I want to enjoy it, of course, but I've read articles that say CO2 can drop to half ambient levels after just a few hours in a sealed GH-which I'd need if I don't want $1000 heating bills in winter.

Well in winter I'm just thinking 63-68 days and 40-50 at night for the most part.

In theory, you could get a heat exchanger that pulls in fresh outside air, gets warmed by exchange with outgoing stale air, and thus supports photosynthesis.

They're used in modern houses now for similar reasons.

Hello and yes many ways to add extra co2 and only when lighting is brightest does it help well(I have read this)and a gas clothes dryer absent wet clothing for several minutes, wine making ect., sugar, yeast and water in 1 gallon containers, gas heaters, if you are serious and yes co2 does help, use caution from either carbon monoxide or plain co2 which can cause dizziness or worse.Always 1st visit plants take care of business then zap with your choice of co2 generator, a sealed grow room is far easier to manage and you will need periods of fresh air exchange then you will need to add co2 again, keep in mind you can tell by breathing co2 for a few minutes if your levels are up especially in a plastic sealed enviroment, co2 tends to be heavy and sink to lower level of grow chamber so use a small ossiliating fan to circulate air.Hope this helps you will have to experiment or buy a device to read co2 levels.

Here is a link that might be useful: Co2 Stuff for I wish I could but can't

Hi, It sounds like wallflower knows what he is doing. You would have to have a postive pressure gh full of plants to need extra co2. In a small greenhouse like your going to build you will have plenty of air exchange.

Air exchange is important all through the growing season.

I visit my local organic tomato grower on occasion ( to lust after 6 foot tall tomato plants in MAY ! ) and I've talked to him on the subject.

His greenhouses are, um, large. And I noticed that the end walls of the hoophouse were half open during the day.

He says it's important to change the air four times an hour. That many plants eat CO2 like candy.

So, the more plants, the more important air exchange is.

During the winter when his plants sleep at 50 degrees F, they don't need it as much.

According to folklore, plants in a sealed GH could deplete the natural CO2 in half an hour or less. And then they'd starve.

Well if I change the air 4 times an hour in winter-I'd have $3000 heating bills.

Maybe I should scrap this whole idea.

I read a lot and have never comae across anything stating greenhouses need additional co2. Contrary to that i have read co2 can increase plant growth but only during hot temps and bright lite something that does not occur too often in a closed up greenhouse since it is usually cold and overcast when they are closed up. If it gets hot and bright you are probably ventilaing and it would be a waste to try to make co2 then as it would just be released to outside.forget generating co2 and just build a bigger greenhouse automate the ventilation or buy a few more of your favorite plants.

Visit local nurseries, garden clubs, superstores that have green houses in use, etc. just to see how the "locals" are doing it. Hopefully someone's got some experience with winter gardening.

You can predict things to a certain extent, but it will be better by far to see one in action. You may need to actually build one yourself to know for sure what's going to be needed at your location and microclimate. The construction style and materials choice, siting, prevalent weather, type pf plants, equipment selection, your care habits, automation, soil choices, everything has an effect that only you can judge if altering something helps or hinders in your particular situation.

I read up a lot but had no idea till mine was built what was needed to heat or cool it.

Overall, larger green houses are more stable temperature-wise and easier to control than small ones. If keeping it warm in winter is the highest priority, perhaps an attached gh is one solution to consider.

-Ed

Your plants probably won't need a ton of CO2 in winter unless you have adittional high intensity artificial light. The plants will probably go semi dormant, but I could be wrong. I am new to greenhouses too, mine is almost built, but not completely. I have read a lot though. I wonder if just having woodchips covering some of the ground in the greenhouse would supply a good balance of CO2. I know the woodchips oxidize and produce Co2, but I don't have experience with greenhouse growing. I've never heard about Co2 problems before now. I would say if you arent growing under intense artificial light you probably dont have to worry about it until it is warm out. A lot of people say it is good to have a fan or two running in your GH, I would atleast do that.

good luck!

Is your greenhouse winter functioning? If so, the main thing is create turbulence in the air which can be solved by just setting up a small fan to keep the air moving. If air is not moving, an envelope of CO2 deficiency is built up around the leaf. Ways of increasing CO2 are:

burning propane or natural gas
throwing a few caged animals inside (smelly solution)
keeping a compost pile in your GH

or the method which I intend to use:

keeping a high level of organic material in my soil as mulch

I had another thought: Would a gas GH heater bring outside air in, heat it, and release? If so that would naturally exchange the air. Or, do most of them recirculate the inside air? (which would of course be more efficient).

regarding the heater, it depends whether you have a direct-vent heater or not. Any gas heater requires fresh air for combustion. Whether it draws fresh air into the greenhouse will depend on whether or not the combustion chamber is open to the greenhouse.

Direct vent heaters have a combustion chamber that is sealed from the greenhouse. The heat reaches the greenhouse through a heat exchanger.

More traditional vented heaters like the Southern Burner (http://www.southernburner.com) have an open combustion chamber. Fresh air is drawn into the greenhouse near the base of the burner, and exhaust escapes up the flue. Much of the fresh air is probably drawn directly into the burner, but I assume there is some turnover of greenhouse air.

Unvented heaters also have open combustion chambers and require a fresh air inlet. They are more efficient, because you don't lose heat up an exhaust flue.

A direct vent heater is probably more efficient than a Southern Burner. An unvented heater would probably be most efficient. With an unvented heater, you would also need to make sure that expanding heated air doesn't push out of the intake, resulting in loss of oxygen and incomplete combustion.

I prefer the peace of mind of a vented heater, and I have been satisfied with the efficiency and reliability of my vented Southern Burner. Since my greenhouse isn't perfectly sealed, I can feel some slow flow of air through the intake, even when the heater isn't on. When the burner kicks on, the flow greatly increases, as exhaust escaping up the flue pulls fresh air in.

I'm in zone 7, so your requirements for efficiency may be higher.

Do unvented heaters cause pollution problems? I mean, I realize for plants, they can get my on much less oxygen and the CO2 produced by the combustion would be beneficial, but how much is too much? Also, can the gas fumes themselves, or other byproducts of the burning be detrimental?

If the unvented heater receives sufficient fresh air, the main products of combustion will be carbon dioxide and water. If combustion is incomplete, you may get carbon monoxide which is potentially lethal to you. There may also be some ethylene, which is potentially harmful to your plants.

I'd recommend investing in a book on greenhouses. Your local Barnes and Noble or Borders should have several different titles.

How does one determine that the heater recieves enough fresh air?

The owner's manual of the heater you purchase should indicate how large the fresh air intake should be.

Is there a way to condense out the water and save it for watering? Otherwise I'd fear 100% humidity all the time!!

I need to seal the GH as much as I can, for energy efficiency. However, I don't want to run out of CO2 and starve my plants, either.

I feel the same way as Hairmetal in his last post. Though I don't think the humidity would be a problem as long as theres a fan blowing. In fact, I worry about too little humidity. I also need to add a ton of insulation to my GH, not sure how besides a pool cover. My GH is 12.5ft x 8.5ft

I was wondering is what kind of fumes propane heaters give off and if there are any dangers including fire hazards. Also, is it true that the fumes from certain burned gasses can make the buds of orchids and other plants fall off?

I think the fumes that are dangerous to orchids are the unburned gases themselves.

Nope. The new unvented heaters are too efficient for that to be a problem. As a matter of fact, there used to be a quite smart orchid grower on this forum and he used unvented heaters for years.

a co2 tank rented from a welding supply company for twenty dollars per year plus co2 for cheap. convert co moniter with selenoid valve. cost total three hundred to six hundred per year. at five percent co2 instead of current half of one percent plants grow twice as big twice as fast just like in dinosaur days yes life existed in a green house gas environment thank you GOD for your greatness making mans wisdom foolish

The importance of all this just may be slightly overblown.
The past two years I used a 6x8 portable GH and had it full of flowers with electric heat and no venting and both years they turned out just fine. This spring I will be using my new 10x12 HFGH and it is sealed about as tight as I can make it and has bubble insulation on the inside and a pool cover over the outside. I'm going to heat it with electric heaters no co2 will be added and I'm not planing on doing anything different than what i have done in the past. We will seee how it turns out next spring

how does one convert a CO monitor to detect CO2, considering they use completely different chemistry?

If I want CO2, I'd rather make it from natural gas, rather than pay lots of money for someone else to do it for me!

If we followed the kyoto convention, I wonder if there would be good money in using reclaimed CO2 in greenhouses.

Heh, follow the Kyoto convention? I'm in America, where Kyoto is seen by Republicans as some evil conspiracy to destroy the country. ;)

It's an interesting concept, although I suspect that even a huge greenhouse complex would struggle to eat up that much CO2. A single coal-fired power plant makes a *lot* of CO2. Of course, the greenhouses would also benefit from the free winter heating; even power plant exhaust is pretty warm still.

As for winter CO2: Your individual needs for CO2 will vary greatly. It's not true that you need grow lights for low CO2 to be an issue in the winter. Most greenhouses in the winter will be CO2-limited unless you have serious leak problems. I've read quite a few studies on the subject; depending on the plant, how well sealed the greenhouse is, where it's located, etc, supplementing the CO2 level just to ambient usually provides 25-50% better yields under natural lighting. These are typically done in commercial greenhouse-style environments, where people aren't as obsessive about sealing off every little leak as some people here are.

Here's just one example:

http://www.actahort.org/books/162/162_4.htm

I agree with Nathan on the use of unvented heaters. I love mine. It sits in the corner, its pilot light glowing. Every so often it roars to life, makes the greenhouse nice and toasty in 30 seconds or so, then dies down. I only got it installed this year, but I've never seen my plants healthier. Like most modern unvented heaters, it has an O2 depletion sensor and a pilot light sensor.

I don't know the whys or wherefors, but will relate my experience last winter, my first with a greenhouse, and perhaps therefore blessed: tiny 6x8 twinwall polycarb greenhouse wrapped in a clear solar pool cover except for the door, pc panels sealed with weatherstripping and any frame gaps sealed with caulk. electric heater. no auxiliary lighting. There is a roof vent, and a fan running 24/7. Lots of plants crammd in there - ornamentals, herbs, lettuce, cherry tomatoes, peas - and they all absolutely thrived. Maybe it's because we all enjoyed being out there so much we contributed sufficient CO2 just by breathing. I'm the only gardener in the family, by the way, the others just wandered out there to talk with me while I was puttering or with a book in hand to read in the "conservatory".

Planning is good, but I hope you won't overthink this and scrap the idea ... take a leap of faith, good luck, and, above all, enjoy!

Diane

link to information on use of unvented heaters in greenhouses.

Here is a link that might be useful: potential problems with unvented heaters in greenhouses

Yes, there are risks with unvented. I, and a number of other forum users, use unvented, and love it. I first got my heater this year, but I've never seen my plants looking better. I never would have expected this, but they're looking healther than they did this summer. I can only guess that it's due to the CO2 enrichment, and perhaps the extra humidity.

To dispel some myths, concerning modern heaters:

* "They'll deplete the oxygen": Modern heaters have oxygen sensors, designed with people in mind (not plants), that often won't let the O2 levels go down even 1%.

* "They'll produce dangerous gasses:: With ample oxygen, any properly functioning modern heater should have a very clean burn -- i.e., irrelevant amounts of CO and ethylene.

* "They're dangerous": More dangerous than an electric heater in a moist environment? Hardly. Oxygen sensors and pilot light sensors are essentially standard on any gas heater that is advanced enough to have a thermostat.

Call me stupid, I don't care, but I really do not get this idea of using an unvented heater in a greenhouse. It would be better if we described the heater as "a heater that requires no flue"

In order for it to work you need a supply of oxygen. An opening in your greenhouse. They work in a garage or home (the places they are designed to work in) because your home is not airtight. A cold climate greenhouse is a sealed structure that has vents to the outside air that are opened and sealed depending on temperature.

I wish those posters that use an "unvented" heater would also in the post tell others how they adapted their greenhouse to provide a supply of oxygen to their heater.

As to an unvented heater providing co2, yes it does. And when does the heater run usually? Night? Umm.. that is when plants are producing co2 as well.

Plants need co2 when light is shining on them, during the day, when most times the unvented heater is off.

I think that those with an unvented heater are seeing better growth than those with a sealed greenhouse for exactly that reason. During the day in sunlight when plants need co2 the most it is getting into the greenhouse by the same route that oxygen is getting in at night to supply the heater.

karenrei,
You stated, ""* "They'll deplete the oxygen": Modern heaters have oxygen sensors, designed with people in mind (not plants), that often won't let the O2 levels go down even 1%.""

You proved my point, in a "tight" greenhouse an unvented heater will shut down. For yours to run you must have air exchange, venting of some sort.

Back to co2 replenishment in winter. Pre-heat the incoming "fresh" air in winter. This is my goal for next spring. Scaled down of course, but it will alow me to have a change of air in my tightly sealed greenhouse on a sunny day without killing seedlings near the air intake due to sucking in below freezing air.

Here is a link that might be useful: Air pre-heater

Chris,
Good analysis of the CO2 issue. It would seem the obsession with keeping heating costs to the absolute minimum misses the point of having a greenhouse in the first place- growing healthy, productive plants.
The diagram of the solar pre-heater looks interesting. Keep us informed on how well it works.

[quote]In order for it to work you need a supply of oxygen. An opening in your greenhouse. They work in a garage or home (the places they are designed to work in) because your home is not airtight. A cold climate greenhouse is a sealed structure that has vents to the outside air that are opened and sealed depending on temperature. [/quote]

Misleading. Lets look at this situation, shall we? Lets look at a greenhouse -- say, an 8x7x12 cube for simplicity.

Volume = 672 cubic feet = 17.75 cubic meters
Mass = 1.3 * 17.75 = 23kg
O2 in "normal" air: 21% = 4.83kg. 16 g/mol
Propane: C3H8 -- mass = 44 g/mol.
Equation: C3H8 + 5O2 = 3CO2 + 4H2O
For 1 mol of C3H8: 44g C3H8 + 80g O2
Ratio: 1.81 times as much O2 as propane
Typical propane consumed in a midwinter day: Lets say 0.5 kg. That would produce 25MJ of heat (quite a bit!).
Oxygen consumed: 0.9kg
Percent of oxygen consumed *In An Entire Day* in a *Hermetically Sealed Greenhouse*: 19%.

It's really a non-issue unless your greenhouse is hermetically sealed. Running out of CO2 is very, very easy -- only 0.035% of air is CO2. But O2, at 21%, is almost impossible to even run low on. In fact, if you could consume that much oxygen, the pressure would be so low that air would readily seep in through any crack.

By the way, to flush in the fresh air for that 25MJ of combustion involves bringing in 19% of your 23kg air mass, I.e. 4.37 kg of air. Lets say outside temperature is -10C -- a very cold day -- and inside you're heating to 20C -- a rather wasteful temperature. Air has a specific heat of about 1000 J/kgK, so to increase 4.37kg by 30C takes 0.131 MJ, compared to your 25 MJ from the combustion. I.e., it's hardly even a relevant amount of wasted energy.

[quote]I wish those posters that use an "unvented" heater would also in the post tell others how they adapted their greenhouse to provide a supply of oxygen to their heater.[/quote]

Gladly. I have a vent, 18 inches from the ground so it won't get buried by snow, which connects to insulated ducting (painted black on the south side so as not to reflect light out of the greenhouse, since they're normally shiny). The ducting connects to the air intake of the heater. The size of the ducting at the intake is artificially reduced to about 1 1/2 inches diameter, and there's a wind guard around it. This, combined with the long, insulated duct, prevents much natural mixing from occurring. The consumption of the propane, however, produces a slight pressure differential from the heat-fueled convection. 1 1/2 inches is more than enough to prevent viscosity losses from resisting inflow at the inlet, so it gets all of the oxygen it needs as it burns.

Of course, the natural gaps in my greenhouse (say, between the vent panes) would probably be enough as demonstrated above, but I'm a safety nut.

[quote]As to an unvented heater providing co2, yes it does. And when does the heater run usually? Night? Umm.. that is when plants are producing co2 as well.[/quote]

1. Pilot light.
2. In winter, you don't have that kind of turnover of air in your greenhouse. In the summer one may have their greenhouse circulating its air once every minute and a half, but in the winter, you want to circulate your air .

[quote]Plants need co2 when light is shining on them, during the day, when most times the unvented heater is off. [/quote]

Just ignoring the circulation issue, a gas heater never gets turned "off". A 25-or-so watt pilot light is constantly burning. Lets do the math on this, shall we? That's 25 joules/sec = 2.16 MJ/day. At 50MJ/kg, that's 43 grams of propane burned to produce 109 grams of CO2. How much CO2 is naturally in the amount of air in the greenhouse? Lets do that math as well. 0.035% of 23kg = 8 grams. In short, over the course of the day, the pilot light alone produces far more CO2 than is naturally in the air.

[quote]Back to co2 replenishment in winter. Pre-heat the incoming "fresh" air in winter. This is my goal for next spring.[/quote]

Preheating has a maximum theoretical efficiency of 50%. I wouldn't want to be circulating in air with those kind of numbers.

Minor corrections:

1) "The consumption of the propane" should read "The combustion of the propane".

2) "you want to circulate your air" should read "you don't want to circulate your air".

Why does preheating have a maximum theoretical efficiciency of 50%? (I had assumed that preheating actually meant solar heating the incoming air in a separate collector, but now I think you are referring some kind of heat exchanger)

A Shurcliff lung could probably get close to 100% efficiency.

I was referring to what I believed Chris was referring to -- preheating your incoming air with your outgoing air. If that was a mistaken assumption, I stand corrected.

Basically, if your outgoing air is at 20C and your incoming air at -10C, you'll never be able to preheat it to higher than 5C, because by that point, your outgoing air will also be 5C.

karen: look up counterflow heat exchanger(http://en.wikipedia.org/wiki/Countercurrent_exchange). They can be as close to 100% efficient as you like in return for a logarithmic increase in size (every extra length x will half the inefficiency).

Chris,
Could you please post the original site for your solar air heater? From the plan you posted, it was not clear what the dimensions were. It looks like one number was 96 feet, so for the smaller greenhouse, some modification would be necessary.

cuestaroble,

That plan is for a grain dryer. They blow hot air into storage bins full of corn to dry it. Normally around here they use propane to heat the air and then blow it in. That plan is for a setup using black and clear plastic to heat the air. Yes it is 96ft long.

It came from this site. http://www.cerc.colostate.edu/Blueprints/blueprints.html

There are many useful plans there.

I was thinking of doing something like that to pre-heat air before it was blown into my greenhouse so I could change the air in there quite often but not be sucking in freezing air.

Probably I will make something out of old windows, junk wood and old tin roofing.

karenrei

OK running the numbers....

8x7x12 cube for simplicity. = 376sqft surface area.
Average insulation R2
Average low for a 12hr night 25F
Target inside temp 50F
BTU needed 4700 x 12 = 56400BTU per night

25MJ = 23711BTU = 0.5 kg propane + 0.9kg Oxygen.

For our experimental greenhouse we need 2.38 times that heat, or 1.19kg propane and 2.14kg oxygen.

As there was 4.83kg of oxygen in the air we still have enough oxygen.

Great so far. No need for a vent.

However the heater will shut down when the oxygen level in the greenhouse gets to 18%

a 3% drop in oxygen concentration, occurs when you use up about 0.7kg oxygen. Then unless you get more oxygen in there before you reach that point then no more heat, no more plants. The theory says you can seal the greenhouse, the practicality is you need air coming in to keep the oxygen concentration above 18%. Our experimental setup quit heating about 4 hours into a cold 12hr night.

We need a "vent"

Later you say ""By the way, to flush in the fresh air for that 25MJ of combustion involves bringing in 19% of your 23kg air mass, I.e. 4.37 kg of air. Lets say outside temperature is -10C -- a very cold day -- and inside you're heating to 20C -- a rather wasteful temperature. Air has a specific heat of about 1000 J/kgK, so to increase 4.37kg by 30C takes 0.131 MJ, compared to your 25 MJ from the combustion. I.e., it's hardly even a relevant amount of wasted energy."" Nice numbers, the heat wasted by heating up the air needed for the proper functioning of the heater is a drop in the ocean, score one more for a vent.

As to pilot lights and CO2, well in this case a pilot light in a sealed greenhouse would contribute slightly more CO2 than just flushing the air in there at the rate of once per hour. Both methods would work to maintain some CO2 in there. However both methods are next to useless if you require elevated CO2 levels. Above others posted links to some serious equipment for maintaining high levels of CO2.

OK nearly done ;)

Pre-heating air. I know you can do it with heat exchangers and copper fins and ducting and fancy stuff, but all I was wanting to do was simply heat up incoming air in a solar collector. An easy way to get a good but warm airflow and air exchange in there on a sunny day. (I smoke..................... )

karen: look up counterflow heat exchanger(http://en.wikipedia.org/wiki/Countercurrent_exchange). They can be as close to 100% efficient as you like in return for a logarithmic increase in size (every extra length x will half the inefficiency).

True -- I was thinking of a concurrent flow system.

8x7x12 cube for simplicity. = 376sqft surface area.
Average insulation R2
Average low for a 12hr night 25F
Target inside temp 50F
BTU needed 4700 x 12 = 56400BTU per night

I'm not getting your calculations here.

1) Where's your IR loss calculation? That's probably the most important on an insulated greenhouse, not conduction.

2) R2 -- please tell me that you're using metric R values there, not American. If that's an American R value, it's way too low. But if that's the case, why are you using BTU instead of joules?

Greenhouse heat loss is a complicated issue, so I simply scaled my actual propane use to adjust for the size of the theoretical greenhouse under discussion.

However the heater will shut down when the oxygen level in the greenhouse gets to 18%

In a *hermetically sealed greenhouse*. ;) Hardly the situation we're talking about. If you can design a greenhouse this size that can stop this small of an amount of oxygen exchange, I'll be very impressed.

Nice numbers, the heat wasted by heating up the air needed for the proper functioning of the heater is a drop in the ocean, score one more for a vent.

I'm not arguing for a hermetically sealed greenhouse here -- I'm not sure why you seem to be arguing that you need a vent. Of course you need *some* sort of air intake -- but as I think I showed, the amount of air exchange needed over such a long period of time would be able to be accomplished even through natural cracks in the greenhouse, between the panes in a closed vent, or whatnot. Flushing 1/5th of your greenhouse's volume over a 24 hour period is nothing. Note that with that low of a CO2 flushing rate, the CO2 that you generate at night will still mostly be there, ignoring the pilot light's CO2.

[quote]However both methods are next to useless if you require elevated CO2 levels.[/quote]

You don't think that 109 grams of CO2 from the pilot light alone, compared to the natural amount of 8 grams, is "elevated"? Please explain.

An easy way to get a good but warm airflow and air exchange in there on a sunny day. (I smoke..................... )

Ah. Well, in your case, I'd want extra air exchange, too. Not only would that be bad for you to be smoking in such a confined space, but your plants would be breathing it in long after you left.

Most new unvented gas heaters sold in the US for the hobby sized greenhouse do not have pilot lights. They use piezo ignition.

cuestaroble: Where did you get that tidbit? Mine indeed has an ignitor, but that just ignites the pilot light. You turn it to "light", press down on the button for a few seconds, press the ignition, hold for up to 30 seconds so that the pilot sensor warms up, and then set your temperature.

I haven't seen one that has a thermostat but doesn't have a pilot, so I'm curious as to where you got that number from.

Of course, as I mentioned, with as little turnover of greenhouse air as you need to operate the heater, you'll easily still have a CO2-enriched environment during the daytime hours (unless you have excess ventilation) on a heater without a pilot.

""1) Where's your IR loss calculation?""

Not there, the IR loss is even more scary than the ACF Greenhouse heat loss calculator we all know and love.

""2) R2 -- please tell me that you're using metric R values there, not American. If that's an American R value, it's way too low. But if that's the case, why are you using BTU instead of joules?"

R2 as we know it in America is quite low for house insulation. I used that number to allow for our test greenhouse to have 6mm twinwall on the south and south roof and some insulation on the North walls etc. I am using BTU and converting joules to BTU because I can visualize a BTU, imagine a BTU, work with a BTU. Heaters here come in BTU/h (Ok so electric heaters come in watts but that is easy to do) Even air conditioners come in BTU/h sizes.

""In a *hermetically sealed greenhouse*. ;) Hardly the situation we're talking about.""

I am sorry but many here with small greenhouses are infact coming as close to an hermetically sealed structure as possible. 10-20 tubes of calking... on a 6x8ft?

The smaller the greenhouse the "tighter" you can economically get it and as we discussed the faster things can go wrong in it.

""I'm not sure why you seem to be arguing that you need a vent. Of course you need *some* sort of air intake""

You need some sort of air intake. Then make it an air intake specific to the task. That is all I am saying. These heaters need ventilation, in a garage or home they get it because garages and homes have more than enough built in ventilation or the occupants would croak.

""You don't think that 109 grams of CO2 from the pilot light alone, compared to the natural amount of 8 grams, is "elevated"? Please explain.""

The pilot light produces 109gm per 24h in a sealed (and I am sorry to use the sealed word but this is what the thread is about.) and I said you pre-heat the air and change it 10 times a day. OK I broke the rules, sealed tight greenhouse to conserve heat but I allow air that is at least the temperature of my greenhouse air in.

Also in this thread nobody has mentioned the water. Unvented heater, sealed up as best you can, no air exchange. Adding CO2 by burning propane makes it wet in there too.

Sometimes I am really glad I am able to grow all I want to in zone 4b without all that messy heating stuff.

:)

(having a beer and visulising water turning to ice and seeing seedlings still basking in 40F surroundings in early March. )

Excellent discussion! You folks are doing a great job!

Chris, I hope you never catch the tropical plant bug, like me.

Cuestaroble, since I would guess that you have spent more time in greenhouses than the rest of us combined, maybe you can cite some real-life experiences with unvented heaters?

SB, having a Corona in November with a lime grown in my greenhouse (OK, well the limes aren't quite ripe yet, but they will be by January!)

Happy Thanksgiving

stressbaby,
Gladly. Greenhouse cucumber operation in Calif. with newly installed unvented heaters. After a cold winter period, severe damage was noted on the crop. Air samples analyzed showed elevated levels of ethylene and mercaptan. Subsequent legal action resulted in the heater manufacturer paying for the crop. The grower replaced the heaters with vented unit heaters. "economic losses to greenhouse growers from ethylene pollution are reported each year" NC State Univ. Unvented heaters are not recommended for greenhouses by the following Universities: KY, TN, FL, CA, MD, WV, Penn State, Cornell, Clemson. All have web articles easily found.

For an interesting thread from about a year ago, complete with more examples of problems with unvented heaters, use the search function, type "carbon dioxide" and read the posts on "plants suffering from propane". Some noted problems in other "real-life" situations. One factor missed in this thread was ethylene.

When we have done ethylene (which causes fruit to ripen before it should, that is why store bought tomatoes, apples etc don't taste like naturally ripened fruit...) Can we do NOx?

http://www.epa.gov/iaq/no2.html NO2 is not nice

I wish greenhouse heaters produced N2O though

http://en.wikipedia.org/wiki/Nitrous_oxide

(imagining sitting in my closed up greenhouse with a silly smile on my face)

[quote]R2 as we know it in America is quite low for house insulation. I used that number to allow for our test greenhouse to have 6mm twinwall on the south and south roof and some insulation on the North walls etc.[/quote]

Heh, perhaps I'm just weird then, but I have metric R2 on my north wall (+parts of east and west, +underground) and about metric R 1.4 for the glazing. Metric R values are about 0.17 times US R values.

[quote]I am sorry but many here with small greenhouses are infact coming as close to an hermetically sealed structure as possible. 10-20 tubes of calking... on a 6x8ft? [/quote]

Well, it depends on what the caulk is being used for. I caulked my insulation on. Let me tell you, that takes a lot of caulk.

Even if you seal up all of the cracks, I would be surprised if the small amount of circulation couldn't occur through things like:

* The drainage system
* Between panes of closed vents
* Through the zipper or doorframe.

Sure, a vent is a good idea. But we're talking about needing a very small amount of air indeed.

[quote]Also in this thread nobody has mentioned the water. Unvented heater, sealed up as best you can, no air exchange. Adding CO2 by burning propane makes it wet in there too.[/quote]

That is true. The moisture beads on the glazing and runs down to the floor; it's like a jungle in there (when I wear glasses, it's instant fogging when I walk in). I haven't grown any plants that are sensitive to moisture-related diseases before, but I've got some in the seedling stage right now, so we'll see if they complain. They're doing quite beautifully so far (I could get pictures if you like), but moisture-loving diseases like powdery mildew take some time to get established. I'll get back to you about them in a month or so and let you know how they compare to the equivalent plants grown outside this summer.

[quote]stressbaby,
Gladly. Greenhouse cucumber operation in Calif. with newly installed unvented heaters. After a cold winter period, severe damage was noted on the crop. Air samples analyzed showed elevated levels of ethylene and mercaptan.[/quote]

Elevated *mercaptan* levels? Wow, that heater must have been doing an awful job. Mercaptans are only in PPM quantities to begin with, so if you're having measurable amounts *after* combustion, something is seriously wrong there.

[quote]economic losses to greenhouse growers from ethylene pollution are reported each year[/quote]

You do realize, I presume, that ethylene pollution can happen even when no heater is used. Decaying plant matter is an especially bad ethylene producer, but even healthy plants produce it (some species more than others).

[quote]For an interesting thread from about a year ago, complete with more examples of problems with unvented heaters, use the search function, type "carbon dioxide" and read the posts on "plants suffering from propane". Some noted problems in other "real-life" situations.[/quote]

Well, for your information, with Thanksgiving dinner, my main course was a delicious vegetarian lasagne made with a heaping handful of basil from my "suffering" greenhouse basil plants. Last night for dinner, I had pasta primavera made using some of my "suffering" tomatoes.

My point? A proper installation doesn't have problems. An improper installation does. Notice how you haven't gotten into the risks of the other common hobby greenhouse heating system, electric. You know, a box of resistors with large amounts of current flowing through it, in a moist environment that usually has a metal frame, and plenty of combustables within, possibly even standing water?

I read the "suffering from propane" thread before I got my heater. I read enough from elsewhere to realize that this person had an improper installation. Notice -- it only took a few days of use of their heater for problems to occur. Mine has been running for two months this winter. Note what was mentioned in the thread: "Sometimes the smell is very strong." Huge red flag right there. Properly combusted propane/natural gas has no smell. The instant they smelled it, they should have disconnected the heater -- it sounds like a leak. Note what others said in the comments trail, such as Orchiddude and trigger_m (who also provided pictures).

[quote]One factor missed in this thread was ethylene.[/quote]

Ethylene was already mentioned several times in this thread. Use your browser's search function; you'll find it.

It is very interesting this thread has gone the same way as most other threads have gone when unvented/ventless heaters are discussed.

The people that use them and have no problems tend to have provided a fresh air inlet (although you don't really need one... or do you?) and the people that have had problems seem to have a "tighter" greenhouse than the norm.

If anyone wants to donate me a heater and 1200 gallons of propane I will check it out and report back!

As to electric heat. Yep some of us are just as anal about it as we are with unvented propane.

I use electric heat when the situation is getting critical in there, I use an oil filled radiator and an oscilating fan. No exposed glowing heating elements.

But the dangers of electricity are slightly off topic, that is why we ain't saying much. :)

Gosh where have I been. I love heater threads...Yall should have been around 6 or 7 years ago when we did this. I still remember that thread, it should have gone down in history, but yall are doing pretty good with this one.

Gas heaters...well...you know how they work. Just a few points from me, I am not going to explain or reinvent the wheel here.

Gas heaters:

1. works great for most size greenhouses
2. are safe, no problems, no worries,
3. Orchids love it. Yep, mine do anyway. I have about 500 orchids right now and blooming.
4. What fumes? Never had any!
5. Like weebus said, learn about your heater, people are still stuck on the OLD INFORMATION. too efficient for that to be a problem
6. Biggest misconception about nonvented heaters. The word vent is referred to the metal pipe that comes out of the back of the vented type heater. The product manufacture had to call it something else because it didnt have a pipe coming out its tail. So they called them non-vented heaters. They still vent and they still burn oxygen and they still work like normal heaters but instead of burning unclean, they cleaned them up so they burn 99.9% clean, plus they have an Oxygen sensor on them that will turn off if there is a problem.
6. they are great for when the electricty goes out
7. you can sleep at night knowing your plants are safe and warm
8. most have a thermostat
9. you can use a simple small fan to blow the warm air out into the greenhouse
10. once you use a gas heater in a greenhouse, you will become a believer, just like the hundreds of other people that found the truth about heating a greenhouse....LOL