The NFI APP makes the five most commonly used mathematical formulas used by hearth appliance installers much easier and quicker to process. The first formula, used to figure the distance a stove needs to be from the corner

Corner Installation Calculator
Setting a free standing stove in place for a corner installation usually means a series of several little moves in order to maintain the proper clearances. This formula makes it simple. Enter the corner clearance requirement, the width and the depth of the stove. The resulting number will be how far out from the corner the front of the stove should be.

Hole Size Calculator
Figuring out the right size hole to cut depends on the pitch of the roof. Simply enter the Rise, Run and the diameter of the pipe plus the clearance on both sides to find an accurate size hole.

Pitched Roof Chimney Height Calculator
This formula enables you to meet the 3'/2'10' for chimney height. Simply enter the rise, the distance to the peak and the height of any object within 10'. The result will be the height the chimney needs to be to meet the requirements specified in NFPA 211.

Extension Calculations for Cathedral Ceilings
Since single wall and double wall connector pipe have greater clearances than factory-built chimney pipe, the chimney must hang down into the room when installed in a cathedral ceiling. Simply enter the diameter of the chimney pipe, the diameter of the connector pipe, the clearance required to the connector pipe, the rise and the run. The result will be the length of chimney pipe that must hang down into the room.

Combustion Air Calculations for Gas Appliances
The Known Air Infiltration Rate (KAIR) Formula helps determine the combustion air requirements if the air change per hour (ACH) is known. The KAIR method must be used if the ACH is known to be less than 0.40. Simply enter the BTU input of the appliance and the ACH to determine the minimum cubic feet required for that appliance.

Ratings and Reviews

R3@$0N ,


Calculation such as the pitched roof chimney height are in accurate. The app offers no reference to any of the material from any of their books and is simply a collection of five formulas. I would’ve liked to have seen something with more reference material.

J.Soper ,

Great tool for the pros

This is pretty great but the extension calculations for cathedral ceilings won’t work on my older iPhone, I am unable to scroll up to include run and get the calculation done


John Hoover
49 MB

Requires iOS 9.0 or later. Compatible with iPhone, iPad, and iPod touch.



Age Rating
Rated 4+
© 2017 National Fireplace Institute®


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

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