Retrofitting for a Batch Box Rocket Bell Heater **Help needed**

Greetings fellow permies,

a friend of mine wants to retrofit a Masonry Heater to his existing, huge, 45 feet high (internal) brick chimney and he asked me to do the install.

His passive solar house is currently heated with a Jøtul stove and electric baseboards. But, as an ecominded man, he does want to be as self sufficient as far as heating goes, so the little Jøtul stove takes over an hour to rise the temps (the floor up) from 16°C to a more comfortable temperature. **
He previously built his chimney with an internal 7 inch terra cota sleeve (outside diameter of the sleeve is 9 inch).

So the outlet would be 7 inch round, or 9 inch square if we figure out a way of removing 45 feet of sleeve, incapsulated in a brick masonry chimney!?!!?!

-He was really interested in having a Batch box bell heater and also in single loading vs multiple loads of firewood per day, similar to what a Masonry heater would do. So maximising the box size is important to him.

-He does not mind having to heat with multiple sources (he will not remove his baseboards).

Some thoughts I had was that the 7 inch terra cota liner would limit the total energy output vs an 8 inch or even a 10 inch system.

So the questioning part:

1 - Would a 8 or 10 inch batch box with an output chimney of 7 inch diameter create a bottle neck effect? (my guess is obviously that it would)

2 - Would the total length of the chimney limit the flow of the gases? (maybe create a single, smaller bell so that the exiting gases could be hotter than the usual system to help them exit the freakishly long chimney)

3 - As you can see in the photo, the bell would ''part of'' the existing chimney, so does the original brick wall need to be ''clad'' in firebricks or would it be wiser to put ceramic insulation boards to block the loss of heat through it?

4 - Removing the inner terra cota liner would be a total pain, put it would give us a 9 inch square, so an approx. 7 inch square would be ideal for an 8 inch system, would a 9 inch be ideal for a 10 inch?

5 - (Lastly for now!) Would it be simpler to just build a traditional Masonry bell heater instead of a batch box? Or maybe just a more ''sexy'' looking batch box rocket stove***.

P.S : (I have almost no feedback from ''real'' cold climates, Montana is cold yes, but here -20°C is a pleasant temperature for a hike! Does anyone here have experience from say, Alaska, Northern Canada or North Eastern Europe?)  

We both live in North central Québec, Canadian zone 3 climate (some -45°C weeks in winter, down to -52°C with windchill).

P.S #2 : I will add the dimensions of the space available for the bell (height of approx. 8 feet, width of approx 50 inches, depth unknown for the moment)
The purpose of the bottom of the bell lined with 12 inches of rock wool has to do with both, keeping the heat as high up as possible (the house is 3 stories high) and because the exit flue is already quite high so the heat would not be able to go below approx. 18 inches from the ground up...

**He does like the immediate rise of temperature of a stove though, anyone here heard or made a bell with a steel top, similar to our good old barrels? If so, thickness of the steel should be close to 1/4 inch ?

***Some of the questions would still apply here for a rocket stove, as for the sizing of the flue vs size of the batch box system.

Thanks a lot for you time and sorry for the mistakes if I've made any since English is not my native tongue!

Samuel  

Well Samuel. That's right up my alley.

First, we need to know what is the size of the house. To see if 7" would be enough.

Secondly, is it possible to remove the terracotta liners?  What is between the liners and the bricks?

The brick chimney itself can become the mass. If the heating is baseboard electric, i wouldn't insulate the bottom of the bell from it. It can cope with heat.

Thirdly, yep, you can make metal bells. A barrel is pretty much that (well, more of a downdraft channel radiator)

But i live with a metal bell.

https://permies.com/t/44806/Cobbling-workshop-heater

Read the whole thread. THis is work in progress.

You start by saying the chimney liner is 7" diameter, but later mentions indicate that it is 7" square. Given a straight vertical internal chimney, you should have very strong draft, and I would guess that it could support an 8" batch box. The critical thing to know is the house size and insulation level, combined with the climate which you have described. A 7" or 8" batch box can put out a lot of heat; a 6" batch box is often used to heat an ordinary cold climate house (not upper Canada).

Instant heat is easily accomplished with a steel access panel in the side of the masonry bell, and serves to allow inspection and maintenance of the heat riser. It doesn't need to be any heavier than what is physically sturdy for sealing (mine is 1/8" thick, and feels extremely robust.)

I am assuming that the base of the hearth is strong enough to support the several tons of mass you are planning to add to it.

There is no need to block off the bottom foot of the bell space; the hot gases will not go down significantly below the exit. Just a bit of insulation on the floor should be sufficient, and if there is a basement, I would consider the bit of warmth radiating down a benefit.

To specifically address some of your questions:
3) Per US code (don't know about Canadian), a masonry heater inner skin needs to be firebrick. Recommended practice in the RMH world is that at least the upper third or so needs to be firebrick, while the lower part will not see heat enough to damage ordinary brick. I think the upper part of the chimney inside the bell space would want some shielding by more refractory material.

4) Again, US code requires an approved liner which is resistant to flue gases, like terra cotta or stainless steel. Bare brick would not qualify, and is likely to be rough textured which would impede airflow.

5) A traditional masonry heater could not have higher heat capacity than a batch box given the existing chimney, though it may be that it could have a larger firebox. Peter van den Berg is the one we need to advise now, as he has done the most technical development work on batch boxes.

Glenn Herbert wrote:You start by saying the chimney liner is 7" diameter, but later mentions indicate that it is 7" square. Given a straight vertical internal chimney, you should have very strong draft, and I would guess that it could support an 8" batch box. The critical thing to know is the house size and insulation level, combined with the climate which you have described. A 7" or 8" batch box can put out a lot of heat; a 6" batch box is often used to heat an ordinary cold climate house (not upper Canada).

Instant heat is easily accomplished with a steel access panel in the side of the masonry bell, and serves to allow inspection and maintenance of the heat riser. It doesn't need to be any heavier than what is physically sturdy for sealing (mine is 1/8" thick, and feels extremely robust.)

I am assuming that the base of the hearth is strong enough to support the several tons of mass you are planning to add to it.

There is no need to block off the bottom foot of the bell space; the hot gases will not go down significantly below the exit. Just a bit of insulation on the floor should be sufficient, and if there is a basement, I would consider the bit of warmth radiating down a benefit.

I may have been misunderstood for the 7 inch square part. I was simply referencing the dimension ratio of an 8 inch system to make sure the result would be the same for a 9 inch square to 10 inch diameter system.

Also, yes I had thought about putting a square sleeve inside the brick chimney if he ever decided to go to these lengths (pun intended!).

Good idea for the inspection panel, could also be made out of an old cast iron ''glassless'' stove door I guess.

The brick chimney has a footing underneath (the heater would be at ground floor, with three other stories above it, including the attic). He has a friend who's an engineer and will calculate if he has to cut, dig and pour a thicker portion of concrete, or not.

Satamax Antone wrote:Well Samuel. That's right up my alley.

First, we need to know what is the size of the house. To see if 7" would be enough.

Secondly, is it possible to remove the terracotta liners?  What is between the liners and the bricks?

The brick chimney itself can become the mass. If the heating is baseboard electric, i wouldn't insulate the bottom of the bell from it. It can cope with heat.

Thirdly, yep, you can make metal bells. A barrel is pretty much that (well, more of a downdraft channel radiator)

But i live with a metal bell.

https://permies.com/t/44806/Cobbling-workshop-heater

Read the whole thread. THis is work in progress.

The dimensions of the house are :

- 31 feet x 31 feet at ground level (rez-de-jardin) with 8 feet ceiling height

- 31 feet x 31 feet at first floor (rez-de-chaussée) with 9 feet ceiling height

- 28 feet x 31 feet at second floor with 8 feet ceiling height

- 12 feet x 31 feet in attic (open attic with loft stairs) with 7 feet ceiling height

Ground level floor is a concrete slab.

293m², and about 700m3 (a bit more actually)

I would advise at least a 10/12 inch batch. And a good two more tons of mass.

Satamax Antone wrote:293m², and about 700m3 (a bit more actually)

I would advise at least a 10/12 inch batch. And a good two more tons of mass.

That's what I thought too... I guess I'll have to figure out a way to remove the terra cota liner or it will create a bottle neck.

Yep, about 3000 square feet, even well insulated, that is a lot of house. In a really cold climate like yours, I expect Max is right. And if you couldn't get enough heat from a batch box RMH, you couldn't get enough from a traditional masonry heater either.

Thanks a lot guys, I'm writing whits sitting on my still warm bench (8 inch standard J-tube RMH to be precise ) and a after discussing with my friend a bit more about this Bell project, he is far from being ready to remove the 45 feet liner from his chimney (it's a rel snug fit so it would be a pain to do so).

So I  am left with maybe more of a ''Rocket Bell Stove'' with a 50 inch by 30 to 40 inch and maybe 7ish feet high steel bell with a little brick stem wall at the bottom, all fed by a 7 inch batch box.
That would be an improvement on his little Jotul stove that's for sure. But he's really anchored, so to speak, on having a ''Mass'' heater and not an ''Air'' heater...

So much for having built a gigantic house...

Maybe a giant column with two heater on different floors? That would be a titanic build for sure!! He's already putting another chimney for an ''ambience'' in-wall wood stove.

I'll add a few more pictures I snagged the other day.

Here are the pictures.

Sam Plante wrote:Here are the pictures.

And the galvanized steel duct is a heat recovery system with a small electric motor downstairs (heat from attic to downstairs that is).

I see no reason not to build an RMH with a masonry bell; it probably won't heat the whole house in the dead of winter, but may do it much of the year. Adding a second chimney and heater would be a good solution.