Marcus Sheffer LEED Fellow 7group / Energy Opportunities LEEDuser Expert4454 thumbs up Mon, 08/09/2010 - 21:19 See the ASHRAE 90.1 User's Manual for guidance related to situations where the HVAC system is not being replaced. Since it sounds like you are modifying/replacing the HVAC system you should just follow Appendix G. You are right.