Non-Vented propane heater for my new greenhouse

Hi all, I just got my new greenhouse last week. We are waiting(impatiently!) for spring and thawed ground so we can start the foundation. My original thought was to mainly use it as a season extending greenhouse. Here in the mountains of north Idaho we are lucky to get 90 days frost free. Of course I am already thinking "gee it would be nice to be able to at least grow greens in over the winter....." I will have electricity to the greenhouse but only enough amps for a light and fan. I have seen a non- vented propane heater that I am considering. Some plants are apparently quite sensitive to the gases produced. (Orchids for one but I wouldn't be using it for orchids) Primarily I would be using it to start vegetable and flower seeds and then have some tomatoes, eggplants, peppers etc in it that don't like our cool, unpredictable mountain summers. So do any of you have an non-vented propane heater? Any other plants known to be sensitive to the fumes?
http://www.greenhousemegastore.com/product/non-vented-greenhouse-heater/greenhouse-heaters
This is the heater I am thinking about. Thoughts???????

Tomatoes seem to be very sensitive to ethylene which is the pollutant that causes the most damage. I bet peppers and eggplant behave the same. This site talks about using tomato plants as a "canary to detect problems.
http://www.oardc.ohio-state.edu/joneslab/t07_pageview/Extension.htm

This one talks about Tobacco Greenhouses. Tomatoes and peppers are closely related and I suspect will have similar problems.

http://www.uky.edu/Ag/HLA/anderson/fl_prog/ghheat_u.htm

If the budget is tight I'd buy a used furnace of craigslist or the local swap sheet. People upgrade furnaces all the time and used furnaces are very expensive. THere seems to be a number on the Spokane craigslist

You'll be safer to up the amps enough for a "milk house" electric heater (no vent required) or provide an outside exhaust for the propane heater.

Thanks for the replies. I will look at a vented model probably. Significantly upping the amps for electric heat is not possible. It would require a total replacing of the main power panel since it is maxxed out with house/barn/outbuildings. Already talked to power co rep and got estimate, more envolved than just panel, as in lots of $ to meet current code. So I am coming off barn power to greenhouse. I use several tank/bucket heaters for the horses in the winter so am limited by how much more I can draw at the same time. Probably could get by with a small milk house heater at beginning and end of the season when I am not using tank heaters. Maybe curtaining off a section for the greens in winter. I will probably end up erecting it without heat and go through one winter and see how it does as a season extending greenhouse. Then I will have a better idea of heating requirement. Thanks for the help. I sure don't want to spend money on a heater that will cause me grief and frustration.

I'm in NW Colo so and by our growing zone, a bit colder. I put 1" blue insulation foam on my bench, then use heat mats. One is from the garden supply and one is a water bed heater. I cover my trays w/clear dome lids, with a rug until the seeds sprout and at night until they get bigger than the domes. I've wondered about a space heater, but have never really needed it as ambient temps haven't required it. My outside temps in March are in the mid 20s. I'd start with setting a thermometer in the house, that records the low temp, to see how much heat you might really need. The heat mats only heat what you need heated!! Good Luck!!!

What size is your GH? Have you considered wood heat? Or depending on what type of foundation it will have, maybe a radiant heat?

I agree with kwikwater on limiting the area and putting the heat right where it is needed.

I've also seen growers that have a smaller greenhouse inside the larger greenhouse for a smaller area to control the climate. Just a couple of thoughts... Kristi

I'm getting a 5 wall polycarbonate 12 X 20 greenhouse. Putting a woodstove in is too difficult going thru the panels and being able to keep a consistent temp and have enough area to store wood etc. (We do use wood to heat our house and love how economical it is if you forget the sweat to get the wood.) After further discussion with my husband, the technical support behind the project, he thinks we may be able to tap off the barn and be able to use a milk house heater or possibly a 240 electric heater. If we can go electric, it would be the easiest solution. I would also get a portable propane backup heater since power outages aren't uncommon. I would risk the ethylene problem for a few days rather than lose all plants in an extended outage. I could section off an area of the greenhouse to only heat an area as large as needed in the dead of winter if it doesn't get too expensive. Some winters we have had -25 and I have heard tell of -35. So far this winter we haven't been much below 0. I do plan to use a max/min thermometer both inside/outside so I can see how much heat gain I can get vs loss over night. I do have a sunroom that I have been using to start plants and overwinter some tender items. It just isn't big enough and sunny enough for number of plants I start.So I may continue to start them in there and then move to the greenhouse a little latter when the temps aren't so cold. I know this is going to be a learning adventure. I used to garden in the pacific northwest and while wet and soggy at times, things sure grew there! After moving here 6 years ago I found the climate even more challenging that when we lived in Montana 30 years ago. Here we have not only a short season but some very abrupt weather changes. But I love it here in the middle of nowhere.