5 Questions with Billy Tesh

1. Why is dehumidification necessary in many crawlspaces?

In a vented crawlspace, the hot moist air from outside combined with the rising damp from the ground drive moisture levels up to the point where condensation forms on surfaces that are below the dew point such as on the floor joist, insulation, plumbing and other surfaces in the crawlspace. This causes a number of problems including mold and rotten wood, cupping hardwood floors, ineffective insulation, attraction of termites and other pests and musty odors in the home.

In a closed crawlspace, vents are sealed and poly is installed and taped to the wall insulation to reduce rising dampness. However, moisture still exists in the crawlspace, finding its way through various penetrations, gaps and cracks which gives the need for dehumidification.

2. What are the mechanisms of drying that can be used in a crawlspace?

The primary methods are supply air inducers and dehumidifiers. The simplest method of drying is using an air inducer. Most crawlspace homes have an HVAC system in the crawlspace. This allows technicians to install air inducers on the supply side of the HVAC system. Every time the HVAC system runs, the air inducer allows 50 cubic feet/minute (CFM) of conditioned air to blow into the crawlspace. You can install multiple air inducers in a crawlspace. In some cases, this can serve as the only dehumidification needed. Always make sure to check the building codes in your area.

3. What if the air inducers are not enough and the moisture levels continue to be high?

If more dehumidification is needed, a dehumidifier can be added. Most dehumidifier specifications will state a maximum square footage of crawlspace that the unit will handle. When sized appropriately, dehumidifiers ensure the relative humidity stays at a level that the operator sets via the controls. We carry Aprilaire, Santa Fe and Mega-Dry dehumidifiers.

4. So if I install a dehumidifier, do I also need air inducers?

If you have the correct size dehumidifier you, do not need to install air inducers, but most companies will opt to install the air inducers as well because they lighten the load on the dehumidifiers and help them to last longer. The conditioned air, whether heating or cooling, also helps maintain the temperature of the crawlspace. Finally, the air inducers also help bring more circulation of air to the crawlspace.

5. Is it a problem if there is no circulation of air in a crawlspace?

It is not a problem, but more about efficiencies. The dehumidifier will lower the relative humidity (RH) in the general vicinity of the unit. If another part of a crawlspace is a source of the high humidity, once the unit reaches the set RH, it will shut off. The higher and lower areas will then reach an equilibrium of the humidity and the unit may need to kick on again. This is where the ATMOX System comes into play. When an ATMOX system is installed in a crawlspace, there are a number of small fans that are added. These small fans can each move up to 225 CFM of air. By circulating the air this way, the dehumidifiers can work properly and reduce the need to cycle on and off as often. Another great feature of the system is the ability to introduce fresh air into the crawlspace. Sometimes the air outside may have a lower humidity than the air in the crawlspace. The ATMOX system monitors air both outside and inside the crawlspace, and if conditions are favorable, it can introduce fresh air into the crawlspace, which can reduce the load on dehumidifiers and conserve energy.