Crawl space dehumidifier quotes

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When a crawl space needs one

A dehumidifier makes sense in a crawl space that is closed: vents sealed and a liner down. In a vented crawl space it would be drying outdoor air. The 2018 International Residential Code (R408.3), enforced in Chattanooga and Red Bank, lists a dehumidifier as one of three ways to dry an unvented crawl space; the others are a small exhaust fan or conditioned air from the house system.

Chattanooga's air is the reason this comes up so often. NOAA's long-term averages for the airport show 85% relative humidity at 7 a.m. over the year, and about 89% to 90% on August and September mornings. The EPA's target indoors is below 60%, ideally 30% to 50%.

How big?

For the dehumidifier option, R408.3 sets the size: 70 pints of water removal per day for every 1,000 square feet of crawl space floor. A 1,500 sq ft crawl space works out to about 105 pints a day (our arithmetic from the code ratio). Ask each company for the unit's rated capacity and how it drains (a condensate line or pump).

What does it cost?

It also uses electricity and needs filter changes; ask what maintenance the company recommends and what the warranty covers.

Check the humidity yourself

The EPA notes that a humidity meter costs about $10 to $50 at a hardware store. Put one in the crawl space for a few days after rain and in late summer. Readings that stay high tell you more than a one-time sales visit.