Long time listener, first time caller. I have a gray area in what system I should be using for my baseline and wanted to poll the general consensus. I have a building addition where my proposed system is electric heat pumps with supplemental heat from a natural gas boiler for when it is real cold / peak heating load. My first thought is that it should be a fossil / hybrid system (Sys 5). However this boiler that I am using as a backup is the primary heat for the existing building, and is across the LEED boundary. If I use option 1 of the district heating guidelines it says I should treat this heat from the boiler as purchased heat. If I do that do I need to change my baseline system to electric only heat? Thanks.

Brendan Hall, M.Sc., LEED AP BD+C