Of all the instruments in an energy audit, the blower door is the one that surprises homeowners most — because it puts a hard, undeniable number on something you could only ever feel before: how leaky your house really is. If you've been told your home is "drafty" or "tight" without any measurement behind it, this is the test that replaces the guess. Here's how it works and what the numbers mean.
What Is a Blower Door?
A blower door is a powerful, calibrated fan mounted in an adjustable panel that seals into one of your exterior doorways. When it runs, it draws air out of the house, lowering the indoor pressure relative to outside. That pressure difference forces outside air in through every crack, gap, and penetration in your home's envelope — and the fan measures exactly how much air it takes to maintain the pressure. That measurement is a direct readout of how leaky your home is.
The whole test takes under an hour and is completely non-destructive. Nothing is opened, drilled, or damaged — the fan simply seals into an existing doorway.
What ACH50 and CFM50 Actually Mean
Two numbers come out of the test:
- CFM50 — cubic feet per minute of airflow required to hold the house at 50 pascals of pressure. It's the raw leakage rate.
- ACH50 — air changes per hour at 50 pascals. This takes CFM50 and relates it to your home's total volume, so it accounts for house size. It answers: how many times per hour would the entire volume of air in my house leak out at this test pressure?
ACH50 is the number auditors and rebate programs care about most because it lets you compare homes fairly. A low ACH50 means a tight house; a high one means a leaky house. Tight modern construction can test around 3 ACH50 or lower, while many older Arizona homes come in two to three times leakier.
Why Air Leakage Costs So Much in Phoenix
In a mild climate, a leaky house is mostly a comfort issue. In Phoenix, it's a financial one. When it's 110°F outside and your AC is fighting to hold 78°F inside, every cubic foot of leaked air is a cubic foot of superheated desert air your system has to cool from scratch — over and over, all day long.
Air leakage also drags monsoon dust and humidity indoors, adding load your AC must remove, and it undermines even a brand-new, high-efficiency air conditioner. Here's the key insight: you can't insulate your way out of a leaky envelope. Insulation slows heat conduction, but leaked air moves right around it. That's why sealing the leaks a blower door finds is almost always the cheapest, highest-return efficiency work available.
Where Arizona Homes Leak Most
Leaks aren't random — they cluster in predictable spots. Paired with a thermal camera and smoke pencil while the fan runs, we can pinpoint them exactly. The usual suspects in Valley homes:
- Top plates — the gaps where interior walls meet the attic, a major hidden path.
- Recessed can lights — older non-airtight fixtures act like little chimneys into the attic.
- Attic access hatches — usually uninsulated and unsealed around the entire perimeter.
- Plumbing and wiring penetrations — every pipe and cable through the ceiling plane.
- Duct chases and register boots — openings where ductwork passes through walls and ceilings.
- Block-wall to frame transitions — in 1970s homes, the junction between CMU walls and framed roofs.
The Best Part: It's Verifiable
Here's what makes the blower door so powerful — it's repeatable. After air-sealing work, we run the test again and measure the improvement, giving you documented proof that the money you spent actually tightened the house. That before-and-after is also exactly what APS and SRP rebate programs want to see to qualify your air-sealing work.
Blower Door + Thermal Camera = A Leak Map
On its own, the blower door tells you how much air leaks. Paired with a thermal camera, it tells you where. With the house depressurized, incoming air cools the surfaces near each leak, and the infrared camera lights those paths up instantly. Instead of "your house is leaky," you get "here are the specific locations, ranked by size, that account for most of your leakage." That precision is what makes the follow-up air sealing fast, targeted, and cost-effective.
The Bottom Line
The blower door turns a vague feeling into a number you can improve and prove. It's the foundation of every serious energy audit and the starting line for the cheapest, highest-return work you can do on an Arizona home. If you want to know exactly how leaky your house is — and what it's costing you every summer — book an audit or call 844-967-5247.