My plan is to use either brickwork ducting or hollow concrete blocks which I have already, cemented together to create a tunnel. is this a possible solution or am I missing something
the internal chimney of the RMH acts as a pump, i.e. the flue gas is under a slightly higher pressure. If there are any cracks in the thermal mass without metal pipes the flue gas is squeezed out. You should at least buy a CO-detector with alarm function and place it close to the RMH. A properly build RMH should burn the CO to CO2 inside the burn chamber but I would not rely on this. CO (carbon oxide) is a very toxic gas and you can not smell it and not see it.
Metal pipes are airtight but concrete blocks are not. If you find a way to make them airtight, I am sure many people in this forum would be interested.
We do try and work at keeping the horizontal stovepipe walls inside our Thermal Bench as smooth as possible, you could paint on a layer of clay slip,
this will allow you to flow the gas faster and further through more horizontal stovepipe but, there will be a sleight trade off in heat absorption,at the
boundary between layers, made worse by any trapped air ! Hope this helps, and is timely .For the craft !
Think like fire, flow like a gas, Don't be the Marshmallow! As always, comments / questions are solicited and Welcome! PYRO - Logically Big AL
1. If you completely coat them with cob (including the bed under them) it should seal, but you can have cracking issues in the cob because of expansion/contraction problems.
2. You need the exhaust to be cooled down a little bit before you hit the concrete, even a little cooler than you need for galvanized duct. So you need an extra piece of pip before you hit the bench.
3. They will not flow nearly as well with the rough surface. But they will probably suck the heat out faster so you just need less bench.
I was going to put this under a stock tank to heat it in the winter, but plans changed and I went to a more freeze-resistant watering system.
Nation wide company in the uk.
Have you heard of the half barrel system? Cheapest easiest way to skip the flues. Tho, i've got nearly endless supply of barrels if i want!
If this can give some inspiration!
I will check out Lindab and the half barrel idea and maybe save the concrete building blocks for an outdoor stove
Thanks again, will let you know how I get on
I think your idea would work as long as you consider CSA and do your best to seal any leaks. I also believe R Scott's 3rd point is the most relevant and will be the reason it wouldn't work if there is one. Friction inside the bench will hurt for sure.
If anyone wants to learn more about the pressures, Donkey's board has good info, and here's a great starting point...
All fixed (ish) now.
Matt Walker wrote:Max, yours is a special case for sure! I didn't mean to imply you shouldn't do everything you can to seal them. One certainly should seal a system in my opinion. Just wanted to offer a differing opinion of what is going on inside a running system. When starting from cold, which you are always doing since you have no mass Max, they will send gasses out of the leaks, but in my opinion that's due to a "plug" at the end of the system from a cold stack, rather than pressure being developed by the combustion core/radiator combo. As Peter, Donkey, myself, and others have noted, once warm and running the pressures are lower within the system. At any rate, upon further reflection, I think as drawn the friction on this one would be too much drag as R Scott so astutely points out, so it's a moot point anyway.
Well, runing a 6 incher batch rocket with 8m of tube, and a 111mm restriction before getting to the weird vertical chimney stack sure doesn't help
But what if there is no vertical chimney? In this case the pumping effect would always pump flue gas in your living room (again, if there are cracks in the thermal mass).
The Venturi effect, you mentioned, is as stronger as higher the speed of the involved gas is. I think the gas speed inside a thermal mass of a RMH is quite low.
Is this enough to suck air through the cracks into the thermal battery?
OK, even if this effect is low, it can work in the same direction as the stack effect of an external chimney. But I think it is too weak to overcome the pump effect in a RMH without external chimney.
Let me tell you a story about a man named Jed. He made this tiny ad:
five days of natural building (wofati and cob) and rocket cooktop oct 8-12, 2018https://permies.com/t/92034/permaculture-projects/days-natural-building-wofati-cob