The following table provides general guidelines for suitable heat pump and supplementary heating systems at different conditions.

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^gRecommendations pertain to portion of home heated by heat pump(s). Supplementary heating is only required if heat pumps cannot meet design heating loads but they are recommended to improve comfort in cases where defrost cycles would blow cold air into the conditioned space. If supplementary systems are appropriately sized, they can also be used as emergency heating; this is recommended where the incremental costs are small.

^hAir-to-water heat pumps are a direct replacement for boiler systems; however, these systems are not very common in residential applications and are not covered by this guide.