Basement Too Hot In Winter: Cool it down and save energy!


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Excessive basement heat is likely originating from the furnace directly or through the HVAC system. Check for and seal leaking ducts, clean the furnace filter, close some vents or registers, adjust dampers, install more return vents, and/or insulate ductwork.

One would think the issue would be how to warm your basement in winter. However, it is possible for too much heat to build up in your basement, even in winter, and it is important to address the matter.

It’s highly unlikely that your new neighbor is magma, so you will probably find the source and solution to your problem in the basement itself. Too hot or too cold? Let’s check the HVAC! There are several appliances and components of your HVAC system located in the basement that can be causing trouble.

Make Sure Furnace Is Not Leaking

How Leaking Furnace Adds to Basement Heat

Your furnace may be leaking air due to poor connection or sealing on the main trunk or on the supply ductwork. This allows heated air to escape into your basement, where the insulating ground around the basement shell helps to trap it.

Boiler furnace in basement ; industrial dirty grunge background

The furnace trunk is the main duct for the furnace and travels throughout the house. If air is leaking from the trunk into the basement, you will probably notice that the rest of the house is colder as it supplies the auxiliary ducting that filters hot air into the whole house.

Your basement is going to get a little too toasty, even for snowy winter weather!

Fixing a Leaking Furnace

If there is a sealing problem on the furnace connections, the solution is simple: you just need to seal the ducts. There are three methods you can look at to accomplish this.

If air is leaking from the furnace trunk, you can use caulk for sealing up smaller holes and a foam sealant (Great Stuff Foam Sealant (amazon link)) for larger ones. An extra layer of aluminum foil duct tape, like TapePlus Professional Grade Aluminum Foil Tape (amazon link), is required to reinforce the sealing of any type of gap.

You need to be aware of the high heat levels associated with that duct line and use appropriate materials, such as Rutland High Heat Silicone Seal (amazon link).

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How This Cools Basement and Saves Energy

By sealing gaps and cracks in the ducting for the furnace, you are restoring the integrity of your HVAC system.

Without the steady stream of hot air being funneled directly into your basement, it can cool to the correct, HVAC-controlled temperature.

You will save energy because the furnace won’t need to work overtime to try and heat the house while most of it is just pouring into the basement.

Check Furnace Filter Is Clean

How Dirty Filters Add to Basement Heat

Furnace filters catch insects, dirt, pollen, etc., that are brought in with the in-flowing air. These impurities are filtered out before the air is heated, then passed through the house.

A clogged furnace filter makes your system work hard to compensate for less airflow and can lead to the furnace overheating.

Senior man changing a dirty air filter in a HVAC Furnace

This excessive heat that your furnace is now throwing off is going to be dumped directly into your basement air.

Filters need regular replacing, not just for better air quality, but also because dirty filters negatively impact your HVAC system.

Cleaning/Replacing Furnace Filters

The filter is commonly located in the blower compartment, near the return air connection. Remove the old filter and follow the manufacturer’s instructions for installing the air filter. Make sure the arrows on the filter align with the direction of airflow and check that the filter is securely placed.

You should check your furnace filter monthly and replace it every few months as needed. Regularly cleaning the furnace filter will help your system last longer and means that your furnace can pull air in properly.

A good quality filter will optimize your HVAC system’s function, which can be determined using the Minimum Efficiency Reporting Value (MERV).

Look for a minimum MERV rating of 7.

Ratings 1-6 will only keep out the largest impurities. Ratings of 13 and onwards are considered high-efficiency filters, and I recommend consulting an HVAC specialist to get a good match for your system.  

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How This Cools Basement and Saves Energy

By keeping the filter clean, you are preventing your furnace from overheating. This helps cool your basement as the furnace is not producing extra heat while it works hard to pull air into the system.

Not only does this reduce the heat transferring into your basement without the regulation of the heating system, but this also saves on energy since the furnace can function at its standard energy usage with optimal functioning.  

Close Some Registers/Seal Some Vents

Too Many Registers/Vents Add to Basement Heat

Return registers or vents can add to your basement heat depending on how they are adjusted to direct and pull air from your basement. Having too many open at once decreases the control that these HVAC components are supposed to give you. 

Closing Registers or Sealing Vents

You might be aware that when it comes time to turn on the heating system, you should be adjusting your vents to help keep your house at the optimal temperature. But, if your basement is too hot, you may need to go against your training.

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For a basement that is too hot, even for winter weather, you will need to close the bottom return registers near the floor and open the top ones near the ceiling. This is because warm air rises while cool air sinks. You are not trying to remove the cool air from a sweltering basement.

Adjusting the supply vents for the heating will prevent extra hot air from being given to the basement.

How This Cools Basement and Saves Energy

Along with not adding more hot air from the heating system by sealing the supply vents in the basement, adjusting the return registers to pull hot air from the basement should give you more control over the house temperature.

You will be saving the energy that would have been uselessly supplying hot air for the basement. And by making use of the natural physics of your HVAC system, you will be getting the most function out of your system without having to use a lot of the electrically driven functions.

Adjust In-System Dampers

How Dampers Can Divert Heat into Basement

Dampers can be adjusted on vents to help control airflow and increase the amount of hot air supplied to the rest of the house while decreasing the amount for the basement.

If your dampers are fully open in the basement and partially open on the upper floors, then the hot air is not going to be leaving your basement effectively.

Adjusting the Dampers

If your dampers are adjustable, they will have levers or dials. Dampers should follow the right-for-tight and left-for-loose rule. But you will be able to see the blades or flaps of the damper widening and enlarging the gaps between them when they are open. If they are closed over, the edges should be lying close to each other.

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You need to close the dampers over in the basement, but not completely. By opening the dampers on your upper floors, heated air will be forced upward.

How This Cools Basement and Saves Energy

This cools the basement but allows the hot basement to naturally rise through the vents to other, higher areas of the house. This removes some of that hot air that is making your basement uncomfortable.

Energy-saving comes from relying less on heating upstairs and the need to run the A/C for the basement. You are using the air that is already in the house to help balance the internal temperature.

Install Return Vents in Basement

Few Return Vents Limit Cold Air Entering Basement

Return vents extract air from a specific area and can be set up to deposit the air directly into the HVAC system for distribution.

Having return vents in a basement can be helpful in removing extra heat from the area in winter and pulling cool air in during the summer. This air can then be utilized in other parts of the house to help heat or cool it while decreasing the demands on your heating or cooling system.

Installing More Return Vents

The return vent should go near the furnace if your basement is segmented. Otherwise, the best place to put return vents to deal with heat would be near the basement ceiling.

Hot air rises and so will sit near the ceiling. Placing your vents here will position them with the best access to the hot air.

If you installed more vents near the floor, your system would be pulling any cool air that has sunk to the floor out of the basement before it can get to the hot air.

Trenton Gifts Furnace Vent Deflector

How This Cools Basement and Saves Energy

The return vents can be used to take heat away from the basement and use it elsewhere in the house. Basements are a characteristically cooler area of a home. If you remove the extra heat, you allow your basement to cool down as cool air naturally sinks.

By making use of the heat already available to you from your furnace, you will cut your utility costs and energy usage.

Insulate the Ductwork

Uninsulated Ductwork Transfers Heat to Surroundings

The very process by which insulation keeps cold air out of your ducting is how it also keeps warm air in.

Insulation functions to prevent the transfer of heat and thereby conserve energy. By covering the ducting for your heating system, you are isolating that hot air in the ducts so that it can only be expelled as intended in the HVAC system.

Best Insulation Options

The best insulation option depends on what you need from your insulation, but there is a minimum standard for unfinished basement insulation as set out in the building code.

Insulation with foil offers not only good thermal benefits at an affordable price, but also has decent soundproofing abilities that help keep your HVAC system noise levels down.

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Fiberglass or polyester insulation options are very effective at preventing heat exchange and are known for their longevity, however, you won’t get as good noise reduction.

Cellulose insulation works for thermal retention and sound levels, but you have to be careful to install it in a way that allows room for airflow.

How This Cools Basement and Saves Energy

By keeping your warm air in the ducts, you provide the HVAC system with the heat it needs to distribute with the minimum amount of heat lost.

When the heat is being transferred into your basement, you are going to have difficulties controlling the temperature of the room.

If your HVAC system doesn’t have to keep heating more air to compensate for the heat lost to the basement, it will not have to work more than necessary and will use far less energy.

You might still have to employ active methods of cooling the basement (like a mini-split), but by taking the above steps, you will significantly reduce the work these unit would have to do to cool the basement.

Sources

https://www.servicechampions.net/blog/where-is-my-furnace/

https://www.servicechampions.net/blog/air-filter-isnt-working/

https://insulationinstitute.org/wp-content/uploads/2015/11/AH121.pdf

https://www.grandrapidsductcleaning.co/blog/types-of-duct-insulation

https://www.energy.gov/energysaver/minimizing-energy-losses-ducts

https://hbmcclure.com/why-is-it-so-cold-downstairs/

https://www.ranckinc.com/adjusting-return-registers-season/

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