This study was undertaken to quantify the energy saving benefits of one component spray polyurethane foam in existing homes. It is well known that reducing the air leakage of a home reduces energy use of that home. And it is generally accepted that foam sealants reduce air leakage. However, it is not well known how much energy savings can be expected from installation of foam sealants in various air leakage locations in existing homes. This case study demonstrates that simple, quick air sealing of existing homes with one component spray polyurethane foam sealant (foam-in-a-can) provides an average payback of 4 months and a 7 year return on investment (ROI) of 4400%. Compact fluorescent lights (CFLs) reportedly have a payback of 6 months and a 7 year ROI of 1400%. CFLs have been heavily promoted as the first step for consumers to consider when improving the energy efficiency of homes. DOE states, "Compared to other energy efficiency improvements, CFLs require substantially less investment, have no installation costs, and pay for themselves much more quickly" (DOE 2009b). However, the results reported here show that quick, easy installation of spray foam sealant in existing homes provides energy savings and financial benefits exceeding CFLs.