I am planning an air exchange system for my house
I am planning an air exchange system for my house and there are a few questions I have.
I am trying to decide between an HRV, an ERV, or a dehumidifier. I live in Maine and have remodeled my house by removing all old plaster and lathe. Then, build a second stud wall inside of that, creating a 9″ cavity. I have done the same thing on the ceiling, creating a 14″ cavity, these are dense pack cellulose.
Most things I read say that for the north east you choose a hrv. I have been monitoring humidity inside and outside. In the last two months, outside humidity is consistently higher than inside. Isn’t a hrv system going to make my inside air more humid ? What I need to do is lower the inside humidity because I am getting condensation on the windows.
Thanks for your help,
George
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Replies
George,
A dehumidifier is not an air exchange system. Nor is it a ventilation system. It won't introduce any fresh air into your house.
During the winter, any type of ventilation system -- an exhaust-only system, a balanced system (such as an HRV or an ERV), or a supply-only system -- will provide fresh air and will reduce your indoor humidity levels. The reason: outdoor air is cold, and cold air can't hold much moisture (so it's dry).
If you have a bathroom exhaust fan, you might start by running the bathroom exhaust fan for 24 hours a day for a few days. You will probably notice that this solves your condensation problems. When your windows have dried up, you can turn off the fan.
If you want to invest in a ventilation system, read this article first: Designing a Good Ventilation System.
George,
When you say the outdoor humidity is consistently higher than the indoor humidity, do you mean relative humidity? If so, the absolute humidity outdoors may still be substantially lower than the indoor absolute humidity.
George-I'm also in Maine. An HRV was installed in my new house. The general consensus seemed to be that an HRV, as opposed to an ERV, was appropriate for Maine.
As you know, it has been more humid that usual this winter. My indoor relative humidity has still stayed at around 45%.
One thing I find useful is to boost the ventilation on the hrv whenever we're adding a lot of moisture, like taking a shower or boiling water. This seems to get rid of the excess humidity.
You can usually more easily find data on dew point than absolute humidity. A higher dew point corresponds to higher absolute humidity. So you can see from the outside dew point (on a weather web site) that the outside absolute humidity is lower than inside.
HRV will do more to lower your winter humidity than an ERV will. The main reason for ERV in cold weather is if you want to ventilate a lot for other reasons, and want to avoid getting the humidity too low.
HRV won't lower the humidity any more or less than an exhaust fan will. But it will cost less to run because you won't lose as much heat in the exhaust.
Thanks for the help,
Guess I did not understand relative humidity.