Humidity & Mold in Seattle
Seattle, Washington sits in a oceanic climate averaging 73% relative humidity. Here is what that means for your home — and the products that actually help.
Quick answer
In Seattle, keep indoor relative humidity between 30% and 50% (EPA guidance). A 30–35 pint dehumidifier covers most rooms up to 1,500 sq ft; a 50 pint unit with a continuous drain is better for basements. The most frequent local problems are winter condensation, basement mildew, roof and gutter leaks.
Top moisture issues in Seattle
Best dehumidifiers for Seattle
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Seattle humidity FAQ
What is the average indoor humidity in Seattle?
Seattle averages about 73% relative humidity (Oceanic climate). Keep indoor levels between 30% and 50% RH, as recommended by the EPA, to limit mold growth.
Why does mold grow so easily in Seattle homes?
The most common local drivers are: Winter condensation, Basement mildew, Roof and gutter leaks. Mold needs moisture, an organic surface and stagnant air — controlling humidity removes the first condition.
What size dehumidifier do I need in Seattle?
For a damp room up to 1,500 sq ft in Seattle, a 30–35 pint unit is usually enough. For a wet basement or 2,000+ sq ft, choose a 50 pint model with a continuous drain hose.
