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will Exit Flue with 5" diameter be a problem? No chance?  RSS feed

 
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Hello all,
I am reading about RMHs for 3 months and I got basic items to build one in my basement. But I've got a problem. In my house I have a built in chimney with only 5"(13 cm.) diameter. I am living in Ankara, located in Turkey. This dimension is the standard for the diameter of the stove pipes in my country. It is very easy , and cheap to get 5 meters of stove pipe in my country. But for example steel pipes with 20" or 25" diameter are pretty expensive. As an addition my built in house chimneys input is in really nice position for my future RMH. I am gonna build the RMH according to well known book of Ianto Evans&
Leslie Jackson with the title "rocket mass heaters:Superefficient Woodstoves YOU Can Build"
. In that book , it is declared that,

C should be the tightest part of the
intestinal system. The size of the cross
sectional areas of all parts of the stove’s
internal ducts or intestines should never
decrease below that of C. In other words,
the cross sectional areas of F, G, H, J and K
should all be greater than that of C.



Here, C is the area of the horizontal burn tunnel,
normally made of brick, in which most of
the burning happens and K is, K is the exhaust, the horizontal
flue that carries hot gas through your floor,
heated bench, bed etc. This should be at least
the size of the heat riser (8" to 10" diameter, my heat riser will have a 7 square inches cross sectional area )
or it could be made of more than one duct,
totaling a much bigger cross sectional area, as
for instance, if you’re using it to heat a floor.

But I've seen some pics on the internet that are showing some people using standard , relatively narrow stove pipes looking like having the diameter equal to standard stove pipes which are sold in my country for the exhaust.

I would like to ask just, what happens if I use that kind of stove pipes with the diameter of 5". No chance? It takes some money and energy to try and to see. Do you have any experience with that kind of stove pipes?
Thank you very much...
 
gardener
Posts: 599
Location: +52° 1' 47.40", +4° 22' 57.80"
69
forest garden trees wofati woodworking
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Please, don't use ordinairy steel stove pipe, it will burn through in less than a heating season. People who claim they've built a succesful rocket mass heater with a steel core, however thick, made some mistake somewhere. In the sense that such a steel pipe could only survive when the stove is running not hot enough and as a consequence, isn't running clean as well.
 
Inanc Akcan
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Thank you very much for your advice Peter.
But actually my concern is the dimension(diameter) of the exhaust. My RMH will have firebrick core. No problem with the core for me.I really wonder if 5" diameter will be enough for efficient exhaust drawing. I don't want any smoke in my house. I can easily replace the whole pipes every year if they burn out or I can clean them periodically in winter time.

Regards
Inanc
 
Inanc Akcan
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Hi,
I've noticed that, the heat riser height and vertical chimney height are the most important parameters for the resolution of this problem. As I said before I have built in chimney in my basement. I has 5" diameter and its height is approximately 8 meters (approximately 26 feet)from the top of the heat riser.
 
Peter van den Berg
gardener
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Location: +52° 1' 47.40", +4° 22' 57.80"
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forest garden trees wofati woodworking
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Outside the core, the pipe won't burn through.
With an exhaust diameter of 5", you have to change the rest of the stove accordingly. In effect: the whole stove should be best the same dimension throughout. Whether or not a larger diameter will work with the 5" flue coupled to the length you mention, I'm afraid you have to try it yourself. My 5 cents: you don't stand a chance in the world with an 8" stove and 5" flue. Maybe, just maybe, a 6" stove and 5" flue combination would work depending on the overall quality of the chimney, but that's only guess work.
 
pollinator
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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books fungi hugelkultur solar wofati woodworking
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Inanc Akcan : Just a little difference in the overall smoothness of the interior wall of your existing chimney will make or break this build ! Lets talk about chimneys-

I am going to talk about Two (2) chimneys, the 1st is the Internal Chimney/ Heat Riser, It will gain a lot of "Draft" from just a little increase in its height as compared
to the depth of the Vertical Feed Tube, there is a point where a really tall Heat Riser Will 'Draft' so well, even discharging through a 5'' diameter final exhaust Vertical
Chimney as to push the hot exhaust gases past the Thermal Mass so fast that very little heat energy gets transferred into the Thermal Mass!

A high enough External Final Chimney with no internal restrictions, and that rises above all other building parts, a Couple of meters above the Highest point of the house
and other close objects, should 'draft' well. Increasing the height of this chimney will also increase this effect ,but not as dramatically as can be achieved with an increase
in the Height of the internal Chimney- The Heat Riser !

So- Allowing for the other points where a slight variation in the Constant Cross Sectional Area can cause the rocket mass heater R.M.H. to fail, it is possible to build a
6'' system that will 'draft' through a very smooth walled 5'' Final External Chimney, I expect that you will need to continue your 6'' system through your Thermal Mass
and create a very generous final clean out that will allow you to build a small fire to prime your systems 'draft', so that your final 5'' chimney will accept the hybrid
system you are trying to create.

As I visualize what you are trying to do- Yes, I think it is possible to build a R.M.H. with a 6'' System, and exhaust it through a pre-warmed 5'' final vertical chimney, IF
you are willing to create a Custom Heat Riser for your system to allow it to draft ! How much more additional Heat Riser height you will need to create the 'Draft' that
your system has to have, and STILL Allow for the Hot exhaust gases to flow slowly enough through your Thermal Mass is something that can only be discovered by
you ,And will probably require your to build a complete system, and give it a good long trial through multiple heating seasons, possibly re-building it several times, to see
what will work for you in that location with that final chimney !

I would not try to create a hybrid system that Uses 5'' pipe for both the Horizontal flow through your Thermal Mass and your final vertical chimney ! I hope this is clear
and that it will help you make your final Decisions ! For the Good of the Craft !

As always, your comments and questions are Solicited and are Welcome ! Think like Fire ! Flow like a Gas, Don't be the Marshmallow ! A.L.
 
Inanc Akcan
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Allen Lumley:Thank you for all the information and thoughts!! They were really useful for me.
I don't like the pipes passing through the walls sideways. I would have really wanted to use the original built in chimney in my basement. But it looks like impossible.
Best regards
Inanc
 
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