My house has a gas-fired boiler and hot-water radiators. I've noticed a strange problem since moving in a few months ago.
If the weather is moderately cold (in the 30F - 40F range), my house feels chilly.
But if the temperature gets very, very low (say between 10F - 20F), bizarrely, the furnace seems to do a better job. My whole house feels toasty; so much so that I'll often be caught off guard when I leave the house.
What could cause this?