Rumford Technical Discussion

Rumford Technical Discussion
Two Flues Better Than One?

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One flue the right size is better than two. A double flue and custom split smoke chamber is convoluted and gets you very little in return because the extra turbulence and surface area in the two flues mean that each of the two flues would have to be almost as big as the single flue that would serve.
You can make custom flues that are larger or wider than available flues by cutting out one of the sides of two flues and putting them together to make a single custom two-part flue.
For example, instead of using a 20"x20" flue, you could make a single 16"x26" flue to vent a five foot Rumford by cutting the faces out of two 16"x16" flues and putting them together.
Similarly the 16"x26" smoke chamber could be made from a 16"x16" smoke chamber with the halves separated by 10" - a gap that could be filled with firebrick, refractory mortar or pieces cut from clay flue liners.

Discussion

>4/29/97
>Hi Jim,
> >I have a 36"x 36" Rumford fireplace with a flush hearth extension to build
>that has a window 5'8" above the floor.
>Can I split the throat and run two smaller flues as the architect has in his
>drawings. If so what size would you recomend.
> >Mike Petty
Michael
I got your fax after talking with you today. If you can reduce the opening height to 32", I'd go with a single 12"x12" masonry smoke chamber and flue system. A single 10" Class A metal chimney on a standard 1212 smoke chamber would also work. You might have to miter and "lean" the smoke chamber a little to make it fit.
If you must keep the fireplace opening 36" tall you'll have to use a 13"x13" smoke chamber and flue or a 12" metal chimney. Still, one the right size is better than two.
The double flue and custom split smoke chamber is convoluted and gets you very little in return because the extra turbulence and surface area in the two flues mean that each of the two flues would have to be almost as big as the single flue that would serve.
I called the project architect, but got his voice mail and have not yet talked with him. I'd be happy to work with you, the architect and builder to design a full masonry fireplace and chimney that will perform well and be sensible to build.
Best,
Jim Buckley