best gas heater for shed/greenhouse

jpm995

Hello everyone i'm new here and need some advice. I have a well built shed 12' x 18' and i want to add a lean to greenhouse [21' x 10'. I have natural gas heat [Navian] in the main house. The sheds about 50' behind the house. The total sq ft is around 450 but the greenhouse is only about a 3 R rating [6mm double wall GE plastic]. I think the most cost effective way is to trench the gas to the shed and use a high efficiency gas/hot air burner. Was looking at Rinnai FC510N or FC824N no vent heater, or a Monterey 25,000 BTU Natural Gas Top-Vent Wall Furnace. I assume the Rinnai is much more efficient but i'm worried about the safety no vent. The Williams burner fits IN the wall and has a rear vent option so i could maybe heat shed and greenhouse as i plan on a large opening between them. Will the Rannai save a lot and the no vent a good way to go? I'm sure there's other options, i'd like to here your onions. Thanks.

Jamie Hall

Do NOT use a no vent heater in a greenhouse. Some plants don't mind so much. Others? They die... which, I presume, is not really what you want.

I doubt that the difference in efficiency is that much -- certainly not enough to justify using a no-vent in that type of application.

jpm995

Thanks for your input, i wanted to use the Rinnai for ease of install [no vent] and assumed efficiency. Would you recommend any other solutions?

Jamie Hall

Go with a direct vent heater, or that Monterey. I agree that the no vent variety is easier to install -- but as I say, they are pretty tough on plants.

SWEI

The Rinnai is a direct vent, no?

Paul48

Efficiency is not possible.I'd use Modine heaters.

jpm995

Rinnai has both direct vent [81%] and ventless [99% efficiency] heaters.
https://www.rinnai.us/documentation/downloads/R-CNHT-E-07.pdf

jpm995

I don't understand your comment Paul, can you explain? I'm thinking Rinnai but the direct vent one. It seems more modern than the others. Needs electric to run but it has no pilot always running and had multispeed fan and different heat temps. It's more complex but if reliable seems like a better unit. It's 81% efficient not as good as i hoped and it's more money but i've always heard good things about Rinnai.

Paul48

It was my thought, that you are essentially heating the "Great Outdoors". Having a greenhouse in the winter may be a necessity, or a luxury, but heating it with a furnace is probably not the most efficient way to do it. I'd imagine there are some very resourceful folks that heat their greenhouses efficiently with solar, passive or otherwise. IMHO

Jamie Hall

Paul48 said:

It was my thought, that you are essentially heating the "Great Outdoors". Having a greenhouse in the winter may be a necessity, or a luxury, but heating it with a furnace is probably not the most efficient way to do it. I'd imagine there are some very resourceful folks that heat their greenhouses efficiently with solar, passive or otherwise. IMHO

Depends on your climate, @Paul48 . In some southern climates, or, say, Kalifornia, you might be able to. Most of the northern US east of the Cascades and especially New England, never mind Canada? No hope. Sorry. No can do.

And I might add that for some farmers, at least -- and the OP may be one -- a greenhouse isn't a luxury at all, but the only way to grow some of the crops which the market demands.

Paul48

"And I might add that for some farmers, at least -- and the OP may be one -- a greenhouse isn't a luxury at all, but the only way to grow some of the crops which the market demands".

My statement covered that possibility, but then it becomes about profitability. I could be wrong, it is just my opinion. Maybe there is an efficient way to heat a greenhouse. You know better, than I.

Paul48

I worked on a house, years ago, that was passive solar. It was a replica of one in Nova Scotia, that spent under $200 year round to heat.

Jamie Hall

Paul48 said:

I worked on a house, years ago, that was passive solar. It was a replica of one in Nova Scotia, that spent under $200 year round to heat.

My father in law, now passed away, was one of the real pioneers of passive solar heating, both for domestic and commercial uses. I have great admiration for his work. A number of his full and partial passive solar houses and buildings are scattered around New England.

One of the things which made his work great was that he recognized the limits of the technology...

Paul48

Absolutely..........And building in such a way as to minimize the run time of a greenhouse heater is probably the best way to be efficient. My only point of reference is that I worked for a company, a while ago, that sold greenhouses and greenhouse heaters. They were anything but efficient. Things may be different now-a-days, as far as the furnaces go. I don't know.

hot rod

Funny thing about greenhouses and passive energy, sometimes you need to dump heat, even in cold climate conditions. Seems like ventilation fans are a key component.

On the heating side, it seems like r-value and green house are oxymoronic. They are typically energy pigs.

Root zone heating is another method, where warming the soil, not necessarily the entire volume of the space, is adequate.

jpm995

I'm no farmer and the greenhouse/shed is strictly for my pleasure. I want the GH to be a mini zoo/botanical gardens with ponds for fish and turtles and the shed to be a man cave. I know it seems like an expensive hobby but i really enjoy the thought of having my own botanical gardens. Just moved into a new home with this big shed and i'm getting crazy ideas. Plus my wife is sick and tired of all my plants and tanks in the house.

hot rod

It can be done, with renewable energy, too. Amory Lovins grows tropicals at his home in Snowmass, Colorado


http://grist.org/climate-energy/amory-lovins-high-tech-home-skimps-on-energy-but-not-on-comfort/

Paul48

I think that's an awesome idea. You might want to talk to a greenhouse manufacturer. Tell them you're interested in alternative ways of heating a greenhouse. They may be able to help. Don't get me wrong....you'll need a furnace, but you don't want to have it running 24/7.

SWEI

Jamie Hall said:

My father in law, now passed away, was one of the real pioneers of passive solar heating, both for domestic and commercial uses. I have great admiration for his work. A number of his full and partial passive solar houses and buildings are scattered around New England.

One of the things which made his work great was that he recognized the limits of the technology...

I suspect I would have greatly enjoyed meeting the man. After decades of studying and messing about with various aspects of buildings and energy my understanding of the value of passive solar design continues to grow. There's literally almost no place on earth where it does not represent a good investment. Insanely good on some places of course, but pretty reliably good.

jpm995

The shed also had a brick fireplace [the shed was a sauna] and i was thinking of adding a wood burning stove for extra heat. Aqua shield has a lean to greenhouse 10w by 20l for @ $12k. Hope i can get this done without breaking the bank.