From: CamRobyn@aol.com
Date: Sat, 9 Jul 2005
Subject: 42" Rumford Flue Sizing
To: buckley@rumford.com

Mr. Buckley,

First I would like to note that as an engineer I find the technical information provided on your website very informative. The aesthetic appeal of a Rumford fireplace first drew my attention, but the level of technical expertise you provide sold me on the idea of including Rumford fireplaces in our new home. I have visited your website numerous times as I have planned our project.

I have just started building a home with two staggered Rumford fireplaces (a 42" open to the 28'X15' Den and a 30" open the other direction to a master bedroom). They will be staggered to keep the depth of the chimney reasonable since it is in the interior of the house. My question has to do with the flue sizing for the 42" Rumford.

The chimney will be approx 33' tall from the hearth to the last flue liner. Based on the IBC link on your site, I assumed an opening of 1700 in^2. Using the chart which stops at 25' chimney height, a flue liner with 124 in ^2 area should easily work. From the flue size chart I can do this with an 11.5X15.5 (12X16 modular) or a 13X13 . But when I look at the smoke chambers offered with a 42" Rumford, the options are 13X18 or 16X16. These have a much larger effective areas.

So to start with, I guess my first question is which size flue liner should I use and can I even install a smoke chamber that will let me run the 12X16 or 13X13 liners with a 42" Rumford that the IBC nomograph indicates will work? I want the fireplace to draw properly, and to do that I think I need to use the smaller flue liners. And this brings me to my next issue, which is that my framer is concerned about maintaining combustible clearances with bigger liners. If I could use the 12X16 liners in combination with 12X12 liners with the 30" Rumford, it seems like this would package really well running up the chimney. If I have to use the larger flues it could increase the depth of the chimney as well as force me to alter the framing.

So to summarize, it seams reasonable from the data I see that with my chimney height I could run 12X16 liners on the 42" Rumford and 12X12 on the 30" Rumford. This would be the cleanest approach. Can I do this by using an alternate smoke chamber and still meet your guidelines as well as code guidelines?

Thanks in advance for your assitance.

Cameron Browder
336-824-4117

Thanks for the kind words about our website and our effort to provide technical support. May I put your comments on our "endorsements" page at http://www.rumford.com/endorse.html ?

In response to your question about flue sizing, in short, yes, go for it.

We specify the 16"x16" or 13"x18" flue system for our 42" Rumford because these sizes provide a flue with a cross-sectional area at least one tenth of the cross-sectional area of the fireplace opening that complies with code regardless of the height of the chimney. That way, as manufacturers and dealers, we don't have to ask the height of each chimney and stock several different sizes of flues and smoke chambers for each fireplace.

But you can. By using the chart in the code that factors in the height of the chimney you can sometimes use a smaller flue. Your calculations are correct and I'm sure the 12"x16" flue size with a cross-sectional area of 131 sq.in. will be sufficient for your 42" Rumford fireplace with a 33' tall chimney. You should order a 12"x16" smoke chamber as well as the 12"x16" flues even though that's the size we specify for a 36" Rumford and our dealer will probably tell you you need the larger size. You still need the 42" throat and damper.

Send me a picture when it's finished.

Best,
Jim Buckley