Cold-air return will boost basement heat
QUESTION: We have a 1,440-square-foot basement under a full two-storey home heated with a high-efficiency gas furnace. We have four warm air outlets in the basement with no cold air returns. A friend, who used to install furnaces, told me to cut a return in the cold air return to the furnace, near the floor. Is this a good idea and if so what size should the opening be? If not, what alternatives do I have? Do I really need a cold air return there to increase heat and efficiency in the basement?
Thanks for your time, Wayne Spittal
ANSWER: A lack of return air ducting and registers in basements is one of the most common issues I see in older homes. While some of the finished rec-rooms in these basements are fairly comfortable in the heating seasons, others are not and often have supplementary electric heaters installed. Installation of proper return air ducting and registers should make the area much more comfortable, especially with your newer high-efficiency furnace that should have a much more powerful fan than the older one it replaced.
Your friend has given you good advice about installation of return air for the basement, but I don’t think you got the whole story. Either you misunderstood his recommendation, or he was giving you a simplified solution that may not be the best one possible. While installation of return air for the basement will improve the air flow to and from the furnace, cutting a hole in the return air plenum right near the furnace may not be adequate for the entire basement and may prevent proper return air movement in your home.
The proper method to achieve what you want is to install one or more ducts directly to the existing return air ducting or plenum. These should run to one or more locations near the basement floor, but farther away from the furnace. Also, installation of proper registers over the end of the ducts will prevent excess dirt and debris from entering the ducting. Installation of these ducts can be through an existing interior basement wall or other accessible area. These ducts should not be installed directly against an uninsulated foundation wall, or within an insulated wall, as condensation can create moisture-related problems.
Because of the size of your basement I would expect more than one return air would be prudent, but if the entire area is unfinished, one may do until further walls are constructed.
A modern forced-air heating system in a home has two main ducting systems, which allow good air circulation throughout the building. The warm air ducting is typically installed below the main floor and will terminate in registers near the exterior walls on the main and upper floors. This ducting is pressurized as warm air is blown past the heat exchanger on the furnace by the furnace fan, into the ducting. This heated air will enter individual rooms in the house through these registers and rise to the upper level of the rooms due to normal convective forces.
Once the furnace fan shuts down, this air will cool and settle toward the floor. The return air registers and ducts are installed to help collect this cool air and draw it back into the furnace housing, so that it can be heated and recirculated once the fan is reactivated. Without return air ducting, as in your basement, much of this cool air may not be drawn back to the furnace, resulting in stale or damp air in that area of the home.
By cutting a hole in the return air plenum right near the furnace, you may collect some of this cool air from the basement, but not from the right location. If you install return air ducting and registers at the opposite end of the basement from the furnace, you will then make the air movement more efficient. The cool air will be collected from the location where it is most susceptible to becoming stagnant, at the far end of the home from the furnace.
This increased air flow will also allow the existing heat registers in the basement to more easily replace the cool air with warm, heated air, further improving comfort.
I’m glad that you are seeking advice from a professional heating technician, even if he is no longer practising, but you should be careful about the application of that advice. While you may be adept enough to do some of the work in the installation of the new return air ducting in your home, this is normally a professional job. Holes in existing ducting and attachment of distribution pipes can be difficult to accomplish, unless you have the proper tools and know-how. A trained heating technician should also be able to do measurements and calculations, if necessary, to determine how many return air registers are required for your basement.
Warming up cool basements in the heating season is often something that many people desire but don’t know how to accomplish. One of the simplest ways to achieve this goal can be to add proper return air ducting to this level of the home. Improving air circulation to the furnace, by this method, can be the difference between comfort and cold in your basement. Another benefit of improved airflow is to minimize stale air and prevent condensation and mould growth, common to basements with no return air systems.