Plenty of information on ASHP is available on this site and very little on hybrid heating systems, i.e. boiler and ASHP. A few manufacturer designed hybrid systems are also available.   When we built our house it was with an Atag gas combi boiler. We then installed an ASHP mostly for cooling, but it also heated our house well last winter and provided hot water via an UVC.   The system below could easily be replicated by anyone wanting to install a hybrid heating system meanin