Michael Robertson

http.www.traditionaloven.com/articles/101/what-is-fire-clay-and-where-to-get-it - doesn't work.

www.traditionaloven.com/articles/101/what-is-fire-clay-and-where-to-get-it does. - works fine.

If a TEG is impractical how about a stirling engine? There has been a lot of discussion about Stirling Engines on other threads if you do a search of this site.

There are lots of sites where you can buy them or if you are skilled make one yourself. They can be made to be powerful generators or tiny engines running from the heat off the palm of your hand.

Some links:-

http://www.howstuffworks.com/stirling-engine.htm





http://dirtsimple.com/

http://www.stirlingengine.com/

I sometimes wonder if the principle behind the pumping action of the RMH is the same as the stirling engine. A kind of "solid state" stirling engine.

The book arrived today so maybe I will have fewer questions from now on. I have re-built and now the dimensions are

Feed tube 7" by 6" = 42 csa (still not worked out how deep to make it yet.)

burn tunnel height 5" width 6" length 12" = 30 csa

Heat riser opening 7" by 6" = 42 csa The height will be 31" by using a thin walled pipe of 7" diameter giving a csa of about 38 sq inches with another steel pipe of 11" diameter meaning I will have a 2" gap for perlite/slip clay insulation. Do I take it that the insulation needs a burn before it sets hard or will it set naturally given time? The gap between the riser and the wall of the drum will be approx 5" all round - is this too big? I could make a bigger outer pipe by making one from sheet so giving more insulation and less "tumble" space. Please advise what is the better option. Oh and I have never used perlite but have just bought 100 litres - does it expand when mixed with the slip clay? Many thanks,

On reflection I think that some microscopic asbestos might get into the flu gasses and come out through the exit chimney making it hazardous. I will drop that idea and think of some other way to contain the perlite mix. I have some corrugated tin roofing sheets which I can probably use if I fix two together and make into a circle. I rang my local authority and they will allow me to dispose of the asbestos at a particular site they run as long as I double bag it and tell them when I am coming and how many bags I have. Thanks for your help Allen but one more question, will the cob I used to narrow the burn tunnel stand up to the heat?

I found the answer to the cob perlite ratio. You make clay slip and mix perlite until it binds and when squeezed it doesn't exude water but still clings together. Ok now another question. Does the cob/perlite insulation on the heat riser have to be contained with something or will it stick of its own accord? Still waiting for the book to arrive! One more thing, I have some sheets of corrugated asbestos left here by a previous owner and they are difficult to dispose of. If I need to encase the perlite/cob insulation could I use the asbestos sheet?

Cindy - Thanks for responding. I think the mass heated bench is most appropriate for a greenhouse, as a warm bench giving bottom heat for seedlings and cuttings.

Allen - I checked a few of the bricks and they all left a lovely red chalk mark so they must be acceptable.

I demolished the heat riser this afternoon and altered the dimensions of the burn tunnel. It is now as short as I can get it which is 8 inches long. It is 6 inches high and 7 and a half inches wide. I narrowed it using cob - is this ok, will it last? Can I now make the heat riser 10 inches by 8 or is that too big? I am limited by the size of the bricks unless I cut them. Is it an advantage to keep it close to the burn tunnel csa? Sorry for all the questions but the book won't get here for weeks. I sent for a 100 litre bag of perlite today for the insulation. One last question (for now) what is the ratio of perlite to cob to make the insulation?

Thanks

A larger csa in the ductwork is not a problem and I can line the inside floor and sides with smooth cob to help flow. My greenhouse will be about 16 feet by 10 feet and I hope to have a heated mass bench about 10 feet long (with a return so 20 feet of ducting in all) and about 3 feet wide overall. The main aim is to ensure a frost free environment. We get temperatures down to about minus 10 degrees centigrade sometimes, although not often, but sub zero temperatures are common from November to April. I think the big warm bench is the way to go. I don't know what "Bells" means so I am off to look in the forum to find out! Thanks for the advice about making the brick duct large - I wasn't sure about that. Could you tell me should I insulate the inside of the burn tunnel or just the outside or both. I hope to start re-building it this weekend.

Thanks Allen - I will check the bricks. I sent for the book today but it will take from two to four weeks to get here and I want to keep working on my rmh so keep fielding my questions in the meantime please. I was able to access an old version of Ianto's book a year ago and remember he mentioned the horizontal run possibly being made of brickwork without the need for metal pipework. Since I have about 1000 bricks lying around (I was going to block pave my driveway but it can wait!) I thought since I am having trouble getting the hvac stuff I could try making a brick tunnel with a steel pipe vent at the end near the heat riser drum. What do you think? Lots of work but I have the time (retired) and the materials pretty much. Let me know your thoughts please - much appreciated.

To Glenn - The burn tunnel is made of solid yellow fire bricks, the old fashioned heavy kind and is not (yet) insulated. The heat riser is made of solid old type red bricks (without frogs) mortared with cob. They came from a chimney off a victorian house. I take it this kind of riser does not need insulation. I have room to apply a coating of perlite/cob mix as a render if you think it is worthwhile. I will be insulating the burn tunnel with the same mix when I rebuild it. Thanks for your replies.