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Wet and extremely wet basements
| Area | Wet | Extremely wet | GE class (wet) |
|---|---|---|---|
| 400 sq ft | 14 pt | 16 pt | 22 pint |
| 500 sq ft | 14 pt | 16 pt | 22 pint |
| 600 sq ft | 15 pt | 17 pt | 35 pint |
| 700 sq ft | 16 pt | 19 pt | 35 pint |
| 800 sq ft | 18 pt | 20 pt | 35 pint |
| 900 sq ft | 19 pt | 22 pt | 35 pint |
| 1,000 sq ft | 20 pt | 23 pt | 35 pint |
| 1,200 sq ft | 22 pt | 26 pt | 50 pint |
| 1,500 sq ft | 26 pt | 30 pt | 50 pint |
| 1,600 sq ft | 27 pt | 31 pt | 2 × 50 pint |
| 1,800 sq ft | 30 pt | 34 pt | 2 × 50 pint |
| 2,000 sq ft | 32 pt | 37 pt | 2 × 50 pint |
| 2,500 sq ft | 38 pt | 44 pt | 2 × 50 pint |
A dehumidifier controls humidity; it does not stop liquid water. If walls seep, budget for drainage or waterproofing too. HomeAdvisor's average waterproofing job is $4,400, and NerdWallet gives $5–$10 per square foot.
Which dampness level are you?
- Moderately damp: AHAM describes a space that feels damp and smells musty only in humid weather.
- Very damp: it always feels damp and smells musty, and there may be damp spots on walls or floor.
- Wet: walls sweat or water seeps in.
- Extremely wet: wet floors, standing water, or a high-load space such as a laundry area.
Measure with a hygrometer for a few days before you buy. The EPA advises keeping indoor humidity below 60%, ideally 30%–50%, to keep mold from growing.
Where basement moisture comes from
| Source | Sign | Usual fix |
|---|---|---|
| Rain and snowmelt | Wet floor edges after storms | Gutters, downspout extensions, grading |
| Groundwater | Water through cracks or under walls | Interior drain and sump pump |
| Humid outdoor air | Musty smell, sweating pipes in summer | Dehumidifier, keep windows shut on humid days |
| Vapor through concrete | Damp under a plastic test sheet | Vapor barrier, foam board, sealer |
| Plumbing and appliances | Local stains | Repair leaks, vent the dryer outside |
Dehumidifier or drainage?
Run the plastic-sheet test described on the other moisture pages. If water collects under the sheet on the slab, liquid water or vapor is coming through the concrete and needs drainage or sealing; a dehumidifier alone will run nonstop. If moisture forms on top, warm humid air is condensing on cool surfaces and a correctly sized dehumidifier is the right tool. Many wet basements need both: a sump and drain for the water, and a dehumidifier to hold humidity under 60% afterward.
Related calculators
Sources
- https://blog.directenergy.com/shopping-dehumidifier/
- https://products.geappliances.com/appliance/gea-support-search-content?contentId=34664
- https://www.homeadvisor.com/cost/basements/
- https://www.nerdwallet.com/article/mortgages/cost-finish-basement