Why would you connect an ERV to remove humid air from a bathroom and then transfer part of that humidity to the incoming air stream? ERVs are more typically specified in the south were we have to deal with hot humid air in the summer and the ERV removes some of this humidity prior to it entering the home, that is unless you have warm humid air from the bathroom on the other side of the heat/humidity exchanger. I can see using a HRV to take a suction on bathrooms since it won't transfer humidity to the incoming airstream, but an ERV does.

Posted By arkie6 on 18 Nov 2012 12:41 PM
Why would you connect an ERV to remove humid air from a bathroom and then transfer part of that humidity to the incoming air stream? ERVs are more typically specified in the south were we have to deal with hot humid air in the summer and the ERV removes some of this humidity prior to it entering the home, that is unless you have warm humid air from the bathroom on the other side of the heat/humidity exchanger. I can see using a HRV to take a suction on bathrooms since it won't transfer humidity to the incoming airstream, but an ERV does.

Are you directing the question to me?

The article was written by a GBA adviser and the recommendations to remove humid air from a bathroom has been studied and validated by numerous experts. As far as ERV vs HRV and which one does or does not add more humidity, read the article, you will see there is no definitive outcome as to which one prevails.

The conclusion is that there is A LOT of misinformation out there as to which system is "better" or which one performs better in different climate locations. Once again, I recommend you read the study and all the professionals agree that it's not as clear as an A or B choice. It's more of a "guideline" then something that is set in stone.

Posted By arkie6 on 18 Nov 2012 12:41 PM
Why would you connect an ERV to remove humid air from a bathroom and then transfer part of that humidity to the incoming air stream? ERVs are more typically specified in the south were we have to deal with hot humid air in the summer and the ERV removes some of this humidity prior to it entering the home, that is unless you have warm humid air from the bathroom on the other side of the heat/humidity exchanger. I can see using a HRV to take a suction on bathrooms since it won't transfer humidity to the incoming airstream, but an ERV does.

That is exactly the same question, and contention, the HVAC technician raised when I was building the house and he was installing the ducts! Here in SW Idaho the humidity runs quite low, less than 20% much of the year. The amount of humidity from the master bath is actually quite low because the greatest source, the shower, is totally enclosed. The only humidity that escapes into the room is the residual after opening the shower door. The small amount of humidity that emanates from the bathroom is welcome throughout the rest of the house.

The ONLY reason I went with the ERV, the Ultimate Air 200DX, was that it was the only one I found that offered the "Econo" mode wherein a switch can be set to operate the ERV with the heat exchange wheel turned off. This works for exchanging warm air for cool night air in the summertime. I would have used an HRV had one been available with this feature. In retrospect, it turns out to not be that great a benefit considering the total air volume of the house compared to the exchange rate of the ERV (~20,000 cubic feet and 200 cfm). I don't know how long it takes to actually do a significant air change. 20,000 cf will be moved in 100 minutes, but accounting for dilution during the exchange I suspect it takes many hours to do a complete exchange to cool all the air in the house. I would have been better off to have custom designed a fan, filter, and ducts with operable dampers to accomplish this same thing.

Posted By dmaceld on 18 Nov 2012 08:42 PM
That is exactly the same question, and contention, the HVAC technician raised when I was building the house and he was installing the ducts! Here in SW Idaho the humidity runs quite low, less than 20% much of the year. The amount of humidity from the master bath is actually quite low because the greatest source, the shower, is totally enclosed. The only humidity that escapes into the room is the residual after opening the shower door. The small amount of humidity that emanates from the bathroom is welcome throughout the rest of the house.

The ONLY reason I went with the ERV, the Ultimate Air 200DX, was that it was the only one I found that offered the "Econo" mode wherein a switch can be set to operate the ERV with the heat exchange wheel turned off. This works for exchanging warm air for cool night air in the summertime. I would have used an HRV had one been available with this feature. In retrospect, it turns out to not be that great a benefit considering the total air volume of the house compared to the exchange rate of the ERV (~20,000 cubic feet and 200 cfm). I don't know how long it takes to actually do a significant air change. 20,000 cf will be moved in 100 minutes, but accounting for dilution during the exchange I suspect it takes many hours to do a complete exchange to cool all the air in the house. I would have been better off to have custom designed a fan, filter, and ducts with operable dampers to accomplish this same thing.

That pretty much mirrors the statements in the GBA article. The small amount of humidity in a bathroom is inconsequential in the grand scheme of things. All but the most tropical southeastern climates would have an issue here.

In a dry climate like yours or mine (Arizona), even in wintertime I can run the shower for 45 minutes and can't get the indoor humidity levels above 40% if I tried. I don't even run the bathroom fans, at all.

Regarding the "Econo" mode in the ERV. Would it not be more effective to just open the windows at night to remove the hot air and let in some cool night air?
Do you have your ERV tied into the main HVAC duct work or does it have its own ducts? How big are your main ducts, both on the intake and exhaust?

Posted By Lbear on 18 Nov 2012 09:47 PM

Regarding the "Econo" mode in the ERV. Would it not be more effective to just open the windows at night to remove the hot air and let in some cool night air?
Do you have your ERV tied into the main HVAC duct work or does it have its own ducts? How big are your main ducts, both on the intake and exhaust?

Yes, except for the dust! When I was building the house I had my pickup parked on the street with the windows closed tight. Still, after several months it was covered in dust all over inside and the cabin filter was dirty. That gives you an idea of just how dusty the air is here all the time, especially in the summer. Thousands of acres of farm fields and sage brush wild land around us. By keeping the windows and doors closed we have very low dust level in the house. I have to change out the HEPA filters in the return air duct only about once a year! After three years we finally had to do some, but not much, serious dusting and cleaning of return air grills. That indicates just how air tight an ICF house can be! The screens for the windows are all still up in the garage attic. I'm glad I only paid to have one half of each casement window to be operable, since they're very seldom open.

See my earlier comment about ERV ducting. The intake and exhaust are 6" or 8", I don't recall, 8" I think. I'd have to go up into the attic to measure them. The run for each from the ERV to outside is only about 15' to 20'.