Blower door testing by floor or room?
Hello,
I’m about to venture into a 3 phase air sealing project. I would like to do everything at once, but it is cost prohibative given other remodel items that need to happen at the same time. So, the phases are: 1) air seal and insulate roof and upstairs walls, replace all windows, 2) air seal and insulate downstairs walls, replace windows and 3) seal and insulate basement. I want to use a blower door test before and after each phase to measure our success, but I’m not sure how accurate this will be since there will be known areas we didn’t touch. My question is, can a floor or section of the home be tested to any degree of accuracy? I have a single door leading upstairs, and while I know there will be movement through the floor, I’m thinking I could put the blower on that door before and after upstairs insulation.
Is this a valid approach, or is there a better way to measure airtightness of just one part of the home? I don’t think I’d like to wait until the whole house is done to know if we did the upstairs correctly. I also think that the whole house may test OK for minimum air exchange, but the bedrooms might be sealed up tight enough to require an HRV system.
Thanks,
Ryan
1450sqft 1.5 Story
Minneapolis, MN
Climate zone 6
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Replies
Ryan,
I'll let an experienced blower-door expert answer your question -- I imagine that one will show up soon.
In the meantime, I'll say:
1. Yes, blower door tests are sometimes performed on sections of a building.
2. If you are performing blower-door directed air sealing, a blower-door test will always teach you something, and is likely to help you identify leaks in your thermal envelope.
3. Most homes have hidden pathways that connect to the outdoors; these include utility chases, joist bays, and interior partitions. These pathways complicate the task you are facing, and increase the chance that you will misinterpret your blower door results.
You could certainly perform four (or more) standard blower door tests--one at the beginning as a baseline, and then one more following each phase of work. That would give you fairly good info on what you accomplished with each phase, and I would certainly do that.
You can try testing sections of a house but it is tricky. With enough time, effort, masking tape, and plastic sheeting you can generally isolate one section from the rest, and then test that section. Using a second manometer, you can measure the pressure changes in both areas at once, giving you information about how well connected the sections are.
Example, you set up your blower door in one area of the house and tape off another area of the house. You depressurize to -50 in the test area, and simultaneously measure the pressure change in the other area. If the other area measures close to zero with respect to outside, you can deduce that it is minimally connected to the test area. If the other area goes to -40 with respect to outside, you can deduce that there isn't much of an air barrier between the two parts of the house, in spite of your efforts.
You can also measure one area with respect to the other--if you get a big difference, you have an air barrier, if you get a small difference, you don't have one.
I think the key is to use the blower door to locate any remaining leaks in the area where you did the work, more than to use it to quantify them. As David says, you can find out how much improvement you made, which is good, but you won't know how much of the remaining leaks are coming from the supposedly finished area vs. from other areas.
Thermal cameras can be helpful in combination with the blower door to locate leaks, and they are now cheaper than blower doors.
My limited experience is that tests with sealing off part of the house with moderate effort are usually inconclusive--the other area is usually close to the test pressure, or else goes to some intermediate pressure, rather than being very close to the outside pressure. It is possible to use that intermediate number in combination with some additional measurements with the spaces open to each other to build a model and estimate how much leakage is in each, even without being able to seal each separately, but doing that modeling is pretty complicated.
More specificially on your plan to put the blower door between floors--if there's an upstairs window you can fit it in and get a good seal, that might be preferable, and then close the door and tape it up. Then you can get some information about how many of the leaks you are measuring are between the floors vs. between upstairs and outside. If you put the blower in the door between floors, you would probably open the lower level to the outside during the test, and lose the opportunity to make that additional measurement as David described.
Note that given your good plan to start with the top, the percentage reduction in infiltration will be better than your percentage reduction in your blower door number. If you have all the leaks at the top sealed, there will be less elevation difference between the remaining leaks, so the stack effect will not be as bad anymore. You might want to change the order of phase 2 and phase, and take care of the basement leaks second, as the first floor windows may be at the neutral pressure plane.