How do I know which whole house dehumidifier is best for my house and how to find the best company to install it?
Laidler
| Posted in General Questions on
I’ve looked extensively on the internet, perhaps not using the best search terms, and have found no information about the best size and brand for my house, which is between 3000 and 3500 square feet, or how to find a company to install it properly, which according to a “This Old House” video that I did find, is very important. I have had two estimates for both these things, but don’t know how to check their credentials. Thank you!
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Replies
I'm curious why you want a whole house dehumidifier vs one or two portables.
As I think Jon is suggesting, you have to be careful about not using a dehumidifier to bandaid over a more significant problem.
What they said- why do you think you even need it?
Whole house dehumidifiers are generally only appropriate for house in regions with high outdoor dewpoints and the house has VERY high ventilation rate requirements, or in houses with very high indoor humidity sources. Is there an indoor pool & hot tub that are normally left uncovered? Is the house chock full of heated tropical fish tanks?
Earlier this summer, this area had weeks of ~75F very humid weather where dehumidification was necessary for good comfort. But combined with open interior doors (or, if you really have to, a furnace fan), portables should be sufficient. Even more so as houses are better air sealed.
I've seen some crazy claims about whole house dehumidifier efficiency gains - 400% where my calculations show 50% (and that's not counting furnace fan power). Exclude installers who exaggerate.
Regarding sizing, I assume that over-sizing has negative effects on efficiency. Maybe an ACH@50 measurement to estimate ACH-natural-peak?
The energy-star rated portables are all rated about 1.8 L/kWh. I think there's one for $350 that's 2.0. But the dehumidifers made by Thermastor, which include stand-alone (but not really portable) basement/ crawlspace units, as well as ducted units, include models rated up to 4.2 L/kWh. So that uses less than half the energy that an energy star portable would. They are much more expensive.
Thermastor has different brand names for the stand-alone and ducted units: Ultra-Aire and Santa-Fe, but the lineup in both of those lines is very similar.
I suspect, but don't really know, that distributing dehumidification around a house with ducts is less important than than distributing heat and cooling is. So getting a super-efficient one and putting it in one place rather than tying it into ducts might not be a bad idea.
Laidler,
You've received good advice. Most homeowners who think they need a whole-house dehumidifier actually have a collection of problems that are best solved by other means. These problems include:
1. A leaky thermal envelope (leaks through the floors, walls, and ceilings of your house).
2. Overventilation (operating a ventilation fan for too many hours per day).
3. A family member who leaves windows open.
In most cases, all you need to do is reduce the ventilation rate, close the windows, seal the big air leaks, and operate an ordinary air conditioner.