By space

Whole house dehumidifier sizing

Ducted into the return, sized for the conditioned floor area rather than one room. Runs at a lower load for longer.

Worked example: 1,500 sq ft, very damp

38 pints per day, which lands in the 50 pint class. Change the condition and the answer moves more than changing the area does, so measure the humidity before you shop.

What is different about a whole house

Whole house units tie into the return duct and treat the conditioned floor area rather than one room, so they are sized on the whole house number and run at a lower load for longer.

The advantage is control: one setpoint for the house, no unit sitting in the corner of a room. The cost is installation, and a dependency on the air handler running.

If the problem is one damp room, a whole house unit is the expensive way to solve it. Size it for the house only if the humidity reads high in most of the house.

See AlorAir crawl space and basement units

Before you size anything

• Fix the water you can see. A gutter dumping against the wall beats any unit you can buy.
• Lay or repair the vapour barrier if there is bare earth. It changes the load permanently, where the unit only treats it.
• Take readings for a week with a cheap hygrometer. Sizing off one bad day buys a unit that short cycles for the other 360.