Furnace Flue, Boiler Flue & Hot Water Heater Flue Sizing

 Category I Linger Sizing Chart

 How to Use Category I Appliance Flue Chart

  1. Measure the length of the chimney flue
  2. Determine the total BTU output of the appliance(s) that is being vented
  3. Determine which type output the appliance(s) are venting (natural draft or fan assisted draft)
  4. Use the above chart to find the proper size chimney liner.

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  1. Flexi-liner systems are UL/ULC Listed for relining existing masonry or factory built chimneys and vents serving Category 1 natural gas or propane fired appliances.
  2. Venting gas fired appliances into masonry chimneys is prohibited unless a “Listed” liner (i.e. Flexi-Liner) or a tile liner conforming to CODE is utilized.  Oversized, misaligned and/or cracked tiles DO NOT constitute a “code” liner.
  3.  The air space around an installed Flexi-Liner System must not be used to vent other appliances.
  4. Insulating of Flexi-Liner Systems is a benefit to the installation but not always essential to effective operation of this venting system.  Consult the Flexi-Sleeve installation instructions for insulation guidelines.
  5. A Flexi0Liner System venting more than one appliance shall not be smaller in diameter than the outlet of the largest appliance being serviced.
  6.  The Flexi-Liner System may be smaller in diameter than the outlet of the appliance being served provided:
    •  The vent height is at least 10 feet
    •  The liner size is not more than one size smaller
    •  The “FAN MAX” is reduced by 10% if the appliance is “fan assisted”
    • The outlet is larger than 4” if the appliance is natural draft 
    • If the vent system contains more than two 90º elbows, the maximum capacity shall be reduced by 10% for each additional 90º elbow or equivalent offset(s). 
  7. If the vent system contains more than two 90º elbows, the maximum capacity shall be reduced by 10% for each additional 90º elbow or equivalent offset(s).
  8.  If the vent connectors are combined prior to entering the common vent,  the maximum capacities listed for two or more appliances shall be reduced by 10%.
  9.  The use of a “Y” fitting rather than a “T” fitting is recommended when common venting into a manifold system.
  10. AVOID CONDENSATION and/or SPILLAGE OF FLUE GASSES
  11. Install Flexi-Liner as per installation instructions.
  12. Setup appliances as per appliance installation instructions.
  13. Local authorities may over rule the foregoing.