"Andrew" wrote in message
...
Maybe I should rephrase that - why can't I convert the top section of
the waste stack so that the 2" mupvc flue enters at 1st floor ceiling
height and exits up through the roof *inside* the waste stack.That way
the flue terminal pokes out above the stack by say 6 inches and the
remaining cross section is still used to vent the stack. Since we are
only discharging acidic steam at this point where does the possibility
of exploding methane come into it ?

Andrew,

There a number of options here. Firstly the waste pipe used for the exhaust
of a Keston has to be mPVC, which is more heat resistant. You can put an
air admittance valve on the top of the existing 110mm plastic stack in the
loft. Then use the same hole in the roof to run the Keston exhaust. The
existing hole maybe too big for the 2 to 2.5" exhaust pipe of the Keston.
Then it may be wise to use mPVC 110mm pipe for the section that runs through
the roof tiles. A bird guard must be fitted on the top of the 110mm pipe.
Then you have no need to go outside on the roof. The air intake can be
terminated at the eves.

Or remove the stack completly and use hepVO drain traps on all the upstairs
appliances.
see:
http://www.hepworthplumbing.co.uk/ and click on HepVO.

Good thinking Andrew. I never ROFLed




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