greenhouse heaters

I live in zone 5b. I have a portable greenhouse-the GronHaus- about 6x8x 7' high. Last winter I used space heaters meant for indoors and that was a bad idea, I went through a lot of them but somehow most of my plants survived even when temps. dropped below freezing a couple times.

Could someone please recommend the correct heater to use. Whenever I look I'm overwhelmed by the calculations they want. I don't know the the r-value of the material or how many BTU's I need.

Any help would be appreciated, thanks.

I don't think the thin little greenhouses like that are really designed to be used with heaters, that film won't really hold in heat very well. Generally if you have a greenhouse that you want to heat, you need to have the twin wall polycarbonate. They make heaters for outdoors, that's important because they can stand up to more moisture and temperature variation than the indoor sort can, but honestly I think you're going to have a really tough time heating that greenhouse and you're going to waste a lot of energy in the process because that greenhouse just is not insulated much at all.

I have a new greenhouse and am working on a plan to heat it also. the best book I have found so far is "Greenhouses for Homeowners and Gardeners" (Nraes (Series), 137.) by John W. Bartok (Paperback - Jun 2000) from amazon.com has it 4 Used & new from $45.36

It shows that you need 10,000 btu/hour or more for Chicago

how does that compare to what others have used successfully ?

Those calculations are assuming you have a greenhouse that's capable of holding in a reasonable amount of the heat that you produce, the one pictured above is not going to hold in much heat at all.

You really cannot figure this out without plugging your numbers into a greenhouse heat calculator like this: http://www.littlegreenhouse.com/heat-calc.shtml

Plugging in 250 sq ft, min outside temp -10F and min GH temp of 40F, assuming it's single layer 4mm poly or an equivalent (the R value probable around 0.8), you need around 15K BTU. That's three space heaters, since a 1500W electric heater gives 5120 BTU. And that, in turn, is three separate circuits, one for each heater, since you won't get two heaters on a single, standard 20amp circuit.

I would be kind of nervous burning propane or kerosene or nat gas in a little GH like that. For one thing, I'm not sure you would have the clearances for a burner like that.

has anyone out there tried the following heater
http://www.grainger.com/Grainger/wwg/productIndex.shtml?operator=keywordSearch&search_type=model&QueryString=3vu33

Heater,Space,120v
Heater, Space, 120v 1300/1500 W, 4436/5120BtuH, 12.5A, Tipover Switch, Power Indicator, Resettable Thermal Switch, 3 Prong NEMA 5-15 Plug, Thermal Alarm Grainger Item # 3VU33
Price (ea.) $46.25
Brand DAYTON
Mfr. Model # 3VU33
Ship Qty. 1
Sell Qty. (Will-Call) 1
Ship Weight (lbs.) 10.4
Usually Ships** Today
Catalog Page No. 3190

For the past 3 years I used a small electric heater to heat my GH. My Gh was 10x12 ft. I used an outdoor timer that could take the heater wattage. I set it for 30min on and 30min off, throughout the night. I did not need to use it during the day, because the sun wood heat the GH sufficiently. The first 2 years I had a GH with plastic on it and I placed insulation around the sides. The heater worked great.

I then went to a hoop house to get more room. That did not work. The GH would not stay warm. I actually lost plants because it went down to freezing. Now I am waiting on my Rion GH in the hopes that the heater will be sufficient in it.

jimrader, I have two *very* similar (same brand and style, different model number) in my 8x12 GH, each controlled by it's own thermostat. This past winter, I held 80's in the daytime and 60's at night, except for a few days/nights that were extremely cold (single digit high temps), when it held low 50's. My losses during those coldest times were insignificant. My Ficus maclellandii 'Alii' lost a grand total of 8 leaves the *entire* winter. That's gotta be some kind of record, heh. Heck, I've moved Ficus from one side of a room to another, and had them absolutely freak out and drop most of their leaves. If you have a twin-wall GH, of comparable size, those heaters will do fine.

HTH,
Eggs

It does hold heat better than it looks. I put it up in mid Feb. and ended up with many hanging baskets and several flats of flowers and vegetables with many consecutive days of temps. in the teens. I was just burning up a lot of space heaters.

Maybe you just need to try getting one that's rated for outdoor use then, indoor ones aren't going to survive very well outdoors.

what are your experiences with various heating radiators?

"Greenhouse Basics - Gardening in Your Greenhouse" by Mark Freeman
page 47 states "A small, portable electric radiator is one of the best ways to provide supplementary heating in the greenhouse" "They sometimes are filled with water, but more often with oil, which has certain advantages, one being that it won't freeze and burst the radiator as readily as water.

I have used an older Delonghi oil filled radiator heater in my PVC hoop house for several years. I also use a Vornado brand fan with the heater running to keep the warm air circulating. The fan is a $5 thrift store find and the heater is one we used to use in the house 15 years ago. My hoop house is 16 x 24 and I cover it with a 7-ml woven cover that I bought from FarmTek. We got down to 17º this last spring and even with the heater set to low, I had no problems.

I have done this before in your zone, try wrapping the greenhouse in bubble wrap. I did that and the space heater worked fine. It is a radiant heater, got it at Big Lots a while back and it still works great after three years.

:) Kim

Thanks everyone. I ended up ordering the Dayton electric heater and a themostat. I also already had one of the greenhouse books that were mentioned, guess I need to read a lot more of that. I prefer reading on the internet while having my morning coffee. It's also more fun to learn from a lot of different people.

Just my two cents, but if you use these little electric space heaters, the best advice that I can give you is to buy a good quality thermostat. Turn the heater thermostat to maximum (tape the dial in that position) and plug the heater into a reliable thermostat rated for the heater load.
I have lost plants on two occasions due to the thermostats in these little heaters. The thermostats are just not dependable and could cause you more grief than the cost of a good thermostat.
Oldude

I was wondering if anyone has heard of, or tried using a hot water heater for heating a greenhouse? There is a Nursery close by that uses one for heating his greenhouse. His is more of a commercial size greenhouse. He runs the tubing or pipe on top of his tables and under the dirt kinda weaving through underneath his plants. He said it was much cheaper to heat that way for him but maybe because electric heaters would be too hard to heat that big of a space.
I used 2 electric heaters to heat my Rion 21' X9' and the electric bill was a bit high. But our home is run on electricity alone, no gas.
Any thoughts?

weeding what type of heater did you use?