In article , Imm wrote:
If it is -5C outside and the stack is laying here unused for 10 hours,
all the plastic walls will be around -5C

Yes but because PVC has a very low thermal capacity and better insulation
than CI it will take a minimal amount of heat to raise the temperature of
the inside wall to above freezing.

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Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm