Misconception: Using HVAC to Control Moisture in Crawl Space

Are you planning to use your home’s HVAC to control moisture in the crawl space? What are the pros and cons of this project? Have you discussed moisture and crawl space humidity control with your Heating and Air Conditioning contractor?

HVAC Removes Humidity

Your home’s HVAC unit is great at removing high humidity. That is part of how it cools the air and distributes it throughout your home in the summer. In the winter, warm air dries your home naturally as heat tends to force wet wood to dry in the crawl space. When the home is humid the HVAC system must work harder to remove excess moisture to cool the air. Is using the HVAC to control humidity in the crawl space a good idea?

Undersizing Your HVAC System

If you have a home that is 1,500 square feet, there is a good chance your heating and air conditioning unit is sized for that space. A load calculation is when a professional HVAC contractor determines the load from the environment to ensure proper sizing of the unit. This involves different factors like how many windows and doors, ceiling height, insulation R-value, and so on.

The Impact of Adding Crawl Space Square Footage on HVAC Sizing

If this load calculation was properly done and you add more square footage after like the crawl space, you just undersized your HVAC system. The unit was able to keep up in your climate based on average humidity, but adding a wet crawl space to the load threw the entire calculation off. This undersizing has now caused your HVAC system to run harder and longer to accomplish your thermostat setting.

Properly Sized HVAC System to Control Moisture

Properly sizing the HVAC system to handle the wet crawl space is usually done during an upgrade or new construction. The HVAC professional includes the load of the crawl space so the HVAC system tonnage is installed properly to handle the load calculation. Many builders perform this practice as a way to not utilize a dehumidifier. The thought is the homeowner will save money on their heating and cooling bills while controlling humidity in the crawl space.

Potential Downsides of Extending HVAC System to Crawl Space

One issue many homeowners face that go this route is the addition of a supply and return in the crawl space. When you have crawl space air directly entering your home it can create soil gas problems, nasty odors, and give crawl space pests direct access to your home.