Mary,
I got my tarps from a seller named buys4u on eBay. These are heavy reinforced green house material with grommets.I'd recommend getting the attachment cords too as they stretch. I used these tarps for a run cover before I put the steel roof on, as I kept getting delayed by a contractor.They let the sun in, which makes them much nicer than the blue, or silver ones.
I heated a 3200 sq. ft farm house with a Fisher Grandpa Bear for 20 years.I also had a second floor greenhouse that had a 8" pvc pipe in the ceiling,and a blower. When the heat got up to 90 degrees in the peak by about 10 AM, a blower kicked on, which pumped all that heat down stairs. Cut down on the wood consumption greatly.