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Also note that one doesn't have to go 'all-in' on heat pumps, and there are dual fuel / hybrid systems available: > A dual-fuel heat pump works in conjunction

Also note that one doesn't have to go 'all-in' on heat pumps, and there are dual fuel / hybrid systems available: > A dual-fuel heat pump works in conjunction with a furnace. During the summer months, the heat pump works like a high-efficiency central air conditioner. In mild spring and fall weather, it provides cost- effective and efficient heat. As the temperatures drop in the winter months, the pump shuts off and lets your furnace take over. * https://www.lennox.com/buyers-guide/guide-to-hvac/glossary/dual-fuel https://www.lennox.com/buyers-guide/guide-to-hvac/glossary/d... * https://www.trane.com/residential/en/resources/glossary/dual-fuel-heat-pump/ https://www.trane.com/residential/en/resources/glossary/dual... More of a thing when heat pumps were more expensive and/or not as capable as they are now: going down to only 5C or -10C, whereas now units can go down to -25C. They could also still be useful in places with less reliable power (rural? coasts?), as a heat pump need more electricity, whereas a furnace just needs to power a fan and an ignition system, so a small portable generator can handle the load (or it won't tax your battery system as much).

bradfa 3y ago
Dual fuel is also useful if electricity is expensive but gas is cheap and if you know what the efficiency curves look like for your appliances. I recently did this calculation and effectively when ever a heat pump would be less than a COP of 4, my gas furnace would likely cost me less money for the same amount of heat output. Our electric rates have effectively doubled in the past 5 years while gas has dropped in price. Obviously this situation is going to be region-specific and gets even more complicated with time-of-use billing. Ideally a smart thermostat would be able to consider all these variables and pick the most cost effective heat source for a dual-fuel setup but I don't think any of them are quite that useful yet. Only a handful of centrally ducted heat pumps on the NEEP list (https://ashp.neep.org/#!/product_list/ https://ashp.neep.org/#!/product_list/) have COP >4 at 5F outdoor temperatures.

bradfa 3y ago

Dual fuel is also useful if electricity is expensive but gas is cheap and if you know what the efficiency curves look like for your appliances. I recently did this calculation and effectively when ever a heat pump would be less than a COP of 4, my gas furnace would likely cost me less money for the same amount of heat output. Our electric rates have effectively doubled in the past 5 years while gas has dropped in price. Obviously this situation is going to be region-specific and gets even more complicated with time-of-use billing. Ideally a smart thermostat would be able to consider all these variables and pick the most cost effective heat source for a dual-fuel setup but I don't think any of them are quite that useful yet. Only a handful of centrally ducted heat pumps on the NEEP list (https://ashp.neep.org/#!/product_list/ https://ashp.neep.org/#!/product_list/) have COP >4 at 5F outdoor temperatures.