8" RMH

I think I understand. Thank you so much! Back to sketch up to redo the design 😊

Peter, in your specifications the pchannel must be 54x16mm, however, in your sketchup of the sidewinder it is 26x56mm. Is this not so important to get correct?

Benen Huntley wrote:Peter, in your specifications the pchannel must be 54x16mm, however, in your sketchup of the sidewinder it is 26x56mm. Is this not so important to get correct?

Both sidewinders on the batchrocket site doesn't have a p-channel, but a floor channel instead. The p-channel is an overhead device, the floor channel is incorporated in the floor of the firebox. Both secundary air channels work in different ways, that's why they aren't the same. It's perfectly possible to have a p-channel in the sidewinder by the way, although I'd regard the floor channel as the better one.

In short, it is equally important to get correct, but you'd better not to mix up two different concepts.

Ah right. I assumed they were the same just in a different location. So I will keep it as is in the sketch and

I feel like I am getting much closer and I can't thank you enough for your willingness to help!

Before I go further. I'd like to clarify that a 150mm system is indeed the suitable size for the space in the sketchup file? It's a kitchen, living and dining. Larger than I'd like but it's what we have 😊

Benen Huntley wrote:Before I go further. I'd like to clarify that a 150mm system is indeed the suitable size for the space in the sketchup file? It's a kitchen, living and dining. Larger than I'd like but it's what we have 😊

Impossible to say, very dependant on what low winter temperatures are at your place, orientation to the sun and wind chill, to name a few aspects. To get a rough idea, revert to the calculator of Yasin Gach. See http://batchrocket.eu/en/building#size

Hmm. Looks like the 8" is the more suitable option for the volume of the house. Particularly since you mentioned that it is always better to size up rather than down. I believe I can fit it into the space and gain most of the extra ISA by extending the height.

Back to sketchup

Benen, you've drawn the heater as a single bell with the exhaust pipe sticking out the side. This isn't really necessary, another way to do it is to build a brick upstream channel inside the bell and create a top vented heater. This results in more mass and a bigger bell externally. There's a catch here: the exhaust opening in the upstream channel need to be very wide, up to 200% of system size if that would fit. Such an internal chimney opens up the possibility of a bypass, which would start a cold and wet heater much, much easier.

Did you read the thread at Donkey's, about a bell inside a bell? See http://donkey32.proboards.com/thread/2260/bell-inside

Hi Peter,

I don't quite understand unfortunately. I did read the article but it read as though it has not been tested a great deal or at all?

The thread I mentioned was quite separate from what I said about the internal upstream channel in the bell. The "bell inside a bell" is a new untested idea as yet but a tantalizing possibility, that's all. As far as I know of the first one is built or being built this week.

The internal upstream channel and the bypass valve in there is built dozens of times and it works for sure.

Ah right. What do you suggest I alter with my current design then? Build mass around the exhaust?

Hmm... I wasn't clear enough, apparently. What I like to call an upstream channel is a brick chimney inside, in a corner of the bell. Two of the sides of that internal chimney would be formed by the walls of the bell. At floor level, still inside the bell, there's a wide and spaciously opening where the gases will be able to stream up.
This way, the exhaust opening is on top instead of low at the side of the bell. And you could build the heater wider at the place where the metal chimney pipe would go.

As an added bonus there could be also a bypass halfway up this internal chimney thing, to allow gases to stream in the chimney at a higher level. Thus making the heater much easier to start when cold.

is this clear now?

Another term for the concept is a "plunger tube", more often referring to a metal exhaust duct going from near the floor of a bell straight up and out of the top. It does the same thing, allowing only the coolest gases at the bottom of the bell to exit, while not occupying any space around the outside of the bell.

Ah man, I have had absolutely zero time to sit at the computer the last couple of weeks to play around. We have been renovating like crazy in the living area plus working two jobs! I will try to find some time this week!

Well I'm back at the computer after quite a while. Time goes so fast and lots of things can get in the way!
More thought and discussion has led us to believe we have an opportunity to pull out a cupboard in our hallway and build a batch heater in there which eliminates the problem of the heater taking up space in the living area.
The cupboard is very central in our home and the hallway is open to a couple of bedrooms as well as the living area, dining and kitchen.

Dimensions that fit well are as follows:
460 deep
920 wide
2.07 tall

This makes it the same depth as the cupboard and leaves plenty of room on the width for wood storage.
I've attached another sketch-up file.
The ISA is around 6% short of the 5.58sqm needed for the sidewinder from the batch rocket website.
All other dimensions are within 5% of specs. I believe the burn chamber is 26mm less deep and 30mm less tall. I can make it a little wider to keep the internal volume the same as Peter's design though, as well as making the entire heater half a brick wider to bring up the ISA to spec.

I would love some feedback on this is anyone has some time

Benen

I've had a look at the drawing. Do yourself a favor and raise the firebox at least 50 cm from the floor. Where is the exit hole of the bell?

Hi Peter,

Thanks so much for that.
I assume that's just for convenient fuel loading? Would you build up a brick plinth for it to rest on and extend the riser down to the floor but brick it closed at the level of the bottom of the burn chamber? I hope that makes sense haha.

The exit will on the right hand side of the bell at the back. I was originally going to have an internal brick exit but since it's now going into a different location it will be easy to just have the exit made from stove pipe and possibly add a clean out also.

Have you ever seen anyone add a wet back to a batch heater? We have a solar hot water service on the roof with no gas or electric boost. It would be great to boost it through the winter from the heater and possibly add a radiator to the other end of the house running off of the thermal mass in the water tank. The hot water is already set up to attach a wet back and a radiator on to.

This is what I've come up with if I raise the box and support it underneath. Gives me an ISA of almost exactly 5.58 which I believe is the correct ISA for the sidewinder having the slightly larger diameter riser. I've also added in an estimate of where the 6" exit will go.

More progress! I've added in a little detail of the location in the house. The downstairs of the split level area is kitchen, dining, living and the upstairs is a long hallway with four bedrooms along it. Very simple house layout, quite open except for the bedrooms having doors. Ceilings are 2.7m downstairs and 2.4m upstairs.
The back of the heater is in the hallway where the cupboard used to be and I've penetrated the firebox into the dining which allowed me to fit in an 8" heater. I believe this size is more suited to our home but I haven't been able to fit that size in to the specs before.
The ISA, if I've measured correctly is 9.4SQM which is excluding the floor, the area that the riser uses against the rear wall and the firebox against the front wall. I've increased the floor channel to 40mmx80mm which is just a 33% upsize of the 150mm sidewinder on batchrocket.eu to match the 200mm system.

Hi Peter,

I have a few more questions if you have some time to answer them.
I'm going to protrude the fire box through the existing brick wall. It has plaster board over the front but I will clear a perimeter around the entrance and clad it with iron or stainless.
My two main questions now are:
1. When building the bell, since there will be around 1000mm between the top of the riser and the top of the bell, how much of the bell will need to be fire bricks from the top down.
2. Since I'm building the unit into a cavity, if some of the bell needs to be fire bricks then I need to laminate the existing wall with another wall when building the bell. Do you think having one side of the bell as double thick bricks cause any problem?

I'm not an authority, but what I have heard is that at least the top third of the bell should be firebrick.

I'm sure it will not be a problem to have part of the bell be thicker; that part will just take longer to transmit heat all the way through, and probably stay warm on the outside longer. Outside corners where the wall is thick, in my experience, never really get very warm to the touch, because heat can radiate away faster than it can conduct through from the inside. Rounded corners maintaining the same wall thickness would give more satisfying results there.

Thanks, Glenn. Top third hey. That's good to know. I didn't mean thicker just at the top. I meant the entire side would be double brick. I just have concerns about too much mass if that's possible!

"Too much mass" depends on your climate. If you are in a place where it gets cold and stays cold, a big mass will even out the heating load. If you can see large swings in temperature from day to day in the heating season, a smaller mass will be more responsive to burning or not, and reduce the chance of having too much heat for a warm day, or taking too long to build up heat for a cold day.

Brick generally has faster heat transmission than cob, and I would expect 8" total of brick to be reasonably responsive. Much more than that would probably only be suitable for deep freeze conditions. For variable weather areas, I might use bricks laid on edge to give a thinner skin while keeping the safety of a double shell.

Thank-you so much. The plan is to begin construction in May.
The last piece of the puzzle is the wet back to boost the hot water and heat the bedroom.
I assume I can put a wetback from a slow combustion heater just above the top of the riser but I haven't found any examples of anyone using them in a batch heater.
Also, should the exhaust be larger in diameter than the riser? Or is 200mm stove pipe sufficient for a 200mm batch rocket?
I plan to start collecting parts soon.

So I've started a smaller 4" batch rocket which will go in the laundry and turn it into a drying room. It will also have a water jacket on the flue to boost our solar hot water.
This will hopefully be a great practice run for the 8" system.
We also found that we sometimes want hotter water but not a hotter house so the two separate rockets will hopefully be an advantage there.

I designed it in sketch up and have cut most of the bricks ready, using the octagon riser design on the batch rocket site.
I'm also planning to clad it in steel and paint it black for a more subtle look.

Totally new to all of this including welding so it has been an amazing learning experience so far!

Hot water jacket should arrive this week and also managed to pick it a newly new stainless flue for next to nothing.

I have opted for the floor channel rather than the p channel for ease of replacement. I will run the saw through the bricks on the fire box floor to nest it flush. Hopefully it does not get too hot on the bare steel on the floor of the fire box with the air being drawn through the channel to keep it cooler.