Some neighbors, Jerry and Linda Dingledine, heard a loud explosion-like noise around 11 p.m. Monday. They did not report it until Tuesday when the saw the damage.
The homeowners, Catherine and James Johnson, were not home. They left around 6 p.m. Monday to visit a relative overnight.
Deputies say there was a propane smell when firefighters arrived.
The incident is being investigated by the state fire marshal, Butler County Sheriff, Butler County Bomb Squad, and the Wayne Township Fire Department. No criminal intent is suspected.