[Stoves] Chimney Project in Madagascar

[Paul Anderson]

Dear Michal,    (and Stovers)

I am sending this reply and your message (below) to the 500+ readers of 
the Stoves Listserv.  Any replies from them need to be sent to you also 
at     Michal Usowicz <usowicz at mail.usf.edu>     because you are not 
subscribed to the Stoves Listserv.

About chimneys, I am not qualified to respond.  My only comment is to 
question the size (and probable expense) of what you are discussing.

Dr TLUD

Paul S. Anderson, PhD  aka "Dr TLUD"
Email:  psanders at ilstu.edu   Skype: paultlud  Phone: +1-309-452-7072
Website:  www.drtlud.com

On 3/23/2013 7:23 AM, Michal Usowicz wrote:
>
> Dr Anderson,
>
> I hope that everything is going wonderfully with you and that your 
> TLUDs are still burning!I recently got to Madagascar for Peace Corps 
> service and things have been progressing well.My host family for 
> pre-service training here cooks with wood inside but they are planning 
> to build a chimney and I would like to help them construct a good 
> one.Large diameter (about 3-4 ft) brick chimneys similar to what you 
> may expect to see in US homes are common in the community that my host 
> family is in and I think a brick chimney will be the best solution to 
> ventilating the home in this context.
>
> A large diameter, natural draft, brick chimney seems like a straight 
> forward problem but I wanted to make sure that I was not making any 
> mistakes.I thought you may be a good person to ask even though I know 
> this isn’t your exact specialty.I expect the chimney will be about 
> 15-20 ft tall and at least the hearth will have a rectangular 
> cross-sectional area of 3.5x4 ft^2 since that it the current size of 
> my host mother’s fireplace (although I am unsure if my host family 
> will construct the chimney with a taper).It will primarily be made out 
> of clay bricks and mortar.Could you please give me some guidance on 
> the following questions?
>
> 1.Is there a good rule of thumb for the minimum chimney height to have 
> good draw from the hearth?The only way that I have to estimate this is 
> using the chimney effect equation (ie flow is proportional to Area, 
> height^0.5) and I found that for practical chimney heights for my 
> situation (ie 15-20 ft) there was not a significant change in the flow 
> rate of the chimney.However, for the equation to apply the chimney 
> needs to be adiabatic, which I think is a bad assumption in this 
> case.Do you think 15 ft will be tall enough or does it need to be taller?
>
> 2.I do not understand the effects of geometry on chimney draw and was 
> curious if there is a problem with necking down the chimney 
> significantly after the hearth?I suspect that my host family may copy 
> the design of a neighbor’s chimney (since they are hiring the same 
> mason to build theirs) which tapers down asymmetrically (ie the left 
> wall is slanted and the right is straight) after the hearth from about 
> ­­­­­­2x3.5 ft^2 at the base to about 2x1 ft^2 over about 6 ft.
>
> 3.Along the lines of the previous question, I am concerned that the 
> rain cap for the chimneys may choke the flow.The rain caps of the 
> chimneys here is a thin slab of concrete set at the top of the chimney 
> with 1-3 bricks at each corner.Do I need to pay attention to the size 
> of the gaps under the rain cap?
>
> 4.I know if you build the chimney shorter than the apex of the house 
> the chimney effect of the house may overwhelm the effect of the 
> chimney.Do you have any intuition or advice about the height 
> difference between the chimney and the roof apex that is needed to 
> avoid this?
>
> 5.I feel intuitively that it would be a good idea to minimize the 
> height of the hearth entrance to capture the smoke plume before it 
> spreads but I am not sure if this matters if there is good draw in the 
> chimney.Do you have an opinion on this?
>
> 6.Have you ever heard of Rumsford chimneys?I had a construction 
> engineer friend of mine build one in his house and he said that the 
> draw from the chimney was excellent.I was just curious if you had 
> heard of it and if you had an opinion of it.
>
> Again I hope that everything is going well with you.I would really 
> appreciate any advice you may be able to give.
>
> Sincerely,
>
> Michal Usowicz
>
>

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