In response to last week’s news story about the lack of progress in home energy efficiency improvements, Colin Salter, from Hertfordshire, wrote in and said:
“Not surprised by findings. SAP rating for combi boilers, do not properly include the correct or reasonable efficiency when in hot water mode.
Most combis utilise a Diverter valve and plate heat exchanger. They generally have to produce about 12 degrees more heat than the asked for output hot water. This is because the boilers main heat exchanger is always looking for this about 12 degrees to operate.
However, there is an alternative type of combi that only produces the heat at the required hot water output temperature. Therefore, this type of combi is at least 20% more efficient in hot water mode.”