Heating a large GH ?

We have a Large (GardenMart) GH. 120(L)x90(W)x14(H)
That has the white poly top and sliding sidedoor panels.
We need to heat this on average of 12 to 14 times in the winter our winters are fairly mild with only a few frosts and a few freezings.What would be the best way to heat the GH?We have Tender Tropicals and a Water pond in it.Most of the Plants are in the ground or in pots in the ground.We have wood chips around the Plants as mulch and gravel around the Cactus.Plus we are over wintering alot in pots.
Thank you for any help you can be.
Pheadra

First read this thread on heating - it's a good starting point...
http://davesgarden.com/forums/t/644362/

I think it depends on several factors.
What fuels are available?
What are the relative costs of the fuels?
What costs are required to get the fuel to the greenhouse and convert it to usable heat?
What temperature do you wish to maintain? (This is tricky since you may just wish to avoid frosts, though I somehow doubt that with the nice big size you have.)
The water inside will definitely help if you are just trying to avoid frost, though as you know, it only takes a few hours to kill some tender tropicals.

Generally, if you're heating for just a few hours per year, you go for lower capital cost at the expense of higher fuel cost. But with the size you have and the current high fuel cost, it's not often a simple decision.
Dave.

Did you mean to say 30' wide instead of 90' wide? It looks like 30' wide to me. I have one that size and I use a 200k btu propane heater ( vented) . I keep the thermostat at 60 degrees and the thermostat is in the middle of the grhouse. How do you cool this grhouse down?

Tigerlily123, Dave, it is 120`x 90`x 14` cooling it off isn`t a real problem all the side panels slide open and the misting system seems to help alot.

This will be our first year with this monster in the past we`ve used a small hoop house and heat lamps and that did the job.you mentioned water I know that watering will help to keep them from freezing but not real clear on when to water them or how much. We do have access to 2 propane heaters (fan forced) and a 100 pound tank Would they keep the chill off of everything? Also would it be better if we sealed the sliding doors with clear plastic or left one side unsealed for air and sunshine.It does get quite warm during the day even if we have a late night freeze.oh so many questions anyone need a large GH..LOL.........

georgia, I hate to question yr numbers, but its important in figuring out your heating needs, and if that grhouse was 90' wide, the width would be almost as long as the length, and its not. Plus, if its 14' high, you can see that the width is only twice the height-which would make it about 30' wide

Never trust a man who says YES DEAR I am RIGHT
Tigerlily,I am so sorry I went out and measured the dang thing MYSELF and it is 26x90x14 (the only thing that was right)
I am so sorry about not stating the correct size.(I knew the numbers didn`t sound right)

This message was edited Sep 22, 2006 10:58 AM

lol no problem, I just wanted you to have the right numbers for the heater.

ill tell you what i would do if it was mine id buy to of the eltric radiators for heat keep theam on low setings ive used theam sents they came out they dont run your bill that high plus if you heat your pond in the winter it will help heat the green house to regards paul

Here is an excellent link on greenhouse heating efficiency: http://www.hort.wisc.edu/mastergardener/Spec%20Training/fruits%20vegetables%2005/Greenhouse%20EC%20-%20Master%20Gardener-%20April%202005.ppt#273,1,Slide 1

Lots of good information in there. SB