Greenhouse heating question.

vp999

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Hello guys! Im looking into building a green house to house my tropicals in the winter like ficus and desmodium etc.. Looking to build one around 12x12 in size and my concern is what type of heater should I use? Also, for those that have greenhouse for your tropicals what temperature do you keep to around? I am in MD zone 7A so winter time its average around 35-40 during the day and 25-30 at night in the coldest months. Thanks in advance.
 

Forsoothe!

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Stand alone, lean-to, exposure, you need to describe it more fully? What utilities are available?
 

vp999

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Electric, it will be a stand alone greenhouse.
 

JudyB

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I use an infrared heater in mine. It's mounted on the ceiling, and I have an oscillating fan behind it that comes on when it does, to spread out the heat to the whole building. I like this type as they don't have potential to start fires.
 

penumbra

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You cannot beat the efficiency and the affordability of propane or natural gas, unless you go with solar panels (long term).
 

sorce

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What kind of fuel do you use for the house?
How is it heated?

Sorce
 

vp999

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I think I have both gas and electric for the house but I want to avoid running the gas line out to the greenhouse, it just sound like major work that involves a professional.
 

penumbra

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I think I have both gas and electric for the house but I want to avoid running the gas line out to the greenhouse, it just sound like major work that involves a professional.
Yes it involves a professional but in the long run it would be worth it. Run it on electric heat for a year and see for yourself.
Whatever you do I wish you the best and I only wish I had the problem of heating a greenhouse. Can't see that I could afford one unless something dramatically changes, and since I am 70 now, I think that is a long shot.
 

sorce

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professional

Do you have forced air?

Are you in one of them HOA's or the sticks?

Depending on how far the building is, you may be able to run some of your current heating to the building.

I always go to radiant heat in the floor of a slab. That would make a wonderful place.

Sorce
 

coachspinks

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Hello guys! Im looking into building a green house to house my tropicals in the winter like ficus and desmodium etc.. Looking to build one around 12x12 in size and my concern is what type of heater should I use? Also, for those that have greenhouse for your tropicals what temperature do you keep to around? I am in MD zone 7A so winter time its average around 35-40 during the day and 25-30 at night in the coldest months. Thanks in advance.
Gas is going to be less expensive than electricity but there is more upfront cost. It does pay off later. Judy B has the right idea for ease of use though. I had one like this when I had a greenhouse and I was very happy with it.


Some more advice -
you need a fan to circulate the air, probably two. I set mine at each end of my greenhouse near the top. It will cut down on issues like disease and pests that pop up.
Go for the highest insulating value that you can. Most kits can be bought with double walled panels. If you can afford it, go with that. An even better option and the one I had, is a hoop greenhouse with inflatable walls. It isn't as attractive as some of the kits but the 3" of air makes for good insulation.
 

sorce

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This would be a dream come true.

I ran some under a wood kitchen floor once. It's easier than one might think, and there are a ton of products for it now.

How nice would it be to have bottom heat all over .....
Matter of fact...

I'd pour shelves to so you can heat everything.

A nice drain in the middle, filtered to a barrel dug underneath for reusing water.

Sorce
 

Leo in N E Illinois

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In zone 7 heating a greenhouse is relatively trivial. Radiant heat, ceiling mount, pointed down, or floor level using the "heat rises" all work. Biggest issue will be keeping the greenhouse cool. On a calm sunny January or February day, it is possible for the sun to heat a greenhouse into the upper 80's or low 90's very quickly. You will need fans and vents.

Fans should keep air circulating around the greenhouse 24/7, so no matter where you set the plants the leaves have a little motion to them. Mimic a gentle breeze. Circulation fans are separate from exhaust fans. Circulation fans are kept on continuously. This is important in keeping disease down, and avoids cold pockets and hot pockets in the greenhouse.

Second you need to be able to vent the greenhouse effectively on a warm day. A 12 x 12 x 10 foot greenhouse will have 1440 cubic feet of air. Ideally for summer you need to be able to exhaust the entire volume of air once every 3 minutes to avoid heat build up in direct sun. This means exhaust fan able to move 450 cubic feet per minute as a minimum. I've seen orchid greenhouses where they can exhaust the full volume of air every minute. In the 12 x 12 x 10 example that would be 1440 cubic feet per minute. This high exhaust rate allows the greenhouse to be used both winter and summer. Exhaust fans would only turn on when temperatures exceed a set temperature, for example maybe 85 F.

I have seen a number of orchid collections destroyed by power failures. If power goes out on a bitter cold day, you have hours to get it repaired or get a generator in place to get alternate heat running. Most interesting is I have seen more orchid collections destroyed by power failures in summer. In summer you only have minutes once the sun is out and beating on the greenhouse to get the air moving to cool the plants. An hour or two in a sun baked greenhouse and all plant life inside can be toast.

Roof vents should be installed. At least a portion should be automatic and not require electricity to operate. There are hydrolic and bi-metal operated hinges for opening vents that do not require electricity. These are key for a set up that survives a power outage.

I personally opted for growing under lights rather than trying to heat and cool a greenhouse in zone 5. If I had to do it over, I might have preferred to go with a detached greenhouse, but these days I have downsized my tropicals collection to the point now a greenhouse is unnecessary.
 

vp999

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Thank you Leo but I don't plant to have any plants in the green house in the summer, the main purpose is for the winter only to house tropicals so I don't have to bring them all inside the house, its just too clutter and a pain in the butt to do so. Thanks again for your detailed write up. I may just try electric heating in the first year to see how its doing and than decide to keep it as is or run a gas line for the following years.
 

JudyB

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Here is the type I have, I only have the small one at the top, and it does a cracking job of keeping my greenhouse above freezing even in the cold winters we have here. And I don't find it that expensive to run. I do have a very well insulated building with plenty of built in heat sinks, like concrete pavers and a water barrel.

and a link to my thread about my building if you have an interest.
 

vp999

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Thank you very much Judy! This is gonna help me greatly.
 

coh

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Leo beat me to it, I was going to ask about backup power and also ventilation. I lived in the DC area for about 5 years and remember plenty of rather mild/sunny days during the winter (complete opposite of here) and a greenhouse could easily become too hot especially in late winter (Feb/Mar).

You could do some back of the envelope estimates of electricity cost but I would probably just test it this winter and see how much it takes to keep it at your desired temp. Definitely get a good max/min remote reading thermometer or a few. Do you have a minimum target temp in mind?
 

vp999

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I've been asking around for the target temperature around here. Some guy who keeps high end tropicals said he keeps his greenhouse at around 45+ in the winter and he said he's trees are doing good, he also brought in a lot of those trees from Vietnam.
 

coh

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I've been asking around for the target temperature around here. Some guy who keeps high end tropicals said he keeps his greenhouse at around 45+ in the winter and he said he's trees are doing good, he also brought in a lot of those trees from Vietnam.
I think things like F. microcarpa, F. retusa would do fine at those temps. Might be a little chilly for willow leaf. Not sure about desmodium, have never grown it. Might be a bit chilly for jaboticaba, grewia...depends what you want to keep and whether you want it growing or just maintaining during the winter. I've kept many ficuses pretty chilly with little light during the winter and they've been OK (microcarpa types) but obviously they don't grow.
 

TN_Jim

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At my place of work it’s only greenhouses. My office is in a greenhouse. That said, I’m sure no expert and it looks like you’re getting very sound advice from very experienced people here.

If I were to contribute any ideas it would be to please heed the advice of cooling and ventilation given by many above. I would even say that if I were you I would treat cooling and ventilation with equal if not greater consideration.

I know weather there is likely not as unpredictable helter skelter as it can be here regularly, but it can be at times as well I’m certain. In March or April before last frost for example, but when you can still get those higher ephemeral temperatures, that’s when your greenhouse’s dynamic abilities to create ideal temps the best will crucial. I love this goal you have, kinda jealous.
Thanks.
 
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