How to Check Your Attic Ventilation With a Smoke Test

When your attic is properly ventilated, your house is more resistant to mold and moisture damage, and your roof lasts longer. You’ll also save on energy bills, and your home will be more comfortable. A smoke test is a simple way to determine if your attic ventilation is working properly. The test involves a few steps to help locate air leaks and determine the amount of existing ventilation. 

When your roof and soffit vents work in unison, hot air is removed, fresh air comes in, and airflow is created. Thanks to the insulation, your attic is sealed off from the rest of your house, so your attic vents don’t draw air from inside your home. Learn how to do a smoke test to check your attic’s ventilation in six easy steps below. 

Project difficulty: 1/5

Time: 15 to 30 minutes

Tools and materials needed:

• Incense or smoke stick

• Lighter or match (if using incense)

• Flashlight

• Ladder (if you have high attic ceilings)

It’s best to conduct the smoke test on a day that isn’t super windy, because you want to see how air moves through your attic on a typical day. Beyond the smoke test, you can get a local roofing repair professional to come out and examine your home with infrared cameras.

1. All the Windows in Your Home

Shut all the windows in your home before you do the test, so you can determine how well the attic ventilates on its own. 

2. Turn Off Mechanical Ventilation

Power off any fans or HVAC equipment so you can properly assess how well your attic ventilates. 

3. Head Up to the Attic

Bring a flashlight and incense or a smoke stick with you, along with a lighter or match if you need one. If your attic ceilings are high, you may want to stand on a ladder, so you can conduct the smoke test closer to the openings. 

4. Light the Incense or Smoke Stick

Now it’s time to light your smoke stick or incense. Hold it up close to the leaks and ventilation in your attic. Test near windows, doors, and around the cable and internet lines that run through your walls. If you puff the smoke a few feet away from the opening, you should be able to see where and how the smoke travels. 

5. Watch the Smoke

Take a close look at the movement of the smoke. Shine a flashlight or turn on lights to get a good view of where and how the smoke moves. If the smoke blows into the attic in some places and outside in others, your ventilation works well. 

If the soffit vents are allowing air in, the smoke drifts inward. If not, you'll want to clean, replace, or unblock your soffit vents. The same goes for your roof vents. The smoke should be traveling outside.

6. Get a Deeper Analysis

The smoke test can give you a good idea of your home's existing attic ventilation, but it may take a roofing contractor or HVAC technician in your area to determine if the amount of airflow is enough, too little, or too much. A professional can also determine the best attic vent options for your home.

Why Is Attic Ventilation Important?

Your attic should be ventilated to help prolong your roof’s life, which is why it’s important for you to learn how to do a smoke test. When extra heat is trapped, it can melt the snow on your roof during the daytime and freeze overnight when the temperatures are low. This can lead to ice dams, interior leaking, and roof damage. Rusty nails, mildew, deterioration, and wood rot can also happen from a poorly ventilated attic.

Not only does poor ventilation harm your roof, but it's also harder for your home to maintain temperatures. You'll have to pay more for your energy bills, and your home might not be as comfortable as it could be.

How Do You Know If There Is Adequate Attic Ventilation?

There’s adequate attic ventilation if, when you conduct a smoke test, the smoke exits out the exhaust vent, and circulates near your intake or soffit vents. 

How Do You Tell If Your Soffit Vents Are Working?

You can tell if your soffit vents are working if you conduct a smoke test, and you can see the smoke moving inward, showing that air from the outside is flowing into your attic. 

Types of Attic Vents

There are two main types of attic vents: intake and exhaust vents. Intake vents or soffit vents sit at the lowest part of the roof under the eaves and pull in cool air from outside. Exhaust vents at the peak of the roof remove the stale, stuffy air from the inside. Both types of vents are necessary to move air properly through the space. 

Within exhaust and intake vents, there are several types of vents to choose from, such as ridge vents and gable vents. The best combination will depend on your house and location.