrace 6y ago
Most of the cost is install. A basement glass block window with a dryer vent (under $100 for a pro to install around me) makes self installing easy and professional a few hours of labor. I've seen new ERV units under $1,000 and some pop up used on Ebay for great prices.

turtlebits 6y ago

I would only recommend an ERV for newer houses. On older houses, an ERV running 24/7 is just going to pull all the heat out of your house and cause your energy bills to go up. Best would to get a blower door test run and see what your ACH50 rating is before considering one.

kev009 6y ago

Was looking to see if anyone had experience with ERV/HRV. I would like to put these on my new to me home when I replace the HVAC units.

blacksmith_tb 6y ago
I've lived for 8yr now in a home with a Zehnder HRV. It has mostly worked well, though recent wildfires were too much for its MERV-13 filters, forcing me to run it at the very slowest speed and use air purifiers.
gwd 6y ago
I retrofitted one on a house we bought a couple of years ago. I'm really happy with it, although it does add a constant background 'hum'. It wouldn't have been possible however if we weren't doing major renovation -- we tore out & replaced the downstairs ceiling and completely redid the second floor bathroom; that meant we could run the ducts down the corner of the bathroom and then through the joists in the first floor fairly easily. And the attic is a bit cluttered with the ducts. You definitely notice a difference when you turn it off.
tzs 6y ago
This report [1] suggests that HRVs only actually have a net energy savings in the US in climate zones 4-8 (and such a small amount in zone 4 that it would take several decades to break even). Is there a good reason to get them if one is in a place where they won't save energy? Here's a US climate zone map [2]. [1] https://www.osti.gov/biblio/1488935 https://www.osti.gov/biblio/1488935 [2] https://basc.pnnl.gov/images/iecc-climate-zone-map https://basc.pnnl.gov/images/iecc-climate-zone-map