* Provided that the waste and/or foul stack can be demonstrated to be able to withstand the effects of the expected temperatures, pressures and volumes being discharged.
Note. A sealed system, such as a heating circuit, will only discharge to the waste system to relieve the excess pressure. The amount of water released will equate to the volumetric increase in relation to the temperature/pressure rise governed by the co-efficient of expansion of water. In a boiler circuit, the volume discharged to relieve the pressure build up will vary with the system volume and should be calculated to suit the individual installation.
Therefore, unlike Unvented cylinder systems that are mains connected, sealed, pressurised systems will only release minimal discharges of water at intermittent intervals. The ability of the waste discharge system to be able to withstand these volumes and temperatures should be viewed in a different way to the way a discharge from an unvented cylinder D2 waste pipe is looked at.
Please note, Polypropylene (PP- push fit and most mechanical couplings), High Density Polyethylene (HDPE) and MuPVC or more latterly labeled PVC-C or C-PVC (solvent weld) are generally accepted by building control to be suitable for use on Unvented cylinder D2 discharges, therefore the use of these particular materials would be preferable because they are accepted to be capable of withstanding far more onerous working conditions than boiler applications.
For other pipework materials, consideration must be given with regards to the above physical conditions of operation. However, if in doubt, please contact your local building control for advice before installation.