[elgaard]

Heat pumps have thermostats so they do not run at max all the time.

So if the heat pump without the miner use 1 kW to heat to room temperature it would need less than 1 kW with the miner to heat to the same room temperature. Plus as you say the COP increases.

So it could be that 5 degC to 22 degC requires 3 kW but the heat pump can do it with 1 kW (COP=3).

The miner use 0.9 kW to heat the the outside air to 11 degC. It would take 2.1 Kw to heat from that to 22 degC. But the heat pump now has a COP of 4 so it can do it with 0.5 kW.

So you lose 0.4 kW but gain bitcoins.

Or you could say that you get 2.25 as many BTC for the same electricity cost.