Well I stumbled on this site looking for information on Outdoor Wood Boilers. My situation is this...Two air source heat pumps that are old and not functioning well. Heating 2,600 feet. The reason for two systems is the second unit was placed in a room addition over a crawl space and cost effective at the time. If I could do this again I would have upgraded the original and tied it into the new addition. I have always hated the quality of electric heat unless it is set on emergency strip heat. Also have electric water heater. I have a shop 80' from the house that is storage only so I could be very flexible on a set up. I had know idea an internal system was even an option until now and they sound so much more efficient. So my question is..Can an internal system be set up for the same $$$ as a stand alone outside unit? Thanks for the site. I am enjoying all of the information.