How to Detect Air Leaks In a House


Energy conservation is a crucial focus for homeowners today. And while insulation is essential in homes, air leakage is the worst enemy of even the best insulation materials.

That said, how can you detect and resolve air leakage in your home? According to the North American Insulation Manufacturers Association, NAIMA, the primary cause of heat loss in homes is through gaps and holes. A small crack or crevice in your grade one insulation and sealant will see you lose a lot of heat from your living space, so detecting air leaks will primarily focus on checking those areas. You can check for air leaks by touch, by using things like incense and candles, by depressurization, and by using air leak detectors.

If left unchecked, this air infiltration then contributes up to 35% of all heat loss in a home as a result due to temperature and pressure differences indoors and outdoors.

But to stop air infiltration from homes, we must first understand what it is, some of its causes, and how to detect the air leaks in homes.


What is air leakage?

An air leak happens when unwanted air enters your house while conditioned air flows continues to flow outside. It mainly occurs when there is a pressure difference or temperature variation.

Air leaks are the fundamental causes of poor indoor air quality and often increase your energy consumption. That is, you would have to spend more electricity maintaining your home at a specific temperature while being exposed to pollutants, despite having an HVAC unit.

Recommended Reading: Does Outside Temperature Affect Air Conditioner?


What are some of the consequences of air leaks?

Air leaks have a chimney effect (also known as a stack effect). This means that hot air from your house flows upwards and outwards. And as this air flows out, it creates a temporary vacuum that draws cold air from the outside. As a result, you can never have hot air in your indoor space.

Note that this air flows through similar vents and holes on the walls or windows.

Consequently, you start to notice some changes in the indoor air quality. Some of the expected effects of air leaks at home include:

  • High heating costs as your HVAC tries to condition this infiltrating air
  • Increased exposure to pollutants, since the air does not go through filters before reaching your living space
  • Unwanted noises, such as metal rattling and whistling during the operation of your air conditioning unit.


Causes of air leaks in your home

Various reasons may encourage the unwanted flow of air in or out of your home. The most common culprits are holes and gaps in your insulation, cracks on the doors and walls, and damaged vents.

Interfaces and seams between two hard surfaces, like the window frame and your wall, are also notorious for air leaks.


What affects the rate of air leakage?

The rate of air infilitration in your home is different from what your neighbor experiences. The rate of air infiltration mainly depends on:



The larger the volume of your home, the lower the rate of air change because the surface area to volume ratio decreases as your home becomes more extensive, which means that the total envelope air expected to leak becomes smaller than the surface area of your home.



New houses are built to be more airtight than older houses. With time, even these homes can develop cracks, gaps, and holes that further worsen the air change rate.


Climatic zone

Depending on your climatic zone, you can experience a moderate or worst case of air infiltration. Air leaks are worse in cold regions, where you heat your indoor space. Winds also affect the rate of air change, with stronger winds increasing the rate of airflow.



Different seasons affect different materials in a varied manner. For instance, concrete and wood that freeze up in the winter expand in the summer. This shrinking and expansion can compromise its intermolecular bonds, causing cracks and gaps to develop, which worsens air leaks.


How to check for air leakage at home

As we know, you can hardly tell of air leakage by observation. You need to feel or hear the air flowing, which is almost impossible in some cases. However, with assisted help from tested techniques, you can at least locate the vicinity of the air leak. Some methods you can use to check for air leaks include:


The hand test

This method works for accessible locations like cracks and openings on your floors and electrical outlets. It works when you want to find air coming into your home.

It’s so simple, it’s almost hard to believe it works – but it does.

On a cold day, place your hand against the area you suspect to have an air infiltration, such as your kitchen air vent or bathroom window. When you feel cold air rushing against your skin, then you have air leaks in your home.

Focus on areas where there are differences in construction materials as these are areas that need to be sealed. For example, check where bricks meet vinyl siding, where the chimney meets the rest of the home, where cement foundations meet walls, and so on. Check for things that protrude towards the exterior like faucets, vents, electrical outlets.

Sounds too simple, but not many people do this on a regular basis.


The visual test

You can detect air leaks visually too.


#1 Checking for Light Coming Through

Are you seeing a halo of light coming through the gaps under and around windows and doors? Are the lines around frames straight, or does it appear like they have gaps in certain corners while they are tight around other corners?

At night, you can also use a flashlight to shine a light from the outside into your home to find potential gaps


#2 Check for Air Movement

Another way to test visually is to detect air movement using something sensitive like an incense stick, a candle, a light piece of paper, and so on. This is best done on a dry weather way. Take the candle, incense, paper and simply waft it in front of areas where you suspect air leakage.

For example, you could check around the four sides of each window or go from electrical outlet to another. If the flame, smoke, or piece of paper suddenly move, there’s air leakage.


#3 Slip a Dollar Bill Through

This one is so simple, but it works. Put a dollar bill on your window sill while the window is open, then do your best to close the window? If you’re able to pull the dollar bill out, you have an air leak. If not, you’ll have a ripped dollar bill, but at least your window is sealed well.



This is a fun and quite engaging technique. Professionals use a powerful blower fan to do this test, but there’s also an inexpensive way you can do a similar test by yourself.

You first create a depressurized zone by closing all windows and exterior doors. The key is to get your home as airtight and shut closed as humanly possible. You’d also turn off anything that can interfere on the inside – like fans, appliances and the furnace.

Next, the idea is to see if an outside smell can enter your home and if so, where exactly. An incense stick is the easiest way to do this. Walk around anywhere you suspect the leaks on the outside of the home and waft the incense stick. If you come back into the home and notice the distinct incense fragrance, you’ll be able to pinpoint exactly where the leak is.


Air Leak detector

An air leak detector is probably the simplest method to use. You will only need to turn the machine on, aim at the suspected air leak regions, and wait to read the values.

The air leak detector will turn blue if the air flowing in is cold, red if it warm, or remain unaffected when there is no leakage.


Measures to stop air leakage in your house

There are common yet effective methods used to stop air leaks from homes. These are:



This is a technique that involves the installation of rubber seals on openings. It could be your door or window. And while weather-stripping aims at keeping water from your house, proper installation can considerably reduce the rate of air leakage in your home.

Said method is best for moving and operable parts like windows and doors. However, it does not offer a fully efficient way to protect your home from air leaks.



Caulking is an air sealing technique used on cracks and openings between parts of the house. Once applied, the caulk dries, leaving a rigid structure.

You can paint your caulk to match your exterior or interior color. Also, you can clean any dirt off the caulk without wiping it away.

However, it is quite prone to cracking when exposed to fluctuating temperatures. With time, the caulk can also crack, giving room for more air leakage.


Foam sealant

A flexible foam sealant is different from a caulk in that the sealant is made of flexible materials. Therefore, foam sealants are the best for regions prone to repetitive expansion and contraction, such as windows and other metal-framed surfaces.

Flexible sealants provide water and airtightness, even in places with the most extreme temperature variations. Most come with a straw applicator for easy use, but you have to be very careful to wear strong gloves when applying it.


To sum it up:

Air infiltration is a common problem in homes today. And just like you cannot leave your home’s ventilation up to the air leaks, you cannot assume the insulation installed will take care of any unwanted flow of air.

The air leak rate in any home depends on the house’s size, age, and climatic condition in the area. And you can use methods like the incense test or an air leak detector to find the sources of air infiltration into your home.

Once you know where the air is escaping your indoor space, you can use weather-stripping, caulk, or a sealant to stop the airflow.

But if you cannot handle all the spots, you can always consult with an air leakage expert for a more efficient home with better indoor air quality.