Also, don't forget that vented heaters aren't 100% efficient. So, if you need 17,000 BTU output, you'll need a heater with an input that is greater

The 25,000 BTU Southern Burner would probably give you about 17,000 BTU output, once you subtract the loss up the flue. It can be hooked up to a propane tank, and it doesn't require electricity. It's fine for orchids.

Others on this forum have said they use envented propane heaters from Lowes/Home Depot with no problems, but I have no experience with that.

For a backup, how about a kerosene space heater?

Thanks for your advice. I was wondering if anyone knew approximately how often I would have to change my propane tank if it is the only source of heat other than back-up heaters. I begining to wonder if this is feasable. Maybe I can get a very large propane tank. Does anyone know of a specific heater that would work well in my case (propane probably).

A gallon of propane has about 91,000 BTU, so you can estimate how much propane you will need to burn per hour to maintain your minimum temperature.

I'm a little confused by your discussion of backup heaters. Are you anticipating that the backup heaters will be used regularly, or only if your main heater fails for some reason?

Don't mess around with little tanks that you change yourself. Most propane delivery companies will rent you a larger tank. The larger the better, because propane is often a little cheaper in bulk, and you won't worry about running out over holidays, etc. I have a 250 gallon tank behind the greenhouse, and the delivery truck automatically tops it off once a month. A 100 gallon (NOT 100 pound!) tank is probably the minimum you'd want in your climate.
.

I'm glad to hear the large tanks work well. About large is your tank space wise (ft)? It's just so hard to determine what to purchase because I'm not sure exactly how much heat I'll need due to leaks. Because of this I also am not sure how much gas I would use per hour.

Another option I thought of was having several smaller heaters running always in case one goes out I have the rest. Or I could have one big heater and have a few small ones that somehow only go on if the big heater goes out. How much does it cost to get a huge tank of propane put in your yard?

DgreenR,

What exactly do you mean when you say "insulated horribly?" Are there cracks and gaps around the glazing?

SB

Yeah it isn't insulated well. It isn't broken, but theres parts of the structure that aren't sealed. Which would be okay if I only used it in warm weather. There's parts where you can see through the gaps in the structure to the outside.

The 250 gallon tank is roughly 6 feet long. It sits horizontally like a little submarine and must be at least 10 feet from an inhabited structure. The 100 gallon (or is it 120 gallon?) is vertical like a giant thermos. It's about 5 feet tall and can sit right next to the wall of the house/greenhouse.

Regarding your idea of running several small heaters, I can think of several difficulties: multiple heaters will require more space and more holes in the greenhouse for venting/fresh air. They will be more difficult to control (one thermostat or many?), and I suspect that one of the heaters will run much more than the others.

Most people with a greenhouse your size have a single heater, a temperature alarm in their house, and a backup heater in their shed or garage. Kerosene space heaters are inexpensive, reliable, and simple backups. If you are really paranoid, you can install a system (e.g. Sensaphone) that will telephone any phone numbers you program whenever the temperature drops below a preset limit. It's not cheap, so you have to decide how much money you have invested in the plants and how much you want to spend protecting them from the risk of heater failure. Most greenhouse heaters really are quite reliable.

Thanks for the advice on propane tanks. I'll have to look into it, but I'm really hoping a 100 gallon tank will be enough. Do you know around how much it costs to get a 100 or 250 gallon tank put in your yard?

For a backup heater I think I want something that will just kick on if the greenhouse goes below about 40 degrees. It would be unactive most of the time. That way if on those cold nights or days if no one is around, and the temperature drops, the backup heater will be there to save the day.

Now I just have to figure out how I'm going to water all my orchids and other plants. I don't know if I'll be able to tap into a water line and if I do it'll cost a lot. I might need a tank of propane and a tank of water!

Phew... I sure hope this whole greenhouse project works out.

Don't forget to try a solar pool cover. It will help insulate and save you a lot of money in fuel.
See 'My Page.'

It cost nothing to have the tank installed, and the annual rental is free as long as I buy at least one tank full. I traded up from a 50 to 100 to 250 gallons as I figured out how much gas I was using, and each time the company switched the tank at no fee.

With the larger tank, I can be on the automatic fillup program. The company just tops up the tank whenever they are in the neighborhood, and I save a couple of cents per gallon. With a smaller tank, I had to keep an eagle eye on the level and call when I was running out. Since they made a special trip to fill the tank, they charged a bit more per gallon.

Some companies may charge an annual rental fee, and some people prefer to buy their own tank instead. You'll just have to call around and see what's available in your area.

I also had the propane company install my heater, and they provided the vent pipe. That all cost a couple of hundred dollars, IIRC.

You will definitely want water in your greenhouse, both for watering and for cooling in the summer (think fogger or mister). You can probably save money by digging the trench yourself and laying the pipe, so that all the plumber has to do is tie it in to your household water.

Myrmecodia,
Thanks again for the info. What size is your greenhouse? Have you ever had any problems or leaks at all with using propane? What temperature do you usually keep your greenhouse at during the winter?

Cactusfreak,

I do plan on getting a clear pool cover thanks to your advice. I might also use some silicon sealer to help insulate. Where did you purchase your pool cover? I want to get one that will really hold up. Also I saw on your 'my page' that there were holes in the pool cover for you to put your bungie cords in. Did the cover come with those or did you put them there?

My greenhouse is 10' x 16', and I keep it at a minimum of 60 F in winter.

I've had no problems at all with the propane heater. In fact, the first winter, it saved my collection. After an ice storm, we lost electricity for 6 days. If my orchids had still been indoors under lights, I would have lost most of them when the temperature in the house dropped to about 38 F. The heater in the greenhouse never missed a beat.

I got my solar pool covers from two different places. America's Best Pool Supply was one. Compare prices and shipping between companies to see which is best for you.
The black clips for the rope I ordered from IGUSA.com. Any place that sells shade cloth should have them.
Why can you not have electricity? You will diffinetly need to run a circulation fan 24/7 and on some days you will need an exhaust fan even in the winter. Can you not run an extention cord?
Also there are connections so you can connect to an outside faucet and either run PVC underground or use the black sprinkler flexible pipe on top of the ground or underground. No need for a plumber.

Hello,

Thanks again for all the helpful suggestions.

Cactusfreak,

Sorry for the confusion... I will have electricty in my GH, but not a lot. My GH is at the far end of my yard next to my garage and the garage has a minimum amount of volts going into it. I will get a line run underground from the garage, but that will only be for lights and fans. I meant that I probably won't be able to HEAT the greenhouse with electricity. The electrician is going to give me an estimate of how much it would cost to run a line from my house, but he said it would probably be a lot. Plus, once I pay for the instulation of higher voltage electricity, I'm told that it will cost a fortune to heat the GH with electricity. I suppose i could do a combination of electric and gas, though I don't know how that would work. And that's only if I get electricity taken from my house.

As for the water... So I can use a thick sprinkler hose (not solid pipe or pvc) above the ground all winter without them freezing as long as the water is only coming out into the greenhouse? That would be fantastic.

Myrmecodia,

What kind of greenhouse do you have? Is it a kit type one? What is it made of? (Like what thickness of polycarbonate or glass and frame material.) Mine is 4mm double wall polycarbonate and it has some kind of heavy duty plastic frame. I think the frame is resin coated too. It is 12.5ft x 8.5ft and barn shaped. I might add onto it next year if all goes well. This isn't official data, but our winter nightime temperatures can be in the 20s or teens fairly often. We also have some nights where it dips into the single digits and we don't get much sun in the day. With that said, I'm going to need a ton of extra insulation and heat. The 100 gallon tank of propane sounds more appealing, but I don't know if will be enough. Do you think I should go with a bigger tank? I have to keep the greenhouse at about 50 degrees, but I would LOVE to have it warmer, like 60 degrees. Right now I'm just praying I can get it to stay as high as 50.

I Sure hope my plants make it through this winter!

You will have to make sure to drain the hose after each use. It will freeze if water is left in the hose.

DGreenR,

Using the Q = deltaT*A/R formula, and assuming you have 25F winter outside temps and 55F inside temps, R for 4mm twinwall of 1.5, surface area of 461 sq ft, you'll burn 73 gal propane a month in the middle of winter.

I'd go with 250 gal tank if it were me.

SB

DGreenR,

My greenhouse is home-made, not a kit. It's 8 mm twinwall polycarbonate on a pressure-treated lumber frame. I have installed "Reflectix" insulation on the north wall and bubblewrap on the other three walls. In autumn, I also put bubblewrap on the north slope of the roof (removed in Spring). The south slop of the roof remains uninsulated in order to admit maximum light.

Our nights in January and February are often in the teens and 20s, with occasional dips below 10. However, we almost always get above freezing during the day.

Propane usage is inversely correlated to the amount of sun you get. On a bright sunny day, you may not need any additional heat, but on a cold night or cloudy day, the greenhouse will lose heat rapidly. Use your minimum night time temperatures to calculate the heating capacity you need on the coldest nights. For total propane usage, I think you should probably use your average temperature, since you won't always be at the minimum. Then add in a 20-50% safety factor.

You'll burn the same amount of propane regardless of the tank size, so all things being equal, I'd go with the tank that requires refilling less often.

Hi All,

Thanks for all the advice! I am a little bit confused on how you calculate how much propane you need to burn. I know you need the minimum temp outside and average wanted temp inside the GH. I also know you need the surface area of the greenhouse. I thought the 'R' value of 4mm polycarb was something like .7 ? I'm confused by the equation so if someone could help me understand how to figure out how much propane I need to burn that would be great. I know it was shown above, but I'm still a little confused, there's some bits and pieces missing.

DGreenR,

I agree with Myrmecodia. When calculating BTU requirements, you want to use the minimum night temps. Minimum night temps will determine BTU requirements in the middle of a January night. When calculating the monthly usage, you should use the average winter temp.

Q is the hourly BTU requirement.
A is surface area of all of the walls and roof of the GH
delta T is the difference in temps as noted above.

I got R values from OhioJay: 4 ½ mm twinwall is 1.5, 6mm twinwall is 1.59; 8mm twinwall is 1.65; 16mm triplewall 2.5; 3mm single glass is .90; 16mm double glass is 2.04.

Using the figures in my post above, Q = 461 sq.ft.*30F/1.5 = 9220 BTU/hr

9220 BTU/hr * 24hr/day * 30day/month = 6,638,400 BTU/mo.

Propane is 91,000 BTU/gal (I've seen other sources listing it as 85,000 BTU/gal)

6,638,400 BTU per month/91,000 BTU per gal = 72.9 gal/month propane.

I think that this formula gets you in the ballpark.

SB

If I understand right, to determine the size heater you need you'd use the average winter minimum (IOW your zone rating=zone 6 would be -10, zone 4 -30 etc) and the MAX inside temp you'd want (say 65F). But for figuring average useage...use the AVERAGE winter temp (which here is 25) since over the course of a month it should be close to average even if one day it dips to -10 and another day it gets to 66 degrees.

Hi All,

Thanks for all the advice! I am a little bit confused on how you calculate how much propane you need to burn. I know you need the minimum temp outside and average wanted temp inside the GH. I also know you need the surface area of the greenhouse. I thought the 'R' value of 4mm polycarb was something like .7 ? I'm confused by the equation so if someone could help me understand how to figure out how much propane I need to burn that would be great. I know it was shown above, but I'm still a little confused, there's some bits and pieces missing.

Whoa that was weird, it posted that old message... I'm not sure why.... Sorry.

Stressbaby, thanks I understand it now.

Cactusfreak,

I only saw one saw one size pool cover at america's best pool supply... what other places can you buy them?

So, do you guys think this whole greenhouse thing is going to work from how I've described it? The kit I bought isn't so hot. Maybe I should just forget it and use it as a cold frame before I spend another thousand bucks on it and possibly have it not work.

DGreenR,

I looked at your GH company web site. I wouldn't give up yet. Can you use a caulk product as a glazing material to seal things up? A favorite product of mine is Vulkem, a polyurethane caulk product that is very adherent, resistant to cracking, and weather-resistant. I have used this on some Pella windows on my house which have had glazing failure. A bead of Vulkem would seal most of your cracks nicely.

Maybe you could get a few tubes of Vulkem and seal it up. You could try it the first winter with a small electric heater to see how it performs before putting all of your nice tropicals in there.

Stressbaby,

I was thinking along the same lines. I've even had a contractor help me out a little bit. I'm trying to find out if its okay to use a silicon caulk instead of the rubber strips that came with the kit that go around the polycarb panels. (The rubber stuff makes the panels buckle) I think caulk would work. I'll probably get some Vulkem or something similar to it to put on all the 'cracks' and seams.

The only problem is if I want more than a few hundred watts of electricity in the GH, I have to spend over a thousand dollars getting a line run from the house. At least that's what the electrician said because there is only a small amount of volts going into my garage ( which is right next to the greenhouse.) I wish I could just use a big heavy duty extension cord from the house for this winter and see if the thing atleast holds its heat.

Part of me feels like two space heaters would totally heat this thing! But another part of me thinks I would need a huge heater and even then it might not work. I mean if I get the darn thing sealed and covered with a pool cover I don't see why it won't work which like an appropriate heater. Plus it isn't a huge GH, it's 8.5ft by 12.5 ft.

yep,you need to caulk up all those cracks.i used a pure silicone caulk.i use an unvented propane heater.i bought a 250 gallon tank(didn't want to pay the 75 dollar a year rent).i used 150 gallons all last winter-to maintain about 52 degrees.last winter i learned a few tricks.late in the season i installed a 3 inch pipe directly behind the heater-to supply oxygen to the heater,and kept the window on the door closed at night.i also installed a box fan over and a foot behind the heater.i'm sure i can keep the greenhouse heated to about 58 at night,and use about the same amount of propane.also,during the day,no propane is used,the sun warms the greenhouse into the 80's,and the automatic vent fan comes on every 15 minutes or so.