Circulating the Cool Air From the Basement Throughout the House
Another forecast with temperatures in the 100’s and my brother-in-law says to me, “I guess I’ll be spending another weekend in the basement.” He pauses for a moment before continuing, “Hey, you’re an engineering. Can you design me some sort of system that pulls the cool air from the basement and dumps it upstairs?”
“You already have one”, I reply. “Just flip your thermostat’s fan switch from ‘Auto’ to ‘On’.”
He wasn’t the first person to ask me about how to move the cool basement air upstairs. If you have a full basement, you’ve undoubtedly noticed that the basement air is significantly cooler than the upper floors during the heat of the summer. Fortunately, in most cases, you already have a means to help equalize the temperatures.
Most thermostats are wired with a fan ‘Auto/On’ switch. During the summer with the thermostat in cooling mode, the air-conditioning’s condensing unit, located outside, turns on when the temperature at the thermostat in the house rises above the setpoint temperature. At the same time, the blower fan in the furnace or air- handler also turns on to blow the cool air throughout the house.
With the thermostat fan mode switched to ‘On’, the blower fan runs continuously. The condensing unit outside will still cycle on and off to cool the house when the thermostat is tripped. The difference is that between condensing unit cycles, the air blowing out of the registers is not conditioned, so the air won’t feel as cool. The benefit of running the blower fan continuously is that it is constantly pulling air from the rooms throughout the house and recirculating it through the system. As a result, the air in the basement mixes with the air in the upper floors before being redistributed throughout the house. Over time, this mixing of the cool basement air with the warmer air upstairs will reduce the difference in the air temperature between the two floors.
Before you run headlong to your thermostat to flip the fan mode to ‘On’ , there are a few things to consider. First, you must verify that you have conditioned air blowing into the basement. If your basement is finished, then chances are you are good to go. Second, what is the condition of the air in the basement. If you have a dank, musty odor in your basement, you probably don’t want to bring that air upstairs, so it may be best to leave well enough alone. Third, you must verify that the basement level and the upper floor are connected to the same furnace or air-handler. Some larger homes have multiple systems, each serving a different level or area of the house. Obviously, the air is not going to mix between levels if the system is not pulling air from both areas.
If you live in the southern half of the country and you do not have a basement, all of this is not necessarily lost on you. Chances are that if you have a two-story house, the ground level stays a bit cooler than the upper level. The same principles apply, just move everything up one story.
The one trade-off to consider is that you are putting more hours on the blower motor when running the fan continuously, which is going to contribute to wear. However, modern blower motors can last up to 20 years, so frequent motor replacement is unlikely, even if running the fan continuously for a few months in the summer. If you have read through this article and think it might help, try running the fan for a couple days and see what happens. You may even decide the results are worth replacing a fan motor every decade or two.
Another forecast with temperatures in the 100’s and my brother-in-law says to me, “I guess I’ll be spending another weekend in the basement.” He pauses for a moment before continuing, “Hey, you’re an engineering. Can you design me some sort of system that pulls the cool air from the basement and dumps it upstairs?”
“You already have one”, I reply. “Just flip your thermostat’s fan switch from ‘Auto’ to ‘On’.”
He wasn’t the first person to ask me about how to move the cool basement air upstairs. If you have a full basement, you’ve undoubtedly noticed that the basement air is significantly cooler than the upper floors during the heat of the summer. Fortunately, in most cases, you already have a means to help equalize the temperatures.
Most thermostats are wired with a fan ‘Auto/On’ switch. During the summer with the thermostat in cooling mode, the air-conditioning’s condensing unit, located outside, turns on when the temperature at the thermostat in the house rises above the setpoint temperature. At the same time, the blower fan in the furnace or air- handler also turns on to blow the cool air throughout the house.
With the thermostat fan mode switched to ‘On’, the blower fan runs continuously. The condensing unit outside will still cycle on and off to cool the house when the thermostat is tripped. The difference is that between condensing unit cycles, the air blowing out of the registers is not conditioned, so the air won’t feel as cool. The benefit of running the blower fan continuously is that it is constantly pulling air from the rooms throughout the house and recirculating it through the system. As a result, the air in the basement mixes with the air in the upper floors before being redistributed throughout the house. Over time, this mixing of the cool basement air with the warmer air upstairs will reduce the difference in the air temperature between the two floors.
Before you run headlong to your thermostat to flip the fan mode to ‘On’ , there are a few things to consider. First, you must verify that you have conditioned air blowing into the basement. If your basement is finished, then chances are you are good to go. Second, what is the condition of the air in the basement. If you have a dank, musty odor in your basement, you probably don’t want to bring that air upstairs, so it may be best to leave well enough alone. Third, you must verify that the basement level and the upper floor are connected to the same furnace or air-handler. Some larger homes have multiple systems, each serving a different level or area of the house. Obviously, the air is not going to mix between levels if the system is not pulling air from both areas.
If you live in the southern half of the country and you do not have a basement, all of this is not necessarily lost on you. Chances are that if you have a two-story house, the ground level stays a bit cooler than the upper level. The same principles apply, just move everything up one story.
The one trade-off to consider is that you are putting more hours on the blower motor when running the fan continuously, which is going to contribute to wear. However, modern blower motors can last up to 20 years, so frequent motor replacement is unlikely, even if running the fan continuously for a few months in the summer. If you have read through this article and think it might help, try running the fan for a couple days and see what happens. You may even decide the results are worth replacing a fan motor every decade or two.