18 X 72 Hoophouse/ Can I heat with Rocketmass?

Hello All,

I am totally new to all of this. I just happened to stumble on this site via some loosely related greenhouse culture stuff. My Mother and I started up a small garden center on her property last year. We have four hoophouses. We do seasonal plants, natives, hybrids,.....we would like to get one house heated so that we aren't beholden to buy annual veggies and flowers in the spring from one the wholesale producers. We are both living on shoestrings, and with the business still in start-up mode, we don't have a lot of cash to throw at a wasteful gas furnace and all the electrical and such that conventional greenhouse heaters require. Not to mention, I think there must be a better way of heating one of those goliaths, than gas!

We would likely need to have it heated starting February 1st. I am in Southern Michigan, it has rarely dropped below the teens here in recent years. Last year we had a zone 7b sort of winter...my rosemary survived in ground (super amazing). I wouldn't want night temps to drop below 50. I am ok with living in the greenhouse for a month or two, to keep fires fed through the night. Daytimes, are obviously less of an issue as long as the sun is shining. I have a bunch of 350gallon water barrels that I was thinking of putting inside the greenhouse...or along the west wall (south wall is obstructed by hill) thinking the mass of water would be additional thermal source of heat....

Questions:

1) How many 55gallon drum style rocket stoves would I need
2) With the aformentioned style of stove, how many lineal feet of in ground exhaust pipe, would be supported
3) In the greenhouse, there will be water penetrating the floor...is that going to rust the pipes out?
4) If rusting from water penetration is a concern, can I cover the radiant channels that the pipes are layed in with polyfilm to divert water? Or would the film melt?

[I am envisioning the exhaust pipes being under the walkways in the greenhouse. Filled with rocks and pearlite, capped with brick or cement paving stones....so that the system can be accessed and repaired in case of rust]

5) Can I build an exhaust system that is entirely a brick tube underground? What would be the problems I would incur with that?
6) How frequently will the fire need to be fed?
7) How often must the system be cleaned to prevent burning my place down?
Has anyone had any problem with rodents moving into their exhaust pipes?

My other thought was to build a lean-to on the back of the greenhouse, hang reflective blankets and put a wood stove in the room (mom has one she removed from the geodesic she built in the 70's). Then just blow the warm air through the house with fans....But I don't have electricity down there and am still using 14g extension cords to run small things like a power drill. Would hate to burn moms house down with a bunch of fans overloading plug at the house.

Fatal : Yes you can do everything you say you want ! You have a lot of work between now and Feb ,and you are going to be a self trained expert by the time you are done! Due to the way that you will be using the heat off of your thermal bench , you will have two different heat loads , With a Raised bench thermal mass set at a height handy for you, your seedling beds can have gentle warmth at their roots with a mini tent above holding in your heat, later during the 'use every cubic inch of Green House times', your heat load will be higher, as you will need more heat in the air in your room !* Your 1st steps are baby steps, You will need Ianto Evans Book "Rocket Mass Heaters" and because you are going to have to deal with high moisture, you are going to need one of the Books on Cob Building**!
By elevating your thermal bench off of the ground you will avoid most of your water problems, but you will need to know how to seal the bench and how to repair it !
Due to your changing heat loads I cant begin to answer your ' how many' questions ,but these forums draw people like yourself with many different skills, someone will have a link to the answer !
A 6" system will support 30', larger pipes more than that !
With an raised sealed bench you should be above your water problems**, but the stove pipe is just there as a form to pack your Cob around, if it rusts no big deal !
An in ground system is harder to build and is usually left for someone with lots of Rocket Stove Mass Heater building experience, If you go that route, one heater to test would be a lot !
There seem to be a dis-connect in most builders minds, wanting turbulence in the J-Bend of the Rocket stove, and demanding Smooth and Round interior Walls in the horizontal runs in the
thermal bench. I would follow the norm here and let someone else reduce the length of their horizontal pipe run with a rough-walled system !
The larger the cross section of the Feed box *** The bigger the chunks of wood you can feed it ! A bigger system needs to be fed less often, that being said 3-4 hrs of tending your wood s stove should get you 20-24 hrs of heat out of your bench !
If you burn dry wood only, you should Never see a 'chimney fire', lack of cleaning will cause the stove to smoke though, so each Rocket stove will need weekly cleaning !
Rodents, birds,bats, and snakes are often found on cleaning furnaces and during 'Service Calls' a pieceof 1/4",3/8ths", or 1/2 '' hardware cloth should keep the critters out w/out blocking your
Hot Exhaust!

Running electrical motors is/are the most efficient use of Electricity, but play it safe and save on Electric Bill

Keep us informed on your" Rocket stove in a green house build", the more we share the more we learn ! Pyro - maticly yours Allen L.

* At this point ,the earth below the seedlings and the seedlings themselves will be insulation, blocking heat escape from your thermal bench. You will need to make an air gap or move your s e seedlings !
** Cob, which is great for building up thermal mass quickly, and cheaply (as cheap as dirt !) will slump when wet, I need more information to help you here !
*** the feed tube,fire tunnel, j-bend,heat riser, cross sectional area of Free space in the 55 gal drum, and the stove pipe in the thermal mass should all be equal to each other !

the water barrel would help to regulate the temperature in its immediate surrounding but I do not think it would do much for an entire green house. That being said I would leave the water out of the plans.

Mice would not get into your exhaust because the system is not open to them, the exhaust pipes are kept closed until they are run outside, at that point i think some large mesh on it wouldn't hurt a bit, i worry about birds too.

My suggestion is that you do heat your walkway but keep the water away from this area by putting your plastic actually outside the mass which is holding your heat, it will be cooler on the outside of that mass by a lot.

The idea of the mass heater is that there is a mass which holds the heat and lets it go over a period of time....put a brick into the oven and see how long it takes to get hot and how long it takes to cool once placed in a cooler area....this mass must hold the heat there is no way around it. If the mass is wet the water will take up much of your energy evaporating and you could end up creating a steam house...not your goal at all... and with the heat going into the water the mass would lose its energy too fast...think of sticking that hot brick into the dishpan, the water moves the energy way much faster and very quickly the water will be the same temperature as the brick. Keep water away from your thermal mass.

cob is not a good match with water, I would not put it under ground, there will be wee bits of water getting into your thermal mass just because it is a green house, I would use brick, sand or stones for the mass, mix them up if that is what you have, they are all mass which holds heat. If you happen to have perlite you could put some between the thermal mass and the poly as it is a fine insulator but it is not thermal mass.

Others would be better for the remainder of the questions but i think the mass heater really is your answer, you wont even have to live in a greenhouse . He is right, even if poor, the 9 dollars to buy the book is a good investment and can save you from a bunch of work redoing things once you have it understood. You might check with your local library and see if they have a book or if they can get one through inter library loan.

Thank You Allen & Laura for your detailed responses!

I will definately have to think of how to secure the exhaust ends to make them critter resistant. I am already having nightmares of every snake in the neighborhood moving into my exhaust and thermal mass.....the mice, and other 4 legged furries make a mess of everything, but they don't freak me out. The rattlesnakes seem to love the greenhouses, especially the new babies....I try to "live & let live", but there is also my liability insurance to consider if a customer steps into a nest of baby rattlesnakes.

I don't know a lot about cob, but having heard that it doesn't get along with water, I was not even considering its use. From the moment the house gets fired up to heat, it will be in FULL USE. There will be hanging baskets on the bows and centerline. The floor will have annuals that can grow in shade and cooler soil temps. The benches will have seedlings and tropicals, early crops of flowers. I am interested in turning the back half of the house into raised beds to do some veggies....but that's not something we are as knowledgeable at doing. We are container growers. We grow annual flowers and potted veggies for sale to home gardeners. We also do heirloom fruit, perennials, shrubs, trees, native (species & cultivars), etc...

Where can I get the book on RMH by the Jacksons? I looked on amazon, and it's like $100.

The hoophouse on the far left is the one I intend on heating. We have lots of softball-sized and smaller rocks. We also have copious amounts of sand.....almost zero clay of any kind. When we excavated, we ran on one ribbon of clay that's almost not even worth mentioning. We found far more beach sand, and we are nowhere near a beach. And lots of rocks!!!

I wasn't really planning on having my thermal mass above ground. I had hoped to have it in ground. Seeing as how we have so much rock and sand, my thought process for surrounding the vent pipes was to create a mortarred rock channel in the ground, that houses the 6" exhaust pipes. Then fill around the pipes with pea gravel, and cap the top with cement paving stones. This way, I could access any deteriorated areas to make repairs, and they wouldn't be burried under a bed of plants.

Though I suppose I could build above ground if I have to...I would have to be solidly set on how I wanted my floorplan for the house to be permanently. That could be slightly restrictive. hmmm....

your right i just looked 100 dollars. funny i ordered one for 36 dollars two days ago..look elsewhere

Go to www.cobcottage (org? com?) for 'Rocket Mass Heaters ', downloadable version -all the copies you can make - $15.00

Just purchased the download from this site:

http://www.rocketstoves.com/

Yup, that works! Or www.ernieanderica.idea/shop

would you believe that amazon just got in more paperbacks at 18 each, which was what i paid (i had large book order so i read the wrong line)

Franklin and Laura : I created the simple forum thread "rocket stoves in greenhouses' for new members to draw them to their own forum thread "rocket stoves in greenhouses " it should also link to here, check in, check often, Allen L.

Franklin, we have a 30x70 greenhouse where I work and it has an outdoor furnace that uses wood. We made the furnace from a piece of pipe (just like a barrel stove) then surronded that with a rectangular box made from plate metal. We have a blower from a central air conditioner unit that blows air from inside the greenhouse, into the rectangular box and around the stove, and back into the greenhouse into a clear plastic tube 18" in diameter, with small holes on both sides, that hangs from the ceiling the length of the greenhouse. It can be bought from a greenhouse supplier. The far end of the tube is tied shut like a trash sack so warm air comes out the small side holes. The trick to heating it though is that we have two layers of plastic over the greenhouse with a small centrifugal fan blowing air between the layers to keep them seperated. The air space is insulation. You can tell a world of difference. In 20 degree weather you will be in a t-shirt and it is warm from one end to the other.