raise efficiency towards the reported laboratory values. Natural Resources Canada also suggests ways to make better use of these boilers, such as combining space and water heating systems. Some boilers (e.g. Potterton) can be switched between two flow temperatures such as 63 °C (145 °F) and 84 °C (183 °F), only the former being "fully condensing." However, boilers are normally installed with higher flow temperature by default because a domestic hot water cylinder is generally heated to 60 °C (140 °F), and this takes too long to achieve with a flow temperature only three degrees higher. Nevertheless, even partial condensing is more efficient than a traditional boiler. Most non-condensing boilers could be forced to condense through simple control changes. Doing so would reduce fuel consumption considerably, but would quickly destroy any mild steel or cast-iron components of a conventional high-temperature boiler due to the corrosive nature of the condensate. For this reason, most condensing boiler heat-exchangers are made from stainless steel or aluminum/silicon alloy. External stainless steel economizers can be retrofitted to non-condensing boilers to allow them to achieve condensing efficiencies. Temperature control valves are used to blend hot supply water into the return to avoid thermal shock or condensation inside of the boiler. The lower the return temperature to the boiler the more likely it will be in condensing mode. If the return temperature is kept below approximately 55 °C (131 °F), the boiler should still be in condensing mode making low temperature applications such as radiant floors and even old cast iron radiators a good match for the technology. Most manufacturers of new domestic condensing boilers produce a basic "fit all" control system that results in the boiler running in condensing mode only on initial heat-up, after which the efficiency drops off. This approach should still exceed that of older models (see the following three documents published by the Building Research Establishment: Information Papers 10-88 and 19-94; General Information Leaflet 74; Digest 339. See also Application Manual AM3 1989: Condensing Boilers by Chartered Institute of Building Services Engineers). By way of contrast Weather compensation systems are designed to adjust the system based on inside, outside, boiler inlet, and boiler outlet temperatures. Control The control of the domestic condensing boiler is crucial to ensuring that it operates in the most economic and fuel efficient way. The burners are usually controlled by an embedded system with built-in logic to control