On Wed, 17 Jan 2007 11:15:30 +0000 The Natural Philosopher wrote :
I can foresee in the future that some form of twin coaxial tubes will be
used to allow hot air to rise out of rooms, heating up incoming air as
it does so...

It's mechanical ventilation with heat recovery. Once you build highly
airtight housing you need something like this to maintain air quality.

The new (as of last April) imposes compulsory sample air pressure testing
of virtually all new housing as air leakage through badly sealed gaps etc
can seriously undermine the gains made through better insulation.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk