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What Causes a Cold Basement?

Bare feet on concrete

You’re lucky enough to have a basement in your home, but it’s so cold that it’s basically unusable. What’s making your basement so cold? And more importantly, how can you effectively warm it up? Nearly every homeowner with a basement has asked these questions. To answer them, we’ve compiled the top three causes of a cold basement along with their best solutions.

Basement Living Room Lifestyle Stock Photo

Cause #1: Below-grade walls and floor

Simply the fact that basements are located underground makes them inherently colder. Dirt is a very good insulator. As a result, the basement will stay cold even during the summer months.

Solution: A supplementary heat source

Space heaters were not designed to heat an entire basement. You’d have to place multiple heaters around the basement to get the desired effect. Instead, we recommend having an in-floor heating system installed before you finish your basement. By placing a cork or synthetic cork underlayment (like CeraZorb®) over your concrete slab, you can then install an electric floor-heating system on top that will radiate heat upward through nearly any flooring material you choose. This will ensure that the concrete slab doesn’t absorb any of the supplementary heat you’re producing, leaving you with a comfortably warm basement.

Cause #2: Humidity

If you walk into a basement and it feels damp and smells musty, it’s because there’s too much humidity in the air. Even if there is no standing water in the basement, moisture migrates through the foundation, increasing indoor humidity. During the hot, humid months of the year, condensation can also form on the walls and floor of your basement, adding to the indoor humidity. Humidity combined with cold temperatures makes you feel colder.

Solution: A dehumidifier

Purchase a dehumidifier and run it during the summer months. You can get a dehumidifier that expels the water through a hose that’s aimed at a drain in your basement, or you can get one that pumps water in the air into a storage bin that must be emptied when it’s full. Depending on your basement setup, you can determine which option works best for you. To determine when your dehumidifier should be running, check the humidity level on your furnace. If it’s above 30 percent, you will probably want to have it on.

Nest thermostat heating

Cause #3: Thermostat location

The third major reason for a cold basement is the location of your thermostat. If you have a two-story home and a single furnace, you’ve probably already noticed that the top floor always feels a few degrees warmer. That’s because heat rises. The same concept applies to the basement; however, it has an added issue: lack of sunlight. The first and second levels of a home feature multiple windows and doors that let sunlight and warmth stream into the home. The basement, on the other hand, does not have the same luxury. Without that solar warmth, it’s inherently colder than the rest of the house. And with the thermostat typically placed somewhere on the first floor of the home, the basement’s temperature isn’t being accounted for. The thermostat is simply monitoring the temperature of the room in which it is installed. This places the basement at a significant disadvantage because it’s the lowest level of the home, it does not have access to sunlight, and it’s not being monitored by the thermostat.

Solution: A smart thermostat

Smart thermostats like the Ecobee3 come equipped with wireless remote sensors that work to eliminate hot and cold spots in the home. For a large home with one furnace — or any home with a basement — these sensors can try to even out the temperature across the home, making every room comfortable.

By addressing the causes of the typical cold basement, you can find the appropriate solution and make your basement finally feel like part of the rest of the house. 

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Is there a way to move the cold basement air to the upstairs in the summer? My basement is always too cold in the summer and my upstairs is always too warm in the summer. If there was a way to continually move the basement air to the upper floor, we wouldn't need to cool the upstairs as much, right?

WarmlyYours Responds...

That's an interesting question. You don't want to directly cycle the air from the basement to the upstairs as the cycling will sap the warmth/coolness from the air as it strives toward equilibrium. One popular alternative is to install an "attic fan" which is designed to push warm air out of the house from the location it is naturally headed (to the top of the house). If you have basement windows, you can leave one cracked which will allow the warm outdoor air to displace the cold basement air, which can then be drawn upstairs. Hope that helps.

Rather than cycling the air from the basement to the upstairs which is not recommended as mentioned, close your basement vents and if they don't close and seal adequately you should block them with strong magnetic vent covers or rubber vent covers. If you're going the magnetic route get strong magnetic vent covers because the ones with weak magnets will fall off the basement ceiling vents. Also, there is a new product called the Ecoflap automatic vent cover which you can use on the upstairs floor vents which helps keep AC air upstairs. It works by automatically closing the floor vent it's attached to when the AC shuts off and when it closes it prevents the AC air from backflowing into the floor vent and flowing down into the basement which is where it goes because cool AC air is heavier than ambient air. Also keep your basement door closed and if possible put a auto door return on it so it automatically closes. Also keep all bedroom doors and other upstairs doors closed if possible which will also help keep the AC air upstairs. Plastic seal strips on the door bottoms will also help.

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