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Calcimator

Fireplace & Chimney Calculator

Size a chimney flue based on the 10:1 fireplace-to-flue area ratio and estimate draft pressure.

Inputs

in
in
ft

Results

Required Flue Area

100.8 sq in

Flue Size

10.04 in

≈ 3 credit cards

Fireplace Opening Area1,008 sq in
Min Chimney Height20 ft
Estimated Draft Pressure0 in w.c.
How to Use This Calculator
  1. Enter the fireplace opening width and height in inches.
  2. Input the chimney height in feet (measured from the firebox floor to the top of the flue).
  3. Select the flue type: round or rectangular flue liner.
  4. Review the fireplace opening area, required flue area, and flue size (sized using the 10:1 ratio, or 12:1 for round flues).
  5. Check the minimum chimney height and estimated draft pressure for adequate draw.

How the result changes with Fireplace Opening Width

Fireplace Opening WidthRequired Flue AreaFlue Size
2570 sq in8.37 in
38106.4 sq in10.32 in
54151.2 sq in12.3 in
67187.6 sq in13.7 in

What each input means

Fireplace Opening Width
Width of the fireplace opening.
Fireplace Opening Height
Height of the fireplace opening.
Chimney Height
Total height of the chimney from the firebox to the top of the cap.
Flue Type
1 = Round flue liner, 2 = Rectangular flue liner.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Fireplace Opening Width = 36, Fireplace Opening Height = 28, Chimney Height = 20, Flue Type = 2 = 4 input(s) provided
  2. Calculate Required Flue Area
    Required Flue Area
    100.8 = 100.8
  3. Calculate Flue Size
    Flue Size
    10.04 = 10.04
  4. Calculate Fireplace Opening Area
    Fireplace Opening Area
    1008 = 1008
  5. Calculate Min Chimney Height
    Min Chimney Height
    20 = 20

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.

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