I have. We live in the northeastern US, so our winters get quite cold. Our house is VERY well insulated, so I imagine you'll get different results depending on

I have. We live in the northeastern US, so our winters get quite cold. Our house is VERY well insulated, so I imagine you'll get different results depending on your situation. We have a CO2 meter, as well as a radon meter. Both work as analogues for air circulation. In the winter, you can measure temperature loss by measuring how often the heat comes on. And of course you can measure CO2 / radon just by looking at the gauges. What we've found is that in the winter putting two windows open a crack makes a very significant different in CO2 and radon builup. CO2 without the cracked windows will be around 1200 or more, while with cracked windows can be as low as 600-800. Not perfect, but like I said, a major improvement. I don't have a precise way to measure if the heat comes off more often, but my experience is that it does not.