Expert: Bart Ogden - 9/9/2007

Question
QUESTION: I am an architect in NY , renovating my house.
I am planning to install a masonary wood burning double sided fireplace between the living room and dining room.

What are the correct mathematical design ratios between fireplace face openings and flue size /length.

Thanks for your help

ANSWER: Hi Nick,

The MINIMUM ratio for a masonry fireplace is 1/10 the area of the fireplace opening.

For a double-sided opening, we figure the area of one side x 1.5 as a MINIMUM.

Always exceed the minimums to err on the side of caution.

Thanks for using AllExperts.Com and good luck with your project.

Sincerely,
A. Bart Ogden, President
Home Safe Hearth & Chimney, Inc.
Wichita, KS
Voice: 316-265-9828
Fax: 316-265-9890
www.homesafeks.com


---------- FOLLOW-UP ----------

QUESTION: am I interpreting you answer correctly ?

If each side opening is 36" wide and 30" high
opening area = 1080 x 1.5 = 1620 sq inches

1/10 = 162"  
r(squared) = 166 x 7 /22 = 51.5
r= 7.15

therefore flue diameter should be 14.3" min

what about length of the flue ? or does this matter

thanks

ANSWER: Yes, that's correct.  Minimum 15" round inner diameter.  If I was building it, I would bump it to a 1/8 ratio and make it a 17" round inner diameter flue.

The height doesn't affect flow to a certain extent, (assuming disregarding friction loss and assuming the flue interior is smooth).

Thanks for using AllExperts.Com and good luck with your project.

Sincerely,
A. Bart Ogden, President
Home Safe Hearth & Chimney, Inc.
Wichita, KS
Voice: 316-265-9828
Fax: 316-265-9890
www.homesafeks.com


---------- FOLLOW-UP ----------

QUESTION:
are the opening/flue ratios different for two fireplaces back to back
versus one fireplace with two sides (ie see thru)?

Answer
Yes.  As I stated before, you figure 1/10 of the fireplace opening as a MINIMUM.

Thanks for using AllExperts.Com and good luck with your project.

Sincerely,
A. Bart Ogden, President
Home Safe Hearth & Chimney, Inc.
Wichita, KS
Voice: 316-265-9828
Fax: 316-265-9890
www.homesafeks.com