Home energy use is responsible for over a quarter of UAE carbon dioxide (CO2) emissions which contribute to climate change. To help mitigate the effects of climate change, the Energy Saving Trust has a range of technical solutions to help UAE housing professionals build to higher levels of energy efficiency. This guide is designed to help installers, specifies and purchasers of domestic central heating systems to select the most suitable system for their needs. It gives advice on how to achieve better energy efficiency, lower running costs and reduced CO2 emissions. This publication is particularly concerned with the encouragement of best practice. While the requirements for satisfying building regulations in various parts of the UAE are described, the main purpose is to explain how to achieve better performance through careful choice of systems and practices. This publication focuses on wet or hydronic central heating systems in which the water is circulated to heat emitters from a gas boiler. ‘Gas’ in this context means natural gas or Liquefied Petroleum Gas (LPG). Other guides in this series deal with systems containing oil and solid fuel boilers. This publication specifically addresses issues concerning the selection of boilers, hot water storage vessels, controls and indeed complete systems. It brings together information on most types of boiler currently available, the systems to which they can be fitted and key points to consider when choosing equipment for a particular installation. It concentrates on the use of condensing boilers since it is no longer acceptable to fit non-condensing boilers in most cases for both new or replacement situations.