Technical Booklet L Combustion Appliances and Fuel Storage Systems·Page 41·3.10
Measurement of flue height for open fires and closed appliances
Flue height is measured vertically from the highest point of air entry into the fireplace (top of fireplace opening or bottom of canopy for open fires, or appliance outlet for closed appliances) to where the flue discharges into outside air.
The height of a flue serving an open fire is measured vertically from the highest point at which air can enter the fireplace to the level at which the flue discharges into the outside air. The highest point of air entry into the fireplace should be the top of the fireplace opening or, for a fire under a canopy, the bottom of the canopy. The height of a flue serving a closed appliance is measured vertically from the appliance outlet.
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