> Having said that, it is a lot easier to sell a cool looking $250 gadget than asking someone to spend $5,000 to modify their home.

I think a little creativity in the payment model could help this problem a lot. The whole point of the system is to guarantee a decrease in the cost of heating and cooling, right? Doing some statistical analysis, it should be possible to estimate how much your customers will save. Tell them you'll pay their bills for them for the next X years. Charge them 90% of their current costs, pay the actual bills yourself, and keep the rest to pay for your system. After 3 years (or whatever statistically works out to be a comfortably-profitable threshold), they own the system free and clear and pay their bills themselves, again. Obviously they can pay off the system in full at any point, to allow for home sales and things.