DIY “blower door” to find air leaks
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I’m trying to see if there is a way I can simulate a blower door to generate drafts and find air leaks. I’m not looking to generate a ach50 score.
Would putting something like this in a doorway work?
https://www.homedepot.com/p/rental/DRI-EAZ-High-Volume-Fan-Rental-F568-HD/316822138
I don’t think I would be able to seal the doorway like a real blower door fan.
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Replies
a standard 20"x20" box fan mounted in a sheet of plywood then taped in a door or window opening should be all you need. It does not need to be a perfect seal just to hunt leaks.
I did this during the Neg 10 degree cold snap we had and had alarming results....so it works.
How about a window fan in a window?
That should work too. Any fan will generator positive or negative pressure within the structure (depending on which direction it's setup to blow), the trick is to be able to generate sufficient pressure differentials to run the test. Blowers intended for blower door testing can handle larger pressure differentials than your typical box fan can. If you're only after pretty big leaks, box fans and the like will be fine. As you start to look for smaller and smaller leaks, you may find that a box fan can't create enough pressure differential for you to easily find those smaller leaks.
If you look at fans setup for higher pressure differentials, you'll notice they have a shroud and the tips of the blades get pretty close to that shroud. That helps with pressure, along with the curve of the blades and some other things. Those fancier fans are more expensive, but they can generate higher pressure differentials.
Bill
Hi, Gary Reysa of Builditsolar.com has a set of very informative instructions re how he built a good DIY blower door at a remarkably inexpensive cost:
https://www.builditsolar.com/Projects/Conservation/BlowerDoor/BlowerDoor.htm
One nice thing about this DIY instrument: it allows you to identify and seal up air leaks over time, as your work schedule may allow.
This is awesome!!! Thank you for that link!
My understanding is that the current draw for a fan is directly proportional to the amount of air it is moving. So you can measure the air volume by measuring the current with an ammeter. Even if it's not calibrated, it gives a simple way of seeing if your improvements are effective.
That's only going to apply as relative measurements against the same fan, and it's not a linear response, i.e. double the current is NOT going to mean double the air flow. I'd consider this only useable as a "did I make it better or worse?" kind of test as you go. Basically if you do something and the current drops, then you probably plugged up a leak and the fan is moving less airflow.
BTW, I'm not sure how well this holds for fans, but for centrifugal blowers, as the pressure increases (such as would be the case as you plug up leaks), the amount of airflow in CFM drops, the blower speed increases, and the load on the motor goes down (less power consumption). This is because the work done by the blower, which uses the input power, is related to the amount of air moved by the blower. You can see this with a shop vac by holding your hand over the end of the suction hose and hearing the pitch of the blower increase as it spins faster. This is counter to what most people think happens in terms of blower power consumption.
Bill
Interesting question.
Would running all bath fans plus kitchen range hood do the job?
Probably not, those kinds of fans tend not to deliver much CFM at any kind of pressure. Even the Home Depot fan linked to may not do the job, it's rated at 2.7A at 120V, or 324 Watts.
When I had a blower door test done they brought in a 240V generator and the fan they used was around 5,000 Watts.
“Would running all bath fans plus kitchen range hood do the job?”
Before my blower test, I did depressurize with my oversized range hood and 3 bath fans. I was able the find and block many leaks. Out of curiosity I had the auditor block his fan and ran my fans that were pulling 12 pascals in the house that tested at 1.2 ACH50.
Walta