twin wall flue system

[barrybrouwer]

I have installed a twin wall flue system to serve a wood burning stove, I have had a hetas engineer to sign off the work. They have said that regulations state that thelength of the 45 degree offset section of the flue must not exceed 20% of the total flue length. Due to the position of the fire I have made it 30%. Does anyone know if the 20% is a regulation or purely a recommendation.

[banksy]

I have installed a twin wall flue system to serve a wood burning stove, I have had a hetas engineer to sign off the work. They have said that regulations state that thelength of the 45 degree offset section of the flue must not exceed 20% of the total flue length. Due to the position of the fire I have made it 30%. Does anyone know if the 20% is a regulation or purely a recommendation.

Hi this is not true, it is mandatory that the angle of the flue must not exceed 45 deg but it is a recommendation that any angled flue run be kept to a minimum. As a rule of thumb the overall height of the flue should be twice the height of any angled part of the system. For example:- 2.5m offset at 45 degrees, then the overall height must be atleast 5m. This rules of thumb is to help create "draw" within the flue pipe to overcome the resistance caused by the angled offset.

For your information an offset of dog leg is made from 2 x No. bends, and a maximum of 2 x No. offsets (4 x No. bends) are allowed in any flue system.