I posted this down below at the end of the discussion on these heaters inside green houses but that thread seems to be dead. I thought maybe if I bring it up as a new thread it might get seen better. Please forgive me if that is not the ops normal way to handle this.
Hi folks. I am new to the permise forums and this is my first post. I have been considering building a greenhouse (perhaps pit type) and putting a rocket mass heater inside for heating the green house. My question is, how do you control the temperature with a rocket mass heater? Is there a way or not? How warm does the mass such as cob usually get. Most plants like a warm place to germinate but then a little cooler temp for growth. Is there any way other than venting the greenhouse to control the heat level? Thanks.

You could germinate inside the house and then transplant 3 days later.
The RMH bench feels nice to sit on so I would think 100F, however the air does not get that hot.
The best way to control the temp is just to try it and figure out how much wood it take to get a given space (200sqft vs 1200sqft).
So just add small amount of wood or a LARGE thermal mass to keep a steady temp.
You are probably still going to need a fan/windows in the ceiling for cross-ventilation.

Hi, Though I do not have my rocket mass heater built yet, I will be heating a greenhouse with it. This is the green house' second winter, and this year is much colder than last year. I don't have any fans etc. I think it depends a lot on how big and the design of the green house whether you need hardware etc to do all that.

You say a pit type greenhouse, and I don't really know what that is. I did make the mistake of building my greenhouse on the lowest corner ofmy land, a little below grade, and so have had to do some earthwork to be sure surface water will flow else where. Just something to consider if you are in the plannning stage.

I built my greenhouse adjacent to the chicken house so they could work together to maintain warmth. The green house is cob-- think of a quarter round. West is the flat chicken house wall, north and east are the curving cob wall, and a flat south wall with recycled glazing. The south wall is about 16 feet long, the south to north direction is about 13 feet. I live in western colordo, with lots of sunny days. But we are having mre thn our share of cloudy days in between the colder than usual nights, so ther eis not much solar gain. Still, the house has only gone down to 28 F, which though it is below freezing, it is about normal winter weather for where i grew up ( small valley in Calif Coastal range, mediteranean climate) so I am pretty familiar with what will grow in those temperatures. Trouble is, I have moringa plants, who don't like it below 40. They are living in my house with me.

Having worked with my greenhouse for a while, I feel pretty certain I will be able to manage a higher temperature at a decent chosen range. I have a maximum- minimum thermometer, and with watching the weather forecast, and some experience with the in progress stove, I think I will try germinating seeds when tat time comes later this spring.

Good luck. I would be happy to tell you more about my greenhouse design, and about the heating system when I get it going, if you are interested.

Thekla

While we're on the subject of greenhouses...has anyone tried a greenhouse here using Pilkington K glass?

http://www.pilkington.com/europe/uk+and+ireland/english/products/bp/bybenefit/thermalinsulation/kglass/default.htm

I see in one of the videos on this site there is were plans to build a RMH inside a cold sink pit type green house. Has that ever been completed? If so, how does it work?

Another question on that same line: If the exhaust is mostly steam can that be vented right into the green house? Is there any co2 coming out with the gases? Thanks.

Denny Nebgen wrote:I see in one of the videos on this site there is were plans to build a RMH inside a cold sink pit type green house. Has that ever been completed? If so, how does it work?

Another question on that same line: If the exhaust is mostly steam can that be vented right into the green house? Is there any co2 coming out with the gases? Thanks.

The exhaust has as much H2O(steam) as there is CO2. Even though the RMH is really good, you still have Nitric oxides/acid, some sulphur oxide/acid and carbon monoxide, VOC and whatever did not get completely burnt. You never really want to inhale fire exhaust the carbon monoxide and other stuff is heavy and will settle to the ground possible killing pets, childrens and even you if you stay in there too long. I just dont think that it is worth it.

S Bengi wrote:

The exhaust has as much H2O(steam) as there is CO2. Even though the RMH is really good, you still have Nitric oxides/acid, some sulphur oxide/acid and carbon monoxide, VOC and whatever did not get completely burnt. You never really want to inhale fire exhaust the carbon monoxide and other stuff is heavy and will settle to the ground possible killing pets, childrens and even you if you stay in there too long. I just dont think that it is worth it.

Thank you. Glad I asked. The thought I had was the CO2 would be good for plants in a green house. Thanks again for clarifying.

Just thought of another question. Is there a limit to the length of flue pipe running through your mass heat sink?

That is a very good question. You dont want to absorb so much heat that the air no longer raises and you stop a getting good draft.
I think it would be a mass/volume not so much just length. It would be a good question to ask though.

If your burn chamber is generating 10x amount of heat and the mass is absorbing 9x then you get a good draft if the mass is absorbing 11x then you dont get a good draft and you get smoke back water settling in your pipe.

Sounds like a good topic to put in a new thread.

I am seeing in some threads on the Rocket Mass heaters that there is some suggestion that they need fed quite often to keep them burning in order to get the mass to temperature that will maintain heat inside the greenhouse say throughout the night. This could be a real drawback for this idea of mine. I can see where if you are inside a home tending a fire throughout the day would not be a problem but, inside a green house you may not want to be inside there all day to tend the fire continuously. Any thoughts on this? Thanks.

Denny Nebgen wrote:I am seeing in some threads on the Rocket Mass heaters that there is some suggestion that they need fed quite often to keep them burning in order to get the mass to temperature that will maintain heat inside the greenhouse say throughout the night. This could be a real drawback for this idea of mine. I can see where if you are inside a home tending a fire throughout the day would not be a problem but, inside a green house you may not want to be inside there all day to tend the fire continuously. Any thoughts on this? Thanks.

Hi Denny,

Well, I can tell you some of what you are asking from my experiences the last couple of days. I have a 24 foot hoop house, that I have insulated with a solar pool cover when the temps are really getting low. The last couple nights it has gone down to 5 degrees. When I got up yesterday and today at 5am, the temp inside the hoop house was 20. I have the plants covered with floating row covers. I built a fire in the morning, and got the temps back up to the forties, with temps in the teens outside. My bench is 20 feet of cob/rock covered 6 inch pipe.

The bench heats up to 100 near the stove, to around 80 where it exits the hoop house; that's with me firing the stove for a few hours. The top of the barrel gets to 500 degrees. To keep the hoop house above 30 on those nights, I would have to get up in the middle of the night and fire the stove. After you get used to firing your stove, it only takes going up once an hour and stoking the fire. Hope this helps...



Mike

Thank you , Mike and thanks for the pics. That helps give me an idea of what to expect . I suppose a double layer of plastic might also help.

Denny Nebgen wrote:Thank you , Mike and thanks for the pics. That helps give me an idea of what to expect . I suppose a double layer of plastic might also help.

Hi Denny,

Glad to help out. There is a way to use double layers of plastic; you use a small pump to put air between the sheets of plastic. Never tried it, but saw it done in a small greenhouse in my area. Also, insulating the sides of the green house would help too
(Those two black trash cans in the pic are filled with water for two reasons: to heat up from the sunlight, and to be able to water plants when the hose is frozen.)

Mike