By the Energy Savings Toolkit editorial team · Updated October 22, 2026
Step 1: Stop bulk water
The dehumidifier can't keep up if water is actively entering. Check:
- Soil grade slopes away from foundation (1" drop per foot for 6 ft minimum).
- Downspouts extend at least 6 ft from foundation.
- Gutters are clean and properly sized.
- No standing water at the bulkhead or basement window wells.
- Sump pump is functional and the pit isn't constantly full.
Step 2: Air seal warm-air infiltration
In summer, warm humid outdoor air leaks into the cool basement and condenses. This single mechanism is responsible for most "I have a damp basement" problems in older homes.
- Spray-foam rim joists.
- Caulk and gasket basement window frames.
- Weatherstrip and gasket the bulkhead door.
- Seal plumbing and electrical penetrations through the foundation.
Step 3: Insulate cold surfaces
Cold surfaces drip. Insulate to keep them above the dew point:
- Insulate cold water pipes with foam sleeves.
- Add 2" of foam board to foundation walls (especially below grade level).
- Insulate the rim joist with 2-3" of foam board after sealing.
Step 4: Size the dehumidifier
For a typical 1,000 sq ft basement at 70% RH:
- Slightly damp: 30-pint unit.
- Moderately damp: 50-pint unit.
- Wet (visible damp on walls): 70-pint unit, but fix the source first.
Set the humidistat to 50% RH and let it cycle. Don't run it lower — every 5% drop sharply increases runtime and cost.
Step 5: Track and verify
Buy a $15 hygrometer and check humidity in different basement corners. If one area stays above 60% while others read 50%, you have an air-circulation problem (add a small fan) or a local water source.
Estimated running cost by basement size
Estimates assume $0.17/kWh and 30 days of runtime. Your cost will vary with your rate, climate and how damp the basement is.
| Basement size | Typical unit | Hours/day | Est. monthly cost |
|---|---|---|---|
| 500 sq ft | 30-pint (~300 W) | 6 | ~$9 |
| 1,000 sq ft | 50-pint (~550 W) | 10 | ~$28 |
| 1,500 sq ft | 50-pint (~550 W) | 14 | ~$39 |
| 2,000 sq ft | 70-pint (~700 W) | 16 | ~$57 |
Sources
Try the calculator
Basement Humidity Cost Calculator
Estimate dehumidifier runtime and cost for your basement size.
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