We received a first bid on a air source heat pump: $5500, installation included, 5 years labor guarantee, lifetime compressor guarantee. It is a Reem heat pump, but I am still waiting for a part numbers.
The air source heat pump limits how much we can use solar energy in our heating system, but I have being thinking on a some options.
The heat pump will not heat the water for hot water usage, so we will install a solar hot water system with electric backup. The storage tank will be made as big as can fit in the hot water closet. The South wall of the garage will be covered with solar collectors. We can install three 3'*6.5' panels, for about 60sqft total. If we buy ready made panels, that will cost $1130 plus shipping. If we buy the collector plates only, it will cost $600. It makes sense to build them ourselves, since they will be integrated in the wall of the garage. They will be protected from the weather by the roof overhang.
During the months when we do not use all the hot water, the excess hot water will be circulated through a heat exchanger installed in the air intake grids of the forced air system, giving some boost to the heat pump. I will have to design a system that will prevent drawing too much heat from the hot water tank for space heating, which would displace energy normally used by the heat pump, to the electric water heater, producing efficiency loss. Since the heat exchangers will only work at high temperature, it makes sense to use the excess heat from the solar hot water system to boost the heat pump. This system should provide a good efficiency during the Spring and Falls, but I don't expect the months of December and January to see much of an improvement from either the solar hot water and the heat pump.
I will detail the design in the coming weeks.