I suspect most houses don't have the capability to switch between different modes of heating: if you have a gas furnace, you're not going to be burning heating

I suspect most houses don't have the capability to switch between different modes of heating: if you have a gas furnace, you're not going to be burning heating oil in it instead. I believe the plan in case of shortage is to reduce the amount of natural gas flowing to power plants, and to make do with whatever alternatives for electricity are readily available (which is probably coal, although maybe nuclear decommissioning will be staved off).