Gas boiler flue

Which flue your boiler needs

A concentric flue has two pipes in one: flue gases leave through the inner pipe, and the boiler draws air from outside through the outer one. It is a short and simple solution if the boiler stands by an outside wall. If the boiler is in the middle of the house or an outlet on the facade is not wanted, the flue is taken out through the roof or up the existing chimney.

A new condensing boiler and an old masonry chimney

The most common situation: an old open-flue boiler is replaced with a condensing boiler, but the flue remains the old brick chimney. The flue gases of a condensing boiler are cool and moist, and they condense in a brick flue. The acidic moisture soaks into the masonry, the bricks crumble, and dark patches appear on the walls. So a liner matching the boiler manufacturer's requirements, with condensate drainage, is fitted in such a chimney. More detail: liner for a gas boiler and condensation in the chimney.

If a stove or fireplace is also connected to the same chimney, the boiler must not stay in it: the building code prohibits connecting stoves and fireplaces to a flue channel that has a gas appliance. Flue gases must not be discharged into a ventilation duct either.

Certificate for replacing or connecting a boiler

When a boiler is replaced with another, the regulations require the flue and ventilation to be checked before the new boiler is used, and a technical condition inspection certificate to be drawn up stating whether the new boiler may be connected to the flue. The natural gas use regulations require the condition and connection of the flue to be confirmed by such a certificate, and in Gaso's simplified boiler replacement procedure a certificate on the condition of the flue channel and ventilation ducts is one of the conditions. If the boiler has been disconnected for more than six months, an extraordinary check with a certificate is needed before it is switched on.

If the flue is already built and you only need the certificate, see chimney check for a gas boiler.

How the work is done

1. Boiler data From the boiler model we find out the flue diameter, maximum length, permitted bends and system type.
2. Inspecting the existing chimney If the flue is to run up the old chimney, we clean it, inspect it with a camera and measure the flue channel to know whether the liner will fit.
3. Installation We fit the liner or install a new flue through the wall or roof, with condensate drainage and a cleaning door.
4. Check and certificate We check tightness and the ventilation in the room and draw up the certificate. Connecting the boiler to the gas and commissioning it is done by the gas appliance installer.

How often a gas boiler flue must be checked

A gas boiler is serviced and checked once a year unless the manufacturer specifies otherwise. A brick flue is inspected and cleaned once a year, while a lined, ceramic or metal flue is inspected and cleaned once every two years. Ventilation ducts in rooms with gas appliances are inspected and cleaned at least once every five years.

How much does a gas boiler flue cost?

There is no single price. It depends on the system type (concentric, liner or new flue), the length and diameter, the number of bends, whether the old chimney must be cleaned and checked with a camera, and access to the roof. Materials are priced separately. In the form, give the boiler model and where the boiler will stand, and the specialist will name the price before the work. Other prices: prices.