By floor area

What size dehumidifier for 800 sq ft

A 800 sq ft space needs somewhere between 12 and 30 pints per day depending on how wet it actually is. The condition matters more than the floor area, which is why one number cannot answer this.

By condition

Two common cases at 800 sq ft

Vented crawl space over bare earth, very damp. The ground and the outside air both feed moisture in, so the fixed additions do most of the damage: 31 pints per day, which puts you in the 50 pint class. Sealing the vents and laying a vapour barrier first will cut this more than buying a bigger unit will.

Basement with a sump pit, very damp. 24 pints per day, the 30 pint class. The pit is an open water surface, so it keeps giving off moisture even in a dry week.

See AlorAir crawl space and basement units

Why not just buy the biggest one

An oversized unit short cycles. It pulls the space down to the setpoint fast, shuts off, and the compressor never runs long enough to drain properly, so you get worse humidity control and more wear than a right sized unit running longer. Oversizing also costs more to run in a space that never needed it.

Check before you buy

• Measure the actual floor area, not the footprint of the house. A 800 sq ft house often has a smaller crawl space under it.
• Take a humidity reading over a week, not once. A single reading after rain reads wetter than the space really is.
• Check the operating temperature range. Crawl spaces sit cold, and a unit rated only to 65 F will ice up and stop working in the months you need it.
• Decide where the water goes before you decide which unit. Gravity drain, condensate pump, or a bucket you empty by hand are three different purchases.