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RMH for heating 60 square meters, questions  RSS feed

 
Posts: 23
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Hi,
were planing some hard reconstruction works in our old home. There are two rooms and one big hallway about 60 square meters (645 sft) all together.
And there are two old masonry heaters for heating all of that space, but they are very old and needs restoration, which costs a solid money.
So i thought about RMH placed in between those rooms and hallway.
But the question is- how do i calculate the thermal mass size or the RMH size for the space needed to heat? Any suggestions?

BTW we are located in Eastern Europe, kind of a cold winters are here.
Masonry heaters size we have is about 1x1x2,5 m (3x3x8ft). And yes- they are pretty old and weak in heating.
 
pollinator
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Kristaps Vinogulajs wrote:Hi,
were planing some hard reconstruction works in our old home. There are two rooms and one big hallway about 60 square meters (645 sft) all together.
And there are two old masonry heaters for heating all of that space, but they are very old and needs restoration, which costs a solid money.
So i thought about RMH placed in between those rooms and hallway.
But the question is- how do i calculate the thermal mass size or the RMH size for the space needed to heat? Any suggestions?

BTW we are located in Eastern Europe, kind of a cold winters are here.
Masonry heaters size we have is about 1x1x2,5 m (3x3x8ft). And yes- they are pretty old and weak in heating.





Welcome to Permies.com, our sister site, Richsoil.com, and the Rocket And wood stove, and Cob Forum threads. With 29,000+ Fellow
Members Worldwide you can post a question and as the day progresses get answers close to home, Western Europe, The Americas, The Pacific Rim
and our Fellow members from N.Z. and Australia . then continue on as the world turns more- waking up to find answers from yesterday/tomorrow on
your Computer

It will be a little bit easer for you to grasp the idea that a rocket mass heater RMH is a 'Space Heater' that needs some attention and tending.

Here in the Americas most of us are quite used to whole house Furnaces, and setting the dial and forgetting it !

Even to me it seems a little odd that you would need 2 Masonry Heaters for that small space !

We are going to need a sketch of the area you want to heat. As we are adapting the RMH to fit in an already existing structure we will have to
make compromises ! Also we will have to calculate the weight of the final Thermal mass, find our load bearing walls and determine the type(s)
of building materials used !

Unless we are able to find you a near Neighbor with RMH and Cob Experience your Best friend is going to be the camera that you use to document
everything !

I am Expecting that we will find that the final location for your New RMH will take up part of the existing location of One of the Existing Masonry
Heaters. We will hope to be able to use that Heaters Existing chimney- this totally depends on its condition !

This will allow you to see how the Masonry heater was put together, and potentially supply you with repair/replacement parts for the remaining
Masonry Heater

Also after you have successfully built a RMH, you will have most of the skills necessary to rebuild the 2nd masonry Heater ! Certainly you will be
able to find where there is wear / damage to your masonry system and talk to a mason about how to proceed and who does what part of the rebuild,
Again saved pictures will be your biggest friends

Also Myself and some of the others who will try to help you will have trouble with meters to feet, and cm to inches ! This will require frequent
checking and re-checking

There is a sweet spot in Your potential RMH sizes, The smallest that I, and most people will recommend for your first build is a 6''or 15cm system, we
will need to know that this is a common size of of stove pipe that is available to you ! Everything else will be sized around IT !

A well made 15cm system will push its hot exhaust gases through 30'-9 meters of ductwork, However this is before subtracting 5' or 1.5 meters for
every Elbow in your system .

Lets start off with a sketch of the areas you want to heat, and find load bearing walls and go from there !

For The Good of the Craft ! Big AL
 
Kristaps Vinogulajs
Posts: 23
Location: Latvia
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Thanks for replay Allen!
It took me a while to make this plan.
First of all i want to say i do not want a barrel and bench in this particular RMH design. Bearing that in mind i could go narrower and higher for the exhaust-thermal mass part by stacking ductwork vertically. Any thoughts?
So i might building heat riser straightforward from bricks. And all outer shell as well from bricks. Inside the thermal mass made from clay,sand and stone.
As for immediate heat radiation i could use custom made plates(from steel or cast iron) placed in the heat riser walls.

A small correction: the other masonry heater i have in the hallway- it is built later, so its not in the house plan and i draw it with the blue stroke(see pic).
As i see by default the hallway was not provided by any heating. And it blocks door to room 2 so it will be removed anyway.

The hallway and rooms floor is from wood(sand beneath it) and im going to replace it, so its easy to put in a concrete base for RMH.
The inner walls is from wood beams stacked vertically, except around masonry heater- there are bricks.

Im planing to place RHM in between the rooms and the hallway underneath the wall that separates rooms from hallway. (see pic , planned RMH is marked red)
And i do not need that space in the hallway between stairway and the wall. Main house entrance is at the left side of the hallway, the secondary entrance is on the right.

No dimensions for RMH at this point.
And im not sure about heat efficiency in the room nr 1 by this design/placement of the RMH.

So thats about it. Heres the plan:

Larger image here



 
gardener
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You say the interior walls are horizontal wood logs; how is the floor above supported? Do you know which wall is the main support? (Which way do the floor joists above run in each room and hall?)

If the hall wall between the doors can be cut out to 2-2.5 meters high, you could switch from ducts in a mass to a masonry bell that wraps around the chimney and gives heat to all the rooms. This would take less floor space than even a stacked duct mass like you show, and be more effective. There are too many turns in your plan to allow good flow in the duct.

. . . . . . H
. . MMMMH
. . M. . . H
. . M. . . H
. . MMMMH
. . . . . . H
. .BBBBC CBBB
. .B . . .C C. . B
. .B .R .C C. . B
=B . F . . . . . B====
. .BBFBBBBBBB

. =open space
H,= =walls
M =existing masonry heater
C =chimney
B =bell
R =heat riser
F =firebox

This would look and work like a big masonry heater, but doesn't take the specialized skill to build a masonry heater. If you can follow directions to build the firebox and riser, and you can build the brick walls around it, you have it.

The next question would be, do you want a J-tube or batch box type of RMH? I think the batch box would work more like masonry heaters you are used to, so it might be the better option, and a J-tube is best when it is in the same room you normally occupy so you can see & hear it and tend every so often. A batch box you load, start, close and it burns for an hour until it's done. There are precise dimensions for a batch box of various sizes in the donkey32.proboards.com forums.
 
Kristaps Vinogulajs
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Thanks for the idea Glenn. I never thought about batch box.
Actually its only a sketch for RMH, just to see where i plan the placement. If anyone have any other simpler versions of ducting- you are welcome. Plan without my RMH sketch: Here
My friend last year built standard 8" RMH, but I have no experience with bell type heater, so i doubt about it.

The inner walls in house is from vertical wood logs.
My construction man said that main support wall is between room 1 and room 2. (That vertical one in the middle of the plan above).

 
Kristaps Vinogulajs
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And i want to keep existing masonry heater between the rooms for now.
I will tear it down just after the new RMH will prove itself as a stable and good heater.
 
Glenn Herbert
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Okay, I wasn't sure if you meant the logs were stacked in a vertical pile, or ran vertically side by side
The bell idea would require cutting out the bottoms of fewer logs, then. Bells work just like some masonry heaters, with a big space that lets the hot gases rise to the top, and the exit at the bottom so only the coolest gases go to the chimney. The heat riser could go inside the bell so you don't need extra space for a barrel. The steel/iron plates you mention could work the way you want.
A bell will have much less friction that a long duct with many turns, so draft will be better.
Go to the donkey32 forum and search for "peterberg batch box" to find more details.
 
allen lumley
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Kristaps Vinogulajs wrote:Thanks for replay Allen!
It took me a while to make this plan.
First of all i want to say i do not want a barrel and bench in this particular RMH design. Bearing that in mind i could go narrower and higher for the exhaust
-thermal mass part by stacking ductwork vertically.

Kristaps Vinogulajs :W.o.w., In a perfect world houses would be built around Rocket Mass Heaters RMHs, and we would not be talking about retro-fitting a
RMH into an existing structure ! THIS CAN BE DONE ! We can offer help our opinions and facts after that it will be your build, this will be a difficult build for
a 1st build,It will need to be tested out doors and then moved inside

There is an old saying about A Camel is a horse designed by a Committee' if you take the RMH design and try and place it inside a masonry heater shell you
are likely going to be unhappy with the result !

Lets look at my list of issues ! Have you been to Rocketstoves.com to download Your copy of ''Rocket Mass Heaters", Right now this is the
oldest book in its brand new 3rd edition, and is 'The Book' used in almost all successful builds !

So i might building heat riser straightforward from bricks. And all outer shell as well from bricks. Inside the thermal mass made from clay,sand and stone.
As for immediate heat radiation i could use custom made plates(from steel or cast iron) placed in the heat riser walls.

The 1st job of our RMH is to get freaky hot- quickly, above 1800ÂșC, to do this we will actually limit the amount of mass that Our flame front is exposed to
until after the Top of the Heat Riser ! Mostly this is done by insulating Around the Combustion core, The feed tube, burn tunnel and the Heat Riser !

Also in the early part of the fire we want turbulence to increase contact between the Wood Fuel Gases and Oxygen at ignition temperatures- immediately
after the Top of the heat riser we want smooth flow of gasses and try and build our exhaust passages to promote that smooth flow, It sounds like you want
the outside wall of your Rocket to be square with sheet metal inserts on 3-4 sides to radiate of that heat, We have couple of problems here !

1) The top of the heat riser is the hottest part of the RMH, you will have the greatest amount of expansion and contraction with your metal plates and your
masonry having different expansion rates, making and keeping an air/ exhaust gases seal at that point will be extremely difficult ! The use of a barrel that
moves the sealing point down about 1 meter allows for prompt heat and cools the barrel are allowing for easier sealing !

2) Converting the Outside of the Heat Riser to a square to match the outer wall with sufficient gas passageway to ensure a smooth flow is difficult as we still
have the need to insulate the outside of the Heat riser at this point, This is an area where our designs are round and smooth and You sound like that is a
problem for you !

3) You should reconsider placing the feed tube in the hallway, this will mean that instead of just listening to your fire in the RMH, and automatically tending
it as needed, you will have to interrupt what you are doing, in order to get up and go check on your fire, Truly, your RMH can only serve you as well as you
serve it !

4) No benches- Again this is your build, my job is to point out ways to increase your options - I think that you have mentally looked at the Thermal Mass
Benches as A loss of space within your rooms. I am asking you to consider the Benches as fine pieces of built in furniture to be treasured and passed down
through your family, generation to generation Think of the pleasure of coming home and sitting on a pre- warmed bench in your hallway while changing to
indoor shoes, think of a small closet with your outside clothing hung up warm and dry. Instead of thinking of the benches as stealing floor area within Rooms
#1, and #2 think of them as additional storage space, at a convenient height for sitting you can have wall mounted shelving that folds back flat against your
walls or opens to provide more storage on two levels !

4b)stacking your horizontal ductwork is doable, and the vertically stacked elbows add back some of the horizontal footage lost to use of horizontal elbows,
this is a minor positive effect and you will need to come up with a layout with 1/2 that number of elbows !

A small correction: the other masonry heater i have in the hallway- it is built later, so its not in the house plan and i draw it with the blue stroke(see pic).
As i see by default the hallway was not provided by any heating. And it blocks door to room 2 so it will be removed anyway.

You have 2 entrances one at ether end of hallway, a door to room #1 a door from room#1 to room #2 and a blocked door from room #2 to hallway ?

The hallway and rooms floor is from wood(sand beneath it) and im going to replace it, so its easy to put in a concrete base for RMH.
The inner walls is from wood beams stacked vertically, except around masonry heater- there are bricks. Are these exposed beams, how thick, and are they
covered with plaster? I expect that the beams are not continuous and there is quite a lot of Plaster or Cob type infill, this can be re-cycled !

I believe that when you say Concrete and I say Concrete we are using different final products and don't want to comment here except about adding insulation
under the slab our around your perimeter walls ! Extra mass must be provided under the RMHs Burner Base to protect your Concrete from Thermal damage.

Im planing to place RHM in between the rooms and the hallway underneath the wall that separates rooms from hallway. (see pic , planned RMH is marked red)
And i do not need that space in the hallway between stairway and the wall. Main house entrance is at the left side of the hallway, the secondary entrance is on
the right. No dimensions for RMH at this point. And im not sure about heat efficiency in the room nr 1 by this design/placement of the RMH.



While a 8''(200mm) RMH System call push its exhaust gases sideways for 50'+(15 meters+) You need to subtract 5' (1.5 meters) for every Elbow you use !

Your sketch as drawn uses 10 elbows and leaves us no room for the horizontal ductwork and sheds most of its heat in the hallway !

Also your sketch leads me to believe that you may have what we call 1/2 chimneys that start 1.5 meters up on the wall instead of starting at the floor, IF this
is True we can work this to our favor !

Glenn Herberts suggestions are all valid and can be considered after the other issues are dealt with !

Think like Fire, Flow like A Gas, Don't be a marshmallow ! For the Good of The Craft ! Big AL

















 
Glenn Herbert
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To advise in more detail, we need some more information. What are the uses for room 1, room 2 and the hall? Where do you spend the most (awake) time? Where will you bring wood in from, and where would you like to store wood indoors for feeding the fire? (You won't need a lot of it at a time.)

If you build a J-tube style, you need to feed it from the room you use most for everyday living so you can be aware of its needs. If you build a batch box style, you can put the feed where it is most convenient to bring wood to.

Allen is right, metal plates in the walls of the bell will need special care to seal so that the metal can expand when it gets hot without leaking or damaging the masonry. There is fiberglass rope that is made for sealing stove doors; people have used this for the job.

The news that the wall between room 1 and room 2 is the main structural support is good - you can cut out part of the hall wall and resupport its top easier than if it was the main structure. What is upstairs? More of your house, built like the ground floor? Or smaller? Do the chimneys start from the floor? Are there cleanouts at the base that you can look at to see the condition of the chimney?
 
Kristaps Vinogulajs
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Thanks all for your replies!

Glenn, i checked out your suggestions and im liking the idea of building bell heater around the chimney(leaving some space between heater and chimney).
About metal plates- they are not needed, because there will be some kind of metal doors in bell heater(which is absent in RMH).

Room1 and room 2 are bedrooms, i did not post whole house plan just to not make a mess.
Upstairs is a small hallway about 7 sqm (75 sqft) with the doors to other rooms. The second floor is roof-floor. space is smaller.
The main living area and kitchen is located below main entrance in the plan. Just as you enter house doors on the right. Main entrance is one on the left side of the plan.
So as those rooms are bedrooms, i do not want to bring any wood in there. Looks like the hallway is the only one option from where to fire heater, as for storing wood too.
Chimneys start at floor level- there are cleaning doors at the floor level. Chimneys are old, condition is satisfactory for the part that is inside of the house, but the part what is on the roof needs to be rebuilt.



 
Glenn Herbert
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That sounds excellent. If you make a bell around the chimney, with a RMH core next to it inside the bell, you would want to have the heat riser on the opposite side of the chimney from the cleanout door, so the gases must flow around both sides of the chimney and give up heat evenly. If the cleanout is in room 1, you would want the riser on the room 2 side of the chimney as in my crude sketch, just keeping the cleanout door open for the bell exit to the chimney.

You say a masonry heater will have metal doors; I presume they have an adequate sealing system so they don't leak when they heat up or cool down.
 
Kristaps Vinogulajs
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Glenn Herbert wrote:That sounds excellent. If you make a bell around the chimney, with a RMH core next to it inside the bell, you would want to have the heat riser on the opposite side of the chimney from the cleanout door, so the gases must flow around both sides of the chimney and give up heat evenly. If the cleanout is in room 1, you would want the riser on the room 2 side of the chimney as in my crude sketch, just keeping the cleanout door open for the bell exit to the chimney.

You say a masonry heater will have metal doors; I presume they have an adequate sealing system so they don't leak when they heat up or cool down.



Yep.
Im in for searching correct measurements and ratios for rocket-bell heater to sketch proper plan for it.
But that is kind of hard to find in "one piece".
If anyone has link to rocket-bell heater plan with measurements/dimensions ill be grateful if you share it.
 
Glenn Herbert
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Dimensions for various sizes of batch box:

http://donkey32.proboards.com/thread/734/peterberg-batch-box-dimensions

Bell size is based on interior surface area and type of material. You want enough surface to absorb most of the heat before the gases exit, but leaving some for the chimney draft. Masonry bells can have a slightly larger surface than metal, because the metal absorbs/transfers heat faster. As a start, I believe the suggested area is about 6 square meters for a 6" batch box system for masonry, and 5.something for metal. This is duscussed in various places in Donkey's forum, you should find it by looking for peterberg's posts on the subject.

By the way, bell surface is calculated on the top and sides above the exit level. The bottom doesn't count.
In your case, I'm not sure how much to count the chimney exterior surface in the bell. It will absorb some heat which will go up the flue, but not as much as if it opened to the room. Asking Peter would be the best way to get an educated guess.
 
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