Clearwater -- A portable heater may be the cause of a house fire that started yesterday (Sunday). Stearns County Sheriffs got a call of a fire at 20722 9th Avenue East in Lynden Township, just after 9:30 a.m. Firefighters were able to put out the fire, which had fully engulfed the building. The home owner, Jeffrey Louis Storms of Clearwater says he turned on a portable heater to warm the vacant building to prepare it for rental. No injuries were reported, while the cause of the fire remains under investigation.