As interest and incentives build to transition space heating and domestic water heating systems away from fossil fuels and toward electricity, a somewhat predictable but only marginally quantified problem is developing. Two words describe it: Peak demand.
Properly sized heat pumps, especially those drawing low-grade heat from outdoor air (e.g., air-source heat pumps) can provide the majority of the space heating energy buildings require on a seasonal basis. Where the problem develops is on those few days (or even a few hours) where outdoor temperatures are at their lowest. This is when the heating capacity of any air-source bottoms out. It’s also when the typical electric resistance auxiliary heat for an air source heat pump kicks into high gear.