A commond woodfired boilersystem for heating, consist of several parts.
The boiler, a heatstorragetank, and distributionsystem with appropiate regulators.
(An oilburner dosnt need the heatstorrage, since the burner can turn on and of, and this way storrage the heat as unburned oil)
A masonry heater should be able to do the same job as the above plant,
so all the purposes of theese different parts should be thought into
the masonry heater.
Not only towards eatchother, but allso to the actual house and the actual (or future) family it schall support.
A masonry heater to, consist of an efficient fireplace, an accumolator to store the heat, and a main regulator to controll the release of heat pr. hour. Radiation of low thermal heat, and movement of air is taking care of the distribution round the house better than most expect.
Unlike a boilersystem, the different functions of the system in a masonry heater is not departed into seperate units. Most parts share the same purpose, but has allso seperate purposes that can be regulated during the creation of the stove. This as well as how its build, as from whitch materials.
The main regulater of heat pr. hour, is therefor set by the stovebuilder
by his choise of heatconductivity of the outherskin of the stove. More
than one layor of brickwork between hot smoke and the livingroom will decrease
the heat pr. hour dramaticly.
To calculate the heatresistance from going into the first layer, through this, and out of this again, maybe into another layer and through this and into another......... calculated with eatch layers heatconductivity, schould be daily exercise for every stovebuilder for at least a week in his education, but it isnt.
The “fine” regulator is set by the user, in for how long time he makes
the fire going eatch day.
You dont make fire to get warm, but for not to get cold tomorrow !
The “Art” in stovebuilding is therefore, to make a heater that provides the nessesary amount of heat in the actual house for at least 24 hours, with one daily fire that dosn´t take more time than the owner can spend.
Norbert Senf, the chairman of The Masonry Heater Association of North
America expressed it this way:
”As heater walls get thicker, the surface temperature drops, and the storage time and the thermal lag time increase.
An optimum design needs to strike the correct balance between these opposing forces. Storage times in exess of 18-24 hours are not desirable, since there will be to much time lag between firing the heater and reaching maximum output, in effect requiring you to predict tomorrows weather.”
There is many very different kinds of more or less fireproof materials to build from.
From nature we have soapstone, that is exelent but quit expensive.
Allso from nature we have clay, that is probably the material with the
best “cost/benefit ratio”.
When we are not in the most vunerable parts of the stove, the core, clay is hardly to be without in stove building.
Industrial fireproof materials has of course been developed for many reasons, and this we can take advantage of.
Bricks from charmotteclay is made for different purposes as: extreme temperatures, big chockresistance, diffenrent chemical exposions etc. Has been develloped in great variation.
The goal is to find the best suitable stone for the purpose of a masonry heater. That will be in between extreme temperatures and chockresistance.
In the core we allso want a rather big heattransferre through the construction to awoid tensions, so a high heatconductivity is allso desirable.
Castables to make prefab constructions is made in great variaty, but
so far non that i can recommend as long lasting, compared to fireproof
One great disadvantage form this material is, that you have to wait for month before you make your first fire in soutch a stove. A stove build from charmottebricks can be fired even before its finished.
For everything thats not exposed for more than 572 C. (about 1000F)
ordinary bricks and claymortar (1 part pure clay + 5 parts of sharp sand)
is most appropiate conserning long lasting and easily repaired if nessesary.
Plaster can be made from clay, but the heatconductivity of the mixture and thickness of layer schoul be taken seriusly into consideration.
Cob, a mixture of clay, sand and straw, is tremendius to make beautifull shapes, but the heatconductivity is very low, so be carefull. (Or make a sculpture in another corner of the house ;-)
Calculate for yourself - here is the help !
I have made a spreadsheet in Exell, where you can "build a stove" with different kinds of materials, different thickness, different amount of layrs between the core and the livingroom, different size of surface, different average temperature of the coor, and this way calculate the output of your heater.
I havent figured out how to put it direct on my homepage to download, but you are wellcome to send me a short email with the word "calculation" in the subject, and i will return you the spreadsheet. Its not idiotproof, so save the original if you by mistake schould change something that schouldnt be changed.
You can try to download it here.
Castiron and brickwork.
The connection between theese materials are very important, since they act very differently in the heat.
You often want a tight connection, but make sure that it allso can move independantly, because they will, even if that means destruction.
To close of the connection between the stove and the chimney, a damper is essential, and it must be pretty tight.
If its not, you have the same situation, as if your hotwatertank is leaking half of you produced hot water into the wast during the night.
A litle hole in the damper means less air going through, but it will be more hot, so the lose of calories will be about the same as if no damper at all.
The Danish institut of tecnologi has messured this loss to allmost 50%, so this is really an issue worth thinking about.