Question: Our house is a bungalow, with an open staircase going into the basement, and every time I go into our basement the thermometer indicates it is approximately three to four degrees Celsius cooler than the main floor. This is perfectly understandable, since cold air gravitates to the lowest level, while heat rises. I am wondering if there are any solutions that would stop the main floor cool air from dropping into the basement via the stairway, and of course the opposite occurs during the heating season. I did address this issue during the design stage of our home, but the builder could not come up with a solution, as the obvious option of adding a door at the top or bottom of the stairway was just not doable. I would be interested in knowing if you have any ideas one could consider to prevent this.
Thank you for your consideration, Lawrence Klippenstein.
Answer: Having a cooler basement than the upper floor of your home may not be fully under your control, but reducing that temperature differential may be possible with a few modifications or adjustments to your HVAC systems. These may help make the cooler basement more tolerable and within a level you can live with.
As you have stated, because cooler air will sink to the lowest level in a building, while warm air rises to the upper levels, a cool basement during hot summer days is a given. Using your air conditioning system to cool the living space can help keep your basement air dry and odour free, but can make that area uncomfortably cold. The normal coolness of the area below grade can be exacerbated by blowing large quantities of cold air through the heating ducts. Many homeowners will block these basement ducts, or the close the registers, during the warm summer months. That may prevent circulation of cool conditioned air, which is exactly the opposite action to take for your goal. By closing the registers, airflow through the ducts is reduced, which can lead to a clammy, damp feeling in the basement. That can also lead to mould growth and odours often associated with a musty basement.
The simplest thing to do to slightly warm up your basement during the cooling season is to increase the air circulation between the basement area and the warmer upper floor. If your basement heating ducts and registers are properly installed this may be achieved simply by turning your furnace fan on continuous operation. Instead of having the blower circulate air only when the thermostat turns on the heating or cooling cycle, which is normally the “auto” setting, changing it to “on” will achieve this goal. This should allow the blower to run at a reduced speed, but continuously circulate air through the entire duct system. That will allow the warmer air on your main floor to combine with the cooler air of the lower level, as each is drawn in to the return air ducting on the two levels. That air will then be pushed through all the heating ducts, mixing warm and cooler air from both locations, helping to equalize the temperature differential.
Once the temperature rises above the thermostat setting on the main floor, the cooling cycle will begin, which can lead to a larger differential, but should be temporary. Once the thermostat is satisfied, the condenser will turn off, the air conditioner coil will warm up and the blower will circulate slightly warmer air through the whole system. That will minimize the inequality between the colder basement and main floor air.
As stated above, this suggestion may only be effective if the basement duct system was properly designed, with proper return air ducts and registers. Many basements are finished well after initial construction, with multiple partition walls installed to make better use of the large space. There are usually enough warm air ducts and registers installed, but often the return air portion is forgotten. Unless you have a properly sized return air register and duct in each room in the basement, proper air distribution may not be possible. Resolving that deficiency may require partial removal of wall and ceiling coverings, and an experienced HVAC technician, to complete the installation of the return air system.
Leaving the stairway open should only help to improve the air circulation in your home, so that is a bonus not a negative factor, in your case. Moving around any furniture that will impede proper air movement in your basement can also help with your efforts. Especially if a large couch, bed, or dresser is blocking a return air register, move them out to allow proper airflow. Also, if there are too many heat registers in the basement ceiling, or if they are poorly located directly above a seating area, adjusting or redirecting the register may prevent cold air blowing directly on the occupants when the A/C is on. Otherwise, modifying the ducts and relocating the registers to better locations can be done by a HVAC tech.
Having a cooler basement than the main floor during the summer cooling season may be inevitable, but making it more comfortable can be achieved with a few changes to your normal HVAC settings and/or duct and register locations.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and a Registered Home Inspector (RHI)(cahpi.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.