Controlling Winter Humidity: A Quick Reference Chart
Here is a great reference table for winter time humidity levels from the Ask Jon Eakes website.
Indoor Relative Humidity levels that will keep thermal pane windows condensation free
Outside Air Temp (°C) Maximum Indoor Relative Humidity at 20°C (68°F)
- -30°C or below 15%
- -30°C to -24°C 20%
- -24°C to -18°C 25%
- -18°C to -12°C 35%
- -12°C to 0°C 40%
When it is really cold outside and you want to avoid having excess moisture building up on your windows, follow the chart and run your mechanical ventilation system until your relative humidity reaches the appropriate level noted above. This does not mean you are likely to run your humidity levels at 15% or even 20% all winter. over time you will find that the humidity levels will be more typically in the 35-40% range.
If you don’t have an HRV or ERV, then the next best strategy is to run your bathroom fans and open a window slightly to pull in the outside dry air. In all cases, I would also recommend running your furnace fan on low continuous speed to help mix the air throughout the home.