We’re in Purley, Surrey.
Our customer has an old atmospheric Potterton Kingfisher II 100,000 Btu in the basement, connected to the internal chimney system.
We could have resited the new boiler on the external wall but the flue outlet would have detracted from the external aesthetics of the house, so instead we discussed the option of connecting the new boiler to the old chimney system. This is always the more expensive option, because the new liner system has to be installed from the rooftop and comprises a large number of parts. However, in this instance, our customer wanted an ‘invisible’ installation so we specified the Worcester Bosch Flexiflue system.
Using a new, high efficiency condensing floor mounted boiler from Bosch, the FS30CDi (FS being floor standing), the Flexiflue system necessitating constructing a closure space under the old hearth termination. This was built using blockwork.
The chimney section above the roofline was found to be unstable, so the upper part had to be partially demolished and rebuilt. This is not unusual as the heat and the tars tend to crack the mortar, allowing water ingress and subsequent frost damage over the years.
The new boiler extracts the exhaust fumes through a 60mm diameter flexible plastic tube all the way to the chimney top; condensed water from the saturated vapours runs down the liner into the boiler and then to the drain. The remaining ‘annulus’ of the chimney (in other words, the space remaining between the brickwork and the 60mm liner tube) is used to provide the air for combustion from the roof. For this reason, the chimney has to be in reasonable condition, making the installation classed as ‘room sealed’, in other words, much safer than before.
We are regularly asked whether the existing flue liner system in a chimney can be reused on a modern high efficiency boiler. With a few possible exceptions for light commercial boiler applications, where a high efficiency boiler with a bespoke flue system may have been installed previously,, the answer is always negative. This is because conventional boiler flues connected to a chimney liner require the liner to withstand high temperatures (up to 260C), and be made of a material not necessarily watertight or corrosion proof. In contrast, a modern high efficiency boiler may only need a flue liner capable of withstanding typically 80C, but has to have resistance to water and acid. The two solutions are mutually exclusive.
Unfortunately, my poor understanding of all matters iPhone has resulted in the loss of a large number of pictures for our installation gallery, but we still have a selection from this job.
NB: Other flue lining solutions we offer are available with Viessmann boilers, both domestic and light commercial.