Greenhouse heaters

What do all of you use for heating your greenhouse during the winter? I have a 15 X 20 greenhouse with double plastic cover. I tried a 1500 watt electric space heater, but it doesn't always keep things from freezing in there.
Also lights. I ran two 100 ft. extension cords from my garage underneath and up into the greenhouse and rigged shoplights. They were working fine until about a week ago and now none of them will turn on. The lights themselves are fine, because I brought one inside and plugged it in and it worked. Something haywire between the garage outlets I'm guessing. Got to be a better method. Help!!

Are your extention cords plugged into a GFCI outlet? If so it turns itself off when it sense a problem (like water in the cords). Also maybe your cords are not rated for outdoor use? Have you checked your fuse box to see if you tripped the fuse?

MollyD

Molly, I don't know what a GFCI outlet is, so can't answer your question. The cords are outdoor use rated. Currently, my garage is full to the rafters with firewood. As soon as I'm able to dig my way to the breaker switch box, I'll be able to answer your last question. I strongly suspect that it was tripped.

Bill

A GFCI outlet it the ones used wherever there is a danger of something electrical dropping into water. They have a little reset button on them. GFCI stands for Ground Fault Circuit Interuptor.

MollyD

I bought a blue flame natural gas heater for my greenhouse which is 12 x 12. Then I installed a ceiling fan in the middle of the greenhouse to blow all of the warm air down. I really like it and it does a good job, unless you forget to turn it on. It was really hot one day so I decided that I did not even need the pilot light lit and then it turned cold fast, and got to about 50 degrees in there. But when I got home I turned the heater on and it warmed up really quick. We have so many problems with our power company here so natural gas was the best way to go in order to make sure the greenhouse stays warm. We were without power a few days ago because of our old breaker box and it sure was nice to have heat for DH and me and my greenhouse since it has been about 25 degrees here at night.

Jesse

I'm guessing that one would have to hook up to a natural gas pipeline...how expensive is your heater to run and how expensive to buy? I like the ceiling fan idea, regardless of the source of heat.

Bill

Lettuceman, if it isn't the breaker, it may be the GFCI as Molly pointed out. I'll just add that garage outlets are supposed to be GFCI protected, I think. GFCI protection can be "downstream." Just because the outlet you are using doesn't have a GFCI on it, doesn't mean that a tripped GFCI is not your problem. Check and test surrounding outlets and you may find one nearby that provides GFCI protection to all of the outlets wired "downstream."

Re: gas/propane heaters, that's a whole new thread, right Molly?!?!? Plantcrazii, there are those who believe that unvented heaters such as the Blue Flame should not be used in greenhouses. If they are used, be very careful that you follow the manufacturer's recommendations on venting. Generally speaking, you want 1 square inch of vent opening for every 2000-2500 BTU of heater capacity.

SB

Heaters have been a very "explosive" subject here (LOL). There are as many viewpoints on the subject as there are choices. Regulations vary not only from state to state but often by communities so it's important to check these out as well when you are trying to decide what you'll choose to heat your GH. The cost of running a heater will vary according to several factors. Among these are the following: the size of your greenhouse, what it's made from, how you insulated it, how well did you seal air leaks, what plants are you trying to grow in it, how cold and windy does your area get. There may be other factors that I've forgotten at the moment.
As to type of heat to choose, well after checking the laws in your community, you'll get to choose between gas (propane or natural), electric, and alternate. By alternate I'm referring to things like wood stoves, pellet stoves, etc. A few individuals have chosen those. I'm not even going to tackle the issue of vented gas versus vent-free gas stoves! Don't want to get burned by the topic!!!
My own hoophouse (17'L x 8'W x 7'H) is currently using a Mr. Heater Big Buddy propane heater along with a 1500 watt milkhouse heater. I grow daylilies so I can have temps down to 35 degrees without fatal damage. I prefer days up to 80 and nights no lower than 45.

MollyD

I live in Granville County, NC - reasonably close to Plantcrazil in Durham. I have a 10 X 20 GH and use two small electric heaters. This is the first wiinter for me with a GH so I really can't speak as to cost - let you know more about that by March after several cold months. It has been really cold for severaldays and when it has been 22 outside at night, the GH has stayed up about 43. That's not bad - not enough for tropicals maybe, but good enough for cool GH plants (the hibiscus, lemon, banana plants seem to be surviving okay and everything else seems happy). As long as it stays in the 40's inside, I think it will be okay - no freezing of plants. The lettuce bed looks very happy with those cool temps. Now when I try tomatoes, the story may be different. Also it remains to be seen how much all this will cost. I got a couple of small portable propane bottle heaters (Big Buddys) in case power goes off. We don't have a lot of trouble with that so far (Wake Electric seems pretty good - better than Duke Electric in Durham).

I have an 8x12 Rion that I've placed two 1500W heaters [1], each plugged into a thermostat [2].

I have the thermostats set to 63F degrees, and the coldest it's been in there, that I've seen, is around 58F. We've had nighttime, outside air temps in the single digits, and I didn't go in the greenhouse until a few hours later. I didn't want to lose any heat that was already in there. When I did enter the greenhouse, it was in the 20's outside, but still 58F inside. My goal is to keep things above 50F, but if I can keep it above 55F, I'll be more than pleased.

All of these temps so far have been reached without my closing off the fan and intake with plastic, yet. That's on the agenda for this weekend. I've also noticed under each roof joint, there's a small air gap. For now, those will stay. At least they provide some air-eggschange with the outside. If, after sealing the fan and louvers, my temps aren't holding well, then I'll address the small holes with some silicone caulk.

I was worried about the electric bill skyrocketing, with two space heaters running a lot, but so far the DW hasn't been anything but eggstatic with the bill. We have steam heat for the house, from an oil-fired boiler. The only electric it uses are for the thermostat upstairs, and the electronic ignition on the boiler. So, using the space heaters should show a significant difference in our electric usage, over past winters, but so far it's negligible.

I also have a 5500W gas generator on standby, between the greenhouse and the house, just in case. I've had to use it once (only for the house, before it got cold outside), and almost had to use it the other day, when a squirrel decided to climb into one of the transformer boxes on the utility pole. This happens about 3 times a year. This time, my daughter (13) had the presence of mind to call me at work and leave me a voice mail, "Dad, I just wanted to let you know that the power is out, and there was a big explosion outside. I'm leaving for school now, but just wanted to let you know. Bye."

I knew right away it was a squirrel. I got the message, apparently right after she left it, and rushed home (45min one way). As I pulled up, the power company had already removed the squirrel, and were about to fuse the link. No reason to fire up the generator this time. I got a cold day off work. My daughter got to pick the dinner for that night, from wherever she chose. Everybody won. Well, except my son. He wasn't pleased, having to shower in the dark, HEH.

Anyway, that's my greenhouse heating system. The second heater was probably overkill, but I figure with two it may be a bit more efficient. One is just inside the doors, pointing into the greenhouse. The other is halfway in the greenhouse, also pointing to the rear wall. This seems to be a good placement, and about the only improvement I can see would be to add a couple of small ocillating fans, to circulate that warm air. That's not doable until spring, when I finish installing the electric and plumbing in the GH.

[1]. http://www.greenhousemegastore.com/prodinfo.asp?number=HT%2D2000
[2]. http://www.greenhousemegastore.com/prodinfo.asp?number=CT%2D1000

HTH

Eggs, can you post some pics of your greenhouse? I'd like to see it.

It's a wreck, right now, sb. It's only function this winter is to survive, heh. I had only time to build 4 benches and throw everything in it, before it got cold. I'll try this weekend, between finally putting up my xmas lights (which this year includes adding two breakers, specifically for the xmas lights, since I have the heaters going in the GH on the circuits I used to use for the lights), and xmas shopping with the DW, to take a couple pics and upload them.

That reminds me that I also need to shoot off the rest of the roll of film on a 35mm, which I think has some construction pics of the GH. I can't remember which camera has those... LOL

*adds another thing to the to-do list* (Thanks, sb. =P )

Lettuceman, Did you have the the electric heater plugged into an extension cord? If so, that could have been what tripped your circuit breaker. Even if you do not have a GFCI installed, your breaker could still tripp because of overload or moisture etc. Are your lights in the garage working? The other question would be "what ratings are your extension cords?" 100 ft. is a long extension cord. You might consider doing what I did as I ran electricity from my garage to my GH which are 50 ft. apart. On all of the outside wiring, I used 20 amp outdoor electric wire (which is gray). First I ran two seperate wires to my garage from my main breaker box. One is a 15amp breaker and the other is a 20amp breaker. I wired my garage with lights and outlets. From the garage I ran two outside 20amp wires underground to my GH. I installed my lights and 15amp and 20amp outlets. I am careful not to run any heavy usage equipement in my garage and my Gh heaters at the same time.

You can ask your utility company about the cost of heating. In my area the cost are as follows: 1. electric 2. propane. 3. natural gas 4. pellet stove 5. corn stove. 6. wood stove (if you collect your own wood) 7. solar. (We don't use oil or coal.) Of course a major consideration is the cost of installing a system and what your return on the dollar will be. I start my GH up around the first of the year and I use electricity and I am in the process of making my own solar panels to supplement my electric heat. At least one will produce AC and the other ones DC. Even making my own, they will still cost quite a bit as solar cells are expensive. It is more of a challenge at this point.

There are 3 types of GFCIs. The receptacle type which will protect the installed receptacle and anything downstream in a branch circuit from ground faults. The circuit breaker type which is installed in a panel box which will protect anything downstream from that circuit. The 3rd one is a portable one which can be plugged into a receptacle or they are preinstalled in an extesion cord. The National Electrical Code has required GFCIs for sometime and they keep updating it so chances are you have one or more GFCI breakers depending on when your house was built or the wiring updated. I have been shocked quite a few times and I don't mind them but in certain conditions and electrical shock could kill a person.

stillwood, I grow a lot of tomatoes and I like to keep my greenhouse above 55 degrees.

Eggs, I trap the squirrels in my area and turn them loose after I have crossed a river. When asked what happens if the return? I reply I will take them half ways across the river.

Good post, bluejack. I'll add that generally you don't want a load of more than 80% of the circuit capacity. So a 20amp circuit should not have a load that exceeds 16amps. If you have a 15amp circuit, a 1500 watt heater that draws 12.5 amps has your circuit sort of maxed out and there is no capacity for fans, lights, etc. That could be your problem, too.

Eggs, you can buy a big roll of foam insulation (mine is blue and about 6 inches wide) at Lowe's. I bought that last year and taped it over or shoved it into any openings on the Rion. I also taped a piece on the fixed door so air would not come in the crack between the doors. It did help.

I bought a kerosene heater last year at Tractor Supply to heat the greenhouse in March for starting seeds and cuttings. It worked really well and cost about $4 a night for Kerosene. I did not heat during the day unless it was very cold. I also have the 8x12 Rion.

Blue, my heater was plugged into a surge protector, which was plugged into the extension cord leading into the garage. The heater just quit and I've not been able to get it to work at all, even tho I brought it back inside the house. I was always careful not to run the lights and heater at the same time in the GH. The lights still work fine out in the garage. I'm sure that once I dig the firewood away from the breaker box, I'll find that it's been tripped.
This is my first year in the GH, and I knew it was going to be a learning experience. I plan to take your advice and consult with my utility co. Will likely talk to a knowledgeable electrician in my area too.
The other factor in all this is the cost. My power bill went up $25.00 above normal last month. While that's not totally unexpected, the cumulative effect over the course of this winter could be considerable.

Bad,

There's no crack between the doors, since I put that heavy rubber strip that came with the kit, on both doors. They fit so tight now, you actually have to give them a "tug" when you open them, and a good shove to fully close them. =) So far, the only real visible gaps are the small holes where each support piece on the roof meets the top of the sidewall. I'll probably run a bead of silicone around the base, just for good measure, when temps warm up enough to do so. At that time, I'll decide if I want to plug those holes by the roof. I almost like the idea of their being there, just for air exchange on days I don't open the doors and go in.

I thought about a kerosene heater, but was worried about ventilation. Electric was much cleaner, and so far these seem to be quite efficient. As long as I'm home, or near home, if/when the power goes out, I should be ok with the generator. Worst case scenario is the power going out, after everyone's left the house for the day. If that happens, I'll consider it "fate", and start over, heh. Almost everything in there is easily replaced. Should it get cold, a lot of things in my GH would simply go dormant. Of course, I'd lose my hibiscus and ficus, and my shrimp plants (which would probably be the most difficult to replace, at least until summer gets here). Most of the rest of the plants in there consist of different ivy's that I saved from my hayracks.

I guess I try not to think too long on "worst-case" scenarios. I have planned as well as my resources allow me, I think. It will be the first winter with the greenhouse, and considering it's really only 80% built, I'll say "so far, so good", considering the winter-like weather that we've had, recently. So far, it's survived 70+mph straight line winds (even before the weatherstripping was in place), low single-digit temps, horrendous downpours, and a nice round of ice/sleet/snow. The structure seems stronger than I could have imagined, considering the materials that it's made from. Plastics have sure come a long way, huh? =)

My biggest drawback so far, is one heater must be plugged into an outlet that's on a "busy" circuit. But, it was really the only one available. It has been decreed to the little people of the household, that noone is allowed to use the microwave, while the dishwasher is running, until spring. =) This makes it the biggest drawback, mostly because I now must make sure I overfeed them at dinner [1], so they're not wanting to pop popcorn, until at least such time as the dishes are done. This is no easy task, with two teenagers. I mean, it's like a whole hour after dinner, that they can't eat! ;)

I'm off to install breakers, outlets, and xmas lights. Then, if there's still light out, I gotta get all the salt off my truck, *sigh*. HAND! =)


[1]. This can be quite eggspensive!

Lettuceman: I suspect the heater was burned out due to the 100ft. extension cord being lightweight. I would question the need of a surge protector however it should not have been a cause for your problems. What you might want to do is purchase 15amp outside electrical wire however long you need it from the garage to your GH. (I assume your circuit breaker is 15amp). You can put heavy duty male and female plugs on the ends. These plugs are almost always yellow and you loosen screws to take them apart to attach the wires. The wire could be used later when you wire direct from outlet to outlet so buy it a little long. I sugguest 15amp wire as it is easier to work with and will run a heater and lights at the same time. Shop at a store where someone can help you with questions. If I ran a second wire, I would run it from a different breaker. Keep in mind a GFIC breaker has a reset button. You may want to buy a "how to" book on electrical home wiring at a box store. Charleysgreenhouse.com and GrowersSupply.com offer some bubble insulation (like shipping bubbles) that they claim will reduce heating cost by 50% and also help on cooling in the summer. They say it will last 4 years when installed inside of the GH. I have used packing bubbles as insulation on windows in the past and it seemed to work real good. It is wise of you to ask questions, when green you grow, when ripe you rot.

I agree with Bliue - there's no need for a surge protector.

I agree with Eggs too - there comes a point when it doesn't pay to insure. When you number is up you pay the price.

About being away from home, it wouldn't take a rocket scientist to program an old PC with a remote thermostat to call you on a cell phone. Hmmm - sounds like a possible Winter challenge! One time away from home on a WInter vacation, I rigged up a flasher and a battery connected to a red light pointed at the neighbor's house. At least if the heat failed when they were home they would see the flashing light. There are a lot of tricks you can play if you have the time and money. And, of course, there are commercial systems for remote monitoring and alarming.

Finally a nice day here today and the snow and ice of last week is finally melting.
Dave.

Instead of investing in monitoring systems, why don't you just run some electric service to the greenhouse? It's the safest, most economical, thing to do. =)

Lettuceman, to follow up on Bluejack's post, if you do run a wire to the GH, be careful what kind you use. The NM Romex you get at the local hardware store is not the right stuff. If you're talking about a damp or sun-exposed location, you should use wire specifically rated for that use. And anything buried should be in conduit all the way.

Hoo Boy! I feel like I've just been through an electrical engineering school. I thank all of you for your advice and expertise. You've given me several options and avenues to explore and I genuinely appreciate all of you. I'll probably just hire an electrician to run a line out to the GH and then choose the most economical heating system.
Gonna cost money no matter which way I get it done, but what doesn't cost money these days? At least I have a far better idea of how to proceed, thanks to all of you.

Bill

Bill, I halfway agree with Stressbaby...don't use NM Romex for underground, or better yet, make sure your electrician doesn't use it. Just to keep a check on who you hire ask them what wire they use for underground, they should only use Type UF (some counties will accept/require Type TW with conduit). Type UF doesn't need to be in conduit so you could save yourself the cost of the conduit.

If you bury it deep enough there will be no incident of hitting it with a shovel but it would also be good to spray paint bright orange or put a board over the trench "just in case" someone digs there one day.

I'd also recommend no less than a 20 amp breaker. This will give you much more options and the cost is apretty much the same as a 15 amp line.

Wish I lived closer...I'd come do it all for ya, and only charge you a big smile and a cold beverage!

Shoe.

My biggest thanks to you for that valuable information, Shoe! Especially the offer to do it all for me. I'll always have a big smile for you, and if your ever decide to mosey your way here, I'll make sure you have all of your favorite cold beverage that you want!

Bill

Yay! Thanks!

This past October I wandered around for a week or so, made it as far as Arkansas and lower Missouri. Maybe next time I get to take off I'll try to go even farther west!

And now, relating to greenhouse heaters, time for me to go take mine apart, do its annual cleaning, put it back together and in the end... I'll be sporting my "chimney sweep" look! Covered in soot I just can't help but sing, "Chim chiminey, chim chiminey, chim chim chereee ♫"!

Shoe

Shoe, if ever in central Missouri, give me a ring!

SB, I'd love to! Thanks for the offer. And if I knew where you were when I was in lower Missouri I would've made it a point to venture further into the state. Maybe I can swing by your place on the way to Lettuceman, eh!?

Shoe.

lettuceman,
I am not sure what kind of heater you are using, but there is one cheap fix that has not been mentioned here that might help. I have the small electric heater from Charley's Greenhouse, the little compact white one. (I am traveling on business, so that is as good a description as you will get out of me today since I forgot the brand name.) It is a wonderful heater but it hates dust. Goes comatose with dust. When it will not go, I take it to the air compressor and blow it out. Then it starts up fine. Since that discovery I store it in a plastic bag when I am not heating the greenhouse.

Thanks for the tip, Mulch! I will definetly check out Charley's Greehouse little white compact heater. Think I have their latest catalog around here someplace. For the rest of you following this thread, I located the GFIC button in the garage, re-set it and viola!...back in the light business out in the GH. Now, about that heater....

Bill

Yay! Congrats on the lights! And finding the GFCI.

As for the heater, I wonder if it has a reset button on it; you might want to look for that. Also, many electric heaters have "tip over" safety switches. If it got tipped over it would cause the power to halt; maybe you could gently jostle it and see if that releases the tip-over switch.

Shoe.

Lettuceman,

I believe the heater you're looking for is the one I linked to, in my first reply to this thread.

Could someone tell me where to find out more information about blue flame natural gas heaters and how they might not be good for my greenhouse? I did not see any more mention here so I guess it is on another thread. Please give me a link if there is one.

Jesse

I have a Daton greenhouse heater..15,000 BTU---220 volts..
I keep it on the lowest setting...does mega job
My greenhuse is 16 X 8....

I have been eyeing that Blueflame heater also. The 30,000 BTU one. Found it @ whiskey-rock.com for $199. $25. shipping. Looking about, that looks to be a great price. There is a similar one @ Master Distributors same BTUs different make for $219. shipping included. Only one snag......
They won't ship it to California. The one state on their "can not ship to" state map! Wouldn't ya know it? Right now I have an oil-filled elect. heater, the 600, 900 or 1500watt kind. It seems to be doing an OK job until it starts getting down in the low 20s. Then it gets too cool in there, still above freezing but way too cold for Brugs. Also when the power goes out, & it does here, The gas would keep going.

BJs, the reason for that, I would guess, is that CA has the strictest laws against vent-free heaters.

Just to throw in my 2 cents about non-vented combustion heaters: Last winter I started out with a kerosene bullet heater. These are the heaters that throw CRAZY heat very quickly by burning kerosene in an almost flame-thrower pattern out the front of the heater. It had a very strong blower so it would circulate the hot air quickly. It had a thermostat built in, so that was very handy. It was way overkill because it was like 65,000 BTUs for my 12x16 greenhouse. It gets cold in zone 6 PA, but not that cold! Anyway, there were many cautions about carbon monoxide and it did get stinky in there (you can't smell carbon monoxide), so I decided to bring home a gas meter from work. I got *zero* PPM carbon monoxide. Yes, I know how to work the meter. Any truck cold-starting inside one of our garages will send the meter into a frenzy of beeping.

After doing a lot of research on the internet about BTUs of different fuels and BTUs of electric watts, I came to an interesting conclusion. I don't have the numbers handy, but to sum it up, when converting electric BTUs into my kerosene BTUs, using electric would have cost me an equivalent of paying about $3.09 per gallon of kerosene. These numbers were based on my cost of electricity at my house. I was paying $2.75 per gallon of kerosene and I hated it. I decided to switch to electric heat half-way through the winter because it was quiet, easy, and clean. No more hauling jugs of kero around, splashing stink on my hands and clothing, spilling toxic fuel on the greenhouse floor, smoking up the place, waking me up at night when it fired up, wondering if it would burn down my house, etc. I was willing to pay the extra few cents to get the same thing accomplished using electric.

You can do the same conversions for any fuel and then compare costs. I have no idea what electricity or kero costs this year and I don't care. I use a 5,000 W electric heater (220V) and so far this year it's more than enough of heat to keep my greenhouse at 70 degrees all night already having a few nights at 15 degrees outside.

This message was edited Dec 27, 2006 9:42 AM

Hey Stosh,

Good Boy, Nice little note...
I , and I'm sure alot of others would love to see what your elecrtical operational costs
finally turn out to be after a month or two.

Propane and Kerosene is also very expensive here in S.E.Mass. Your caution
and diligence to heating relatives are to be applauded.

I have a (well insulated) 10x12 outbuilding in which we are storing our Tropicals this
year. We want to build an 8 x 14' GH in the spring, "God willin". But for now we
are also using an oil filled electric heater to do the job. Way too much moisture for this little building.

Very interested to hear your elect. kwh rates & usage in the months to come.
Hope it really works out great for you and your plants.

Merry Christmas, keywest

OK, here goes:
My electricity is billed at tiered levels (the more you use, the cheaper it is per KWH). Since I already have to run everything else in the house anyway, I can figure the greenhouse heat electricity rate at the cheapest. PPL (Pennsylvania Power and Light) charges me 0.04564 for generation, 0.01862 for distribution, 0.00605 for transmission, and 0.01114 for transition, whatever that is. That's a total of $0.08145 per KWH. Since electricity gives 3413 BTUs for each KWH, that's about $0.00002386 per BTU. That number is pretty ugly, so I'm going to make a wild guess at a mid-winter electric bill increase of $100 per month. That's about 4 million BTUs, so let's use 4 million BTUs as our standard to compare.

4 million BTUs from my electric = $95.46

Kerosene has about 127,000 BTUs per gallon, so to get 4 million BTUs, I'd need 31.5 gallons of kerosene. I haven't looked this year, but last year I paid 2.75 per gallon. I have no idea if it's up or down this year.

4 million BTUs from kerosene = $86.63

What's interesting is that electric heat is always 100% efficient, but fossil fuel heat is not. It depends on the efficiency of the heater, but I suspect bullet heaters like I have are very close to 100% because there is no exhaust for heat to escape unused. The only problem that could arise is if the kerosene isn't being 100% burned because of a dirty nozzle not atomizing the fuel to the best of its ability. So you can see that at least with the cost of my electric, I'd be really crazy not to pay the extra $9 per month to have quiet, clean, safe, convienent heat.

While the numbers are handy, propane generates 91,500 BTUs per gallon. That would take about 43.7 gallons to make 4 million BTUs. Last time my Dad ordered propane it was about 1.60 per gallon. That's about $70. But remember, only a non-vented heater will created this much heat for $70. A vented furnace, depending on age and design, can be anywhere from 60% to 90% efficient. Let's say you have a relatively modern furnace which would range from 80% to 90%. So 85% efficiency would cost $82.29 per 4 million BTUs.

I already have an oil tank to heat the house, so if I purchased another oil furnace, I could do that. Oil gives 140,000 BTUs per gallon, so 28.6 gallons would give the proper heat. I don't have a bill handy, but I think it's around 2.50 for oil. At 85% efficiency that's about $80.

After looking at all these numbers IMHO you'd be nuts not to go with electric. The heaters cost less up front and don't cost that much more to run. But the other benefits far outweigh any of that - no stink, no danger of fumes, no refilling fuels, no storage of fuels, no loud burners, no spilling of fuels, etc. If you're on a tight budjet and have land with trees, you certainly can get cheap heat from wood (or corn), but that's not convenient. Some people say that when the electric goes out I'm sunk, but almost all other forms of heat that run on a thermostat use electricity to control it. My kero bullet heater would also quit when there's no electricity. My backup is a 40 lb propane tank with a burner on top - no thermostat, no electric, just heat. My community has underground electric wires so we've been very lucky with continous power. In the 8 years I've lived here the electricity NEVER went out for more than a minute.

I hope somebody gains from this info.

Stosh, very nice analysis, good job.

I would add a couple of things. "Almost all other forms of heat that run on a thermostat use electricity to control it." I assume you mean "from the grid" and subject to loss of heat in the event of loss of power.

The Empire DV heaters I use come with a microvoltage thermostat, standard. This thermostat is powered by a "generator" at the pilot light and the circuit is independent of the power supply to the rest of the greenhouse. I will not lose heat in the event of loss of power. I do not know how common these systems are, but I suspect that they are underused.

Second, regarding vent-free heaters, I think in addition to CO buildup, another problem is plant damage from ethylene. For everyone else, the vent-free heaters are not really vent-free, they generally require some outside air exchange. Stosh, I suspect you were as attentive to the ventilation requirements of your kerosene heater as you were to your energy calculations, and that this is why your CO levels were zero!

SB

SB, I was not aware of your kind of heater that does not use 110 line voltage. That is very interesting. Thanks for sharing that.

As far as being attentive to the ventilation requirements for my kero heater- unfortunately, the answer is no. It probably had more to do with my greenhouse not being air tight. I have a home attached greenhouse and the joining of the 2 buildings was not very well sealed. I wasted a lot of heat last winter because of that - especially on windy nights. This year I believe I solved the problem and the heating bill went down tremendously.

But there is one more area of discussion where I think many people will disagree with me. In my experience it is possible to burn fossil fuels without releasing any CO. CO is created by the incomplete combustion of these fuels. From chemistry class these fuels are just hydrocarbons that when burned properly release CO2, water, and heat. I think my kero bullet heater was either new enough, or designed well enough to burn cleanly. With the insane amount of fire, wind, and heat that it threw when it was on, and the very sensitive measuring capability of the gas meter, *something* would have shown up on the meter while the heater was running no matter how good the ventilation was. This is by no means a green light for everyone out there to burn fossil fuels and not worry about ventilation. My sloppy greenhouse seal eased my tensions about ventilation, but it wasn't planned that way. CO is a VERY dangerous gas and should never be taken lightly. It's not like people think - you don't just smell something and leave. You get the classic symptoms like headaches and nausia, but you also get disoriented and can't think clearly enough to get out. You just lay down and die. I know because it happend to someone close to me. This is part of the reason I went to electric.

Stosh