[quote=]I'd like to compare them to the cost of replacing components and/or making the house/HVAC system more efficient.

What advice do you folks have?[/quote]

One of these. It cut my gas usage from about 12,000 pesos per year down to about 3,000 pesos per year, or a savings of about $450 USD per year. Cost of product and installation amortized in less than two years. You will not see a similar percentage reduction in your bill because in my case the hot water heater was my biggest gas expense; in your case it is more likely the furnace. But you should see a similar dollar savings. Or maybe not. You don't have as much solar input as I do high in the mountains of central Mexico.

tanstaafl.