Heating a small greenhouse

[Katahdin]

My father and I have recently finished building a small greenhouse (8ft x 10ft x 8ft). Its glazing is made of nice triple wall polycarbonate panels which supposedly have a r value of around 2.2. The greenhouse sits in a decent southerly exposure where it gets around 7 hours of sun daily. I intend to house my small but growing collection of orchids within it, so I am guessing that to keep the largest selection of species happy during the winter, I would have to keep the temps at a minimum, in the mid 50s at night and high 60s during the day. I live in eastern New England where the winters are fairly long, but we rarely have a night below -10 F. My question is, in your experience, what is the best way of heating such a greenhouse?

thanks

[Jx3]

Not an expert, but i think thats going to be tough for you. The size is small so it will not hold its heat as long as a larger greenhouse plus even if you have the majority of your winter temps in the 20's-30's its gonna take alot of energy to heat even that small space. I personally would look into getting a small air forced heater like the ones used in small trailers and campers. They run off propane or fuel oil and are quite energy efficient. Electric baseboard all the way around the base of the greenhouse would probably work too but may be expensive in the long run.

[raybark]

Let me start with a general comment: whatever you do, set a minimum nighttime temperature and be done with it, and let the sunlight determine the daytime temperature. Raising the daytime temperature causes the plants to grow faster, and if that is done on days when there is insufficient sunlight, you will end up with weak, floppy plants.

As to the "best" way to heat - look at the cost of electricity and fuel. I don't happen to have natural gas available, so went with propane, and two years ago, when a heater died, I replaced it with a vent-free model that requires no electricity to operate.

I have warned people against vent-free models forever, as incomplete combustion can result in the production of ethylene gas, which is toxic to the plants, but modern burner design seems to keep things pretty clean, and I have had no issues.

By avoiding vents, your costs will go down and they won't suck the humidity right out of the greenhouse, either.

I have a heater sizing calculator available on my website.

[Brutal_Dreamer]

My greenhouse is heated with a large natural gas heater (with electric fans and thermostat) suspended up in the air, but we supplement the heating with plug-in radiator (oil filled) heaters. Just two of those electric heaters knocked down my gas bill significantly last year. I also make sure to add additional fans in the winter months to dry off the orchids after watering faster. In the summer our greenhouse has four, high-capacity ceiling fans to move the air around in addition to the two large units that pull air through the Kool-Cell to keep the space cooler and humid. In the cooler months I add in free standing oscillating fans that blow right at the heights of the benches and physically move the foliage of the orchids. This works well to keep my slippers, bulbos, phals, and oncidium type orchids from getting damage from water mixed with cold temps. The larger plants Vandas, Cattleyas, etc... are all hanging and do fine with the normal air movement and since heat rises have no issues with cold (so far!!).

I also water with heated water (not hot, but not cold.). A few years ago we installed an electric "instant' water heater. This really reduced the cost in the greenhouse too and the water is forever warm when we need it. See my article on it here: http://www.rv-orchidworks.com/orchid...reenhouse.html

Best of luck!

cheers,
BD

[Katahdin]

First of all, thanks everyone for your long and informative posts. Raybark's suggestion and the idea of using a water heater both sound good to me. I will do the waterheater idea if I can manage to snag one from our local dump

Not an expert, but i think thats going to be tough for you. The size is small so it will not hold its heat as long as a larger greenhouse plus even if you have the majority of your winter temps in the 20's-30's its gonna take alot of energy to heat even that small space. I personally would look into getting a small air forced heater like the ones used in small trailers and campers. They run off propane or fuel oil and are quite energy efficient. Electric baseboard all the way around the base of the greenhouse would probably work too but may be expensive in the long run.

Yea, I am afraid this is the case, for the smaller an object, the more surface area to interior area you have. Therefore, for its size, my greenhouse will be much less efficient than a larger one.