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Vented vs. Non-vented heater?

Discussion in 'Growing Areas' started by mrbreeze, Aug 12, 2012.

  1. Aug 12, 2012 #1
    mrbreeze

    mrbreeze Anglican Supporting Member

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    Here is my latest question: Vented vs. non-vented heater?

    I seem to recall that Marni has at least one non-vented but I wonder if the size of the gh is the key to wheter one can get away with no vent? With mine being much smaller, I wonder if I should go with vented.

    I talked to the guy at Southern Burner and he said that 80% of his orchid greenhouse users buy the vented type.

    He said that their vented ones are ~80% efficient and have a capacity of 25,000 btu.
    The non-vented are over 90% efficient (99%?) and have a capacity of 20,000 btu.
    Vented is an extra hundred bucks and would require some hassles to frame in an opening in the roof and to obtain the vent pipe, flashing, etc.

    I believe he mentioned ethylene gas as a potential issue with the non-vented and that it can cause bud blast. I'm curious if there are other gasses that might be a concern. But I'm also thinking that the vast majority of my plants won't be blooming during the winter anyway so bud blast may not be an issue. The source will be natural gas and with that level of efficiency maybe other gasses aren't really a concern? As always, any input is appreciated.
     
  2. Aug 12, 2012 #2
    Marni

    Marni Well-Known Member Staff Member Supporting Member

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    I have 3 unvented Southern Burner. My oldest is over 20 years old. I have no damage to plants or flowers from gas. My first greenhouse was 12 x 14 with a low roof and it worked just fine. My biggest now is 21 x 21ft and 13 at the peak. On the big one, if the outside temperature gets below 25, I have some trouble holding 56F, but I have double wall and lots of gaps. I have seen installations of the vented and would not consider having one. They take up more space, are awkward to light the pilot (unless something has changed recently) and are hot on top. Mine are part way or all the way under a bench and so aren't intrusive.

    I think a lot of people get the vented because they are told that they will trouble if they don't. After all my positive experience with the unvented, I still have people tell me I'm going to be sorry. Really!? So far, none of those warning me have had an unvented Southern Burner.
     
  3. Aug 12, 2012 #3
    msaar

    msaar Member

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    My PhD. chemist friend told me emphatically years ago that you could not generate ethylene from natural gas. LP gas would be another topiic. Carbon monoxide could be a problem (maybe) for the grower, but most greenhouses are not nearly that tightly sealed. I used an unvented NG heater for 20 years with no ill effects. Why would you not have orchids blooming in the winter?
    The real concern might be whether 20K Btu will be enough @ 0 deg.
     
  4. Aug 12, 2012 #4
    RadioFreeKirkwood

    RadioFreeKirkwood chloroplast envy Supporting Member

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    In the process of spec'ing out a greenhouse I have been told that unvented heaters are bad news, but I haven't been given an argument that makes sense to me.

    The product of burning natural gas is carbon dioxide and water - which seems like a win-win for a green house - you raise the temperature, humidity, and CO2. The ethylene thing, which an HVAC guy also told me, sounds scary. Ethylene makes fruit ripen and I don't want my plants to ripen, but ethylene is super flammable, so I find it difficult to believe that ethylene would come out of a fire to make my buds blast.

    Are there any unvented greenhouse heater horror stories out there or is this a myth perpetrated by the heating-industrial-complex?
     
  5. Aug 12, 2012 #5
    mrbreeze

    mrbreeze Anglican Supporting Member

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    Thanks for the replies. I'm definitely leaning toward the unvented type. I consider Marni's real-world experience more valuable than the conjecture about potential issues. Msaar, most of my orchids bloom in the spring, summer, and fall. There might be a few here and there that will bloom in the winter but not enough for me to have their potential bud blast be a deal breaker. Hell, I sometimes have bud blast now with no vent/no vent considerations at all. And as for the heating capacity, I believe last year we had *maybe* one week where it got into the 20s at night. Over the past several years our so-called winters have been a lot more fall or spring like. I could always get a small electric heater to supplement or even another gas one if I really needed it.

    Actually, my biggest concern would be the pilot light going out. The guy at Southern Burner said as long as there were no fans right near the heater it shouldn't be a concern. But i do wonder, with the small size of the gh, and the propensity for hellacious winds in Oklahoma....if I should be worrying about that a bit more. In theory the gh will be buttoned up pretty tight but i do plan to have fans going 24/7 year round. Any issues with pilot lights going out y'all?
     
  6. Aug 12, 2012 #6
    Marni

    Marni Well-Known Member Staff Member Supporting Member

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    I have fans on the ground blowing in the direction of the heater. If pilot light blow out in a particular situation becomes a problem I re-orient the direction of the fan a bit or put a piece of metal or aluminum flash so that the air flow doesn't get a direct shot at the pilot which is near the bottom of the heater. A much more frequent problem is when I am watering the plants hanging over an adjacent bench and water the heater so that it puts out the pilot. There is a bit of gas smell to alert you before the heater shuts off the gas.

    I forgot to mention that that heater I've had for over 20 years was well used when I got it.
     
  7. Aug 13, 2012 #7
    Ray

    Ray Orchid Iconoclast Supporting Member

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    Ethylene (C2H4) comes from incomplete combustion of hydrocarbon fuels, and I agree with msaar's PhD friend, and cannot see how it would be created from methane (CH4), but it certainly could from propane (C3H8). (We're talking decomposition products, not recombinant.)

    Incomplete combustion comes about from dirty, or poorly-tuned burners (i.e., the gas/air mixture is poor).

    Unvented is OK if you have a very leaky greenhouse, as Marni mentioned. Hers is vented, but not intentionally. It also drives up the cost to heat. I use propane, so would not take that chance, so always recommend a vented heater.

    A disadvantage of a vented heater is that the venting of the exhaust takes heat and humidity out of the greenhouse.

    I wanted a "tight" greenhouse for efficiency, plus vented heater for safety, so I bought a Reznor V3 UDAS heater with separated combustion. The combustion air intake is a pipe that runs inside of the exhaust flue that passes through the north wall of the greenhouse. Exhaust preheats the incoming air (enhancing efficiency), and there is no consumption of air from within the greenhouse, saving heat and humidity. When I changed from a Modine vented heater (that used interior air for combustion) to this one, my propane bill went down 40%.
     
  8. Aug 16, 2012 #8
    Uluwehi

    Uluwehi angraecoids, dendrobiums and more Supporting Member

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    I originally got a non-vented heater but then got freaked-out about a friend's experience with flowers and leaves blasting and distorting, so I got an upgrade to a vented heater. I can't speak from personal experience whether or not blasting will actually occur.

    Installing a vented heater comes with extra requirements regarding its placement in the greenhouse for effective venting. There were a lot of extra complications for me in my DIY greenhouse when I installed my vented Southern Burner Heater. The heater works great, but do review the manual as soon as possible so you can figure out where the heater will have to go before you install benches and stuff.

    It's good you have a natural gas hook-up. Mine is propane since I can't get natural gas out to the greenhouse; it's more expensive and I have to get tanks refilled. Natural gas is really the way to go.