Dehumidifier size calculator: how many pints do you need

Read the pints from floor area and dampness, not from the room count. On the 2019 DOE test conditions a 1,000 sq ft moderately damp basement needs about a 14 pint a day unit and an extremely wet one about 23 pints; a 2,000 sq ft space roughly doubles that. The calculator above interpolates between the published rows, and it is worth buying one size up if the space drops below 65 F, because a compressor loses capacity in the cold.

Yes, the capacity table this calculator reads is the standard chart: floor area down the side, dampness class across the top, pints per day in the cells, on the 2019 DOE rating conditions. Older charts and older labels used the pre-2019 test, which produced larger pint numbers for the same machine, so compare a chart and a label from the same era or convert one of them first.

The DOE test conditions changed in 2019 and now run at a lower chamber temperature, which is harder on the machine. The same physical unit that was sold as 70 pint before the change is labelled around 50 pints after it. Nothing about the machine changed, only the test it is measured under, which is why old sizing charts oversize.

Not usually. An oversized machine satisfies the humidistat quickly, switches off, and cycles repeatedly, which dries unevenly and uses more power than a right sized unit running steadily. Oversize deliberately only where the space is very cold or the moisture load is extreme and seasonal.

A standard compressor model loses capacity as the air gets colder and can ice up below roughly 65 degrees Fahrenheit without automatic defrost. Models that state low temperature operation handle it, and desiccant machines work down to much lower temperatures at the cost of using more power for the same water removed.

Between 45 and 50 percent relative humidity is the usual setting for a basement. Lower than that costs power for no benefit, and the aim is to stay reliably under 60 percent rather than to make the space arid. Put a separate hygrometer somewhere other than beside the machine to check what is actually happening.

The dehumidifier, first and by a wide margin. Musty smells come from moisture supporting growth, and drying the space is what stops it. A purifier captures spores already airborne, which helps with the symptom while the cause continues. Dry the space, clean what is already growing, then filter.