By space

Garage dehumidifier sizing

Big door, poor sealing, and a car that drives in wet. Load spikes after rain and snow rather than sitting flat.

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 garage

A garage is the one space on this list where the load is spiky rather than steady. A car driven in wet carries litres of water with it, and the door opening drags in outside air. The average is low and the peaks are high.

That argues for sizing on the peak rather than the average, and for a unit that can be left on a humidistat rather than a timer. It also argues for checking the low temperature rating in any climate with a real winter.

An unheated garage in a cold climate is a hard case for a refrigerant unit of any size. Below about 40 F the physics stops cooperating and a desiccant unit is the honest answer.

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.