One Source Equipment Rentals has portable, temporary natural gas and propane heaters for rent or sale from Heat Wagon, L.B. White, and Sure Flame. Direct fired heaters move the air through the flame and are the most efficient, and cheapest way to heat a jobsite or work area. Unlike indirect heaters, direct fired heaters exhaust the fumes (carbon monoxide and water vapor) into the space, so air quality and moisture can be a problem in small areas. Models range in size from 155,000 Btu’s/h to 1,500,500 Btu’s/h.