House Humidity vs room temperature

I’ve been doing an experiment in my house for the last month or so. It’s mid December and here in Quebec, it’s cold outside. We’ve seen temperatures as low as -20C. I did not start the electric heating yet. This is an experiment to see how much electricity I can save by postponing the heating in the automn. I’ve had many comments by my friends and family how bad it was for the house to be that could and how I’ll have humidity problems. I didn’t have any logical reason to think so, but not any proof to show them they are wrong. I just plugged a Dallas DS2438 with an Humirel HTM1735 to get absolute and relative humidity readings and here are the results:

My idea is that it’s not relative humidity that is bad but absolute. My guess is that if I don’t heat, less water evaporates so I have less absolute humidity in the air than if I was heating at 20C. The dew point lower that it would be, so I should not see any condensation on the walls. In fact, I started the heating in the basement as it was too cold to do something as calm as using the computer. I’m currently at 15C near the computer and 10C upstairs.


Place Temp RH Dew
Computer 15C 25% -4C
Living Room 10C 33% -5C

The temperature outside is around -15C today, but it gets as low as -25C sometime. I doubt the wall temperature will get as low as -4C, so there’s no fear of condensation to have.

Next, I’ll begin to heat the house and see how it affects the dewpoint. My guess is that even though the RH will be lower, the dewpoint will be higher, as there’s more absolute humidity in the air from the fact that evaporation is increased.

To be continued…..

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