M Ahmed

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

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

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.

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

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

thomas rubino wrote:Hi M;
It sounds like you want a simple J-Tube design rocket stove.
Although they can be built with many materials, preferably, you want your core to be built with solid clay bricks.
As you are just building an outdoor trash wood burner and not a mass heater there is plenty of leeway in build parameters.
Dirt is suitable to use in place of clay to fill holes.

The basic dimensions have one requirement.  They must keep the same diameter from the feed tube all the way through and up the riser. (chimney)
A Standard  8" rocket stove core has an 8"x8" feed tube that is most commonly made 16" deep.
The horizontal "Burn tunnel" has a "roof length of 10" -12" and is the exact diameter of the feed tube  8x8.
Your riser is also the same diameter 8" and it should be apx 3-4' tall.
If you have 9" material to use then keep it all 9" and you will have no problem.
Cracking is the biggest issue as the rapid heat changes stress most materials.
Solid clay brick will last the longest if true firebrick is not available.

With an open burner like this most anything will burn.
Yes, it will burn painted wood... if you or the neighbors do not mind.
Be very aware that nothing flammable is above your riser(chimney)  once lit and gotten up to working temperature, you can have flames showing.  

Thanks for the reply buddy.

The ceramic chimney stacks that I have are shaped, so the diameter might be 8 inch in some parts and 10 inches in other sections. however, the top and bottom are 9 inch.

With respect to the length of the feed/tunnel/riser... where exactly do I measure for the 1:2:4 ratio?
Is there a diagram I can refer to?

Thanks

M

Hi guys

I'm making a RMH to burn some waste wood in the garden.

I don't understand where exactly to measure for the 1:2:4 ratio.
Can someone share a diagram that makes it clear for me please?

I've got some 9 inch diameter ceramic chimney stacks which i intend to use.
Does this impact the height/length of the feed/tunnel/riser?

Will standard garden soil be ok to seal any holes? I don't expect it to be perfect. just functional and not too smokey.

Will the Rocket heater accept painted wood?

Thanks

M

Glenn Herbert wrote:Sounds like a plan

Yes, you can make the firebox from standard old red bricks. Firebricks would last longer, but are not essential for a short-term build. Especially for a short-term build, fireclay slip is probably the best mortar, as it can be knocked off leaving clean bricks when you want to build something new. It may or may not meet building code where you are; it is a bedding/sealing agent only and not a cement. (US "International Building Code" requires refractory cement mortar which is strong and sticks to bricks, though I don't know how often that is actually used.)

It sounds like you have a good tall interior chimney which should have good draft. I hope both houses do not share one flue, as that might cause complications with draft.

Thanks buddy
Flue is not shared with neighbour, nor with any of the other fires in the house.
I've had a look at the internal mortar flue from another fire in the house when I needed to do some remedial work a couple of years ago, it was stained black with soot but no creosote build up.

Its plausible this particular mortar flue in the basement has not been used in decades if at all ever.
Do I need to do anything special before I start directing my vent there?
I'll be sure to do the standard smoke test using a coloured smoke bomb,

Thanks again
M

Glenn Herbert wrote:No matter where you are, you can probably find bricks, which will be a good material for building a rocket mass heater. Firebricks for the combustion core will last longer, but as this sounds like a short-term setup, you just need to be sure the bricks are not concrete-based, as that will disintegrate in RMH core temperatures. If you are in a remote area and have clay easily accessible, cob is a good reliable material. You can build a complete RMH out of cob - I have done it.

The easiest thing to build would probably be a J-tube inside a masonry bell (hollow brick box). A 6" equivalent size would probably suffice for warming and drying a basement, and is likely the most common chimney vent size to find.

Thanks buddy.
I think I'll go for a 6 inch batch box with a 5 (or 6) minute riser.
I might go for a steel barrel instead of a masonry bell.
I will build it outside first as a test (and to grill some food).

Couple or questions....
Can I make the firebox out of standard (reclaimed) red brick? Are some bricks better than others?
What should I use as mortar?

I live in a victorian terrace house in Lancashire, England.
Our chimney is shared with the neighbour. It travels up 3 stories before it exits the roof.
Are there any considerations I need to make about using it to vent out the gasses?

Thanks again
M

Thanks guys for ruling that out.

I'll make the effort to clear the area around the chimney and get it all properly vented.

Which RMH is the easiest to make using materials easily available in the UK?

Primary purpose: to dry the basement; a test run for when I move into my next house; to provide residual heat to the room upstairs.
In the future I might want to have a play around with hooking my water central heating up to the system although I understand this is more complicated than it sounds.

Thanks again

M