That seems like an awful lot of work and the pipes aren't cheap. You'd also have to always be there in cold weather to watch it and make sure the GH is warm enough and not too warm etc. Lot of work and time.

Using a circulating pump, hot water radiant heat is clean, effecient and relatively cheap to operate and wood was the source of heat for the earliest steam boilers, so of course it could be done- as long as you don't mind the need to stand by to feed the fire heating the boiler, particularly in the dead of night when temps. tend to be lowest.

But unless you have access to cheap to free pipes and a pressurized boiler and proper controls as well as wood, it may be time to do a serious cost-benefit analysis on your GH heating system and perhaps invest in a very high effecient conventional heater.

Or- install your wood stove inside your GH. If your GH is very well insulated, the stove would give off quite a bit of heat. Then, set a tub of water atop it for humidity. That's how most all GH's were heated before we had gas or electric space heaters.

However, whatever you do for heat, first and foremost, look to your insulation. The best, most energy effecient heater available is a waste of money if the heat is allowed to escape as fast as it's generated.

With energy costs only going up, it may be a good idea to consider, if:
1. You are good in plumbing skills.
2. You are good with mechanical and electrical skills.

You can find heat exchanger from old air conditioners, car radiators, or from ebay that can be very useful. You do need a big waater tank to store the heat .

dcarch

My husband is very good with carpentry, plumbing, electric & mechanical skills as well as very innovative. We have a lot of scrap lumber & metal siding that we could easily construct a shed behind the greenhouse to house the stove. He doesn't mind tending fire this winter - as supplemental heat only. We never intended for this to be our only heat source. Will see if he can locate a heat exchanger. Any idea on how big a water tank would be needed to make it worth the effort?? Right now we have a hickory & oak tree down from a recent storm just going to waste.

Kim

I am not sure I remember correctly. I think 1 btu = one gallon of water raised one degree f.

You can figure out how many btus you need to heat up you house.

dcarch

This is an interesting issue to tackle. The link below shows how I am going to approach part of the problem with solar panels and underground piping. The pump switch will be hooked up to a temperature sensor that will turn the pump on and off based on the potential for solar gain.

I also have plans to build a waste oil heater that drips oil into a fire chamber that burns hot and clean with a blower. It will heat inside the greenhouse as well as large water barrel storage and underground piping.

Any heater system will only be used for a season jump start and a season extender. I don't want to be in the business of fighting nature. My heat is considered supplemental only, just like yours.

Wood heat will work, but it is inconvenient and a bit messy. The key to any system design will be drain back. When the system is shut off, you'll need to make certain it drains back into a large tank or underground where the water won't freeze.

If not, then you'll have to use anti-freeze, and that becomes expensive as well as toxic to the garden if there is a leak.

The importance of underground heating is that the roots really are the things that respond to warmth, not so much the tops of the plants. I'm going to reconfigure my system to heat the entire floor of the greenhouse, and set it up so I have the option of heating:

-just the ground
-just the 300 gallons of water storage
-ground and water storage

My heat sources will also be plumbed so I can use solar or waste oil heat. And, everything has to drain back into a safe configuration to protect against freezing because I don't use anti-freeze. One way to protect against freeze damage without anti-freeze is to keep the water moving. A circulating pump can run 24 hours for about 30 cents.

This is all a challenge, but if self-sufficiency and an extended gardening season is what you're after, this goes a long ways toward achieving that.

By the way, piping is not expensive for such a system. Use Pex piping and a 100 foot roll of 3/4 inch is about $28. It is also highly resistant to freeze damage, although I would set the system up to protect against that.

Clair

Here is a link that might be useful: solar underground heater

Clair, thanks so much for your response. I'd just reviewed your link & responded on another thread regarding your heating systems. It sounds so much like what we were going to attempt to do.

Freezing shouldn't be as much of a problem for us here since there aren't a whole lot of below freezing temps here in NW Tenn in a normal year. We'd already talked of putting in a small circulating pump for water movement. We haven't quite figured out the switch yet - had considered a simple fix for now being just a timer for the overnight hours - a temperature sensor would be better. Like you, I'd like to avoid antifreeze.

We'd also discussed drums of water, but hadn't considered burying them undergroud as you have. Will have to consider how to do that & the drain back issue. I'm really glad to hear that the pipe is not that expensive - Just wish we'd thought to do all this before completing the greenhouse.

Our greenhouse is on a hill near a retaining wall, and while constructing it we did extend an underground pipe from the interior of the greenhouse out the through side of the retaining wall. The stove would be located near that drain pipe. That should help with running the piping from outside to the interior of the house.

I think the project is doable. The wood heat is a bit messy, but the wood is free & should help with the cost of maintining a higher greenhouse temp without breaking the bank - at least we hope so. We'll have to iron out a lot of the details, but I think we'll give it a try.

Thanks for the input.

Kim

1 btu will raise 1 pound of water by 1 degF
so it`ll take about 8.5 btu to raise a gallon by 1 degF.