Repurpose chimney breast as a bell

Hi guys

I have an old Victoria house with a typical chimney breast that spans along each floor of the house until it vents the Flue at the roof.

I will be removing the chimney breast in the 2nd and 1st floor either way.

I want to remove the chimney breast in the ground floor and rebuild it using the same bricks for the bell of a batch box RMH.

The fire box will be sticking out of the chimney breast (now repurposed as the bell) due to its depth. The chimney breast is currently only 35cm deep. I might look in to the side winder design to save space.

I also want to line the far wall of the bell with Ceramic Fibre wool or similar insulation so that I don't lose all of the heat through the wall in to the neighbours house. Is this an effective strategy?

How low below the ceiling should I cap the bell so that I don't cause heat damage to the ceiling/coving?

Will a single skin bell suffice? Any drawbacks to this?

Let me know any other thoughts or ideas.

Thanks

M

Hi, some photos and or diagrams would help us to answer your questions no end.

Hi M;
I'll try to answer some of your questions.
A single bell will share its heat sooner, but will also lose that heat more quickly than a double skin.
In this case, you want that heat to travel upstairs and not create a super warm basement.
A double bell takes longer for the heat to transfer to the outer skin but holds that heat much longer and sends it upstairs sooner..
If you have headroom concerns, the roof of your bell can be insulated to limit how hot the bell roof can get.
You should use an insulator between your home and the neighboring house or any outside wall the bell is close to.

One important thing to calculate is the (ISA) internal surface area of your bells.
There is a limit to just how much ISA can be maintained hot to keep a steady draw up your chimney.
Bypasses can be installed to direct your heat to the outlet sooner and then be opened to heat more bell once things heat up.

A Sidewinder core would stick out into your room slightly less, either core would need to be heavily insulated to put that heat into the bell system and not into the basement.
Heating an old Victorian house is a big job for any wood burner.
Hopefully, your home is modernized with  better insulation and double-pane windows.

thomas rubino wrote:
In this case, you want that heat to travel upstairs and not create a super warm basement.

I'll just clarify this one Thomas - In the UK the fist floor is the first upstairs floor, so what you might call the second floor for us is the first floor. It sounds like M may have a three story house, with the RMH on the ground floor and two stores above which he is removing the chimney from. (Side note M. do make sure that you check that out structurally as well!)

Pictures or a diagram always help! I'm also interested to see what you come up with M. I don't see why it shouldn't work if the bricks are of suitable quality.

Many thanks for all the replys guys

I've attached a picture which hopefully make things clearer.
The chimney will be removed in the floors above (subject to structural engineer approval) but I really want to keep the ornate coving, so i will knock the chimney out above and below the coving and then rebuild the bell up to a point that it can support the weight of coving +- brickwork on to which it is fastened.
I just need to make sure that the top of the bell is sufficiently insulated to protect the coving/ceiling from heat damage.

thomas rubino wrote:A single bell will share its heat sooner, but will also lose that heat more quickly than a double skin.

I think that is a massive plus point (especially because I want to harvest some of the heat to heat water, however I just don't have the space for a second internal skin for the bell as it will greatly diminish the bell volume :S
The external dimension of the chimney is 0.35m deep, 3m high, 1.7m wide.

thomas rubino wrote:If you have headroom concerns, the roof of your bell can be insulated to limit how hot the bell roof can get.
You should use an insulator between your home and the neighboring house or any outside wall the bell is close to.

What are my options for insulation materials in terms of best performance and best value for money?

thomas rubino wrote:There is a limit to just how much ISA can be maintained hot to keep a steady draw up your chimney.

The ISA will be quite small. I haven't calculated it yet but I know the ESA will be 7.3 sq m.
If I end up going for an 8 inch system, this size bell will be well within the limits where a bypass won't be required.
Either way, the flue is going to be going through the bell, so it will get plenty of heat.

thomas rubino wrote:Heating an old Victorian house is a big job for any wood burner.
Hopefully, your home is modernized with  better insulation and double-pane windows.

It is! I also have a backup gas boiler :)


Any concerns about an 8 inch system? I know there are some who advise against as the weight increases exponentially the bigger the core diameter, however I'm taking comfort from the fact that I'm not making the system any heavier than what is currently in situ.

Thanks again.

M

An 8" batch box is a beast, and while it may well be what you need to heat most of your house, it will need a significantly large ISA to harvest the heat. Otherwise you will just get a very hot exhaust, throwing much of the heat away. Per the sizing table at batchrocket.eu, an 8" system wants 9.4 m2 ISA in the bell.

I don't know if this is possible in your situation, but it has been done to have essentially a two story bell, with the space open through the floor so there can be heated mass at first floor level. Another option would be to have the flue from the lower floor bell feed into a second bell at the upper level.

That looks like a beautiful house!
As you live in England, I would as a first step, contact building control and enquire about installing a ‘Masonry’ stove and then further check with your insurance company.
I think you may hit a brick wall unless you have a very understanding building inspector who  may be willing to help you get through the red tape.
I dont actually  live in England but, in Guernsey we largely apply to UK building codes and in our case, any form of self built stove will never past building control without a lot of effort!
However I do believe there may be sone leeway when building Masonry stoves if they are independently  designed and specified by a heating  engineer.
Dont mention,  Batch box or rocket stove but, stick to the term of Masonry stove.

Thanks for the comments guys

Please let me know recommendations on insulation at the roof of the bell to protect ceiling/coving and insulation against the neighbours wall.

Glenn Herbert wrote:An 8" batch box is a beast, and while it may well be what you need to heat most of your house, it will need a significantly large ISA to harvest the heat. Otherwise you will just get a very hot exhaust, throwing much of the heat away. Per the sizing table at batchrocket.eu, an 8" system wants 9.4 m2 ISA in the bell.

I don't know if this is possible in your situation, but it has been done to have essentially a two story bell, with the space open through the floor so there can be heated mass at first floor level. Another option would be to have the flue from the lower floor bell feed into a second bell at the upper level.

I don't really fancy a bell upstairs. I prefer to send heat upstairs via wet underfloor heating. I'm planning on sending a coil of pipe into the bell which will heat my vented hot water cylinder. The cylinder will in turn provide hot water and central heating.
I'm hoping the coil will extract enough heat from the bell to stop it all going up in to the chimney.
What do you think?

Fox James wrote:However I do believe there may be sone leeway when building Masonry stoves if they are independently  designed and specified by a heating  engineer.

Appreciate the heads up. I'll ask my heating HETAS engineer if he will sign it off. Should be ok.

I suspect the internal volume you will have in that one thin bell will make it difficult to get enough coil to absorb enough heat from an 8" batch box. A bell in the existing chimney breast space on the upper floor would occupy little room and be much safer than lots of water coil in the first very hot bell.

Glenn Herbert wrote:I suspect the internal volume you will have in that one thin bell will make it difficult to get enough coil to absorb enough heat from an 8" batch box. A bell in the existing chimney breast space on the upper floor would occupy little room and be much safer than lots of water coil in the first very hot bell.

Thanks buddy.

The problem that I have is that I have little space upstairs for another bell. Even if I did... I can't really afford to have a hotspot in the upstairs bedroom where the 2nd bell could be... That room would be far too hot to sleep comfortably in.

Looking at the batchrocket website, it says the maximum ISA before the bell hurts exhaust temps and a bypass is required is 9.4 sq m for an 8 inch (20cm) system.
My ISA will be 5.4 sq m.
Is there a minimum ISA?

Furthermore, If I have 10mm x 25m coil of copper tubing going through the bell, the copper tubing will add an additional 0.8 sq m of surface area.
Could the effective surface area be higher as the water running through the tubing will mop up the heat almost instantly?

Copper also has 8x greater thermal conductivity than steel. I have a superficial understanding of physics., does that mean the effective surface area of the coil increases 8x too from 0.8 sq m to 6.4 sq m?

Thanks again

M

The copper coil will be thin enough that conductivity will not matter much. The water flowing and keeping at least part of it cooler will be more significant. I still don't think it would approach enough absorption to equal up to 9+ m2.

If the ISA is much less than the optimum in the table, it will just not absorb all the heat you have generated and send the rest up the chimney. If your space is that constrained, I would go with a 7" batch box. This will come closer to balancing heat generation and absorption.

Glenn Herbert wrote:The copper coil will be thin enough that conductivity will not matter much. The water flowing and keeping at least part of it cooler will be more significant. I still don't think it would approach enough absorption to equal up to 9+ m2.

If the ISA is much less than the optimum in the table, it will just not absorb all the heat you have generated and send the rest up the chimney. If your space is that constrained, I would go with a 7" batch box. This will come closer to balancing heat generation and absorption.

Thanks buddy
I am prepared to drop down to 7 inch if required.

What if I put some bricks standing up on the floor of the bell to increase absorptive surface area?
if my calculations are correct... if I have 40 brick upstands, that will fill give me a total ISA of 9.4 sq m.
Alternatively, I could have 74 bricks sticking out horizontally on the inside of the bell wall, acting as fins. This will also fill the deficit to give a total ISA of 9.4 sq m.
Could this work? Any drawbacks to this system?

I have a question about maximum and minimums. Correct me if I'm wrong but isn't ISA 9.4 sq m (CSA x 300) a maximum? What is the minimum?

Thanks again

M

I dont think there is a specified minimum, there are examples of batchbox hot plates that have no mass, you just waste  a lot of heat up the chimney.
Most rocket stove designs work without mass, they have the benefit of quick start ups and hot temperatures but sort of defeat the objective of super efficacy!
I have never built an 8” batchbox but they have the reputation of being fierce fiery monsters!

The table figures are not so much maximums as optimums. The system in most circumstances will work reliably and efficiently at the given ISA. With excellent draft or a startup bypass, a larger ISA may work fine and be even more efficient at heat recovery.

The idea of internal brick columns or fins is a recognized practice for increasing ISA - I forgot to mention that earlier. Just remember that the floor or items very low are not counted in ISA, because the hot gases do not really go that low before they reach the exit. Individual bricks internally will only absorb so much heat before they are saturated and match the gas temperature; the more massive the columns, the longer they contribute to ISA. Fins will transmit heat to the exterior, so remain effective indefinitely.

M Ahmed wrote:

Glenn Herbert wrote:The copper coil will be thin enough that conductivity will not matter much. The water flowing and keeping at least part of it cooler will be more significant. I still don't think it would approach enough absorption to equal up to 9+ m2.

If the ISA is much less than the optimum in the table, it will just not absorb all the heat you have generated and send the rest up the chimney. If your space is that constrained, I would go with a 7" batch box. This will come closer to balancing heat generation and absorption.

Thanks buddy
I am prepared to drop down to 7 inch if required.

What if I put some bricks standing up on the floor of the bell to increase absorptive surface area?
if my calculations are correct... if I have 40 brick upstands, that will fill give me a total ISA of 9.4 sq m.
Alternatively, I could have 74 bricks sticking out horizontally on the inside of the bell wall, acting as fins. This will also fill the deficit to give a total ISA of 9.4 sq m.
Could this work? Any drawbacks to this system?

I have a question about maximum and minimums. Correct me if I'm wrong but isn't ISA 9.4 sq m (CSA x 300) a maximum? What is the minimum?

Thanks again

M

I would sure have a calculated plan or have it confirmed that the "fin" plan might work, while a bell is all about heat slowly falling to the bottom exit and thus heating your bell (energy adsorption) I don't know if restrictions such as your 74 brick fin idea, would work, but betting someone may have gone down this path.  

I can tell you 40 brick "upstands" as you call them, at the base is where the coolest gases congregate before exiting.  Thus you would have the least chance to gain much heat there vs the top.   I can tell you I have a stratification of heat in my bell from top to bottom (6' high) of about 10-15 degrees per foot down.  of course the bottom is the coolest.  Top if 225 degrees will almost always mean the base at 160 at best.

While there is so little ash in the bell, I would tend to think a layer collection of ash- on your "upstands" will render this much less effective for your efforts than what you may have planned or hope for. a 1/4" layer of ash is very effective insulation. But might be considered only insulating the top of your up stands.. So might work better than what I am thinking.

With proposed up stands, having a way to actually get inside once per year for a clean out might be well worth planning,  I did this on my build, and have actually be able to get inside, but pre-planning your build would certainly need considerations up front.  The tag below shows how I did this.  Certainly not for everyone.

Best of success.
Scott