Do NOT sign contract until you locate a person with knowledge of building the "house as a system". Check your local utility, do a web search for energy raters in your area. Have this person make changes that will build your house to lower utility bills, increase comfort, and improve IAQ. Do NOT depend on the builder or HVAC contractor to do this. The vast majority do not have the knowedge or the desire to change. If the builder won't do the changes that an independant consultant recommends, fire him and replace him with someone that will. This is YOUR house--YOU have to live in it--and it's YOUR money.