The Inside Outside Guys: Basement ventilation is key to clearing the air

Ken Calverley and Chuck Breidenstein
Special to The Detroit News

Ask anyone to describe basement air and you will hear terms like “dank,” “musty,” “moldy” and other adjectives that generally apply to moist, stagnant and unhealthy air.

The air we described can cause sinus conditions, stimulate asthma reactions and worse. Radon, accounting for 20,000 deaths a year from lung cancer, generally originates in the soils below the foundation system and, because it is heavier than air, can accumulate in high concentrations at the floor level.

A single-room dehumidifier is an ideal tool for removing limited amounts of moisture from the air. You'll need to regularly dump the water.

Our tendency to store solvent based products in the basement can lead to further air contamination along with the possible accumulation of carbon monoxide from gas fired appliances like furnaces and water heaters.

We need to move, condition and filter that air while removing potential contaminants.

Molds that create the musty smell are everywhere. They require temperature, oxygen, food and moisture to thrive. The only one of these we can reasonably control is moisture. If we can avoid high concentrations of humidity, we can effectively stop mold and fungus growth and the accumulation of mildew.

One cause of high humidity in the basement air is vapor diffusion. High concentrations of moisture “seek” lower concentrations and so move through foundation walls and floors from the damp earth surrounding the home. A related issue is capillarity where moisture is drawn through porous foundation materials. This capillary pressure can draw moisture through 20 feet or more of surrounding soils.

How can we reduce humidity and the concentration of other contaminants?

One component of this battle is the surrounding drain or weep tile that takes active water out of the surrounding soils. Another is sealing the basement walls and floors to reduce vapor diffusion and capillarity and caulking cracks and gaps to reduce radon movement in to the space.

Use of a good de-humidifier that drains to a permanent floor drain can help, as can running the air conditioning for longer cycles to de-humidify the air.

Moving the basement air is a key part of the strategy. If we “force” that stagnant air to co-mingle with larger volumes of less humid, less contaminated, air we will lower relative humidity and disperse contaminants.

Simple box fans can help do the trick, as can open windows in the space on hot, dry days.

Installation of more, and lower, HVAC supply registers in the basement can force air movement along the floors. Done in conjunction with the installation of a multi stage blower motor in the furnace this can be an economical, yet efficient way, to help resolve our basement air issue.  

There are mechanical fans that install in the Rim Joist above the foundation wall. These are intended to draw moist, contaminated, air off the basement floor and exhaust the air to the outside. One drawback to these units is that they typically do not include make-up air but, rather, suggest “opening the basement door” when the unit is in operation.

Whenever we mechanically exhaust air from a home, the home will try to replace that air by sucking it in through any available gaps and cracks around windows, doors, top of foundation, fireplace chimneys, furnace vents, etc.

This is not how we want to deliver make up air to the home. Moist air drawn in through a crack around a window may “deposit” its moisture inside the wall.

New homes require the installation of recovery or make-up air supplies. These may be a simple insulated pipe running from outside into the supply air side of the duct work, or it might be an insulated pipe running from outside to just above the basement floor. These can be retro-fitted to existing homes with crawl spaces and basements.

Another option for our basement air is a device like an Energy Recovery Ventilator, ERV. ERVs have been in use for decades. They were developed to deal with the issue of stale, contaminated air in well-insulated, well-sealed buildings. They remove stale air and replace it with an equal volume of fresh air. But that’s not all.

In the winter, they will extract the heat and humidity from the exhaust air, and then add it to the incoming fresh air. In the summer they will “pre-cool” the incoming air using the energy derived from the exhaust air. ERVs can function as “spot” units dedicated to a single room or space, or can be incorporated in to a whole house system.

The lower level area of a home does not have to fit the convention of “typical” basement air. Take steps today to move and condition that air for the sake of your home and your healthy family!

For housing advice and more, listen to the Inside Outside Guys every Saturday and Sunday on News/Talk 760, WJR-AM, from 10 a.m. to noon or contact us at