Carbon Dioxide and HRV

The things one learns about ventilation... Our heat recovery system is set to by default to replace 1/3 of the house air volume every hour, and we have nifty little Netatmo sensors that measure carbon dioxide (amongst other things). I say 33% of the volume by default because the bathroom and kitchen contain booster switches that increase the replacement to 50% for 30 minutes - designed to clear the effects of cooking, showering, and other such activities.  Here I've attached a "normal day" from last week. It is fairly clear when the parents leave their bedroom to start their day, when we get home, and when we go to bed.



In comparison our old house, had no mechanical ventilation but did leak like a sieve. The carbon dioxide levels in the living room of the old house would routinely get above 2000ppm, and quite often didn't quite get back to 400ppm before we came home from work/school unless the windows were left open. In the new house carbon dioxide levels in the living room peak at about ~ 800ppm when everyone is home and decline to about 400ppm about the time we get back home.  While I had thought about dropping the ventilation rate while we were at work/school, it is clear that the default ventilation rate is about right.

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