How about geothermal, for every 100ft you get an average increase of 5 degrees.
Read about the Comstock mine, at 3000 ft down you have a temp of 200+ degrees. A hell of a place to work but if you’re looking for geothermal heat it’s a great example. Now the temps will vary based upon geography but if you go down far enough you’ll get plenty of heat.
Just drop in a coil on the end of two pipes, fill it full of some liquid that is not going to breakdown or corrode the pipes. Hook up a circulation pump and plug in a heat exchanger on the top end and vola, you could then place the heat exchanger into an existing forced air system. Should work as well as a heat pump, system would have to be pretty hefty for colder climates. I would guess that a good deep well drilling rig could reach those kind of depths.
Should save a great deal of energy, all you’re paying for is the electricity to run the pump and you might be able to go solar with the right array setup. I would suppose you could use the same system for hot water. Just make sure you’re using a submersible heat exchanger.
You know the same system would work for cooling also. You would just make it a shallow system, were the temps are in the 50 degree range.
I’ve got a schematic for the system laying around someplace. Let me know if you’re interested.
I’ve been meaning to use a similar setup under my driveway so I don’t have to shovel the snow off of it in the winter. Ah, another for the to do list.
Free heat free cooling.
Well there is a slight 
inital cost
Yes you could run the heat exchanger to a steam turbine, then a generator much the same way the nuke reactors work.
No the pump wouldn’t need to be massive, you’re just circulating not doing a “dead pull” no heavy head pressure required, In fact you might not even need a pump, for heating. Ergo heat rises cold falls…
