Plants Suffering from Propane

wolflover(z7 OK)December 13, 2005

I first moved my plants into the greenhouse on October 22. They TRHIVED for the next seven weeks, blooming beautifully and never dropping leaves, until last week when I first used my propane heaters. Prior to that I had been using electric heaters to heat the greenhouse. I try to keep the temperature above 50*. Most plants I grow are tropicals.

Last week we had very low temps in this area and I had to start up my propane heaters. These are non vented, Pro Com propane heaters. Within just a couple of days, the leaves of my plants started yellowing badly and they have now dropped many if not all of their leaves, and all the blooms have died and fallen off. The temps in the greenhouse during this cold spell never dropped lower than 45* and were usually no lower than 50*. I truly believe it is the propane that is causing this yellowing and leaf drop on my plants.

Does anyone have any suggestions of something I could do to prevent this from happening again? Should I have these heaters vented even though they are non vented heaters? Do you think the heaters might be faulty? Sometimes the smell is very strong in the greenhouse when I first open the door, and I can actually smell it when I walk up to the greenhouse some days. (My heaters in my home are hooked up to this same propane supply and I am used to the smell). Last winter I used these heaters almost exclusively to heat my greenhouse and my plants really suffered all winter. Then, I thought it was due to not having shade cloth on during the winter months and it being wayyy too bright in the greenhouse. This year I have shade cloth on the greenhouse and my plants were thriving until I first turned on the propane heaters last week.

I would appreciate any comments or suggestions. It's been painful to watch my plants drop all their leaves and blooms. Thank you for your help.

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I am certainly sorry to hear about your plight. I know very little about tropicals, but I have been doing a tremendous amount of research about growing tomatoes in a greenhouse. To me, the problem that you describe sounds like it is a problem which is a direct result of not having your heater vented to the outside.

I know that you said that it is a non-vented type, but you must remember that in a greenhouse you are typically talking about a lot smaller sq. ft. area of heated space than what you would have in a dwelling. And I know that so-called non-vented heaters can cause severe problems (up to and including death) in small or poorly vented homes. The oxygen in a small greenhouse (especially in a well sealed one) is quickly depleated by a flame and can result in the propane not burning cleanly and completely. The end result is a gas (or gasses) that are highly toxic to humans and to lots of plants.

Here is a direct quote from the "Environmental Control For Greenhouse Tomatoes" .pdf publication from Mississippi State:

"Other than when using a heat pump or an electric heaert, vent all burners to the outside.

Never allow gasses to remain inside the greenhouse, as tomato plants are very sensitive to certain pollutants found in fossil fuel exhaust. Especially with kerosene and propane space heaters, the potential exists to poison plants with toxic pollutants. Also, space heaters may consume oxygen and deplete it so that incomplete combustion may result, producing harmful by-products. Or the lack of oxygen may cause the flame to go out and the burner to shut off. In either case, the use of unvented heaters is too risky for the greenhouse grower."

I know that this came from a publication about greenhouse tomatoes, but I feel sure that the same information can be readily applied to other plants such as your tropicals. If you would like to read more about this, click on the link below, scroll about half way down the page, and click on P1879, "Environmental Control for Greenhouse Tomatoes" PDF link.

Good luck,

Here is a link that might be useful: Mississippi State Publications

    Bookmark   December 13, 2005 at 8:31PM
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weebus(Z8 Sunset 5 WA)

I use a non vented propane heater, growing tomatoes with absolutely no problems. The references being used and the pub being used for info by Beebiz is 13 years old. A lot has happened since then and I would look for something within the last two years for information...

    Bookmark   December 13, 2005 at 8:41PM
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stressbaby(z6 MO)

I think your problem could just as easily be one of temperature rather than propane.

Some tropicals require temps over 55*F. Guava, notably, drops leaves under 55*F. Other tropicals and subtropicals have roots which shut down under a given temp. Citrus roots will not take up water and nutrients under 54*F. Plants like citrus which are heavy feeders can get nitrogen deficiency and winter leaf drop when the photosynthetic processes in the leaves continue despite the lack of water and nutrient uptake in the roots. My lychee tree is suffering from leaf drop currently, and I suspect temps as low as 49*F as part of the problem. Shade cloth helps by reducing the "demand" in the leaves, so you are right to try this intervention.

If you cannot change your heater, I would suggest that you try putting some of the plants in some relative shade with some bottom heat for a while. If you leaf and blossom drop correct, then temperatures may be the problem. SB

    Bookmark   December 13, 2005 at 9:25PM
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I don't know how your were able to date this publication. I have been all over it in Adobe and have not been able to find a publication date. Still, this is not the only publication or place that I have read this. It just happened to be the easiest place that I could locate the inforrmation. Almost any information that I have read about using fossil fuel burning heaters in a greenhouse has said that for safety purposes (human and plant), they need to be vented to the outside. The temps may have played a large role in Wolflover's problem, but I would not rule out the possibility that using a non-vented, fossil burning heaters in a greenhouse has or can cause a toxicity problems.

    Bookmark   December 13, 2005 at 9:50PM
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trigger_m(7b georgia)

i use only propane to heat my greenhouse.this is my second year,and i've never had any heater is vent free.there used to be a lot of posters here on gardenweb.i grow over 100 brugmansia,hot peppers,bananna plants,and many other plants-and they have thrived.this is my 1st year growing tomatoes in the greenhouse,and they have not done well.BUT,i keep the temps a little cold for them.(it's gotten down to 49F).but all other plants absolutly thrive-my brugmansia were in full bloom last january!as far as i can tell,if the heaters are funtioning properly,there is no reason for them to suffer.could be a number of other factors-daytime heat,air circulation,nightime lows.

    Bookmark   December 13, 2005 at 10:30PM
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cottagefarmer(z4b WI)

I have been heating with an unvented propane heater without problems. Mine has an oxygen depletion sensor. Have you checked for diseases and pests?

    Bookmark   December 14, 2005 at 9:14AM
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seedbandito(7 NC)

I'm using a Pro Cam propane heater. Temps are staying between 50 & 55 degrees. I have Tom's growing , too. I noticed some yellowing withered leaves. Upon further investigation, I had pests. I suspect the problem was the Aphids and the White Flies. I cut off the badly infested leaves and sprayed. The Tom's are doing well now.

Have you checked your plants for any pests? I also gave Tom's some aspirin water.


    Bookmark   December 14, 2005 at 10:02AM
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I am just a newbie but might the propane be leaking into the air and causing problems?

    Bookmark   December 14, 2005 at 1:05PM
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seedbandito(7 NC)

Propane has a real distint odor. If your 'sniffer' works, you'll know when you're losing propane.


    Bookmark   December 14, 2005 at 2:50PM
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I suspect the problem is not leaking propane or lack of oxygen, but carbon monoxide. It is as toxic to plants as it is to humans and a result of any combustion(except maybe hydrogen engines). I use a non vented propane heater for supplemental heat but it is very risky in any air tight environment. If you have a CO tester for your house(which you should for your own sake if you burn fossil fuels) take it into your GH and take a few readings. The bad news about CO is that it is odorless and colorless. Sometimes it will make you sick to your stomach or give you a headache before you blackout but don't count on it. Plants usually react as you describe. Don't try to confuse carbon monoxide(CO) with carbon dioxide(CO2) which plants utilize.

Most people get away with unvented heaters but every now and then someone looses plants (I have) and vary rarely the gasses from an attached GH will leak back into a living area and either make the residents seek hospitalization or worse. If you are presently having problems then you probably should vent the unit or at least have it checked.

    Bookmark   December 14, 2005 at 3:04PM
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wolflover(z7 OK)

I appreciate all of your replies. I'm still not sure what caused my plants to turn yellow and drop all their blooms and many of their leaves, but I suspect it probably is carbon monoxide or a lack of oxygen. I don't believe it is pests because there are 350 plants in the greenhouse and they were in beautiful condition UNTIL I turned on those two propane heaters for only 3-5 days. As soon as the temps warmed back up outside, I went back to using the two electric heaters only to heat the house. I also don't believe it was due to low temps because they were no lower than they've been throughout the winter months. I'm sure it has something to do with these propane heaters, just not sure what.

Let me throw this at you and maybe it will help y'all help me get to the bottom of the problem(s). Twice during the few days I was using these propane heaters, one of them went out (pilot light died also). I noticed the temperature in the greenhouse was dropping and went outside and relit it. I can remember this happening on a few occasions last year also. Would this happen due to a lack of oxygen or do you think the heater is faulty? Also, the smell I am smelling strongly in the greenhouse and sometimes OUTSIDE, just walking up to the greenhouse, is a strong odor. We use propane in our home also and this is not the same odor that propane smells like. I don't know how to describe the smell except it's a strong enough odor I can smell it outside the greenhouse occasionally. Also, these two heaters were cheapo Pro Com heaters I bought from Northern catalog last winter.

Bmoser, I will take your advice and get a CO tester. I am really afraid of the propane heaters anyway and would prefer to use the electric heaters full time. But I'm afraid of them too in case of a power outage, even though I have an alarm. (G). Since I am paying $1.80 a gallon for propane now, it's probably cheaper for me to use the electric heaters right now anyway. I'm ordering one of Cactusfreak's solar blankets this week to help even more on conserving heat (thanks Cactusfreak)! Again, I really thank you all for helping me to solve this problem. It's been about to drive me nuts, and DH, who can usually fix anything, is clueless also.

    Bookmark   December 14, 2005 at 10:55PM
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wolflover(z7 OK)

I just thought of another thing that perhaps is causing my problem. The heaters in my greenhouse are radiant heaters, but on the back heater, the middle burner shoots blue flames out above the burner instead of heating up to a glowing red. I hope that makes sense. Do you think this means the heater isn't working properly? I hate to sound like such a dumb butt but I truly don't know much about heaters. I do know I have never been happy with either of these heaters... Another thing, I think I would like to vent the heaters even though they are ventless heaters, but I don't know how to vent them. They are mounted to the frame on each end of the greenhouse, attached to the twinwall polycarbonate. The ends of the greenhouse are polycarb panels but the sides are doubled plastic separated by a blower. How would be the best way to vent the heaters? Again, thanks for your help.

    Bookmark   December 14, 2005 at 11:41PM
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Although non vented heaters do no have to be vented they still need a fresh air supply.
Last year we posted a formula of so many inches of air space per BTU. I will see if I can find it. It's about 1 square inch per 10,000 BTU.
Even Southern Burner heaters recommend doing this for their non vented heaters.
Leaving a door slighty ajar or a vent slighty open would help. But if you could run a pipe from the outside to just under the heater similar to the plan below would be the best.

Here is a link that might be useful: Providing fresh air.

    Bookmark   December 15, 2005 at 1:18AM
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Carbon Monoxide gets my vote....

As an aside, we never did get any feedback on this thread.

Here is a link that might be useful: Was it a spider?

    Bookmark   December 15, 2005 at 1:44AM
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cottagefarmer(z4b WI)

If you are smelling a strong odor of the propane gas (rotten egg smell) you have a leak. Don't use a lighter to find it (that may make you a candidate for the Darwin Award). Instead, mix up a soap solution with water and with a small brush, paint all the joints and hose couplings in the entire gas supply system with it. If you see any bubbles produced at all, you have a leak.

If the amount of propane leakage into the greenhouse was significant, the plants may have reacted to the hydrogen sulfide (the "smell" additive) which is poisonous to most plants.

    Bookmark   December 15, 2005 at 9:32AM
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tranquility(z6/7 Wagoner,Ok)

I also live in Oklahoma and heat with natural gas and no vents....I have had the same is the carbon Monoxide and lack of oxygen....It burns my throat in the mornings if I have to burn the fire I will have to vent it first nice weather we have....mainly my angels trumpet, house plant and ferns are suffering the most they are losing leaves,or the leaves look burnt..I never let the temps drop below 60 so it has to be the build up of gases....I never had that problem with my small 12x16 gh...but, my new one is 20x36 and we are having problems....

    Bookmark   December 19, 2005 at 8:59PM
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weebus(Z8 Sunset 5 WA)

Is your stove made to be a vent free stove? If it is, you need to have it adjusted. You have your throat burn in the morning should be telling you something isn't right with the heater. I never have a problem with my propane.

    Bookmark   December 19, 2005 at 10:05PM
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This vent free thing is a myth...... The "vent free" tag that is attached to propane heaters basically means the combustion products can be released into a living space without harm to the occupants. Much like your gas stove is OK in your kitchen.

For propane to burn it needs oxygen. There has to be some sort of inlet for outside air. The gas stove in your kitchen is OK because your home is not sealed 100%, if it was you would die.

The "vent free" heaters some people are using in greenhouses are really designed for living spaces or garages which by design are NOT SEALED AND AIRTIGHT.

A greenhouse is capable of being sealed and airtight. Look at the amount of caulking a HFGH needs for example.

The vent free heaters people advocate on here have an oxygen sensor. Big deal, do you calibrate it every month? Is it fail safe? (as in if it develops a fault do you know?)

Carbon Monoxide is a human and plant killer. Show me a vent free heater that has a Carbon Monoxide sensor and shutdown facility that is fail safe and I will be impressed.

All I can say to anyone who uses a vent free hydrocarbon fueled heater is buy a Canary.

    Bookmark   December 19, 2005 at 11:44PM
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trigger_m(7b georgia)

i've talked to many folks that use a ventfree propane heater int their with any fuel burning device in a closed location,a carbon monoxide detector is a must.i have one,and it's in the greenhouse.they are cheap,and accurate.mine hase NEVER gone off in the greenhouse.when propane burns,it produces lots of water vapor and carbon dioxide.plants consume carbon only heat source is my ventfree is economical,regulates the temp within 2 degrees-AND most important,the plants are THRIVING.last year was amazing.i had dozens of angel trumpets in bloom-some over 8 feet tall!all in the middle of winter-and being heated with my ventfree heater!i don't have any blooms on the angel trumpets yet,but there are buds forming.however,some plants may be more sensitive than others.but i've got over 200 plants in there now,and they are my grandma says"if it ain't broke don't fix it".i plan on continuing to enjoy my plants with heat!try googling "ventfree heater and greenhouse".49500 hits recommending,and selling this for greenhouse use.the only problem i've ever had is my plants growing too well,too big!

both these pics from the greenhouse,middle of winter,full unvented propane use at night.i'm not sure but these look pretty happy,and healthy.look in the background.yep,that ventfree heater....

    Bookmark   December 20, 2005 at 9:20PM
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weebus(Z8 Sunset 5 WA)

I just love it when those of us who DO need to learn a little from those who WANT to do...

    Bookmark   December 20, 2005 at 9:55PM
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Great! ""as with any fuel burning device in a closed location,a carbon monoxide detector is a must"" You got yourself an electronic canary. Notice how many of the new ones have a flashing light to tell you they were triggered? That is really good advice to give readers on here.

Now, you say your plants are thriving but yet others on here are saying their plants are dying. What is the difference in the installation and operation? That is what we need to know.

Do you have a fresh air intake near the heater? Do you have a "vent" at the top open all the time to allow air exchange?

As to ""plants consume carbon dioxide"" yes they do, and they release oxygen... when in light. The rest of the time, like at night, they consume oxygen and release carbon dioxide.

The point is, things may be happening at 3am in a greenhouse that is killing plants. For those who are running "vent free" heaters with no problems you are...

1. Allowing outside air into your greenhouse to supply your heater.

2. If outside air is coming in then the combustion products are are being vented back outside somehow.

As an aside, I cannot understand why anyone who pays six thousand dollars for a structure then saves $300 by using a garage heater.

    Bookmark   December 21, 2005 at 3:32AM
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trigger_m(7b georgia)

well,i have a small pipe that lets fresh air in,that is mounted directly behind the heater,also,the door in not airtight,neither are both the vent louvers,there is some fresh air coming in.but,the heater itself is not vented.but,wolflover does definitly have a problem.wolflover-have you solved your problem?i would suspect a faulty heater.are the flames solid blue?there shouldn't be much,if any yellow flame.this would indicate a problem.also-are you positive the heaters are set up for propane?natural gas heaters will burn propane,but they will not burn properly.they will smoke,and put off soot if they are hooked up to propane.also,they will smell.i only occasionally use my propane gas logs,and when we do use them,i can faintly smell them.i can't smell anything at all from the greenhouse heater.if u can-there is a problem with that heater.

    Bookmark   December 21, 2005 at 6:46PM
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Looks like you got a good set up. You planned for fresh air coming in and your greenhouse is not air tight.

To correct an earlier post I said "This vent free thing is a myth" I knew I was using the wrong word and only later did the correct word spring to mind.

Should have been ""This vent free thing is a misnomer"

mis÷no÷mer Pronunciation (ms-nmr) n.
1. An error in naming a person or place.
2. a. Application of a wrong name.
b. A name wrongly or unsuitably applied to a person or an object.

The heater itself has no vents, no specific air intake fittings and no flue. But the SPACE the "vent free" heater is heating MUST have adequate ventilation, as in a dedicated air intake, an open window etc.....

As an aside, did anyone wonder why these "vent free" heaters have a standing pilot light? Did anyone wonder what this high tech Oxygen Depletion Sensor was?

I did, and what I found out made me smile. A propane powered Canary!!!

    Bookmark   December 22, 2005 at 1:32AM
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I had an occasion to ask a hort specialist about this from UCONN and he talked about carbon monoxide issues, he said easiest way to deal with it, is to vent the structure for about 1-2minutes to refresh the air.
wont do damage to plants

    Bookmark   January 4, 2006 at 3:01PM
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wolflover(z7 OK)

I do appreciate everyone's advice and suggestions. No, I have not yet solved my problem for sure, but have gone back to using electric heaters full time. My plants are looking sooo much better, putting on new leaves, and a few are starting to bloom again. Before I use the propane heaters again, I will vent them, and if that doesn't solve the problem, then I will replace them. I have never been happy with them from day one. And yes, they are definitely propane heaters. I double checked in case they shipped me the wrong heaters.

Thanks again for all your help. You all had some really good ideas and suggestions, and I liked hearing how everyone was heating your greenhouses too...

    Bookmark   January 5, 2006 at 10:09PM
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orchiddude(+7b ALabama)

I love topics like this, brings back old memories.

Hi Weebus.

Sounds like everyone is still learning.

I been using these non vented heaters for 5 or 6 years now and love them. I really all depends on how tight your house is as to if you vent or not. I grow orchids, palms and tree ferns and I have never had a plant problem with non vented heaters.

Here is a pic from the orchids this year.

My question is, "How is everyone coping with the higher gas prices?" I am sure that question has already been talked about. So far I have been able to keep mine the same.

Good to see everyone still talking about greenhouses. They are the Best!

    Bookmark   January 6, 2006 at 2:02PM
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stressbaby(z6 MO)

Orchiddude, great to hear from you! I can say that I personally have passed on your advice on a number of occasions (credit given).

You could inspire us with some more of your pics.


    Bookmark   January 6, 2006 at 7:43PM
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trigger_m(7b georgia)

orchiddude-it's great to hear your posts again!your advice last year on setting up my ventfree heater has worked perfectly.i'm with stressbaby,lets see more pics.

    Bookmark   January 6, 2006 at 7:56PM
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weebus(Z8 Sunset 5 WA)

Hey there Mr. Orchidude! Boy, have I missed you. Hope you're back for the long haul, and if not, post some pictures before you go, but remember to check back now and again.

    Bookmark   January 7, 2006 at 8:43AM
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Xylene gas, a byproduct of natural gas combustion is the problem. It causes tomatoes and orchids to wilt. You have to use electric heaters.

    Bookmark   December 21, 2006 at 12:41AM
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I have to laugh when I read post about air tight greenhouses! No such animal folks! If the GH were airtight you could never stay in there for more than a few minutes during the day. Every structure (including residential houses) leak some air. It's a necessary evil because otherwise the humidity levels go sky high and mold and fungus begin to grow.

As for the vent free heater using up all the air that too is hog wash since they have oxygen sensors built in nowdays. If the oxygen levels drop the units shut off. Heat would drop, you walk in to see what's up and oxygen follows you through the door. Oxygen levels would never get extremely low and stay that way for any prolonged period of time.

As for Wollovers problem there is something very wrong with your set up (or the heaters) if you smell propane as you approach the GH ! That is not normal. I suggest you follow cottagefarmer's advice and check it out very carefully.


    Bookmark   December 21, 2006 at 8:08AM
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orchiddude(+7b ALabama)

MollyD your a god send....thank you for your post. No, I am not opening another can of worms so keep the lid shut folks.

MollyD....I have been preaching this for years, and people still dont understand, I am so glad you showed up.

I can't say to much about this subject, I'll get the whole thing started all over again, and we dont want that.

    Bookmark   December 21, 2006 at 8:52AM
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laserfan(Zone 8b)

>Posted by orchiddude +7b ALabama (My Page) on Thu, Dec 21, 06 at 8:52

>I can't say to much about this subject, I'll get the whole thing started all over again, and we dont want that.

Yeah I do wish people would look at dates, before resurrecting year-old threads! I did get a laugh tho out of this:

"If you are smelling a strong odor of the propane gas (rotten egg smell) you have a leak. Don't use a lighter to find it (that may make you a candidate for the Darwin Award)." If you've found your way back here, thanks cottagefarmer! ;)

    Bookmark   December 21, 2006 at 10:33AM
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You're right lazerfan. I didn't check the dates on the post. Just read through and it all seemed so current that I never looked at the dates!
Greetings Orchiddude!


    Bookmark   December 21, 2006 at 11:32AM
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orchiddude(+7b ALabama)

I dont look at dates either. If I see someone talking, I talk back...LOL

    Bookmark   December 21, 2006 at 2:40PM
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And it was a December post which sounded right (LOL)


    Bookmark   December 21, 2006 at 2:52PM
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nathanhurst(VIC Aust)

Your both wrong about sealed greenhouses. I presume you are suggesting that a perfectly sealed greenhouse would suffocate you or something. But in fact during the day a perfectly sealed greenhouse would make you high from the reduced CO2.

Even without plants a 10x12 HFGH would only gain about 5ppm CO2 per minute you stand in there. Normal atmospheric CO2 is 381ppm and is considered potentially harmful to humans at about 1000ppm (and it's gone from 200ppm to 381ppm in the last century, most of that in the last half!). So in a completely sealed greenhouse without plants the CO2 level would take 2 hours of heavy breathing for you to start to notice.

So if you are truly worried about CO2 levels in your greenhouse, stop burning fossil fuels!

    Bookmark   December 21, 2006 at 5:07PM
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orchiddude(+7b ALabama)

Thank god no one is worried about CO2, I know I'm not. Now, lets move on to something else. I think we all know how to heat our own greenhouses, we dont have to talk anymore about it.

    Bookmark   December 21, 2006 at 8:53PM
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Hey orchiddude, You don't have to talk anymore about it. The rest of us are free to discuss anything we want to here as long as it is concerning Greenhouses, and let me also state Garden Structures.

I resisted the temptation to add to an old thread, others couldn't. Let this be the new unvented thread because it is a DOCUMENTED and REAL LIFE experience of two members where the use of an unvented heater caused problems, and plant damage.

None of the pro-unvented lobby suggested a cause or a fix. The concensus was "mine works, you must be doing it wrong"

We never found out what the "wrong" was now did we?

I am amazed that not one of the members that are using an unvented heater sucessfully are not activly addressing the issue of "When unvented heaters go wrong"

Unless we address the issue then one day one of the members that has succesfully used an unvented heater for many years with no problems may find they have a greenhouse full of dead or damaged plants.

As to,

""I have to laugh when I read post about air tight greenhouses! No such animal folks!"" Yes there is such an animal, they exist.

If there is a foot of snow on the ground mine is.

    Bookmark   December 21, 2006 at 9:43PM
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nathanhurst(VIC Aust)

chris: there are many things that can go wrong in a greenhouse, especially when inexperienced. The question, as always, is what is the expected cost. I don't post explanations about how to stop meteorites from killing people, because though it happens, and has a high cost, it has a very low probability.

(Oh, and as I've said elsewhere, I don't have any heater either, which solves that problem completely!)

    Bookmark   December 21, 2006 at 9:49PM
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I am with you on the no heater and no worry attitude!

Basically what I am trying to say that in this thread we had two people with new installations of unvented heaters that failed to perform. WHY???

As to predicting what can go wrong, you do your best and try to have a plan. For example, my plan for an expected low which I feel would cause major plant loss is to have enough cardboard boxes ready so I can pack up my plants and bring them inside into the basement.

I posted on here about having a sharp knife...

Nobody asked me how a sharp knife can save my greenhouse.

It is for slashing the covering if any part of it is breached in a very high wind. I have a solid north wall and north roof, a big air scoop. Plan is, slash the east and west sides if the south side gets torn in a southerly wind. Otherwise the whole thing would get blown over.

Here is a link that might be useful: Sharp Knife thread

    Bookmark   December 21, 2006 at 10:04PM
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wolflover(z7 OK)

I am the OP of this thread, and I finally figured out what the problem(s) were. First I vented each heater, which basically didn't help much, just made the greenhouse harder to heat. Then I had my propane delivery guy check the heaters out and he said they were faulty, that some of the grates were broken and the propane was not being burned properly... I don't know if the grates got broken during shipment, or if the heaters were duds from Northern...

I got a new propane heater last winter, and life is somewhat better in my greenhouse. BUT, I still hate using propane. My plants do not thrive on propane heat like they do on electric heat. I prefer to use electric heaters, but in January of this year, our electricity cost doubled, so even at $1.80 a gallon, it's still cheaper for me to use propane than electricity to heat my greenhouse.

For those of you who are successfully using propane to heat your greenhouses, would you mind posting the brand names of your heaters? All of mine are/were ProCom, and I hate them! I would like to buy a different brand that some of you are having success using. Thanks.

    Bookmark   December 21, 2006 at 11:38PM
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Thank you so much for coming back to us!!!

Faulty heater....

Glad you found the problem and I am really happy you are still growing stuff.

For others on here.... Note that, and remember it, an ODS only kicks in when the oxygen is depleted below 18.5 to 18% It does not protect against harmful combustion by-products.

This is a classic case study on unvented heaters.

    Bookmark   December 22, 2006 at 12:00AM
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I'm using a Mr. Heater Big Buddy with no problems. Next year I plan to upgrade to a heater with a thermostat so I can regulate temperatures better than this year.I'm considering the Heathrite Blue Flame Heaters.

So glad that you found the source of your problem. Have you contacted the seller of those faulty heaters to get your money back?


    Bookmark   December 22, 2006 at 8:17AM
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orchiddude(+7b ALabama)

I guess if we are keeping score, I will add 1 point for unvented heaters at this stage.

    Bookmark   December 22, 2006 at 9:27AM
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Interesting statistics and nice presentation. Type in an internet search for : unvented heaters university, and a different conclusion is found. Many of the recommendations to avoid unvented heaters in greenhouses are based on actual research and or documented cases of problems. Even though some mention the use of kerosine or crops such as tobacco, the basic conclusions are sound.

    Bookmark   December 23, 2006 at 12:41AM
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You are wasting your time and so am I.

I asked on another thread that someone created a FAQ on how to install an unvented heater and use it sucessfully and safely in a greenhouse and not one of the pro unvented crowd had the inclination to do so.

There is a gap in the heating requirements of our greenhouses that unvented, designed for a home, heaters fill.

The small blow away greenhouses can be heated by electric.

The larger greenhouses can be heated by large gas powered, specifically designed for greenhouses, vented heaters.

The middle ground, too large for electric, too small for real heaters attracts the unvented, I got one it works great crowd.

As you can see, from the above specially designed graphic the unvented heater is in the lead nine to zero for greenhouse heating!

I, because I have read anything and everything I can on heating for 6 years and still have no heater feel I could install and use an unvented heater and be confident it would be both safe for me and my plants.


Write an FAQ on how to install an unvented heater, you did most of the FAQ's on this forum. Write another so that whenever this topic comes up again we can all refer them to your FAQ on how to do it correctly, and safely.

Ball is in YOUR court orchiddude we are nine to nothing down at the moment.

    Bookmark   December 23, 2006 at 2:08AM
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orchiddude(+7b ALabama) bring up a good point. We as a forum, need to create a heater FAQ that will represent all types of heating ideas. If we can come up with a list of heating ideas for different size greenhouses, I will post it in the FAQ, this way, like you said, we can refer new people to the Heater FAQ.

In all fairness, I want different ideas. This will not be a one sided answer. I would like to see ideas that work, ideas that people are using in greenhouses today. If we have a problem with one idea, we will need evidence that it is being used or it wont be allowed to be in the running. I would like to get all ideas out on the table and let the grower choose what they want to use.

I will make a new post and we can start there.

Thanks Chris for the great idea! I hope you and Nathan, stressbaby, Mary, and some of the others will pitch in and help.

    Bookmark   December 23, 2006 at 8:51AM
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stressbaby(z6 MO)

I kind of like the graphic, Orchiddude!

Wolfover, I use Empire 24K BTU vented heaters.

It would be nice for something productive to come from this back-and-forth. How does one get questions added to the FAQ? Over the years I have thought of several questions that could be added.


    Bookmark   December 23, 2006 at 3:52PM
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orchiddude(+7b ALabama)

I have the password to add to the FAQ. I am the keeper of the key. LOL

    Bookmark   December 23, 2006 at 10:06PM
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laserfan(Zone 8b)

>I finally figured out what the problem(s) were...the grates were broken and the propane was not being burned properly.... All of mine are/were ProCom, and I hate them! I would like to buy a different brand that some of you are having success using.

Er, um, well duh but "the grates were broken"! (assuming actually the ceramic tiles) Probably in shipment--this should have been noticeable to you as it was to your propane guy, and this issue is noted in the instructions (to check that everything is intact, whether burners or tiles or logs as the case may be), which btw...

...appear to be the same regardless of what brand you buy. At least Pro-Com, Empire, and Hearthrite all look to be made by the same Chinese mfr, and it's clear from seeing others at Home Depot et. al. that Charmglow and other brands are made basically the same, with minor diffs in appearance, badging, and packaging.

Broken heaters don't/won't work properly, regardless of who made them!

    Bookmark   December 24, 2006 at 11:52AM
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I wonder if anyone ever did a cost comparison between propane and electric heat. In recent years propane has gone up in price much faster then electric.
Most seem to be using the small tanks and they are more expensive per gallon than a large tank. Since you need to use a vented heater or pipe fresh air into your unvented heater either way you are bringing in cold outside air then heating it. The only ones that don't need to vent are those who have a GH so drafty that it don't need a vent.
If you sealed the GH as good as you could and did not have all that heat loss would electric be cheaper than LP.
People have lots of opinions but has anyone actually did a accurate comparison.

    Bookmark   December 24, 2006 at 12:58PM
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trigger_m(7b georgia)

My unvented heater is a DESA Vanguard.Think It's 27k BTU.One of my main concerns when building my greenhouse was power outages.We get ice storms every year that knock power out for several days.One power outage,in the middle of the night,Would kill every plant I Grow.Got over 600 in there now.The ventfree does not use any electricity.Last year when power went out-the greenhouse was perfect!!I did install a small pipe directly behind the heater to ensure a fresh air supply.I also have a ceiling fan,and 2 box fans to circulate the heat.I bought a 250 gallon propane tank.So I just have it filled every summer-and don't have to worry about paying winter propane prices.By owning the tank-I can buy the cheapest gas.When you rent one,you have buy the "Rental" gas price.The small portable tanks can cost about 3.00 a gallon to have filled.My greenhouse is a 14' X 20' Twinwall polycarb.I maintain 50F at night-and use less than 140 gallons of propane a year.Propane cost 1.80 a gallon-252.00 a year-or 42.00 a month for the 6 months I keep plants in it.Wow-propane sure has gone up-last year it was 1.40,year before it was just over 1.00.I don't know how much electric would cost-but I like to idea of not having to have a heat back up when power goes out,and my plants thrive.Just my 2 cents worth.I'd like to hear from folks that use electric heaters.Mark

    Bookmark   December 24, 2006 at 3:53PM
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nathanhurst(VIC Aust)

LPG (incorrectly called 'propane' in the US) has an energy density of 22.16 MJ/L or 23 kWh/gallon. Assuming resistive heater, we get 1kWh heat for 1kWh electricity. A ventless heater will give nearly 100% efficiency converting lpg into heat. So it comes down to how much 23kWh of electricity costs vs 1 gallon of lpg. Here I can get a 9kg bbq cyclinder refilled for $30, for 85kWh of energy. Electricity costs 16c/kWh or $13.6 to replace.

(You will also need to consider the loan repayments on the hardware)

Depending on where your electricity is sourced, it can either be lower carbon emissions (wind, nuclear) or higher carbon emissions (coal) than lpg. We have wind and hydro sourced electricity, so electric heaters would be a much better bet, unless you want the additional CO2 in your greenhouse.

    Bookmark   December 24, 2006 at 6:43PM
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I think what type of heat is best depends on your location and the size of the greenhouse and what you are going to use it for. Nearly all large greenhouses will use gas but the small ones often use electric heat.
I have a small GH 10x12 and it is only used about 6 weeks a year to grow flowers from seed. The plant are put in the ground outside for the summer and the GH sits empty.
Since I had to run electric to the GH for the fans and grow lights using electric heat was no more work I just used a much bigger wire.Well that is not entirely true because I installed several extra outlets but I had the heaters I did not have to buy a $ 200.00 gas heater no tanks and pipe to install so electric seems to be the best bet for me. Last ice storm that took the power lines down was 1967 so that don't happen all that often. I figure if it did go out for a day or two I could use a portable kerosene heater and leave the door cracked open for air.
At the time of year that I will be using my GH I could go one night without heat and not have a loss it would not be that cold normally.
We have a tendency to think that what we use is what everyone else should use also and that is not true. We all have different needs. Someone in Mississippi would not need the same heating system as someone in northern Michigan.

    Bookmark   December 24, 2006 at 7:21PM
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maineman(z5a ME)


"LPG (incorrectly called 'propane' in the US) has an energy density..."

Nathan, I am disappointed in you. Both propane and butane are sold as separate products here in the US. They are fractionated from LPG. Industrial LPG contains both as well as small amounts of other light hydrocarbons.

I'm sure that the liquid carried in our propane trucks is not chemically pure propane, nor is the product carried in butane trucks chemically pure butane.

But they are primarily separate and distinct products, with separate and distinct properties and uses. The higher carbon content of butane gives it a higher heating value, but its lower vapor pressure makes it very unsuitable as a fuel in colder climates, such as here in Maine, as well as in many other states, as this link explains.

If you are heating a greenhouse in a colder climate, it very important that you do use propane, and not the industrial LPG.


    Bookmark   December 26, 2006 at 1:58AM
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nathanhurst(VIC Aust)

MM, if you read the link that I provided you would see that LPG includes the gases sold as 'propane' and 'butane' in the states. The 'propane' you buy is not propane, but a mixture, and is correctly known as LPG. There are different mixtures sold, and what you have called industrial LPG is just another of these. When you buy 'propane' you will not get pure propane (most likely it will have some ethylene - hence the earlier argument; propene, both butanes and all three butenes). You can call it what you like though (and probably will :).

Nathan, I am disappointed in you.
(And I'm sorry I am not living up to your high standards :)

    Bookmark   December 26, 2006 at 7:10AM
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laserfan(Zone 8b)

If you brainiacs could take a moment or two away from picking your nits ("For every expert, there is an equal and opposite expert." --laserfan) would you comment please on two things I have seen which purport to filter-out impurities in LP fuel lines:

1. Canister filters (here's a sample

2. Traps (6 inches or so of a pipe vertically-dropped just ahead of the appliance, recommended in most installation instructions for heaters)

Wondering just how much junk actually is in propane transportation systems and how often valves & whatnot fail due to impurities.

We all know about getting the cobbies out of grates/burners/orifices et. al. what what about the junk that's in the propane supply? Do suppliers use a "final filter" much as exists on every gasoline pump these days? Is this a concern we propane users ought to pay more attention to?

    Bookmark   December 27, 2006 at 9:38AM
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nathanhurst(VIC Aust)

"For every expert, there is an equal and opposite expert." --laserfan

Hehe, too true!

I personally have never had trouble with lumpy bits. I'm not sure how much stuff would get transported around, as in most systems the stuff in the pipes is gas (it boils inside the cylinder). The canisters I've seen were to remove chemical impurities, particularly acid and H2S, but that was a specialist application.

    Bookmark   December 27, 2006 at 1:02PM
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jimmydo2(z9 Calif)

I think we all just need to go back to the old method of Unvented heating. Cows...

I think about 1 cow per thousand cubic feet.

On the Extra cold nights a wick could be added to the cow to burn off the Excess methane (Just be carefull not to explode your cow, or you will have problems with your greenhouse getting to cold the next night)

    Bookmark   December 27, 2006 at 6:25PM
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nathanhurst(VIC Aust)

And of course you can produce lots of heat by composting the cowpats.

    Bookmark   December 27, 2006 at 7:45PM
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laserfan(Zone 8b)

>most systems the stuff in the pipes is gas (it boils inside the cylinder).

Hmmm, izzat right? I mean, it's called "Liquid Propane Gas"--I thought that it was transported as a liquid and entered the gaseous state only upon release from the container i.e. at the end of the pipe at the burner itself?

    Bookmark   December 27, 2006 at 9:36PM
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nathanhurst(VIC Aust)

No, it boils inside the cylinder - after the regulator the pressure is usually only a few hundred kPa. That's why the cylinders get cold when you use them heavily.

    Bookmark   December 27, 2006 at 10:41PM
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Amazing...I've read the entire thread and learned a lot. Thanks. Our electricity is 6.7 cents/Kw but scheduled to almost double due to a price freeze Illinois imposed on the utilities several years ago. Everyone is screaming that they'll freeze this winter...but after reading some of these seems we'll be paying basically the going rate for electricity in the future. Confusion like this always seems to happen when the gov't. gets involved in 'helping' us.

    Bookmark   January 2, 2007 at 9:19PM
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kuroc(z8 AR)

So Which would be better for someone living in zone 8A propane or butane?

    Bookmark   October 14, 2007 at 5:12PM
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orchiddude(+7b ALabama) doesnt matter, its which ever is cheaper and you get easier.

    Bookmark   October 14, 2007 at 5:44PM
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wolflover(z7 OK)

Wow, I haven't been on Garden Web in 7-8 months and what a surprise to find this thread I started several years ago back on the first page, LOL.

Last year we moved in December and left my greenhouse at our farm for the rest of the winter. DH installed two "new" propane heaters in my greenhouse before we moved, and I have to admit they worked great on their own all winter without any help from me. I went back about twice a week to check on the greenhouse, water my plants, etc., but the greenhouse was basically on its own all winter. The plants didn't really thrive with the propane heat, but at least none of them died. My problems from the previous year had been caused from those piece of shi+ Northern heaters, which were defective from the very first day they arrived. I bought three of them, and it seems strange they were ALL defective. I highly recommend you don't buy your heaters through the mail from Northern.

I do believe electric heat is a much cleaner source of heat, and better for my plants. I know this is a big argument here on this forum, but that is how I feel. If I could afford it, I would use electric heat and only use propane for a backup in case of power outages. But our electric rates have sky rocketed here, so even at $1.90 a gallon, propane is still cheaper to heat with. So that's what I'll be using this winter. Hopefully my experience here using propane will be more successful.
We finally got the greenhouse moved here to our new home this week. I sure hope to get it up and running before freezing weather gets here. I'm looking forward to enjoying it again soon since I didn't get to last winter due to our move.

    Bookmark   October 23, 2007 at 12:37AM
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