Firstly for information I am not a “Gas Professional” but a Chartered Electrical Engineer now on the (unpaid) management committee of a block of flats with two elderly U-ducts. We have been working with our managing agents to sort out problems partly due to ducts working poorly with modern boilers (even SE boilers are much more efficient than the 1960s boilers for which the ducts were designed, giving insufficient waste heat to properly drive the (thermal convection in) the flues). Also there are fears that modern colder flue gases can cause more corrosion than in former times. Like Benmay, we are struggling on how to install new (condensing) boilers when inevitably non condensing boilers disappear.
Though older standards refer to flue inspections, the document raising the bar for shared flues is IGEM/UP/17 from the Institution of Gas Engineers and Managers. This was published in July 2011. According to its description it “summarises best practice in the use and maintenance of new and existing "shared flues" systems i.e. shunt duct, Se-duct, U-duct systems, and fabricated shared chimney/flue systems (communal flue systems (CFSs))”. The requirements of this standard are onerous on anyone managing shared flues, or those considering connecting new boilers to them The Building Regulations people seem to have accepted this IGEM document as the Required Standard.
The information we have gathered so far is totally inconclusive, full of “perhaps” and “maybes”, thus the vague warning in my earlier post. British Gas refused to give a Gas Certificate for one boiler (in a Rental Flat) because it was connected to the U-duct, but another Gas Safe Engineer did issue. Some Installers will connect a new SE boiler to the duct, others won’t. I gather there is discussion in many areas on how to move forward, but meanwhile as most installers will only come across a U-duct very rarely, few are properly informed, and even the back-up bodies seem to be unclear.
Sorry to be unhelpful, and too wordy, but we have been looking at this for nine months or so, and have not identified the best way forward, maybe this thread will find someone with helpful advice.
