I came across someone's video on youtube for a heater he built. He used fire brick to build a J tube and heat riser. He then covered the heat riser, no insulation around it, with a barrel, 2 inch between top of drum and heat riser with a flue coming out of the bottom of the barrel. Pretty standard but his exhaust flue coming out of the bottom of the barrel had an elbow on it that pointed up and his chimney flue went straight up to the roof and out. In his case he did not use mass to store the heat instead used the heat given off from the barrel only. He said that the gases leaving the barrel needed to travel through a flue that was layed in an upward angle and not level. He referred to the mass heater flues of 10 to 20 feed buried in cob mass for heat storage that he has seen on utube.
Question is this: Does the long flue buried in cob need to be at an upward incline or can it be level? Not yet having built a one I thought I would ask for thoughts and input.
Please answer the posters question instead of denigrating the source of his interest.
The best answer I can give based on following the topic is based on the rebuild of the RMH in Paul Wheaton's house. It has a waist high pebble bench and the flue makes a gradual rise to the end of the L shaped bench from the bottom at the barrel exit to the the top of the bench at the flue to the roof. He rates it as not the absolute most efficient but the most goof proof for inexperienced users.
I am always building things in my head. One of my imaginary builds was to have a wall of cob or rammed earth in the center of the house but toward one end minus the door to the bedroom with the bedroom and bath on one side and the living room on the other with the RMH on the end of the wall on the open end where the kitchen/dining would be. The flue would zig zag all the way up through the wall and never be exposed to the inside before it exited the roof.
Getting back to the answer as I read it The flue can be level in the bench but starting the flow through the bench may be more difficult. If when the feed to the RMH is opened, air always wants to flow up the flue and not down it will work But that often depends more on the air flow through the house than the configuration of the flue.
As far as the question about level or angled flues, I would expect that a level flue (what would go through the mass) is probably going to work, but having a slight rise (an inch or two every 5 feet or so) can help. Not only would it help with drafting, but also with moisture. Especially when the mass is drying out, you'll find a lot of moisture needing to go somewhere. Directing it intentionally is better than not.
In the case of my RMH, an accident appears to have helped. My mass is made from poured concrete. We laid the flue pipe with a slight rise and made sure it wouldn't sink lower as we poured the concrete. Unfortunately, we didn't expect that the pipe might try to float. A mad scramble ensued as we saw the problem happen, and we ended up with a flue that rises from the barrel, reaches a peak (serendipitously right where I keep my shower towel!), and then slopes downwards as it exits the building. What happens now is that some of the water comes back down, but some drains out, and there is a warmer spot on the mass bench. Last winter it created a nice stalagmite as the water drained outside.
I'm hoping this winter there won't be as much moisture created as the mass is much drier and so is the wood I'll be burning.
Creator of Shire Silver, a precious metals based currency. I work on a permaculture farm. Old nerd. Father.
Location: Northern woods of Minnesota
posted 4 years ago
I want to thank you all for the input. As of this writing Dec. 16, 2015 I'm still in the planning and education stages. I built a 16x28 barn/workshop (the first structure after clearing build site in wooded land) and a travel trailer as a 3 season residence. Actually it was the second building I put up. The first was the out house. I have my prioritys. I plan to insulate and make the barn a 4 season structure this summer and building a RSH in it. Then I will build the cabin and plan to expand and capitalize on my experience by building another RSH.
Also, anyone have any luck with mixing cob in a 4.1 cubic foot 1/2 hp electric cement mixer, is it practical and doable?
Thanks again, Dan...
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''