How Do I Keep the Air in My Basement?

How Do I Keep the Air in My Basement?

The basement is a crucial location to consider when building a new house or wanting to improve one’s existing residence. There are many factors to take into account, even if you are not planning to finish the basement or use it as a living space.

How does air escape from one’s basement? Most of the time, both hot and cold air escape from your basement through some form of leak. This could be due to cracks in the foundation, gaps around air ducts and pipes, or openings around windows and exterior doors. Another possibility could be your sump pump if you have one.

In this article, we will discuss how to locate the source of a leak so homeowners can work to fix the problem. This knowledge will help you to improve air quality while making your home more energy-efficient. 

Knowing the building codes, using appropriate construction materials, and preventing moisture buildup and air leakage will make a substantial difference in longevity and owner satisfaction.

Determining If there is a Leak

Before taking steps to find the solution to a loss of energy, homeowners or contractors must first determine if there is an air leakage in the basement causing the problem.

Knowing the basics of basement construction can help determine the location of the leak.

Air Leaks

Air can enter and escape in many different areas of a home. Most commonly, the air is able to leak out from either the basement or the attic.

Air leaks are common in both multi-family and single-family homes, usually caused by issues with the foundation or sealant components. 

Leak Detection

Homeowners, technicians, or contractors can find air leaks. When energy bills start rising, or someone feels air coming in or out of the basement, it is a good indication that an air leak is the root cause.

Residents can do a simple initial test for air escaping by holding their hands over typical leak spots. When the homeowner feels air (usually cold) coming into the basement, he or she has found that an air leak exists.

Homeowners can conduct visual inspections to find the location of air leaks. There are many areas inside and outside of the home to check for openings and cracks you can fill. 

Visual checks at night can help locate fine cracks with the aid of a flashlight. If light seeps in or out of a suspected gap, air leakage is occurring. 

Other ways homeowners can find leaks are by using candles or incense.

Using a lit candle, they can hold the flame up to typical leakage spots around the basement and look for movement from the flame. If the candle flickers, one has found the spot where the air is escaping from the home. 

Incense sticks can have the same result. With inside air currents, such as fans or HVAC systems, turned off, the smoke from the incense will be blown sideways, either towards or away from the leak. 

Another test that either residents or professionals can perform is using a leak detector to check for the location of escaping air. These devices are more costly than the smoke tests, but they can also provide more accurate results. 

The leak detectors use radar technology to find air leaks. When you find a leak, a light on the tool changes colors. On some detectors, the light changes not only due to leaks but show both cold and hot air leakage.

Technicians and contractors might use a blower door test to check for air leaks. After completing an energy audit, the professional will place the blower fan in an exterior door, with all other exterior doors closed and interior doors open. 

With the fans on, it sucks all of the air out of the home. This lowering of internal air pressure makes it easier to find the areas in which the air pressure from outside is seeping into the house, indicating the location of a leak (source). 

Locations of Leaks

There are both internal and external sources of air leaks. While some areas might be more evident than others, it is essential to check out all the possibilities to seal all potential leakages. 

The first locations many people check are the outsides of and weatherstripping around exterior doors and windows.

Many basements do not have exterior doors to worry about, but improper window seals and gaps between the panes and frames can contribute to substantial losses of energy.

Gaps where the foundation meets the corners or walls, holes in drywall or plaster, or cracks in the foundation itself can also contribute to air leaks.

The areas where pipes and wiring enter and leave the basement, as well as rim joists can also be culprits for air escaping.

There are also areas where one might be surprised to find air leaks. Air vents that do not adequately close can let out air from the basement, as can electrical outlets and switches on exterior walls. 

Sump pumps on basement floors and openings in and around the baseboards can also let air escape from the home.

Basement Construction Materials and Components

Both the type of foundation and materials used in constructing a basement can affect the possibilities and types of air leaks.

Most basements have a full foundation, made from concrete blocks, pours, or even bricks. Most of the foundation lies below the surface and supports the rest of the house.

Even if your home doesn’t have a full basement, partial foundations usually exist to form a smaller crawlspace.

If you have a poured-concrete basement foundation, there are a smaller number of places where air can leak out.

Most of the air escapes from along the joints between the walls and floors. Air can also escape the basement if cracks develop in the concrete foundation.

It is also possible for concrete block foundations to develop air leaks in the spots where the floors and walls meet. Additionally, air can escape between the blocks, where the mortar holds the blocks together.

As is the case with many older homes, builders may have used brick, stone, or clay tile to form the foundations. Although these are sturdy materials, they also pose more issues for air leaks.

Not only can air escape from the perimeter of the foundation, but also from between gaps and cracks in the walls themselves.

Along with the foundation itself, insulation can be used in basement construction to help control the temperature and reduce the influx of outside noise, as well as adding another layer of protection. 

Many types of insulation include vapor barriers too, which can help lessen the possibility of air leaks. 

Effects of Air Leaks

The most significant effect of basement air leaks is due to something known as the chimney effect.

Since the furnace and air conditioning units are usually located in the basement, they will both have to work harder to compensate for the air leaking in and out of the home. 

When someone turns on the heat during colder weather, it naturally rises through the house, up into the attic. The furnace then has to run more consistently to make up for the loss of heat and an influx of cold air seeping into the basement. 

In warmer months, the air conditioner loses a lot of energy to the hot air coming into the basement from leaks or cracks. 

Not only does the Chimney Effect cause comfort issues within the home, but it can also account for up to 25 percent of the home’s total heat loss, increasing both the amount of energy lost and heating bills (source). 

Air Sealing the Basement

There are a variety of ways to stop air from leaking out of the basement. Homeowners can choose to work on sealing the basement themselves or hire a professional to help solve the problem. 

While stopping the air leaks and drafts should be the primary priority, improving the windows and doors, as well as adding insulation to the walls, can also help. 

Homeowners and professionals have a variety of choices when air sealing a basement. Some of the most commonly used materials are caulk, spray foam, weatherstripping, and insulation materials such as foam board.

Solutions to Common Areas for Air Leaks

Whether residents choose to air-seal their basement themselves or hire a contractor, they first need to understand the level of work they need to do.

The size of the gap or crack and the location will determine the best solution for the problem.

After determining the location of any air leaks, residents can get to work repairing the issue. If the gaps or cracks are small enough (less than three inches), you can use caulk or insulating spray foam to fill them. 

For larger spots, you will need foam board to close the opening first. Then, use insulating foam to seal it up. 

If there are any outside doors or hatches, you can address gaps around the edges with weather-stripping. Adding a layer of insulation to the interior side will also help seal the door.

Adding weather-stripping with the additional protection of caulking or spray foam (depending on the size of the gap) can also help to seal air leakage spots around basement windows.

Do not forget to completely insulate the areas where the window frames meet the walls.

If a basement is older and has windows that are not in the best shape, it might be time to consider replacing the windows with new ones. 

Single pane windows tend to let a lot of air in and out of the home. Double pane windows will not only help insulate, but also be better suited for preventing air leakage. You might also need to replace doors if they are warped. 

Unless the homeowner wishes to seal the door or window permanently, he or she should not apply the caulking or foam around the entire frame.

It is essential to think about the need for both ventilation and fire escape routes before completely closing any openings.

Although poured concrete foundation walls are usually tightly sealed, they may develop cracks over time. You can plug smaller cracks in the walls with caulking, but larger holes might need spray foam as well.

Along with the foundation walls, cracks may develop not only in foundation walls but in the foundation floors as well.

If there is a sump pump in the basement floor, air could also escape through this opening. Instead of just relying on filler materials, consider replacing the lid on the sump pump. 

Sometimes shrinkage may occur, allowing gaps to develop between the floor and the walls.

If the outside soil is loose or porous, it could be allowing air to enter or leave the house. Before filling these types of gaps with caulking or spray foam, the homeowner will need to clean the area first to remove any debris. 

In some basements, there might be chases that reach up from the ceiling to the attic. Along with filling gaps at the top in the attic, you may need to fix the bottoms as well. Air can get into these areas and move around until it finds a way to escape.

Other locations in the basement ceiling that could contribute to air leakage include where a bathtub drain comes down, holes for plumbing, or spots where electrical wiring comes down.

Before sealing these gaps, homeowners might want to consult a professional to avoid potentially dangerous situations.

Electrical wires, gas, and water supply lines, telephone and cable lines in the walls that lead to the outside of the home can also have areas around them that let the air out.

You will need to check these penetrations on both the interior and exterior of the basement.

Air ducts are another area that you might need to address. The basement could have ducts that lead up through the ceiling or clothing dryer vents that lead to the outside. 

Gaps may develop around these ducts and let out the air. You can use caulk or foam to plug these gaps. It is also important to check the exterior of the home to ensure gaps around these ducts are sealed as well (source).  

Gaps and Cracks Around Rim Joists

Rim joists are also reasonably common areas for air to leak out of the home. Since the rim joists’ role is to connect components of the basement, they are not usually insulated. Using caulking and spray foam can help seal these areas. 

If using spray foam, it should extend from the top of the foundation wall where the rim joists meet the wall up to the subfloor above.

Rim joists do not need to be covered, and drywall is usually not necessary, but the homeowner can add it if they wish to do so to conserve internal energy. 

Homeowners also have the choice of using rigid foam instead of spray foam to help insulate the rim joist areas. This type of insulation will help keep the basement more temperature-regulated, as well as being less expensive than using spray foam. 

You do not need to cut the rigid foam perfectly as long as it will fit the necessary space. Once you have put it in place, use spray foam or another adhesive to connect it to the wall and ceiling.

If additional insulation is desired or required, you can add a second layer of rigid foam or fiberglass batts (source). 

When to Hire a Professional Contractor

Professionals not only add peace of mind to a home improvement situation but also can provide valuable insights and resources. Contractors can use diagnostic testing at both the beginning and end of a project to ensure the project is done correctly. 

Before beginning to work on air sealing a basement, contractors can check to see if the area is adequately insulated and install any necessary equipment to complete the project.

After completing this step, they can help with planning the entire project, so everything is done logically and effectively. 

If a homeowner starts a project but notices potential safety hazards, he or she should call an expert immediately. 

Wet insulation or even mold or mildew should be addressed by a professional as they could be causing health problems for those living in a basement.

Condensation near air conditioning units can signify ventilation or carbon monoxide problems.

Fire hazards can also exist. If a resident needs to seal gaps around light fixtures or electrical wiring, a contractor should be involved to help eliminate the risk of dangerous hazards. 

If you or someone else uncover damaged wiring, homeowners should stop immediately and involve an expert so that a potential fire does not occur. You should also conduct combustion safety tests.

Final Thoughts

Not only can air leaking from a basement be an annoyance, but it can also contribute to rising energy costs and low air quality.

To eliminate these potential issues, homeowners have a variety of choices to seal the gaps and cracks where the air is escaping from their home. 

Before beginning any home improvement project, especially one involving potentially dangerous issues, residents should consult experts. Experts can perform diagnostic testing, which will determine the next steps to take. 

Once the location and size of the air leakage spots have been discovered, homeowners can decide to fix the problem themselves or hire a contractor. 

Either way, fixing the air leaks in your home will save both energy and your money.


I'm a Pharmacist and a passionate researcher into clean air and pure water for the home. I believe these 2 elements play a significant role in our health and overall wellbeing.

Recent Posts