The Green Home

Better airflow: The cure for the common household cold?

Posted January 3, 2013

Winter is officially here, and with it people are spending more time indoors, sealing out the cold and damp weather with closed windows and doors. If you’re finding that your home suddenly feels stuffy or clammy, or if common colds now seem like a chronic condition for your family members, it might be time to check the airflow in your home.

Properly sealed ductwork

It’s sad but true that most duct systems installed to current building codes still leak almost 30 percent of the air that flows through them.

Leaky ducts are inefficient. You are paying to heat and cool air that is supposed to come out of the vents in your house, not leak into the attic or crawl space. Leaky ducts can cost you an extra 10 to 20 percent on your heating or cooling bill.

Leaky ducts can also cause your house to be under negative or positive pressure, which can cause your house to leak conditioned air to the outside, or suck unconditioned air into your home. Either of these conditions put undue stress on your HVAC system, costs you money and can lead to unhealthy air inside the home.

A sufficient-sized air return

Every central heating and air system should have an air return that is large enough for the same volume of air to return that the system puts out. A rule of thumb on the size of this opening is 1 square foot per one ton of your system's size.

Many homes aren't designed to allow proper airflow, even when the return opening is large enough to accept the necessary volume. Every interior door in the home should have sufficient space beneath it to allow the return of any volume of air that is dumped into the enclosed room from the HVAC unit.

Air return shaft accessibility

Wherever the return shaft is located for the HVAC system, you should take care to keep it accessible. As a rule of thumb, use the width of the air return vent as the measure for how far from the wall your furniture should be placed to allow proper airflow.

The importance of the lowly air filter

The "lowly" air filter is one of the most neglected parts of a central heat and/or air conditioning system, and yet it is so vitally important. Depending on the type of filter you have, you may be able to clean it rather than throwing it away, but the important concept is to keep it clean to allow your heating or cooling unit to work the way it was designed. A cleaner filter means higher efficiency performance.

Clean or replace your filter every two or three weeks and this one small task can add years to the life of your HVAC appliance.

The exception to the rule: Closed Crawl space sealing

Your crawl space is the only thing that stands between your living space and the earth – and the earth is damp. Crawl spaces are a primary source of excessive moisture in our region, and moisture is a leading cause of structural and air quality issues.

Most experts recommend that properly closing and sealing a crawl space is best practice for green, efficient and healthy buildings. Luckily, even old-fashioned, ventilated crawl spaces can be upgraded, with energy reductions of between 5 and 20 percent.

Cleaner air means a healthier environment

'Think of the airflow to your unit as you do your own breathing. If you can't get enough air, your life will be shortened, but having an abundance of clean air will help to keep you healthier and for a longer duration.


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About this Blog:

Bobby Ferrel, founder of Green Horizon oversees The Green Home blog. Ferrel is co-founder of Green Horizon, with offices in the Triangle and Charlotte, offering home owners and builders a one-stop shop for energy efficiency and green building. Services include home performance assessments, weatherization, closed crawl spaces, all types of insulation, HVAC and geothermal installation and maintenance. Reach Bobby directly at or visit him online at