>Some naysayers will say that it doesn't work the 3 days of the year where it's -15°C outside, That used to be true but modern air-source heat pumps are better

>Some naysayers will say that it doesn't work the 3 days of the year where it's -15°C outside, That used to be true but modern air-source heat pumps are better. But even so the efficiency drops it's just physics. Even if a heat pump can grab heat at -15C it will need to run longer when it's very cold, reducing lifespan of the unit. At some point it will just switch over to pure electric so your power to heat 1:4 is now 1:1. Ground source heat pumps are far better and even more efficient that air source but quite expensive to install.