This past winter was my second with a rmh. the first year we had a wet core & mass and our woodshed never got filled before winter. I guestimated that I burned 7 cord that winter. Prior to having a rmh we burned 12-15 cord in the greenhouse ! I was very pleased with only burning 7 cord ! This last winter I put 5 cord in the greenhouse woodshed (thats all it holds) burning season began in late aug.-september now it's mid may and i am still lighting a fire in the early morning (not because it needs it ,but to make it warmer sooner) It has been one of our warmer winters here, but we still went below zero for a while. All winter and I have burned a little over (get this) FOUR CORDS !!! Hot damn this is fricken awesome !! That is keeping the studio at 65 F + all day and at night with no fire from 10 pm- 7am or so it was always over 40 F . I have attached pictures showing the full 5 cord in the woodshed and then pictures from today showing that there is still plenty of wood still left over! This is a solex /plastic covered building with high ceilings and a dirt floor... no insulation here! If you are considering building a rmh in your insulated home, plan on having free time or extra $ on your hands that you used to use getting firewood! Have no doubt that a properly built rmh will save you time & money!
Hello fellow Montanan and congrats on your rmh success! Can you share your method for heating the greenhouse? I am planning on installing a greenhouse next season and would like to get some ideas to incorporate into my plan. Thanks for your time.
Hi Jeremy; Glad to share any details ! My greenhouse/artist studio is 12x20 and has a stone foundation wall on 2 sides. We have a mud room entrance to isolate the mass and reduce heat loss from opening doors. Timber frame construction ,with 12x12 pitch roof (easily sheds snow) building has large single pane windows on one side that have to be covered over in the winter. Dirt floor. North wall is framed and has 4" insulation , the stone foundation is insulated from my mass with 4-5" of perlite. Rest of the building uses "solexx" A not cheap but very awesome, flexible, insulated, opaque covering that was worth every cent we paid for it. Both upper ends of the building are hinged to open up to allow free airflow in the summer to help with cooling. Now on to the RMH. I went with an exposed aboveground mass, rather than a buried one. 8" system with apx 13' straight run, than a 180 and 9' return towards the core, with another 10-12' pipe indoors rising to the peak of the roof. My mass is a coblasagna of slate and cob encased with clay brick. The exposed mass works as a heated table to set trays of starts on, or if you are growing tropicals they would love keeping their feet warm on it. Our greenhouse was intended to grow vegetables all winter... however the artist in residence here decided that it would be used as an art studio and we would grow succulents for her art instead... Typical winter day I go out around 7-8 am and start the first fire. If someone is working out there fine, but if not then every 40 minutes we troop out and restock the feed tube. This continues all day depending on just how cold it is that day. On a typical winter day with teens outside we happily have an indoor temp of 60-70 degrees. By 9 or 10 at nite we let the feed tube burn out then cover over the hole with bricks. Next morning it will be 40-45 degrees at 7 am! Hope this answered your questions. I am located 2 hrs nw of missoula in the clark fork river valley off hwy 200 (near trout creek) RMH fans are always welcome to visit.
Not all who wander are lost... J.R.R. Tolkien
posted 5 years ago
Thomas, thanks for the details ands additional photos, it really helps a newbie like me get a better understanding for this project. I'm really glad to see your solution as I've been considering the cob wrapped in brick or time as a solution for myself as well. My only sticking point or more accurately, a mental hurdle, is the cob creation. I get it on a fundamental level. I'm just not sure about the step by step for cob. Does you buy clay material or use onsite stuff from your land?
I'm buying a pre fabbed greenhouse so my modifications are limited a bit more. My current plan is to have the j tube and exhaust outside the greenhouse.
Trial and error are am important step I'm getting ready to take!
As far as clay & sand goes , some people buy bags of dry fire clay & mix with dry bags of builders sand . I have a neighbor with a backhoe, who happily loaded my f-250 full of nice clean clay. I could have used clay from my land but would have had to dig by hand !!! Then there is a spot here in town where you can stop on the side of the road and shovel all the coarse clean sand into your truck that you want. I went with brick around my mass for several reasons. Its a greenhouse and I wanted to use a hose to water, didn't want to wash my mass away. Rock / wood / metal /even sheetrock can be used to enclose your mass, or cob itself can be made water resistant with a sealing coat. I really liked working with clay brick , it looks good and it adds to your mass. Making (mixing) cob is work , no way around it. But it's not rocket science ... easy... mix 1 part clay to oh .. 3 parts sand add water and work it into a gooey sticky glop , not too wet not too dry and walla COB ... surround your horizontal pipes with cob , add rock & cob to make a lasagna and your mass is on its way. Last but not least, your plan of the J tube outside and the exhaust pipe outside are not a good idea in cold country. Make room inside for both the core and your chimney and gain the extra heat from them as well as keeping your exhaust warm enough to keep drafting.Remember it's a plastic greenhouse and you're asking it to stay above freezing with no fire, on montana winter nites ... you will need all that heat to sit inside and radiate all nite long. Any contact with the outside cold temps will suck precious heat away from your core and your greenhouse.
Not all who wander are lost... J.R.R. Tolkien
Rocket Mass Heater Plans: Annex 6" L-shaped Bench by Ernie and Erica