Heater for Small Greenhouse - Orchid Board

HDCochran · #1 11-30-2007, 02:20 PM

My orchid collection has outgrown my orchidarium and I am building a small 12' x 12' greenhouse and will need about ~10,000 Btu/hr of heat to keep it warm enough next winter. I cannot find a ~10,000 Btu/hr vented propane heater. Does anyone know of a source? Alternatively, can anyone provide reliable information on any detrimental effects on orchids of using a vent-free propane heater? I've read arguments on both sides of this question.

Jerry Delaney · #2 12-01-2007, 02:04 AM

I would do a google search for Williams, Empire and Kozy heaters. I know that all of these companies make vented heaters in about that size (I am not sure if you are talking input or output of 10,000BTU) for natural gas and I would imagine that they have them for LP or can offer an orifice change to convert one from natural gas to propane. I currently am using both a Williams and a Kozy heater that direct vent thru the wall (both have sealed combustion chambers so you need not worry about LP gas or ethylene getting into the greenhouse. If you have a Home Depot nearby, I know that they handle either the Williams or Empire heater. If you are a gambler, you might also try e bay. I bought the Kozy heater from a e bay listing and it was brand new and was about 1/3 the cost of a regular retail store. Another nice thing about these heaters in this BTU range is that they operate off of a thermopile so they need NO electricity to operate.

Ray · #3 12-01-2007, 12:02 PM

I did a quickie calculation using my Heater Sizing Calculator using 600 square feet of surface area, a 0° minimum outdoor temp and a 50° desired minimum interior temp, and came up with 19,000 BTU's needed. At that, it seems that a Souther Burner heater is probably a good idea.

I would definitely opt for a vented- versus a non-vented heater.

Jerry Delaney · #4 12-01-2007, 02:55 PM

I think that all the heaters mentioned are available in a size up to 25,000 to 30,000 BTU input. Southern Burner is a time tested greenhouse heater, but the others will work as well. I did not address the issue of vented vs non vented, but I think Ray is 100% correct to definitely use a vented heater. I do know some people who say that they have successfully used non vented heaters and I have tried it myself. Result - way too much water vapor produced and lots and lots of bud blast.

chulaorchids · #5 12-14-2007, 02:30 AM

Souther Burner is the way to go. Inexpensive for a heater nowdays, I think vented it's $485.00, it has the big advantage of using a 750mv Honeywell valve that does not require line voltage. Power goes off, no problem!!

orchids3 · #6 12-14-2007, 06:22 PM

The Southern Burner is a good way to go. Those I know who use them are having good luck and it is designed to be used in a greenhouse. I used a non greenhouse heater once before in a previous greenhouse and it rusted out - I dont believe you will have that problem with a Southern burner.

Jerry Delaney · #7 12-15-2007, 04:52 AM

I just noticed that I misspelled the name of Cozy heaters (I had it spelled Kozy). Maybe they are both the same company for all I know. Southern Heater is a time tested, excellent heater but I have used Williams heaters for many years and have never had a problem with them. The sealed combustion chambers on all are of stainless steel and other than the metal shroud, I have personally never had a problem with rust. I added on to my growing space this spring and found a 25,000 BTU input Cozy direct vent heater brand new in the box on ebay for <$200 including shipping. I do remove the heaters each spring. It only takes about 10 minutes. Perhaps that contributes to the lack of rust problems.

orchids3 · #8 12-16-2007, 12:24 PM

If its stainless steel Its probably ok!

Jerry Delaney · #9 12-17-2007, 02:12 AM

Quote:

Originally Posted by orchids3

If its stainless steel Its probably ok!

Boy, I sure hope so. I'm going to be really upset if it isn't! So far, it's working like a charm. I'm also glad that Ray jumped in with his calculation on heater size. The reason I added the Cozy heater was not only because I added space but also that last winter it was cold for a longer period of time and the minimum temp much lower than usual. The Williams heater just couldn't keep up. Having installed an undersized heater is just one of the many things that can make one feel really dumb!!

Ray · #10 12-17-2007, 09:38 AM

Someone needs to design a heater with a proportional controller and a burner that's super efficient at all fuel flow rates. Right now, most are simply on-and-off at full flame, which is wasteful.

Heaters are working at their maximum efficiency only when the heater itself is up to temperature. Once the thermostat tells it to shut off, it cools, only to need reheating. That's why it's foolish to buy a way-oversized heater, as it will come on, pump out large amounts of heat, then shut off too soon for it to level out. What you want is a heater that stays on for long burn cycles of moderate output instead.

Ideally, a heater should be on at all times, adding energy at exactly the rate it is being lost. If anyone can devise a control/burner combination to do that, they'd get real rich.