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R-49 is the common target for the roof or ceiling in cold and mixed climates. That is about 20 inches of blown fibreglass, 15 inches of blown cellulose, 16 inches of fibreglass batt or about 8 inches of closed-cell spray foam. Air seal the ceiling plane before adding any of it.
Dehumidifier size is the pints of water it removes per day, and the right size depends on the area and how damp it is. ENERGY STAR recommends 20–30 pints for a damp space under 2,000 sq ft, 25–40 for a very damp one and 30–50 for a wet one. Enter the space's size and condition to get a capacity, the common unit size to buy, and whether you have outgrown a portable unit.
With these inputs:
| Result | Value |
|---|---|
| Capacity needed | 32 pints/day |
| Size to buy | 35-pint portable |
| Area | 1,200 sq ft |
| ENERGY STAR range for this condition | 25–40 pints (< 2,000 sq ft) |
| Rough equivalent on pre-2019 ratings | about 46 pints |
Why dehumidifier sizes changed in 2019. Until June 2019, capacity was measured at 80 °F and 60% relative humidity. The Department of Energy's current test uses 65 °F, closer to a real basement, and colder air holds less water, so the same machine now carries a smaller number. A unit sold as 70 pints before 2019 is typically labeled about 50 pints today. When you compare an old unit with a new one, compare like with like; ENERGY STAR notes that capacity labels changed for this reason. Basements and crawl spaces. Most basements are 'very damp' by ENERGY STAR's description: a musty smell all the time and damp spots on walls or floors. Fix the water sources first — gutters, downspouts that drain at the foundation, grading that slopes toward the house — then size the dehumidifier for what's left. In a crawl space that is being encapsulated, the dehumidifier is sized for the sealed volume and usually drains to a sump or condensate pump. Aim for 30% to 50% relative humidity indoors; a cheap hygrometer tells you whether the unit is keeping up. If it runs nonstop and the humidity stays above 60%, it is too small or the space has a water problem. Portable or whole-home?. Portable units top out around 50 pints a day (2019 rating). Past that, a ducted whole-home dehumidifier is quieter, drains itself and treats several rooms. Two portable units on opposite ends of a large basement also work and keep you covered if one fails.
Up to 2,000 sq ft: pints = low + (high − low) × (area − 500) ÷ 1,500, using ENERGY STAR's range for the condition (500 sq ft gets the low end, 2,000 sq ft the high end). · Over 2,000 sq ft: ENERGY STAR's floor (30, 40 or 50 pints) plus 4, 5 or 6 pints for each extra 500 sq ft, the steps of the older AHAM chart. · Pre-2019 equivalent ≈ pints ÷ 0.7 (DOE moved the test from 80 °F to 65 °F in June 2019).
| Area | Damp | Very damp | Wet |
|---|---|---|---|
| 500 sq ft | 20 pints | 25 pints | 30 pints |
| 1,000 sq ft | 23 pints | 30 pints | 37 pints |
| 1,500 sq ft | 27 pints | 35 pints | 43 pints |
| 2,000 sq ft | 30 pints | 40 pints | 50 pints |
| 2,500 sq ft | 34 pints | 45 pints | 56 pints |
| 3,000 sq ft | 38 pints | 50 pints | 62 pints |
Source: ENERGY STAR, Dehumidifiers — recommended capacity ranges (checked October 11, 2026); values between are interpolated by area.
A 1,000 sq ft basement that is very damp needs about 30 pints a day, so a 30- or 35-pint unit; a 1,500 sq ft basement about 35 pints, a 35-pint unit. Wet basements with seepage need 35 to 50 pints.
ENERGY STAR's chart tops its small-medium column at 2,000 sq ft: 30 pints if damp, 40 if very damp and 50 if wet. Above 2,000 sq ft it recommends 30+, 40+ and 50+.
Within reason, yes. ENERGY STAR says it is better to oversize than undersize: a larger unit reaches the target humidity and cycles off, while an undersized one runs constantly and may never get there.
Between 30% and 50% relative humidity. Below about 30% the air gets uncomfortably dry; above 60% mold and dust mites thrive.
It doesn't — new units are rated under DOE's 2019 test at 65 °F instead of 80 °F. The same capacity class that used to be labeled 70 pints is labeled about 50 pints today.
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