The Number Behind
Every Job We Do

A calibrated fan mounted in an exterior doorway pulls air out of the house, lowering the pressure inside so outdoor air flows in through every gap. A gauge called a manometer measures the pressure difference and the airflow through the fan, which gives an exact number for how much air the house leaks. That is the Department of Energy’s description, and it is what we do on every envelope job.

CFM50 is the cubic feet per minute of air the fan has to move to hold the house at a 50 Pascal pressure difference, a standard test pressure that roughly mimics a steady 20 mph wind on every side at once. ACH50 converts that to air changes per hour by dividing by the house volume, so homes of different sizes can be compared. Lower is tighter.

The 2021 energy code requires new homes in our climate zones to test at or under 3 air changes per hour at 50 Pascals. Existing Front Range homes from the 1960s through the 2000s commonly test several times that. We do not quote a single typical number because every house is different; we quote yours, before and after.

Because the test is how we find the leaks, not just count them. With the fan running, a thermal camera and a smoke pencil show exactly where air is pouring in: top plates, the rim joist, recessed lights, the attic hatch, duct boots. The work gets aimed at the biggest paths instead of caulking the windows and hoping.

So the result is proven. The second number tells you, in the same units, how much tighter the house is. It also catches anything we missed while the crew is still on site. A job without a second test is a job that was assumed to work.

Setup and the test itself take under an hour. The diagnostic walk with the camera and smoke pencil while the fan runs is where the value is, and that is another hour or so depending on the house.

Close exterior doors and windows, open interior doors, make sure fireplace ashes are cold and dampers closed, and turn off combustion appliances and exhaust fans for the duration. We walk you through it when we schedule.

It is the core of one. Our home energy audit pairs the blower door with a thermal scan, insulation depth checks, duct testing, and combustion safety testing, and produces a prioritized report. The blower door alone is the right choice when you already know you want air sealing and want the before and after numbers.

A house can be tighter than its ventilation plan. Below a few air changes per hour, a home needs mechanical ventilation to bring in fresh air on purpose instead of by accident. We tell you when a house crosses that line and what to do about it. Most Front Range homes are nowhere near it.

EPA estimates that homeowners save an average of 15% on heating and cooling costs by air sealing and adding insulation in attics, over crawl spaces, and at basement rim joists. Savings vary. Find out why in the seller’s fact sheet on R-values. Higher R-values mean greater insulating power.