Q. My upstairs doesn’t cool well. Do I need a bigger air conditioner?
A. I get asked this question frequently. With heat’s natural tendency to rise, temperatures in a home tend to stratify or layer. 2nd story homes consistently struggle to cool the upstairs and usually run 5+ degrees off from the thermostat reading on the main floor. This layering is exacerbated by open floor concepts. When there is no barrier between floors to keep the cold air upstairs, the air-conditioned air that your system worked to get up there falls back to the main level. This happens to be right where most thermostats are located! A thermostat senses temperature at only one point in the house, and that point tends to be in the core of your house where it is easiest to heat and cool. The thermostat will be tricked into thinking the whole house is at your set point when in actuality the master bedroom upstairs may be 82 degrees.
Many people think that the issue is that the air conditioner can’t keep up and it is undersized. However, the issue will only get worse with a bigger air conditioner. A bigger air conditioner will cool the home faster. The thermostat, being on the main floor away from the walls and windows will typically be blasted with that easy cold air and will be satisfied in a matter of a few minutes. All the while the supply registers on the 2nd floor haven’t even had a chance to get tepid. On top of that, the short run cycles the air conditioner will now be running will limit the amount of humidity the system is able to extract out of the home. A cold damp main floor and hot humid 2nd floor is a miserable place to live!
The best solution for hard to cool 2nd floors is to install a supplemental cooling system for that level. A ductless heat pump such as a Fujitsu unit is the easiest and most cost-effective solution to add cooling to the area of greatest need. The cheapest option though is to turn you fan from “auto” to the “on” position. This runs your blower motor in your furnace 24/7 and will constantly mix the hot air in the upstairs, the ice-cold air in the basement, and the just right air from the main floor. It will not completely eliminate the layering effect, but it will limit the extreme ranges. If your ductwork is completely exposed in the basement, booster fans are another option to improve comfort. If at a loss, you can always ask an expert!