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Fireplace Design & Dimensions

Fireplace Design Literature

The Brick Industry Association (http://www.bia.org) has two excellent pamphlets about fireplace and chimney design and construction. Go to their web site and find the section on Technical Notes. Scroll down the left hand list of articles and click on the following titles:

#19 Residential Fireplace Design

#19A Residential Fireplaces, Details and Construction

Fireplace Sizing Table

All of the following dimensions are given in inches, except for Chimney Height. That value is given in feet. The firebox design is critical. Here is a photo of a new masonry firebox in my own home. The rear wall of the firebox rises vertically from the floor of the fireplace and then begins to slant towards the fireplace opening just at the top of the gas logs. The sidewalls of the firebox are vertical. Note that the firebox is not the same width front to back. It gets narrower towards the rear of the firebox!

The firebox depth does not include the thickness of the brick - or marble in my case - that faces your fireplace. This is very important! You can mix and match flue sizes with chimney heights. To properly size a flue, you must use a Nomograph. See the Brick Industry Association's Technical Note 19B - Residential Chimneys. It is always better to use the smaller flue size when you have two choices. When using the smaller flue size, you will be required to raise the height of the chimney. Taller chimneys draw better than short chimneys of the same flue size.

The smoke chamber height and design is very critical. You generally can't see this space as it is hidden above your fireplace damper. The height of the damper is very critical as well. The bottom of the damper should be a minimum of 8 inches above the top of the fireplace opening. If your damper is not at least 8 inches above this spot, you will have problems for sure! I urge you to read the pamphlets I have mentioned from the Brick Industry Association. They have excellent illustrations which will enable you to clearly see what I am trying to explain! The following table and its values are courtesy of the Brick Industry Association.

Firebox Dimensions and Chimney Heights

Fireplace Opening Width 24" 28" 32" 36" 40" 42" 48"
Fireplace Opening Height 24" 24" 29" 29" 29" 32" 32"
Firebox Depth 16" 16" 16" 16" 16" 16" 18"
Rear Firebox Width 11" 15" 19" 23" 27" 29" 33"
Rear Firebox Wall Vertical Height 14" 14" 14" 14" 14" 16" 16"
Nominal Flue Size 8x12 8x12 12x12 12x12 12x16 12x16 16x16
Minimum Chimney Height 15' 20' 18.5' 20.5' 13' 19.5' 16.5'

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17 Responses to Fireplace Design & Dimensions

  1. Hi , i have a room (size 30ftx20 ft height 12ft ) i would loke to install chimney in the middle open all around , but i cant exit the hood direct from the roof . Can i open the hood from side ? what size of the exhaust is requested ? do you have material in brass?
    thanks

  2. I'm putting a mantle on my fireplace , how many inches do I need from the fireplace to the mantle ? On the hight and width ? Please help I know legally u required so many inches I'm just not sure how much .

  3. I have a customer that wants a 48 inch damper. They want the opening to be 60 inches tall. The fireplace opens outdoors to patio. Is it possible to do this ? All research says that it cant be but 38 inches tall.

  4. my house (and fireplace) was built in 1923, it has a 8X8 flue and the fireplace opening is 29 high x 42.5 wide and I set off my smoke detector every time I use the fire place. (18 deep and sides tapper to the back). I grew up around wood stoves and fireplaces but can not get this this to not smoke ( I use paper to start a draft, wood is now 2 years old, smokes using kiln dried oak boards) Based on the table from your website , do I need to reduce the opening to stop the smoking? and if so how.

    • Sheldon,

      Read all my past columns about the shape and sizes of fireboxes, smoke shelves, flue sizes in relationship to fireplace size, etc. and then determine if your fireplace was doomed from day one.

    • The mason's rule of thumb for your flue is it needs to be at least a 10% ratio of the opening of your fireplace: 29 x 42.5 = 1233 (10% is 123) Your flue is an 8 x 8 =64 than 123.
      You require a draft inducer or power vent fan that is designed to be installed at the top of your chimney & flue; and runs off electricity. Would be cheaper to order one yourself and hire an electrician to install and run control switch to fireplace room --may need another contractor or sweep to install on top; expect to spend at least $1500 for reasonable combined costs.?.
      I've been a custom FP professional for 15 years and am telling you this is about your only solution.

  5. Hi,

    I have to replace doors on the wood-burning fireplace.
    The opening in the wall is 25.5" x 36.5"

    What door format fits in this : small, medium or large (I'm a bit puzzled by the fact that actually any of the doors size specs available eg. from the LOWE's can fit that opening).

    Thank you for your time and consideration,

  6. I have a fireplace that is 34"H X 28"W with an 8" diameter flu liner. My chimney is 30' tall. This fireplace is in a room that is 16' X 16' with a door (my den) .. The liner is brand new ... The chimney has a cap on it that sits about 18' off of the top of the chimney...

    I started a fire the first time today in the fireplace after seventeen years... I have been refurbishing an old house that was built in 1750... The fireplace was the first thing that I had a contractor work on about 15years ago... The flu is a masonary liner that was poured inside of the chimney..

    The chimney smoked ??? Any suggestions ?? I opened two windows to allow for make up air.... I decreased the opening height by about four inches... The only thing other thing that I have not tried is to raise the height of the fire box by putting fire bricks in the bottom ...

    I have waited to have a fire in this den for 17 years hope you can help..

    God bless
    Denny

    • Yes I can help. Please READ all my columns about fireplace design and look at the tables about measurements with respect to all aspects of the shape and size of the fireplace. Pay attention to what I discuss about smoke shelves. Flue size is also important. They have to be perfectly sized. Fireplaces are very complex.

  7. I'm building a masonary fireplace and I would like to have an opening of 48" wide x 48" tall. What would the remaining dimensions be? ( depth, rear wall width, rear wall vertical height, etc.....)

  8. We are renovating a large floor to ceiling brick fireplace that overwhelms our small family room. Plan to remove the brick and reface with smooth finish/tile. We'd like to reduce the size of the fireplace opening (currently 25" tall x 40" wide to 20" tall. We do not want to put in gas insert. Fireplace is masonry w gas/gas logs.
    Is it possible to reduce the size of the fireplace opening?
    Thank you.

  9. We have a wood burning fireplace in a new home. When I try and light a fire, there is air blowing down the flu and the smoke goes back into the house. Someone has told me that this is called negative pressure. Once the fire is lit and gets the flu hot it will burn. I have tried opening a door when lighting the fire but it doesn't help. When the home was being constructed, the builder added a finished 3rd floor to our home and the top of the chimney is lower than the floor on the finished 3rd floor making finished area higher than the top of the chimney. My question is: Does the top of the chimney need to go higher than the fished area on the 3rd floor?

  10. I have a very large fireplace. The opening is presently 52" wide, and the thing doesn't draft well at all. I would like to rebrick that opening down to 42" wide so I can install off the shelf, rather than custom, doors. It's a 2 story house, and the chimney is about 30' tall. Thoughts?

    • Yes. My thoughts are for you to go back up and read this column and look at the table that shows you all the relative sizes based on the opening. Just do what I say in the column and the smoke will go up the chimney.

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