Resistance heating is the most expensive heating one can normally use. 60K btu would not be overkill. I don't know if it would be enough in New England winters but that would depend on the heat rise you require and whether you just need to keep it above freezing. Once a certain temperature is reached, each degree above it costs more than the degree before it. It's not a straight-line incremental increase.

How long have you had this pvc hoophouse? Is it built for snowloads?

I have natural gas heaters in my houses, and before that they were propane. Last year was the first year I did not keep at least one house fired all winter long in my range. I culled out a lot of my propagating stock and moved the barest amount necessary to my rigid lean-to we heat.

I don't know what your electrical rates are, but I can promise you it will make your hair stand on end when you see what a winter's heat will cost in an 18x22. It's not a large g'house, but neither is it a tiny one. I use double layered poly with an inflation blower on my plastic skinned houses. It gives the good insulation but with a better light transmission. Let's put it this way, when I kept my smallest greenhouse (20 x 48) running all winter at around 55 degrees, it cost more to heat than our whole house. A two story with about 1.5K square feet per floor.

Hi thanks for your message! So 60K is not so much, I'm hoping to keep it at 60 or above. I'm hoping that some reflection insulation and bubble wrap would help keep the cost down? Do you think the pool which is so far at 62F with only the plastic and no insulation potentially a help? I've just put it up last week. The plastic is pulled nice and tight and I have a cast iron pipe going down the middle for any possible extra support as far as snow is concerned. I wonder if I should try to install a blower in between the plastic?
Jenn

I'm a different sort of GH (all glass) and a different size (16x10), but I was considering all electric heat. My BTU requirement was much lower than yours but after checking out how little BTU a 110V heater puts out, I realized I'd be tripping breakers constantly and I opted for Propane with an electric backup. There are 220V electric heaters that put out more BTU, but I didn't have the means to get that sort of power to the GH. I'll be attempting this winter without Bubble-wrap...so we'll see how it goes. Good luck. As far as the pool, I'm no expert, but you may get some thermal mass (i.e. the water heats up during the sunny parts of the day and releases that heat at night. It may help.

HI Thanks for your input! I'm thinking electric because of the familiarity of it but maybe Propane might be a better choice. Are there some good brands or types that you might be able to point me in the right direction for? I'm not sure how practical an electric is if I have to run a heavy duty extension cord to the only 240V plug avail which is in the house. I'm hoping the pool helps with the thermal mass too. How long have you been running your GH in the winter with propane?
Jenn

Hi Jenn
I think you`d be better off with the propane too.
An extension lead wont work too well as it would need to carry around 75 Amps :)
I dread to think how much the cable would cost and it would have to be wired directly into the consumer box.
A standard wall outlet wont handle the current (17.6KW),its around twice as much as an electric cooker or shower draws.

Hi, the more I hear the more I don't want to use electric. Also I'm still not sure if my est. of 60,000 BTU's is right. I'm trying to figure what or how to go about the insulating. So a 240V would need to be wired into the breaker...and the cost of the cord.Maybe I should set my ideals a little lower. Maybe keep it at 60F.
Jenn

HI, by the way I figured out that the BTU number is closer to 34,000. That feels better. I'm looking into propane and solar pool covers? Any one have any luck with clear ones? DO it go on top of the house or inside?
Thanks again for any and all answers!
Jenn

My greenhouse is about 1600 cubic feet, with 200 sq ft of floor space. I live on the edge of zone 7B/8A. I have two 10,000 BTU kerosene heaters which heat my greenhouse only at night. On a cold night when the temperature goes to 20-25 degrees, these TWO heaters keep my gh at about 60 degrees. I have rigid, polycarbonate on the skin. On the occasional night when the temperatures go down to 10-15 degrees, I can keep the gh at 50 degrees. Yes, it is fairly tight but I do need some air intake for continued combustion. With temperatures a lot colder than here, I can't imagine that 60K BTU will be enough. Most of our days the temps go up into the 40s and 50s so I turn off the heaters around 6 a.m. You will have lots of days in Dec, Jan & Feb when temps never reach 40.

A question was asked but I didn't see your answer. Are you satisfied your gh can handle the snow load? What are you using for backup heat if the power goes off? Schlepping around outside in the cold trying to set up heaters sucks. My temporary back up is a large portable propane grill.

Please keep us updated.

Terry

Hi, thanks for the help and interest. I have a cast iron pipe going down the middle for any possible extra support as far as snow is concerned. And the plastic is pulled nice and tight. The house is 18 X 22 with out any insulation. I'm still not positive what or how to insulate but I'm thinking that some reflextive insulation board on the front and back where there's not a lot of sun potential would help and along the sides from the ground up ( which is covered with crushed stone) to 3-4 feet. And put clear bubble wrap over the entire top of the hoop house altho I'm not sure if the BW should be under or on top of the 2 layers of 4 mil that are already in place...
Jenn

I think to do what you are talking will require more than 60,000 BTU but 60.00 BTU will require 82 amps at 220 volts
Check you power bill for how much per KW you are paying.
If you check the price you will find out why ALL commercial GH of that size use gas the electric bill will be a couple thousand dollars each winter.

Hi, I'm starting to look into gas. THinking natural. I still going to put a lot of thougth into insulation too.
I'm also hoping for a warm winter:)
Jenn

Hi to you all, thanks for all your help and interest in my hoop house heating situation/drama. The thing is I still can't seem to figure out how much BTU's. Is there any one out there who has a hoop house and has heated it succesfully to a constant 60F throught out the colder months in New Englad???I've tried out a few different scenarios and have come up with 34,000 or 60,000. Can any one offer the suggestion of a good site/calculators? And maybe some good sites for reflective insulation (with or without bubbles?). Any ideas about brands of good gas heaters?
Thanks in advance,
Jenn

My propane heater (Empire DV-35) will be completely installed this Fri and this is my first year, so I'm probably not the best source of heating info. I'm attempting this year (my first year) with no insulation. My GH is a home attached, so my north side is protected/insulated already by my house. If I can't maintain the temps I want I'll either try to insulate or move the plants that require warmer temps into the house. It's a very experimental year.

I tried to calculate your BTU needs as best I could. I assumed the height of your gh to be 9 feet, and the length of the bows from one side to the other to be 30 feet. This may not be precisely accurate, but close enough to complete the calculations. With a double-layer of 6-mil plastic, and assuming the worst night of minus-10F, that would require 48,000 BTUs to maintain 60F.

The swimming pool may help to moderate your low temps, but I wouldn't count on it. The problem is that the energy-transfer rate from a static source of heat storage is not efficient enough to compensate for the relatively quick loss of heat through the walls.

I agree that propane is probably your best bet, although my vote would be vented with this much heat energy required. There have been heated arguments vented versus non-vented on this forum, and I guess it boils down to what you plan to grow. Some plants are sensitive to the fumes, others are not.

-Bruce

The two layers of six mil won't give you much more R value than one layer, unless there is an air pillow between them. Try this link on for size, since it seems to deal with hobby houses. It should spit out a BTU requirement, and you should be able to find calculators from there to convert that into KWH or BTU output of gas driven heaters.

Here is a link that might be useful: heat calculator

Hi Bruce and Calliope, thanks for your help. I agree that I need to add to the two layers of 6ML. I'm looking into covering it all up in a clear pool solar cover and I've found some reflective bubble wrap for the inside. I'm hoping that this will help me keep the area to 60 F even when the outside is down to 10. Alsong with some heat. I still don't feel very comfortable with gas but Bruce I agree with vented because it would seem to me more safe but I don't know alot about it at this point to have a strong education on it just yet:) In the meantime I'm thinking of the idea of finding and installing solar pool panels to heat the water up to 70-80. And using propane to heat the area of the green house up. Just some ideas I was wondering if any one had any thoughts on. In the meantime I'm going to keep looking into gas and or propane. Calliope, that BTU sounds good. Better then the 60,000 I can up with and that was with the outside temp as low as 20. You were right about the size of the house it's 9 ft tall.
Jenn

I see your BTU usage in the 60K range using that chart. You do not want to under-rate your usage or your heater will crank continuously. I have run Easter lilies (and they sometimes require 72 degrees at certain points) through a winter with days on end of temps dipping into the minus twenties to below freezing high-end. My heaters cranked so hard they threw the safeties several times, and I ended up more than once sleeping in the g'houses to manually over-ride the automated systems after my alarms went off.

If you call any reputable commercial g'house distributor, they'll have an engineer handy to tell you in a moment's notice what rating you need, and then recommend a system. I have a background in engineering before I went into floriculture and I still let their systems designers spec out my heater needs.

What are you growing that needs 60 degree minimum temps? I erect a simple pvc pipe hoophouse in my zone 7 yard and heat it with a small electric space heater with the thermostat set to come on at 32 degrees. For nights that get really cold (maybe 12 nights throughout the winter where the low is in the teens) I drag in a regular kerosene heater and let it run all night. If we're going to have multiple cold nights or high winds I will cover the whole hoop house with a plastic tarp.

Tricks I do to help keep it warm inside: I soak the soil floor with water on sunny days; I pack the hoophouse with as many potted plants as possible, even large empty pots of soil or bags of soil mix; I store water in buckets inside the hoophouse; I run a large box fan all the time with it pointed up towards the ceiling at an angle to circulate air. Even with all that work it will still freeze one night per winter in there but I rarely lose anything because the coldest of the cold temps is only for an hour or so rather being all night long.

I mostly grow plants that can handle cool but not frozen temps. Things like citrus, brugmansias, begonias and tree ferns do better if they get a cool winter instead of a warm one.

...do NOT skimp on a heater. In other words, don't get a small one trying to "just get by". A larger one will heat up faster and not have to run as long. When we do fire them up when we start planting, the heat has to be in the 70's.

We have four greenhouse--one 30x72x12h, one 16x64x7.5h, and two 24x68x11h [heights are app.]. Our propane heaters are all in the 200k range. They are "hanging" heaters or "unit" heaters. One is a Modine, one is a Reznor, and two are Sterlings. My favorite is the Modine; it appears to throw the heat farther than the others.

Temps drop like a rock when its cold and the sun goes down, even w/ two layers of plastic w/ an air cushion for insulation.

If I were you, I'd opt for either propane or natural gas, whichever you can get. These heaters run on regular 120v current and that is only for the fan. As a backup, we have a generator but several of the heaters you put on top of small propane tanks [like the ones on a bbq grill] might do in a pinch just to keep things from freezing.

Wish you lived close---I've got a few large heaters I bought last summer and I'd be glad to sell you one at a good price.

Best,

Tom

I use hanging Modines as well. The guts on commercial g'house heaters are better suited for the damp and sometimes chemically laden atmospheres in a g'house environment. I am also wired up so that they can be switched to generators if needed. I find that even in the larger houses like I have (and they hold heat better than the small ones) can drop to the freezing point without heat in four hours on a cold winter night. It gives me just enough time to rig up my back-up systems or gear up for using a generator and make coffee so I can stay awake to man them. LOL. I use a big torpedo heater for emergencies.

BTW you also do not want to use the household type mercury stats, because 1) their temps range usually does not go low enough and two they are sensitive to vibrations. I use in-line 120 volt stats designed for g'houses. It sounds expensive to go to commercial equipment, but in the long run, it comes out cost effective because they do the job right off the bat, and do it well.

Hi to you all, sorry about not getting back to you sooner...I've had to backtrack a bit and put my attention where I guess It should have been first-insulation. I've put up on the back and front of the house bubble wrap with both sides covered with reflective material. I'm now thinking of covering the top and sides with either clear bubble wrap or this wrap with the reflective on both sides. I'm thinking of maybe even a third idea of keeping the reflective on the side that's in the house but keep the clear bubbles facing the sun...what do you all think?? Tom, I interested in talking about the heater. Could you write back some specs on them and the cost? Triangle john, I also have a 15 ft pool in the house filled with water that I'm hoping will help me this winter. I'm quite sure that anything under 60 would not be good for the water that I'm trying to help the house up. This is my first and very experimental year.
Jenn

All those electric heaters will run non stop in that size green house. I have 16 x 24, with a 70,000 btu.propane modine heater. It does a good job, but still runs frequently. GH have little or insulation value in the walls. Bubble wrap pool covers are hard to keep from flying off in strong winds. Moved mine to the inside. The electric heater is ok for a smaller GH, but in New England in a big house , it would not keep up.

Jen... good luck!

I'm a bit scared for you with a pvc hoophouse in NE. I've seen a few collapsed steel hoophouses.

My main question is: What are you planning to grow? That makes a huge difference in how you plan your greenhouse.

A 15' pool inside an 18' wide GH? Ugh! That leaves you 1 1/2 feet on either side to get around (if you have centered it). Knowing how wet the walls get in my GH from condensation, i wouldn't want to have to get by that pool too often. Raining down my neck, sending shivers down my spine just thinkng about it!

On the plus side, I added a 8' "pool" 4 ft deep (1500 gallons) and i do think it helped. I never see ice inside my GH now. Last year it dropped to -14F outside for 3 days and still no ice inside.

Poppa