Greenhouse: Heating suggestions for this greenhouse, 1 by flagardener

flagardener wrote:
Hi all,
My greenhouse is finally done, I think....I am now in the process of getting a heater for the cold nights up ahead. It is a 12x14 with height of 7-8 ft. As you can see the lower half of the greenhouse is made of pressure treated wood and the roof is of corrugated polycarbonate panels. The windows are single pane glass (used) so doesn't really keep the heat as much at night. I have done some insulation on the wood part of the GH with fiberglass and reflective foil/bubble/foil sheets, however, haven't quite finished it yet as the budget is all gone. Just have enough leftover for a heater. ;-)
Any suggestions on what to buy/used to keep it warm on some freezing nights here at the Florida panhandle? Also, would covering the windows with a 6 mil plastic help keep the heat at night ? thanks and will greatly appreciate any feedbacks ;-)

Eileen