Building Research Establishment, which is the UK's major research body for the building industry, produced a leaflet on domestic condensing boilers. According to the Building Research Establishment: modern condensing boilers are as reliable as standard boilers condensing boilers are no more difficult to service, nor do they require more frequent servicing servicing is not expensive; the only (minor) additional task is to check the correct function of the condensate drain condensing boilers are not difficult to install under all operating conditions, condensing boilers are always more efficient than standard boilers Exhaust The condensate expelled from a condensing boiler is acidic, with a pH between 3 and 4. Condensing boilers require a drainpipe for the condensate produced during operation. This consists of a short length of polymer pipe with a vapour trap to prevent exhaust gases from being expelled into the building. The acidic nature of the condensate may be corrosive to cast iron plumbing, waste pipes and concrete floors but poses no health risk to occupants. A neutralizer, typically consisting of a plastic container filled with marble or limestone aggregate or "chips" (alkaline) can be installed to raise the pH to acceptable levels. If a gravity drain is not available, then a small condensate pump must also be installed to lift it to a proper drain. The primary and secondary heat exchangers are constructed of materials that will withstand this acidity, typically aluminum or stainless steel. Since the final exhaust from a condensing boiler has a lower temperature than the exhaust from an atmospheric boiler 38 °C (100 °F) vs. 204 °C (400 °F) a mechanical fan is always required to expel it, with the additional benefit of allowing the use of low-temperature exhaust piping (typically PVC in domestic applications) without insulation or conventional chimney requirements. Indeed, the use of conventional masonry chimney, or metal flue is specifically prohibited due to the corrosive nature of the flue products, with the notable exception of specially rated stainless steel and aluminum in certain models. The preferred/common vent material for most condensing boilers available in North America is PVC, followed by ABS and CPVC. Polymer venting allows for the added benefit of flexibility of installation location including sidewall venting saving unnecessary penetrations of the roof. Cost Condensing boilers are up to 50% more expensive to buy and install than conventional types in the UK and the US. However, , at UK prices the