They are electric resistance, and thus are no more or less efficient than any other electric resistance heater. You also don't get to use the CO2 generated in the production of heat. I think their claim for most efficient is pushing the boundaries of the truth...

I would just buy a sealed oil radiator if you want to use electric heat - you can buy a 2.5kW one here for about $25.

heebiejeebie,
The econo heat electric heaters will work just fine in a greenhouse. However, there are several other factors to consider in getting the most cost effective electric heater. Where do you plan to use these heaters? If you can give the size of greenhouse, temperatures you are dealing with, etc,more specific answers can be provided. For example, a 1500 watt heater can be used in a standard 110 volt , 20 amp circuit. The 2.5 kW recommendation in a prior post would not work under these conditions. Also, the only way to "get to use the CO2" is to use unvented propane or natural gas heaters, which are illegal in some states, for good reasons.

I have a 8 by 6 HFGH.
I live in Buffalo, NY. I plan using it to start seeds beginning in Feb.
Temps in Feb usually hover in the 30s, though sometimes it dips to the 20s or teens.
I'd like the temp to be at least 55-60.
I'll insulate the greenhouse, too, if that would help. Not sure what would help.
I could tolerate my electric bill increasing by 50$ a month for those months. I also would consider a gas heater if I knew which type worked.

heebeejeebie,

I'm in Canandaigua. Currently I'm using an electric heater to keep the GH at 35 (lowest night temp). I've been eyeballing the non vent propane heaters at Lowes and trying to calculate how much propane it would take to heat it the same. After your winter storm knocked the power out it got me to thinking of the same thing happening here.

MollyD

Heebiejeebie,

I ran your numbers through a heating calculator. If your minimum low temp were 20F, you could maintain 55F with a single 1500W electric heater. However, you list zone 6, which generally gets a low temp of -10F for the purposes of the heating calculator. Using -10F, you'll need 9828 BTU, and that would require two heaters (each 1500W heater is about 5120 BTU). Two heaters will generally mean at least to circuits.

We can calculate your heating costs if we know your average Feb temperature. I just quickly Googled it and didn't come up with it.

[quote]Also, the only way to "get to use the CO2" is to use unvented propane or natural gas heaters, which are illegal in some states, for good reasons.[/quote]

Only in a few states, such as California and Wisconsin, and in a number of municipalities. Even then, usually it's only illegal in houses. So, unless you're living in your greenhouse . . .

Be smart about it, and get a carbon monoxide detector. However, there's no reason for paranoia. Even without a detector, most modern propane heaters have oxygen depletion sensors.

If you want to talk about hazards, let's talk about an electric heater surrounded by all of the moisture in your typical greenhouse . . .

I should add that, also, many states differentiate between portable and fixed heaters.

MollyD!

I was in your neck of the woods recently. I was staying in a B&B in Honeyoe and hung out alot in Canadagiua. I'll be coming back soon!

How much does the heater spike your electric bill? What do you use the greenhouse for? Which greenhouse do you have?

Stressbaby:
Ooooh I found a site that gives more buffalo weather: http://weather.msn.com/local.aspx?wealocations=wc:USNY0181 Scroll down for a monthly graph

Feb Average Temps: 19-33 degrees, Record Low -20 degrees

I'm not planning (so far) to use it in the deep of the winter. Yes, sometimes it DOES get below zero here, but that's more often in Dec-Jan.

I should probably get a propane back up heater (sigh... cost...) since we lose power every now any then. We lost it for 4 days this year and in 2002 we lost it for 5.

Our "zone" is misleading. Our weather is so strange here, because of our position next to the lake. There is NO consistancy in how the weather will be year to year.

So I'm thinking an electric heater, plus a back up propane heater.
Or just a propane heater.

I don't care about illegal CO2. I'll get a carbon monoxide detector.

Here is the Monthly data for Buffalo for Feb of this year

BUFFALO`S FEBRUARY STATISTICS FOLLOW...
TEMPERATURE DATA
AVERAGE MAXIMUM............ 34.2
AVERAGE MINIMUM............ 21.4
AVERAGE MONTHLY............ 27.8
DEPARTURE FROM NORMAL...... PLUS 1.9
HIGHEST.................... 61 ON 17TH
LOWEST..................... 7 ON 19TH
NUMBER OF DAYS
MAXIMUM 32 DEGREES OR LOWER..... 15
MINIMUM 32 DEGREES OR LOWER..... 23
MINIMUM 0 DEGREES OR LOWER...... 0
HEATING DEGREE DAYS...BASE 65.. 1034
DEPARTURE FROM NORMAL.......... MINUS 76
SEASON TOTAL FROM JULY 1....... 4207
DEPARTURE FROM NORMAL.......... MINUS 597

Seems to indicate that about 20F is the average Minimum Low for Feb. Although the departure for average is kinda extreme at 7F. Yikes 15 days where it never got above freezing, but clear wx should allow for solar heating to get the GH up to 55-60 during the day.

What is really surprising is the Tiny difference between max and min temperature(I would love to have a 13F degree avverage difference between high and low temp), I guess that is from the heat sinc effect of being so close to the water.

I was wondering if Heating Degree Days could be used to determine heating requirements for a Greenhouse. Admitedly HDD is based on Heating to 65 Degrees, but there should be some sort of adjustment that could be used to compensate for a lower target temperature...

Sounds like a Job for Nathan

A friend and I tried to correct HDD for other temperatures. If you assume that the curve is a sine wave over the year, going from the coldest in feb(july), to the hottest july(feb) and with a mean defined by the HDD then you can draw a graph and work out the area under a given temperature (or integrate asin). Unfortunately, this doesn't include the variance of the temperatures (especially if you have things like lakes to put lumps in the sine wave).

To see this, if the year were only two days long then 100F, 35F would have a HDD(65) of 30; similarly 50F, 50F would have a HDD(65) of 30. But if you want HDD(50) the first is 15, the second 0! In practice the weather is better behaved, but not enough.

In conclusion, if you want HDD to say 60F, that is doable fairly easily, but for a greenhouse you are more interested in HDD to say 45, and the error is too much to be very practical.

Having said that, if you have monthly climate data, you can use the mean minimum as a reasonable starting point for working this out. Better is to use Karen's gmodel to get quite accurate estimates of performance. Perhaps if you are interested in that, and are intimidated by the code, tell me (or perhaps Karen?) your postcode and some basic details and we can try it out. (This is useful to us to tune the model over a wider sample)

Re: CO2, all the commercial growers I know seem to not care in the slightest about ethene from natural gas heaters (which are more common here). There is at lot more ethene in natural gas than LPG (often called propane, but actually a mixture of lots of similar hydrocarbons) Carbon monoxide is a danger, as is high levels of CO2 in well sealed greenhouses. Both are monitored. I have no idea the effects of things like NOx (smog), although a 10 second search indicates that at least N2O and NO are plant active. Practically, unless you are trying to get 100% recycling of everything (perhaps for your space station or biosphere 3 project) the natural leakage rate of greenhouses seems enough to make this not a big deal.

Has anyone tried using fermentation for heat and CO2? An aquatic plant grower I know brews a lot of beer for this reason, but he says that you need to know a lot about both to make it economically attractive.

Re 2.5 kW heater, I forgot that the US has only 110V and the lower power ratings that result.

Hmm, I never thought of Fermentation... I do some brewing, but I do not think I do enough to stabilize the greenhouse, and since I still can not get my Day/night GH temperature variations to less than about 35 degrees, it would not be good for the Brewing... It would be good for the GH, but the fermenting beverages really need to be kept to a Temp of Plus or Minus 5 degrees, but it is definitely something to think about in the future

If you are producing a significant amount of CO2 (remember there isn't much in the air) you might pipe it from your vats to the greenhouse. Fairly quickly the gas coming out of a fermentor is nearly pure CO2, and air normally is 0.4% CO2. So you don't need much CO2 to top up the greenhouse. (someone can work out how many einsteins per L of CO2 I guess)

People who grow water plants probably care a lot more about this (birdwidow?). Better to bubble your CO2 through your tanks first, as the gas will dissolve more readily that way than the other way.