If I wasn't renting I would install a heat pump but, we don't have that option at the moment. I do throttle it back to 60F ambient temp in the evening when no one is there. I use a raspi with a temp sensor to control the speed of the hashing in the cluster.
Heat pumps only work at that level of efficiency above about 10 degrees C. That is why they often have integrated electric resistance heaters.
Not true anymore. Check out eg the Mitsubishi Hyper-Heat, if I’m reading the COP right, it’s something like 280% efficient at -8 C.
This is an antiquated figure. Modern heat pumps maintain competitive performance at much lower temperatures.