Cooking Air Quality

July 21st, 2023
airquality, house
Our stove doesn't have a hood that vents to the outside, so when we're cooking something smoky we put a box fan in the window blowing out. I happened to have left my air quality meter running, and got a neat picture of how well this is working when cooking something very smoky:

Here's the floorplan, marking the stove, fan, open windows, and meter:

When we started cooking the windows were closed. When we noticed the smoke we opened three of the windows and put the fan in one of them blowing out. You can see this on the chart, because CO2 (the yellow line) starts to fall. Around 6:20 we stopped cooking, and you can see it almost immediately in the pm2.5 level (blue line). The pm10 level (red line) is pegged at the maximum (1mg/m³) so it's not clear if this started falling at the same time, but they usually move together. You can also see around 7:15 when we stopped eating dinner (nine people, including two kids, one toddler, and one baby) and went outside, because CO2 levels fall again.

We can use that last phase to try to estimate how much the fan was doing. Zooming in on just that section and only showing CO2, here's actual CO2 vs modeling it as decreasing toward atmospheric by 18.5% per minute:

I think this is equal to 11 ACH: changing out 18.5% of the air each minute means the amount of air changed each hour is 60 * 18.5%. If we guess the effective volume is 24x24x9 then that's consistent with the fan moving about 1,000 CFM which is plausible for a box fan.

While putting the box fan in the window does get the smoke out, pm2.5 levels still measured above an unhealthy level of 50µg/m3 for ~45min. This is a pessimistic estimate, since one of the dining room windows was open and the people were in the dining room, and the meter was in the living room without any open windows. Still, not so good. Ideally we'd have a proper exhaust hood: if the fan were pulling directly from where the smoke was being produced it probably would have taken more like 500 CFM to keep up with it, instead of it taking a fan twice as powerful to play catch-up. We don't have any plans to redo the kitchen right now, but it does need to happen at some point and this is something I'll keep in mind!

In the mean time, aside from trying to remember to open the windows sooner, I'm going to try swapping out the fan for a more powerful one I have sitting spare in the basement. And probably also run the air purifier when cooking smoky things.

(We only cook things this smoky about once a month, so this is a relatively extreme example.)

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