# Heat source for greenhouse



## PrepN4Good

What would ya'll recommend as a heat source for a greenhouse when electricity is NOT an option? (stand-alone, not attached to a building)

This is for Zone 7B, so we're only talking about needing it for a few months (hopefully).

I've done a search & found a few mentions here & there, but if there's a dedicated thread, please point me to it.


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## cowboyhermit

Well, we are dealing with much colder conditions but the same things apply depending on temp-area.

Most common method is simple propane/natural gas fired heaters. These can be not vented as long as there is some ventilation and they have 02 sensors etc. The increased carbon dioxide is a benefit to most plants. Anything from a on the bottle catalytic heater to a "herman nelson" style work fine though with both you will have to deal with stratification (hot air on the roof). Overhead radiant heaters work excellent, these are long bars that provide even heat and heat what they "shine" on more than the air, this can save some money.

Kerosene or other fuels you need to be more careful or vent, they simply aren't as clean but they will work.

A wood stove will work and it can be a camping or military style one if it needs to not be permanent, this of course needs to be vented properly. You can add barrels of water or similar to store heat so you don't have to have the fire going 24/7. Of course much can be done with heat storage to reduce heat requirements in general.

Compost can be a great source of heat, a large amount of material being composted in a greenhouse can keep temps above freezing and again the C02 is useful.

Lots of options.


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## crabapple

Root cellars are to keep fruit & vegetable from freezing, this will work in green house too.
So start with a 36 inch deep or deeper pit on a hill with one end for door way.
Block up walls to hold soil back.
Fill the floor with dark grave to hold the suns heat.
Water will hold more heat then rock,soil & metal.
So if you have room, put in a few 55 gallon drums of water to hold heat.
A rocket mass heater or wood stove could help also.


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## *Andi

We use a Portable Propane heater in ours, kind of like the one in the link ...

http://www.tylertool.com/mr-heater-...am=31282435&zmas=47&zmac=480&zmap=mrhnf232000

All I want to do is keep the temps at 33 or above. (we are also in zone 7ish)

http://www.preparedsociety.com/forum/f14/greenhouse-10085/index2.html

We did add a water barrel last year and it does help but on some nights you will need a little extra heat.


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## crabapple

Andi, we used portable propane in a woodworking shop that was filled with wood & sawdust, never had a fire.
They are real good & the cost is minimum IMO.
But I was looking for low tec/ passive ways to keep the heat up.
The green movement may be the answer the TSHTF, as well as the miser way of doing things.
I have used a devise that turns on 60/100 watt bulbs when the temp drops below 40 degrees, to heat my pump pipes.


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## UncleJoe

We have friends with a couple large commercial greenhouses and they heat them with a coal furnace.


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## *Andi

crabapple said:


> Andi, we used portable propane in a woodworking shop that was filled with wood & sawdust, never had a fire.
> They are real good & the cost is minimum IMO.
> But I was looking for low tec/ passive ways to keep the heat up.
> The green movement may be the answer the TSHTF, as well as the miser way of doing things.
> I have used a devise that turns on 60/100 watt bulbs when the temp drops below 40 degrees, to heat my pump pipes.


I did try every green way I could ... but in the end, We needed the propane when temps go into the teens. As tonight the outside temp is 30 and dropping the greenhouse is 42. (per my handy dandy remote temp gage. ) I will turn the propane on low for the night... before we go to bed.

The water barrels help, as long as the outside temps are at 30 ... give or take. I tried the 100 watt bulbs and then a heat lamp. We put in the heavy black matts ... etc.

The propane works and if the shtf ... I will go with all cool weather crops.


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## jeff47041

I read once that you can heat a greenhouse using rabbits. They put off a lot of body heat. Sorry, I cant find where I read this at. 
When I read the article, it told approx. how many you would need for your zone for different sizes of green houses.


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## *Andi

Heating a greenhouse, with animal manure is a centuries-old technique. Heating greenhouses with a manure bed was popularized in the 18th century. Thomas Jefferson used this technique at Monticello. Rabbit manure can be used for this same process, as any manure and bedding combination create heat as they decompose

http://www.ehow.com/how_8183849_heat-greenhouse-rabbits.html

My greenhouse is rather small even tho I went with the larger one... To me (and just me) it is like the water barrels... They work but it depends on the crops in the greenhouse... (and well the space).

But a lot of folks may not have heard of the method. So Thanks for posting! :congrat:


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## cowboyhermit

Livestock is a great way to heat a greenhouse (or other space) if that works in your situation.

A cow will produce somewhere around 4000btu, that's about 1/5 pound of propane/hour, in 12hrs that is 2.5lbs. Chickens are about 10btu/lb of body weight, rabbits are in the same ballpark IIRC, probably a bit higher.
10, 10lb hens would produce somewhere around 1000btu



It looks like I misread the question, if the heater need not be portable there are many more options like the coal. There is of course so much that can be done with passive solar and also with the glazing itself, double layer is huge difference for example.

ETA; Andi beat me to it


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## *Andi

For me it all falls back to how much space you have in your greenhouse... A large commercial greenhouses can go coal... or so many different ways. But when it comes to small... The backyard greenhouse, where every inch is in use... things differ. 

For me the small propane heater has worked the best... but that is just me.

If the shtf ... plans change but work, if only on a different scale.


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## hiwall

When I was in Minnesota the business where I worked sold flowers from local nurseries. We tried heating our greenhouses with unvented propane heaters. This damaged the flowers (we were warned of this by the nurseries). It did not kill them but they did look sick after awhile. We seldom had vegetables so I do not know the effect on them and it worked for *Andi so it might not bother them but I am just passing on a warning. Electric or any vented heater may be the best answer.


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## *Andi

hiwall said:


> When I was in Minnesota the business where I worked sold flowers from local nurseries. We tried heating our greenhouses with unvented propane heaters. This damaged the flowers (we were warned of this by the nurseries). It did not kill them but they did look sick after awhile. We seldom had vegetables so I do not know the effect on them and it worked for *Andi so it might not bother them but I am just passing on a warning. Electric or any vented heater may be the best answer.


This is my second season with a propane heater...For me it worked for others it my differ ...

We only use it when temps dip below 30... but as to date (today) I've had no problems... but that is just me ... others may vary.


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## worldengineer

I have heard of people heating their tobacco greenhouses here with those outdoor wood heaters one can see springing up. Instead of using the heat directly he heated water and radiated the heat throughout the greenhouse. That way the fuel source is readily available now and most likely way past any of our life times. Plus depending on how you have to get it, it may be basically free.


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## cowboyhermit

hiwall said:


> When I was in Minnesota the business where I worked sold flowers from local nurseries. We tried heating our greenhouses with unvented propane heaters. This damaged the flowers (we were warned of this by the nurseries). It did not kill them but they did look sick after awhile. We seldom had vegetables so I do not know the effect on them and it worked for *Andi so it might not bother them but I am just passing on a warning. Electric or any vented heater may be the best answer.


This might have been from ethylene gas, which can build up without enough ventilation and/or incomplete combustion. I have been around commercial and government greenhouses that used unvented and they were fine but it is surprising how much ventilation is required. It can be counter intuitive because in colder temps you have to increase the ventilation a LOT when most people's instinct is to seal things up.


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## *Andi

worldengineer said:


> I have heard of people heating their tobacco greenhouses here with those outdoor wood heaters one can see springing up. Instead of using the heat directly he heated water and radiated the heat throughout the greenhouse. That way the fuel source is readily available now and most likely way past any of our life times. Plus depending on how you have to get it, it may be basically free.


And that is the difference with the big boys and the backyard garden house...I would rather go no heat and cool weather crops... but that is just me.


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## Meerkat

Good info since we hope to be using our bigger greenhouse soon. Of course it will be made from greenhouse plastic so wood burners may not be a good idea, melting would be a bad thing.


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## dirtgrrl

I was going to comment on ethylene gas but cowboyhermit beat me to it. Bulbs, flowers, and ripening fruit are most affected by it. If you were growing lettuce or the like (where you eat stems or leaves, not fruit) the gas would have less effect.

To me, a winter greenhouse would be most useful to extend the season for cold-hardy crops that wouldn't need much heat anyway. All you'd need to do is keep the soil from freezing, and that would probably happen just from heat gain during the day. It would also be useful to overwinter freeze-sensitive species in containers. Much more than that would probably cost more than your crops are worth. My work houses (3456 SF) suck about $800 worth of propane a month in the winter in Zone 8, keeping night temps at about 55 degrees.

Dual-wall polycarbonate sheathing is worth the extra cost if you can afford it. The R-value is about 5, whereas single wall is almost nothing. If you do decide to heat, be sure your set up is safe for fire and carbon monoxide. Houses are generally leaky enough so that CO isn't a problem for humans, but poly burns like a son-of-a-b****. It'll be gone before you can even call the fire department, and emits toxic smoke. Fiberglass burns too, but I have no experience with that.

I like the rabbit idea myself and will probably try it when I get my own houses.


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## LincTex

You can say I'm wrong, but if I could start from scratch I would definitely build against a hill or have a sunken slab for earthen insulation. 

Second, I would run tubing in the slab (or in the packed dirt) that warm water could circulate through (though a pump needs energy) and heat the water with solar (and store it in large tanks). All of this takes a lot of surface area, both for heat and electricity (solar).

I think a long cob-made rocket mass heater would work great, though if the heater were too small you would need to "employ" someone to feed it sticks through the night. 

How much heat is really needed? If you aren't commercial flower ops (food only), all you need to do is keep the veggies from freezing, right?


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