Where should the supply and return ducts be in a separately ducted dehumidifier system?
There’s a lot of ink spilled on this site about dehumidifiers, but little ink spilled on best practices for a dedicated dehumidifier duct system. This might be a nice GBA article.
In this scenario, where should the supplies and return be (eg basement, bathroom, bedroom, etc)? How many supply and return registers is usually sufficient?
Humidity occurs in the basement, kitchen, and bathrooms, so I presume returns would be in those spaces, similar to an ERV (minus basement). I just want to make sure my logic is not flawed.
I’m in Cleveland where we have cold wet winters and warm wet summers. We have an unfinished masonry basement within the thermal envelope, for what that is worth.
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I’m guessing you don’t have an existing central air system with ductwork? Lowest retrofit cost would be to repurpose that same ductwork.
Get a unit that has two inlet ports, similar to a ventilating dehumidifier and install the unit in your basement. Then, one port will be connected to ductwork and pulling from rooms on your main living area while the other port will just be open to your basement to control humidity there. You could also duct the basement port if you want to. Keep in mind humid air is more buoyant and so your top floor (or attic if you have a conditioned attic) will have higher RH all else being equal. Energy Star recommends no more than 3 Pascal pressure differential between rooms so that will be your determining factor when it comes to where to put the supply ducts.
Thanks. You’re correct that I do not have existing ductwork. We’re putting in an ERV, so I’ll run dehumidifier duct at the same time.
Understand a dehumidifier is mostly an electric heater that happens to collect some water.
If your goal get rid of the damp smell in the basement, then disposable portable dehumidifier from a box store will do fine no ductwork required.
I have not lived in Cleavland but it seems like it would be a dry enough place that outside of the basement no dehumidifier would be needed. Unlike some warm swampy place like TX, LA or Fl.
In the winter most older homes are so leaky that low indoor humidity is a common problem. If you have a tight newer home with a winter humidity over 60% then you want a HRV that will easily dry the place out. In the summer a correctly sized AC unit should remove enough moisture.
If you do put in a ducted dehumidifier, be careful where it discharges the 110° air.
Note ERV is designed to recover heat and moisture from the exhaust air and that seems counter to your goals.
Note I think ERV & HRV a total unnecessary unless you have a blower door test under 1.5 ACH50.
Walta
Thanks for the input. Our house is medium tight now, but we’re working on tightening the house up and insulating further.
I didn’t realize the air exiting the dehumidifier was so warm. That’s an interesting piece of information to mull over. We do run a dehumidifier in the basement, but it’s constantly running, even much of the winter. January and February are usually fairly dry, but October to December can be damp, and it starts up again in March
I was of the mindset that an ERV isn’t necessary for our house—I like opening windows. My wife has numerous allergies, however, and prefers to keep the windows closed much of the time. An ERV seems like the right solution to keep IAQ healthy and prevent it from getting stuffy.