Humidity & Mold in St. Louis
St. Louis, Missouri sits in a humid continental climate averaging 68% relative humidity. Here is what that means for your home — and the products that actually help.
Quick answer
In St. Louis, 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 basement humidity, sump pump load, summer mold growth.
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St. Louis humidity FAQ
What is the average indoor humidity in St. Louis?
St. Louis averages about 68% relative humidity (Humid continental 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 St. Louis homes?
The most common local drivers are: Basement humidity, Sump pump load, Summer mold growth. Mold needs moisture, an organic surface and stagnant air — controlling humidity removes the first condition.
What size dehumidifier do I need in St. Louis?
For a damp room up to 1,500 sq ft in St. Louis, 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.
