The measure installs a strip of flexible material at the bottom of an exterior door to reduce air infiltration. This saves energy by reducing heating/cooling losses by air sealing the gap under the door. Gap height has a significant impact on savings but is a substantial source of uncertainty because there are no sources for the 'average' door gap size. There are also no known sources on effective useful life, another source of uncertainty. To address this uncertainty the RTF adopted a research strategy aimed at collecting data on the existing door gap area. The strategy proposes doing this across housing types (multifamily, single family and manufactured homes) and across deliver channels (leave-behind, mail-by-request, and direct install) with specific focus on ensuring the door sweep is installed correctly.