Heating a greenhouse.

orchidnickDecember 2, 2010

It has gone down to 36F once, under 40F for about a week so for the first time the heating system in my relatively new greenhouse has been in full use. Kept the temp at 60 all the time without problem. It's the quality of heat that I wish to discuss.

I circulate hot water from my house hot water heater to an industrial copper radiator which has 2 fans pushing air through it. A thermostat turns on the fans and the circulating water pump when the temp drops below 60F. It has not adversely affected the hot water use in the house. All the pipes to and fro are insulated to prevent heat loss.

A friend of mine has a greenhouse which is heated with the conventional natural gas burning heater. It works fins and keeps his plants warm, no problem. We both have noted a difference when you go into the GH in the morning after a night of heating. I can't find the right words to define it but the warm air in mine feels 'nicer' than his. Its a comfortable enveloping heat with humidity which is simply not the same in his greenhouse. Other factors are also at work as the 2 structures are not the same.

The difference is subtle and neither of us would consider for a moment changing his heater, both of us however agree that in a future GH, we would use hot water to heat it.


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His heater works fine, it does not have fins.


    Bookmark   December 2, 2010 at 11:40AM
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highjack(z6 KY)

I have propane heat and mine feels great when I walk in. I figured the reason was if the heat is running, the outside is very cold............or it is here in cold KY. My heat's been running day and night for the last three days. The sun is MIA.

If I had it to do over I would install hot water heat with the pipes running under my tables. The only problem with hot water is it takes a while to heat an area rather than the instant heat with the forced air.


    Bookmark   December 2, 2010 at 6:30PM
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We have a couple of people who have copper pipes with fins running under the benches. That's the conventional and accepted way to do it. Once the area is warm, it stays warm, good system. These copper contraptions, however, are expensive. I used the copper radiator because I found a used one, 2' x 4' for $50 when I needed it, otherwise it would have been the copper pipes. With 2 powerful fans the heat is there instantly. Ordinary car radiators won't do as they cannot withstand city water pressure, they expand and explode.


    Bookmark   December 2, 2010 at 6:54PM
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How large is your greenhouse and what is the capacity of your water heater? What is the lowest temperature you expect during the winter? How many sub-freezing nights do you get each year? What materials are used for your greenhouse walls and roof?
We are getting a week of 20F nights here and sunny 50s days. The gas heater only needs to work at night, and I am hosing the crushed rock floor for humidity in the late mornings. Would like to consider the hot water option when this heater needs to be replaced.

    Bookmark   December 2, 2010 at 10:20PM
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The greenhouse is 12' x 18' x 8' tall. It is made out of 2" x 4" wood construction with a layer of 6 mil agricultural plastic serving as walls and roof. I have several big windows, now closed for ventilation in the summer and 2 doors. Me being an imperfect carpenter, there are plenty of cracks.

Don't expect much below freezing however will see a few spells of temp down to freezing. It has only been tested to 36F when it maintained the set 60F. At 32F it may drop the temp to 56F, I don't know. I can always seal the cracks to increase the efficiency if necessary. The water heater is a regular 50 gallon set at a fairly high temp, higher than we would have it during the year when the greenhouse is not being heated. It's about 15' from the greenhouse, the pipes are insulated with air conditioning material. My gas bill has jumped $20 this last month. Hope that answers some of your questions.

The hot water does not add to the humidity but I would think flames would reduce the humidity.


    Bookmark   December 2, 2010 at 11:11PM
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