Next factor is the design of the heating system. *At some time the builder
should have run the calculations of how much *heat is required to keep your
house at the design temperature under severe conditions. If -10 is the worst
it ever gets there, it is about the limit of the system. *If you often get
say, -25, your system was not sized properly and should have been larger.

Windchill applies to any object, but not the same way. It draws heat
faster out of anything the creates heat.... but only down to the true
air temperature, not below it.

Mark