Since the specifications of the heater give no mention of the btu output, it is not possible to determine what exactly it will be able to produce.

I sense panic setting in.

Can anyone else run the numbers for heebiejeebie,

I ran it rough at 244sqft (what is the 6x8 surface area?)
Outdoor 20F
Indoor 50F
Heat loss 0.7 (4 mm (5/32") twinwall polycarbonate)

BTU required 5124BTU/h

Dear Chris,
Please stop responding to my posts.
You are being annoying and unhelpful.

Actually, this is helpful information, Heebie.

I get the same number, around 5124BTU. This, coincidentally, is almost precisely the BTU output of an inexpensive, 1500W electric heater, the kind you could get at Walmart. Do you have power out there? If so, that could be a quick solution for you.

Thanks so much for the link heebiejeebie,
my hubby and I were looking for this stuff for quite a while. Personally, we think it is a great way to heat the greanhouse. It is very cost efficient comparing to using electric heater because the fuel cost us a penny. Good investment, it will be on the way to us today Hooray!

stressbaby:
all of his "informatioN" is not wanted, because it is presented in an incredibly obnoxious way.

Stressbaby:
Electric is VERY expensive in our area compared to other areas (go figure... right next to Niagara Falls). I'm not interested in electric.

Looking at this further I see this is probably not the heater for me, appears to unreliable.

Rough guess 1300btu/h

You need four of them to get to 50F on a 20F night in a HFGH 6x8

I'll reiterate that I really don't like those "amount of heat" you'll need calculators because they're overly simplistic. Greenhouse heat loss is a very complex issue.

karenrei,

I agree, but they are really the best we have. It gets us in the right "ball park", gives some idea of the requirements.

In my case using the simple method of heat loss calculation made it quite obvious I shouldn't even bother getting a heater at all.