For me the numbers worked out to be a cost of about $1,500/ year for heat, air conditioning, AND hot water. The calculated cost for my current set up which is an oil furnace, and electric water heater was projected to be about $4,500/yr. so the savings would be more like $3,000/yr. At that rate it'll take less than 5 years to completely pay for itself in savings, that's not considering that my old furnace is probably already due for replacement so if you take out the cost for a new high efficency furnace and A/C the pay back time is reduced even further. Now where I'm at I'm limited to oil/ propane or electric, no natural gas service, if your on NG your pay back will be much longer.