How much do ‘eco improvements’ such as whole house fans add to the value of your real estate? With a little bit of math, and some financial formulas, we can figure that out. Here is an example of a homeowner who installs one of our 4.4e WHF models. Let’s take a conservative value for energy savings ($500 per year), with a desired return on investment of 8% (you could not get that anywhere else..). What we do is use the financial formulas to figure how much money would need to be invested at 8% interest in order to return $500 per year, over the life of the whole house fan. At the end of the 20 year life span, we assume (also conservatively), that the WHF has no remaining value.