Chris Dales

Fox James wrote:Piped mass is not so popular anymore as the Bell system has become more popular.
The type of pipe that has been used might depend on other factors like…. are you going to load tons of mass over the pipe because you will then have to use a strong pipe.
There is another thread going on about using hollow concrete blocks instead of expensive pipe.

Thanks for the reply.
I unfortunately simply don't have the space for the bell system. By using the floor as the mass, I am hoping to save space.
The 6inch pipe would be in a 10inch concrete floor, with no significant loading on the floor. From the research I have done, it seems the flue needs to be as smooth as possible, and need to incorporate clean-out access points. I'm not sure how to achieve this with hollow concrete blocks. If going with pipe, I don't know what sort of temperatures to expect and so not sure if simple spiral ducting would be up to the job. But the videos I've seen do seem to use the simple spiral duct. Am I safe to assume that by the time the gasses fall down the inside of the drum, they are cooled enough for the use of spiral ducting? Or do I need to cough up for expensive flue pipe?

Hi.
I am slowly producing my bespoke design for an underfloor RMH. I'm almost there with it now, but, I am trying to work out what product people use for the flue pipe within the mass. Looking at various videos and images, it doesn't look like people use actual flue pipe (which is very expensive by the time you factor in bends, junctions for cleaning etc). So, what do people use?
Chris

thomas rubino wrote:Stick with an 8",  if it gets too warm then burn it less often.
I'm not sure what your best fill would be beyond cob, I guess dirt would be my next choice rather than concrete.

Hi Thomas.
Thanks for the reply.
I can’t help but think that the mass must be solid enough to be the floor itself otherwise I’d be putting a deck on top which would act as an insulator, which I don’t want.

So, I’ve been researching brick bells (thanks for the tip), and they are certainly on the radar for a future project. I can certainly see the benefit.
However, I simply won’t have the space in my small office build. I think on this occasion I need to utilise an under floor mass.

Having done more research, I’m now uncertain about 2 things…
1) I still don’t know what material to use for the floor mass given cob isn’t a feasible option for me.
2) will an 8inch system be too much for such a small space (12ft x 10ft)? Would I be better downsizing to a 6inch system?

I really wish there was more interest in RMH in the UK so there would be more advise over here.

Hi Baxter.
I would love an update on this please.
I’m about to create a similar set-up with the mass being the concrete floor. However, I’m worried the differential temperatures will cause the concrete floor to crack.
Have you experienced any cracking of the concrete?

Douglas Alpenstock wrote:Concrete is a big investment. It works with liquid piping, which has a limited high temperature.

My worry is that the differential temperature within a contiguous concrete slab will cause cracking, and as the piping degrades, exhaust leaks into the living space. Perhaps I'm over-reacting, but frankly, I think it's a big gamble.

There must be a better way. What is your subsoil made of?

This has been one of my concerns too. I’ve considered expansion joints, but these would interfere with the thermal mass. But then why would it be any different to any modern underfloor heating? That doesn’t break up.
Also, I understand cob would crack exactly the same and that I t is the stove pipe that is relied on as the exhaust is at a lower temp when exiting the manifold, and therefore shouldn’t degrade.

Like I say, RMH are far and few between here in UK, and so I’m working on internet research and my own theory only. A gamble.

The sub-soil is a decent top-soil to quite a depth. It’s old farm land with lots of organic matter. On top of that, the location it will be on is where previous owners mounded more topsoil when excavating for a pond.
Being a uk city location, there is very little space to locate it.

thomas rubino wrote:Hi Chris;
The UK has plenty of bricks readily available.
Have you considered a brick bell ?
All above the floor in any shape that fits your tight space.

I understand the bell needs to displayed heat as quickly as possible in order to create a downdraft. A brick bell would retain the heat which would interfere with this.
Or have I misunderstood your suggestion?

*flues

Hi. Thanks.
Multiple flies are a bad idea then. Best sticking with 1 larger glue bent around the space?

I did consider the Roman hypocaust design, but didn’t go far with it due to the amount of excavation I would need to do (planning limits the height I can build) and I felt there would be a lack of heat retention due to lack of mass.

PS: yes, I have purchased and read the RMH builder’s guide.