DIY Tracer Gas Testing?
I’ve begun air sealing my house (mainly the rim joist area, attic, and some windows and outlets), and I’ve opted to not have any blower door tests done, at least until I’m to the point where I have plugged the obvious leaks (and need to find the leaks I missed or didn’t think about), because the cost of these tests are not trivial.
But Allison Bailes’ interview of Joseph Lstiburek from the other day turned me on to tracer gas testing, and I’m wondering if this might be a cheaper option that I could do myself. From what I’ve found, the decay method seems very simple: Release CO2 into the home and distribute it with a powerful fan, until the concentration hits 5000ppm (still considered safe but can induce drowsiness/nausea). Then measure the concentration every few minutes for an hour or so. I can do all that. The missing link is the math used to turn this time series data into an ACH figure. How do I do that?
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Unless you're going to do it on a hot day, a cold day, a calm day, a windy day, and so on... I don't see the point. And why buy a CO2 meter you'll never use again? They aren't particularly cheap.
Why not cobble together a "blower door" using a box fan or two in a window or two, and do your guided air sealing that way. When you think you've done all you can, get someone with a blower door (and some experience) to run the test, maybe do a bit of last minute sealing, and give you your ACH50 number.
David, yes, I would need to test multiple times under different conditions. My concern is the one outlined in the referenced interview: that blower door numbers aren't realistic, I presume because air leaks differently when the house is artificially pressurized.
You're right that pressurizing the home is useful for finding leaks, but that's not what I am aiming for with this. I would enjoy having a good sampling of the air leakage of the home under different conditions, and being able to tailor mechanical ventilation based on that information. I also just prefer doing things myself, when feasible, and not being dependent on hiring someone.
A CO2 monitor is one-time cost of about $150 and can be sold to recoup a good portion of that when I'm satisfied with my data.
List the time (t) and the concentration (C). Fit an equation of the form C = exp (-t/a) to the data, and find a single value of “a” that gives the best fit. You might need to use solver routines. The value “a” is the time constant. The half-life is the time constant times (–ln(0.5)) where ln stands for natural log.
What’s an air change? One definition might be, assuming perfect mixing, that it is the time it takes to reduce the concentration in half. Picture an inflatable house; bring in an additional house volume of outdoor air, mix it up, then exhaust that mixed air. You cut the concentration in half. In that case, hours per air change is the number of hours needed to get to the half-life concentration. And air changes per hour is the reciprocal of that.
Nick,
You might consider getting a theatrical fog machine: Pinpointing Leaks With a Fog Machine.