I'm being deliberately provocative here to stimulate out of the box thinking, please bear with the explanation and numbers, but then feel free to critique.    In summary I am proposing that, for retrofits (at least in the South of England, where many of the UK houses are), we should abandon the insistence on achieving low flow temperatures in favour of accelerating roll out, which is necessary to mitigate climate change.  So here goes:   I think we all know that ASH