Flue outlet size

I am curious as to the engineering footwork behind the sizing of the flue outlet as it relates to the burn grate area. This would be important to someone [hmm] that might want to build a scale model of a favorite stove that would actually work when complete.I am reluctant to start working on a half size when I do not know if the half sizing would hold true for the flue outlet /grate area relationship. As we all know if you are going to cut and weld it is so very nice to do it just one time. Anyone have any data on this element of the build? Thanks, Mike

https://inspectapedia.com/chimneys/Chim ... 9C.php#C9B

https://inspectapedia.com/chimneys/Chim ... 9C.php#C9C

Why should the value change if kept to scale?

A flue of 4.3 inches in diameter only has 50% the volume capacity of a flue of 6 inches in diameter even though it's almost 72% as wide.

what is the dia. of the grate burn area in the favorite you wish to shrink ?

steve

Thank you for the replies. I have calculated the areas of round flue pipe from 3 inches to 6 inches which is the size of the full sized stove. A 3 inch pipe [half scale] will only provide 24.9 percent of the area as a 6 inch pipe [not even close to 50 percent] which tells me that I will not have a working half scale model if I keep it truly dimensioned. I still am curious as to the grate/ flue outlet relationship. The grate opening is 11.5 inch diameter in the full sized version. I did not add up all the areas of all the slots in the grate. 11.5 inches of grate area will make 170 square inches of full opening before dropping the grate into place. That is roughly 16.6 percent of flue opening for this grate area. That does not sound right so I now am wondering if the openings in the slot have to be calculated. It is looking more and more like this half scale unit will have to be a 5 inch flue but I can no longer call it true to scale . right???. Isn't this stuff neat? Mike

i'd call it 2:1 then.

make the new grate space 6" and the flue collar 3." make every piece and area 1/2 as big as the original.

try not to over think it, the originators knew their stuff, just copy it all in scale.

I hear what you say KC and you can be sure that I will not be counting sheep tonight, rather grates and collars as I continue to churn this over. Thank You, Mike

stovepipemike wrote: ↑

Wed. Oct. 11, 2017 4:37 pm

Thank you for the replies. I have calculated the areas of round flue pipe from 3 inches to 6 inches which is the size of the full sized stove. A 3 inch pipe [half scale] will only provide 24.9 percent of the area as a 6 inch pipe [not even close to 50 percent] which tells me that I will not have a working half scale model if I keep it truly dimensioned. I still am curious as to the grate/ flue outlet relationship. The grate opening is 11.5 inch diameter in the full sized version. I did not add up all the areas of all the slots in the grate. 11.5 inches of grate area will make 170 square inches of full opening before dropping the grate into place. That is roughly 16.6 percent of flue opening for this grate area. That does not sound right so I now am wondering if the openings in the slot have to be calculated. It is looking more and more like this half scale unit will have to be a 5 inch flue but I can no longer call it true to scale . right???. Isn't this stuff neat? Mike

Just to throw this into the mix.

The Glenwood 116 Modern Oak uses a 5 inch pipe.
The Glenwood #6 base heater uses a 6 inch pipe.
Both have 16 inch fire pots and hold close to the same 50 pounds of nut coal.

The GW 118 Modern Oak and the GW #8 both have 18 inch firepots and hold about 35-40 % more coal than the 16 inch firepots.
And both also use a 6 inch pipe.

With all four of those a fire brick liner was an option so not having the liner would increase the coal capacity by a lot. So an unlined 116 would hold roughly 70 pounds of coal, yet it's still designed to work, and works well, with a 5 inch pipe.

And in the 6 inch pipe range you have the #6 with 50 pounds lined pot and about 65-70 unlined on up to the 118 and #8 also only using a 6 inch pipe lined or unlined pots up to probably 80 pounds of coal.

So, you see, using the examples of well known, and well designed stoves there's quite a bit of leeway for pipe size compared to how much coal capacity the stove has.

Paul

I don't think that flue size can be directly related to grate area.

stovepipemike wrote: ↑

Wed. Oct. 11, 2017 4:37 pm

I still am curious as to the grate/ flue outlet relationship. The grate opening is 11.5 inch diameter in the full sized version. I did not add up all the areas of all the slots in the grate.

As to how at least some commercial coal stoves seem to be rated, the dimensional relationship of the fire box's (not the grate areas) depth x width (as sq-inches) to BTUH works out to be something on the order of:

(Firebox sq-inches) x 375 = Max BTUH rating (Commercial, or advertised)

For example:
Firebox depth = 12"
Firebox width = 16"

(12 x 16) x 375 = 72,000 Max BTUH rating

***I generally cut this in half to determine a coal stoves more realistic "real world" nominal maximum output potential.***

So Mike, is your intent with this "model", to actually heat a room? Or is it just a hobby project for aesthetics?

BTW, Wilson has about a half-scale working kitchen range that he uses for public demonstrations. You might pm him and ask what size pipe it uses.

Paul

joeq, my intent with this stove project is to have a perfectly operable unit that I could use to display like at a tailgate type event as well as cook a pot of beans etc on as a curiosity feature. Folks would have an increased interest in coal burning appliances if they can see one in useful operation. I am getting too far along to sling the full sized versions around the way I once could have. For these reasons ,it has to work right and behave itself in public. Paul, thanks for the tip on Wilsons cook stove because as the old saying goes, what is good for the goose just might be good for the gander. Thanks to all for your help. Mike

Just remember Mike, supply & demand!!! Been discussed many, many times way back. $$$$$$