2.4 CONNECTIONS
2.4.1 FLUE OUTLET
The height and type of flue will be subject to local planning regulations and approvals.
The following information is only intended to provide assistance for the installation of a simple
flue. Where multi-boiler flues or difficulties are experienced, specialist advice should be obtained.
An appropriately sized flue should be connected to the flue gas outlet at the boiler. A 45° Boot
Tee termination from the back of the boiler is recommended. The correct flue size and draft
control is most important for correct burner operation. The flue must be as large as or larger than
the outlet on the vessel. Avoid flue piping and elbows by placing the equipment as close as
possible to the chimney.”
The flue should rise continuously to the connection at the chimney and should contain no more
than two bends at 45 degree angles or less.
There should be min 0.6m of straight, horizontal flue before any change in direction, fitting or
draft regulator. This is to prevent potential pilot or main flame failures due to back pressure
build-up during ignition.
The run in the total distance of flue ducting, as measured in a straight line from the outlet of the
boiler to the outlet of the flue, should not exceed 70% of the rise. With the exception of the duct
run previously described, horizontal sections of ducting must be avoided and should not exceed
1.5 metre total.
The flue, chimney, and any components must be constructed from material that is rated for a
300 °C operating temperature and sized for 280 °C operating temperature – Twin Wall
construction, 316 Stainless Steel.
The flue and chimney material shall comply with all applicable codes.
A condensate drain should be included at low point.
Adequate provision must be made for the support of the weight of the chimney and stack to avoid
having a load imparted to the outlet connection of the equipment.
The installation of a draft regulator by the client/contractor will help maintain the required draft.
Where a chimney cowl is fitted, care should be taken to ensure that the distance between the
lowest point of the cowl and the top of the flue is 1.5 x the diameter of the flue and that it is of the
terminal stub type.
The VSRT requires a flue design that generates draft conditions of -0.25”W.C. – 1.5”W.C draft of
the boiler.
Note: Ensure all flue pipes from the boiler to the main flue have a rising pitch.
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