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What is Blower Door Testing?

Reading Time: 4 minutes

What is Blower door testing you ask? First off, no we are not going to come to your house and blow on your door. We are, however, going to set a series of panels up in your front door (as pictured here) and in the bottom panel we will place a rather powerful fan.


Depending upon the size of your home, there are a series of rings that can be taken out or put in the fan to get the airflow we need to depressurize the home. Every home is under a small amount of negative air pressure to begin with and we are going to use our fan to increase the negative pressure in your domicile so we can to discover what your home does in terms of leaking air and where those leaks are.

Negative air pressure is one of the reasons we experience discomfort in some rooms of a home. What I am about to tell you goes against a lot of what you know when it comes to science. Everyone knows that heat rises right? In the case of a typical single-family home, the answer is yes and no. The heat of the attic wants to pull into a home because of guess what? Negative air pressure.

Let’s dig a little deeper into our attic and detecting air leaks. The walls in your home are hollow and the top of the walls are open into the attic. These connection points are called top plates. The top plates being open to the attic allow hot air to stream down the walls and come out where ever it can. These places can include, outlets, light switches, smoke detectors and basically around anything that has penetrated the wall cavity.

So, we have set up our blower door and now want to begin the testing. First, we are going to check off a few boxes before we start. Air conditioning system off, fireplace if present sealed, all interior doors open, check, check and check.

Air pressure is measured in pascals and we want to get the home down to at least negative twenty-five pascals for the best test results. On a completely side note, your fun trivia fact for the day is that 100 pascals are called a hectopascal, which is in turn equal to one millibar. Being South Floridians, we all understand that millibars or positive air pressure is what makes hurricanes spin and the lower the millibars the more powerful the storm.

test meter

Okay, our fan is up and running and we have reached the negative pressure goal that was set on the manometer. Manometers are used to measure all different kinds or air and gas pressures and the one we are using in this test has a port that measures outside air pressure and then increases or decreases the speed of our fan to maintain the set point of negative air pressure. Another trivial side note; if you are in the home when a blower door test is being conducted you are likely to experience your ears popping, somewhat similar as to what occurs when you are flying.

The first thing we are going to test is the duct system. Remember, our air conditioner is off so we should have no air coming out of the ducts, right? Wrong. Unless the duct system is properly sealed we are going to being pulling air into the duct system with our fan. We use another device called a flow hood to measure the CFM’s (cubic feet per minute) of air coming through the duct system. We also use thermal imaging to detect heat being pulled down the walls and theatrical smoke to determine what the air currents are doing in the home.

After around thirty minutes or so I can tell you all the places your home is pulling in heat and losing that ever so precious air conditioning, which in turn allows me to write the correct prescription to make the home as comfortable and energy efficient as possible. That is the whole purpose of blower door testing. We want to be able to give you a road map for making your home the best it can be.

As with any other testing, the last thing we do when we are testing is to test the home again after repairs are made. Test in and test out for the best results was one of the first things I learned in building science. If you are looking to save some money and improve the comfort of your home I recommend a blower door test – it’s the perfect place to start.

Until we meet again ladies and gentlemen, I was watching a video the other day and the opening credits said don’t try this at home, so I called a buddy of mine and asked if I could come over. I want to try something.

House Whisperer out!!


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