Newbie questions

Hi!
I just started trying to navigate in the wonderful world of rocket mass heaters. I want one! (Or several, in the greenhouse, the workshop, etc.)

First batch of questions:

How do I choose a suitable dimention for the needs of my house? It is only 44 m².

My house is small, and the space for the burner part is limited, how compact can they be, and how close to a plywood wall?

I was thinking the thermal mass could replace my current sofa, but due to the geometry of the room and placement of the current chimeny, maybe I should make a corner sofa out of the mass. But then the pipe length would be something like 11 metres. I have no idea if that is too long.

I live in a climate with wet, foggy and windy winters, temperatures most of the time slightly below or above freezing. I think I need some way to help the draught start in the right direction.

And how do I stop the draught pulling the warm air out of my house between the fires?

I read about batch boxes today, and I can see how one anxious teenager in the house is really going to be relieved at having a closeable door. The open hole would freak them out.

Please, be my guides on these first steps of my journey! Assume that I don't know the american names of materials and components, as I'm Swedish. I may need just a bit more detailed explanations of special words. Please bear with my metric brain...

Tuve Lundberg wrote:How do I choose a suitable dimention for the needs of my house? It is only 44 m².

Hi Tuve,
This is greatly depending on your climate, the orientation and insulation of your house. A 150 mm batchrocket system is able to deliver about 20 kWh per batch of 6 kg of bone dry fuel. This 150 mm is the diameter of the chimney and riser at the same time.

Tuve Lundberg wrote:My house is small, and the space for the burner part is limited, how compact can they be, and how close to a plywood wall?

Since the house is small, a single bell might be better than a bell/bench combination. My heater is about 10 cm away from a wood stick/ plasterboard wall. On the wall behind the heater is a steel corrugated plate mounted on spacers. While the heater warms up the plate, an air current will start which in turn cools the plate. When my heater is too hot to touch this heat shield is still about hand warm. Works wonders!

Tuve Lundberg wrote:I was thinking the thermal mass could replace my current sofa, but due to the geometry of the room and placement of the current chimeny, maybe I should make a corner sofa out of the mass. But then the pipe length would be something like 11 metres. I have no idea if that is too long.

Please don't build a piped bench, if at all, coupled to a batchrocket system. This specific combustion system is very picky about friction in the smoke path.

Tuve Lundberg wrote:I live in a climate with wet, foggy and windy winters, temperatures most of the time slightly below or above freezing. I think I need some way to help the draught start in the right direction.

As long as you run the heater every day you'll find there won't be a problem. Lighting a warm heater is the easiest, by far. You might get problems while drying out the heater and further down the timeline, starting up a stone cold heater in autumn. A bypass would be a very handy in this regard.

Tuve Lundberg wrote:And how do I stop the draught pulling the warm air out of my house between the fires?

Close the heater's door and the air inlet. See that you'll get a tight closing door and there'll be no problem.

Tuve Lundberg wrote:I read about batch boxes today, and I can see how one anxious teenager in the house is really going to be relieved at having a closeable door. The open hole would freak them out.

Batchrockets are very reassuring in this regard, it can be loaded and top lit very safely. Basicly it's loading, lighting, closing the door, seeing and hearing that it comes up to a healthy burn and walking away. Easy peasy, sort of.

Tuve Lundberg wrote:Please, be my guides on these first steps of my journey! Assume that I don't know the american names of materials and components, as I'm Swedish. I may need just a bit more detailed explanations of special words. Please bear with my metric brain...

I am from the Netherlands, ISO system is what I grew up with.
Question from my side: what's the diameter and height of your existing chimney? Is it straight, cylindrical, smooth inside and higher than the top ridge of the roof? No other buildings or trees nearby?

Peter van den Berg wrote:
This is greatly depending on your climate, the orientation and insulation of your house.

I don't know how many kWh I need. My house is 840 x 590 cm big, with one of the long sides towards south, with biggish windows, giving me some amount of passive solar, if we get sun in the winter, so far, this winter almost none.
The house is actually two builder's barracs connected to each other. The outer walls have 95 mm rockwool insulation, the roof 120 mm and floor 145 mm.
Southern Sweden har variable winters, both in temperatures and duration. Imagine just a little colder than the Netherlands, and almost as moist.

Peter van den Berg wrote:
Since the house is small, a single bell might be better than a bell/bench combination.

My main aim is to store heat. My current stove doesn't do that.
My (limited) understanding was that a heated seat gives so much more efficient heating than radiating the heat into the room. Will a single bell  keep the house warm 24 hours on only one firing?

Peter van den Berg wrote:
My heater is about 10 cm away from a wood stick/ plasterboard wall. On the wall behind the heater is a steel corrugated plate mounted on spacers. While the heater warms up the plate, an air current will start which in turn cools the plate. When my heater is too hot to touch this heat shield is still about hand warm. Works wonders!

Coll, I have something similar for my current stove, I might even be sble to reuse those.

Please don't build a piped bench, if at all, coupled to a batchrocket system. This specific combustion system is very picky about friction in the smoke path..

That's a disappointment...
No thermal mass, no heat storage? Or does it do that another way?

Peter van den Berg wrote:
As long as you run the heater every day you'll find there won't be a problem. Lighting a warm heater is the easiest, by far. You might get problems while drying out the heater and further down the timeline, starting up a stone cold heater in autumn. A bypass would be a very handy in this regard.

I don't know enough about bypasses.

Peter van den Berg wrote:
Question from my side: what's the diameter and height of your existing chimney? Is it straight, cylindrical, smooth inside and higher than the top ridge of the roof? No other buildings or trees nearby?

I attach a photo of the chimeny above the roof. No trees or obstructions. About 130 or so cm above the roof, 165 cm below the ceiling, and I guess about 20 cm through. I can't see the inner diameter. It is insulated  and about 22 cm outer diameter. I have a lid cover from the stove which is 174 mm in diameter, wich might correspond to the inner chimeny diameter. Straight up. Probably smooth.
But depending on the rmh design I choose, maybe I need to put a bend on it, to avoid it coming down straight on the heat riser.

I'll try to show the inside space in a later post.

Forgot to mention: I do intend to add a slanted roof, which will change how high above the ridge the chimeny reaches, but I also calculated that when I do, I might need to add a section to make the chimeny higher too.

Your chimney sounds good but you will need to know the inside diameter as this will define the max size of stove you can have.

Tuve Lundberg wrote:My main aim is to store heat. My current stove doesn't do that.
My (limited) understanding was that a heated seat gives so much more efficient heating than radiating the heat into the room. Will a single bell  keep the house warm 24 hours on only one firing?

That depends on the size of the system, the brick bell should be matching the size of the combustion core. Larger core, larger bell and therefor larger mass.

Peter van den Berg wrote:Please don't build a piped bench, if at all, coupled to a batchrocket system. This specific combustion system is very picky about friction in the smoke path...

Tuve Lundberg wrote:That's a disappointment...
No thermal mass, no heat storage? Or does it do that another way?

With a batchrocket, there's no need for a barrel at all. The mass of the thing could be in a single bell, double bell, bell and bench, whatever. For example, a 150 mm system could be housed in a double skinned brick bell, lots of mass. Let's see... which could weigh in at anything between 2000 and 3000 kg. In case you aim for a 24-hours heater, the mass in that bell would be best above 2500 kg, 100 kg for every hour of slow heat dissipation.

Of course you could choose to charge the heater with a single batch morning and evening in freezing weather. Or build a slightly larger one, say 180 mm, and charge that with one batch per 24 hours or two batches back to back when need be.

It might be a good idea to study the batchrocket website. Most information is there, including drawings and examples. The link is to the English version, the site is in nine languages although to date nothing in Swedish.
Lots of information to digest, also how bells work.

Thanks, Peter!
Lots of new things for me to learn about, since most of the things you mention here is new to me! I will visit that site.

I'm sending out some emails to find out the inner diameter of my chimeny, and how much weight my floor can hold. 2500 kg on how much floor surface? If it is not a bench, I guess it's heavier per m² instead.

I did get some specifications from the company that built my barrack home. Not in the form of "you may load X kg/m² on it". More "this is the type of board and this is the dimentions of the beams, go and ask someone else what that adds up to". Not sure who that "someone else" is.

Peter van den Berg wrote:

It might be a good idea to study the batchrocket website. Most information is there, including drawings and examples. The link is to the English version, the site is in nine languages although to date nothing in Swedish.
Lots of information to digest, also how bells work.

Oh, yes, now I see it's your site. Found it yesterday. But it'll take me a while to read it all! Taking it in portions.