How do you heat a greenhouse during the winter?


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How do you keep a greenhouse warm in the winter. What about moisture and ice. Is there anything I should know, before I attempt to build a small greenhouse?
 
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Natural Gas Vent-Free Heater Procom MN100HPA 10000 btu

Natural Gas Vent-Free Heater Procom MN100HPA - 10000 btu
Brand: Procom

SKU: MN100HPA
Mfg Number:
  • BTU /hr.: 10000 btu
  • Fuel Type: Natural Gas
  • Dimensions: 19-1/8" H x 14-1/8" W x 6-3/8" D
http://www.durgan.org/URL/?HNFOH I use this one in a 10 by 12 by 7 sized greenhouse in Zone 5. It will keep plants above freezing during February to June by keeping plants near center of greenhouse on very cold nights. It is not perfect but uses natural gas which is low cost. Simple to install and to vent.

Here is my greenhouse.

http://www.durgan.org/URL/?NTVTE 30 March 2013 Greenhouse
The greenhouse is used for growing plants from seed.The objective to have strong healthy plants for the outdoor garden starting about 15 of April for some seeds and plants. Tomatoes will be planted about 24 of May. The outdoor temperature at night is usually slightly below zero. The little greenhouse keeps the plants above freezing.The real advantage is the sunlight available.
 
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I have the Cedar Ridge 20k btu blue flame heater which is hooked up to my natural gas line I shut it down between mid November and mid March asit is too expensive to operate year round.
 
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There is a lot you need to know, actually. I am having this discussion now with my significant other who thinks he can just slap something together and call it a greenhouse. He has "experience building things" and thinks it's no big deal, but a greenhouse has to be properly put together to provide warmth when needed and you have to be able to cool it off as well.

Since you haven't built it yet, you should look into the different types - if it's cold where you are, you may even want a year-round growing house that is partially underground depending on where you live. I have a bunch of greenhouse plans and info saved on Pinterest:
https://www.pinterest.com/cdgautreaux/greenhouses-and-rainwater-collection/

BTW - You can use water and stones and let the sun heat it for you.
 
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Meant to mention that last winter was the first with this heater and because it was unusually cold last year, that may be yhe reason for the high usage. I may be able to start up earlier this year. Hopefully the beginning of MArch.
Well, one hopes ...
 
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I experimented with solar heated water and it did work in spring and fall to help moderate temps. I used pv (solar panel) powered water pumps rather than depending on thermal induction.
For colder temps i switched to the blue flame heater because someone had advised me not to use infrared . I will try to find the source of this advice and post it here.It might have been baloney advice but I fell for it!
 
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Durgan, I want your yard!!!
Yard is not a lot to look at now, but It is pretty nice in the Sumner.

I heated will electricity, propane, wood and natural gas. Wood was the best and cheapest. Natural gas is similar and I don't find it expensive. Mind you the greenhouse is only used for growing seeds and making plants large for transplanting in the garden. I don't over winter any plants.
 
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If you have natural gas, using those blue flame vent free heaters is the way to go. Most of those that I have used will run on natural gas or butane/LPG. Heating is the easy part. If you have a clear winter sky on a warm day it can heat up a small greenhouse quickly so don't overlook the cooling.
 
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New to the forum. Hope this question fits this thread - apoligies if I should have posted new. Recently did a signifacant addition to my garage, mostly for a woodworking shop, but glassed in the southest corner with the idea of framing in that corner for a 5' x 9' greenhouse. Without enclosing the corner, I monitored the temp there all last winter and the lowest it got was 41. The sun through that glass is the only sources of hit and we get bright sunshine about 90% of our days. Our typical winter temps are highs in the high 40s to high 50s. Lows are typically low 30s to high teens. Extremes can be -10 below to mid-60s - mid 60s much more likely to occur than anything below zero. Sun through that glass is the only source of heat, so I'm thinking enclosing that 45 sq. ft. area within the 780 sq. ft. area with insulated walls should significantly increase the average temps. My thought is to line the interior walls with gallon bottles (like windshield washer fluid comes in), paint them black, and hope that will retain the heat well enough to increase the lows from the current low 40s by 10+ degrees.

Finally, my questions; 1. Just as described above, what plants can I grow? Interested mostly in herbs and greens. 2. I did my tomato starts (from seed) in that corner last spring. They grew but did not thrive, sort of just stayed alive. Will the "improvements" I describe increase the temp enough so that tomato plants thrive? 3. Will the two black walls disrupt the circadian rhythms of the plants? Does that matter and do I need to compensate with grow lights?

Thanks!
 
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If your lows in that area already do not drop below freezing, you've got a fanastic area for growing lettuces and other cool loving plants. If you enclose the space, you might find that it will really elevate the temperature. I would enclose it first. See what temps you get. You may not need those water containers. I tried this and yes, they do moderate but not much unless you want to entirely fill the room but for a small area.

My thinking, enclose it and you'll probably be pleasantly surprised!
 
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You should first consider to clip a layer of bubble wrap to the inside of your greenhouse frame will reduce heat loss and block icy winter draughts. You can buy a bubble wrap insulation from garden centres since this is toughened and UV stabilised. You can then install an electric fan heater to heat your greenhouse. Consider buying the one with a thermostat so that your greenhouse will be heated when necessary.
 
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The bubble wrap on the inside does very little to help. I tried this two years running and I didn't just clip it on the inside, I taped it so as to elimate any gaps and it was just a waste of time and money. I've heard that people have success using pool covers that go over the entire outside of a greenhouse.
 
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Low temp outside last night was 27, low in the greenhouse was 44. I use one of these set to low for really cold nights. Greenhouse is basic Harbor freight 6 x 8 over cement, Wife said modest use of the heater isn't too bad on the electric bill. There are only a few months of the year where using it might necessary.

The heat is gradual and gentle. Next helpful thing I could do would be sealing it better to retain heat better.

http://www.homedepot.com/p/DeLonghi-Comfort-Temp-Oil-Filled-Radiant-Portable-Heater-EW7707CM/204631985
 
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Low temp outside last night was 27, low in the greenhouse was 44. I use one of these set to low for really cold nights. Greenhouse is basic Harbor freight 6 x 8 over cement, Wife said modest use of the heater isn't too bad on the electric bill. There are only a few months of the year where using it might necessary.

The heat is gradual and gentle. Next helpful thing I could do would be sealing it better to retain heat better.

http://www.homedepot.com/p/DeLonghi-Comfort-Temp-Oil-Filled-Radiant-Portable-Heater-EW7707CM/204631985


I wish I could afford to run one of those. Our electricity is extremely expensive because we no longer have coal powered plants and the replacement green powered producers cost mightily.
 
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A main consideration is heat loss through the ground in cold weather. I imagine most folks here have a greenhouse that sits on a slab, pavers, gravel bed or directly on the ground.

The soil underground, if properly insulated, can act like a huge battery for the greenhouse, storing thermal energy and stabilizing indoor temperatures both in the summer, but more importantly, in the winter.

We all know heat loss can occur through a greenhouses' walls and roof, but it can also occur through the floor, accounting for about 15% of an average greenhouses total heat loss. This is because the ground, if left un-insulated, freezes in the winter just like the air does. Preventing this heat loss is imperative for growing in a winter greenhouse.

By preventing heat loss to the surrounding topsoil, the soil underneath the greenhouse can now trap and store heat, creating a pocket of warmer soil underground. Soil is a source of thermal mass. Like water, stone and concrete, it stores thermal energy (heat) and slowly releases it later. Insulating underground connects the greenhouse to this huge store of thermal mass.

A neat and rather inexpensive way to keep the soil directly under the greenhouse floor stable year round is a method called a "Swedish Skirt". You can incorporate this method into the building of your greenhouse or retrofit it even to an existing greenhouse.

sweedish skirt insulation.png


The idea with the Swedish Skirt is that you lay rigid foam board horizontal starting at the base of the greenhouse, and extending 4’ away from the greenhouse. This insulation needs to slope gently away from the greenhouse for drainage, which will require some minimal digging or raking. It’s also best to cover this foam with gravel or soil, as direct UV rays will damage the insulation. This system prevents very cold or frozen soil from creeping under the greenhouse, while keeping the warm soil where you want it, directly under your greenhouse. Ideally, you want the ridged foam board to be 4" thick.

This image is of a greenhouse where the surrounding soil has been prepared for a Swedish Skirt.
untitled copy.jpg


Unfortunately, I do not have a Swedish Skirt around my greenhouse but am seriously thinking of retrofitting one. It makes a lot sense!
 

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