Quote:
Originally Posted by shepardmike
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Pretty much. My canned thoughts on dehumidifiers:
Short version:
They work very well if sized properly. "Sized properly" means an adequate "pints per hour" rating and a decent-sized tank. I'd prefer a tank size of closer to 1 gallon than to 1/2 gallon.
Long version:
Good dehumidifiers are rated in "pints" and use a compressor, essentially a small air conditioner in design but without the cooling.
The "pint" rating is the number of pints of water that can be removed from the air in 24 hours under optimum conditions. There are 8 pints per gallon, 128 ounces per gallon, and 3,785 milliliters (ml) per gallon.
We use a 30 pint unit in our 38' motorhome (about 300 sq. ft.) and it removes 0.4 gallons of water overnight. I know because that's the tank size and it beeps that it's full between 10 and 12 hours day or night when we set it to 50% humidity. 🙂
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BUT 30 pints is the equivalent of 3.75 GALLONS yet ours barely removes 1/3rd to 1/4 of that in 24 hours of running continuously.
Supposedly, our 30 pint compressor dehumidifier is good for 1,500 square feet but our motorhome is only about 300 square feet.
The takeaway is to buy LARGER than the advertised "square foot" rating because the manufacturers lie. 🙂
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In a shorter RV that 30-pint unit would lower the humidity faster and its tank would fill more slowly. A friend with the same 38' motorhome uses a 70 pint unit and his unit drops the humidity a lot faster than ours.
When in Florida for the winter I need to empty the 0.4 gallon tank twice a day and sometimes three times a day.
That means our 30-pint dehumidifier is removing 0.8 GALLONS of water each day from the air and sometimes more. Yes, we keep the entry door closed and the windows and vents closed.
To be honest, that 30-pint unit sometimes struggles to lower the humidity so I'll go with a 40-pint or larger unit with a larger tank next time. We keep the dehumidifier in the bedroom set to 50% humidity and it rarely shuts off. A humidity percentage meter in the main living area sits in the 50's generally and only occasionally drops into the 40's. Yes, this is with both air conditioners running almost constantly.
Some inexpensive dehumidifiers use "Peltier" technology and are rated in "ounces". A large Peltier unit is 95 ounces but 95 ounces is only 6 pints of water removed from the air in 24 hours under optimum conditions and there are 8 pints per gallon. Yet people think that "95" is a big number so that's good. But it's not.
0.4 gallons, what ours removes overnight, is equivalent to 51 ounces. Or about 3.2 pints. But you'll never see that in real life.
In summary, the amount of water that can be removed from the air is what's important, not some "square foot" rating because people live in cubic feet. The advertised water removal rate is the absolute maximum and ours performs at about 50% of its advertised rating. So "go large" rather than "just enough".
As a rule, the smaller the size of the tank the lower the performance. A dehumidifier that advertises a 1,000 ml tank only holds one-quarter of one gallon.
Ray