I see what you're saying with this, but the comparison isn't a world where electricity is used for the heating, it's one where gas is (gas heating is almost alw

I see what you're saying with this, but the comparison isn't a world where electricity is used for the heating, it's one where gas is (gas heating is almost always more efficient than electric heating, since you lose a lot of heat at the generator). So either the heat is radiated out into the atmosphere uselessly, and some amount of natural gas is burned, or the heat is used and 20% less natural gas is burned. That's a carbon footprint of -20%.