Original Greenhouse Heating Question

Just to clarify the question, here's my original post to the home improvement group:
We have a small greenhouse attached to the south side of our home. It's 14' X 12' with a shed roof tapering from 10' on the house side to 6'. Roughly 1,400 cubic feet. It's a 2x4 frame with double-walled polycarbonate sheeting, 10mm for the roof and 6mm for the sides. We're in Maryland, near Baltimore, so it rarely gets below the mid-teens in the winter.
We heat it with a 220V electric heater, 5,600 watts and 19,110 BTUh rating. This generally keeps it at the 50 degrees the plants require but occasionally my wife puts on a 110V supplimental heater on cold nights.
The power hasn't failed in the winter since we got the greenhouse but it's probably only a matter of time. I was thinking of getting a kerosene heater as back-up to the electrical heaters. Home Depot has a 23,000 BTU heater for $129 which seems to fit our needs. Could I use home heating oil for this or would it be better to stick with pure kerosene?
I was wondering about a propane heater; would that be more efficient than kerosene? We have a propane ball/tank for some other applications which aren't used in the winter.
Paul
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wrote:

We use a propane non-vented heater in a personnal greenhouse and it works well in conjuction with automatic roof vents and a circulation fan. I'm not sure you need as much heat as this unit puts out, but I assume they make many sizes. I suppose the CO2 put out may make a difference, but have not noticed it.
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Pavel314 wrote:

If you want to cut down on the heating bill you can add some insulation. Home Despot has 1/2" polyiso (R3):
http://www.rmaxinc.com /
I use it in my solar stuff, works well outdoors and is non flamable and relatively green.
You aren't getting much light from other than your south facing vertical wall (with the sun so low), so you may wish to have a winter cover for this. It would add R3 to your R2 walls and roof. Take it down when you don't need it. Cut the bill in half or so...
Just an idea.
Jeff

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<http://attra.ncat.org/attra-pub/solar-gh.html
Lots of stuff.
Bill
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Garden in shade zone 5 S Jersey USA


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Here is a BTU and an Area calculator that may help, however it sounds like you have a good primary and a very good supplement/emergency system. http://www.littlegreenhouse.com/area-calc.shtml http://www.littlegreenhouse.com/heat-calc.shtml
Try transparent bubble wrap insulation inside instead of insulation material and clear packing tape to secure it. Comes in 4 ft rolls but buy it from a place like here: http://www.starboxes.com/medium-bubble.aspx?CategoryIDD and not the UPS or the FEDEX stores. Much cheaper and free shipping.
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wrote:

Some plants will refuse to bloom or struggle with growth if there is too much propane, natural gas, or petroleum vapors in the air. Electric heating makes more sense, safer, cleaner and expensive. Kerosene heaters are not recommended due to increase of fire risk.
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wrote:

That would depend on concentrations, heating a greenhouse would never reach such concentrations due to the fact that rarely are greenhouses anywhere near airtight.

True, electric heating is typically expensive.

Kerosene space heaters are never safe, they also pump soot into the air.
Gas is typically the least costly fuel and as to fumes from combustion there is no reason that combustion needs to take place inside the greenhouse... a gas hot water heater can be placed outside with hot water baseboard piped in, with a thermostatically controlled circulator. Which fuel to choose is primarilly based on climate, in warm climes where heat is needed only occasionally then inexpensive electric heaters may be the way to go but in colder climes the cost of a gas heater will quickly pay for itself.
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Good point. I was thinking of building some sort of outside enclosure for the propane burner and transferring the heat inside. I was thinking more of convection than hot water as this would just be for emergency use.
Paul
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Pavel314 wrote:

Explain emergency use. If you mean for only very occasional use then gas is probably not the best solution. For occasional periods of low temperature a radiant electric heater would be more than sufficient and requires no installation whatsoever (except to plug it in) and no pilot light to deal with, just set the thermostat and forget it. More than any other factor climate determines what system to employ. The only other point I'll make is that with a greenhouse I'd not try any *iffy* system, you only get one chance at a cold spell with plants and they're all gone, and then there was never any reason to have a greenhouse at all. Whether gas or electric I'd also install a low temperature alarm... they are very inexpensive (~$30-$100) depending on type, some will simply turn on a lamp and/or a bell while more expensive units will also dial your phone number so a prerecorded message can alert you that your plants are about to recieve frostbite. And since you are already using electric and you are satisfied then during cold snaps simply add another electric heater. But if you're concerned with power outages than obviously you need a back up that requires no electricity (or use a generator). I suppose in extreme emergency you can resort to a kerosene space heater but I'd definitely use clean/filtered kerosene made especially for a wick type heater. During the '70s oil shortage I used a kero space heater for a while, they are awful filthy things and dangerous... if you decide to go that route I'd recommend monitoring it often while in use, they don't have a thermostat and the wicks are prone to flare ups that will generate excessive heat. If your greenhouse is important to you and you intend to use electric heaters in your climate, and you are prone to power outages of any duration then I'd strongly recommend having a portable generator on hand, it will cost a bit more initially but I think that's a far better solution than kerosene. If you are prone to power outages of duration then you really should have a whole house generator permanently installed, it can run off your propane.
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By emergency, I mean if the power goes off and our electric heaters stop working. I have a generator for the pump, refrigerator and furnace, but it's only 5,500 watts and the greenhouse heater is 5,000 watts. A propane heater would be a cheaper alternative to buying another generator for a rare outage.
Paul
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Pavel314 wrote:

That's only about 15,000 BTU. The single head infrared/radiant tank top heaters supply that. They are widely available and cheap (~$50). They usually have a reflector and are directional. So you may wish to get two and either heat from both ends, or the middle out.
The convection heaters will be overkill.
Jeff

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