seani wrote:
I'm thinking or replacing some fairly elderly (20+ years I believe)
hardwood double glazing including a large set if hinged patio doors.

I'm thinking about good quality triple glazed units in both cases. Am
I likely to see much of an improvement given the extra layer and the
passage of time?

It's generally reckoned that upgrading from single to double glazing has
a very long payback time (very many years) so I would expect that
changing from double to triple would be far less cost-effective than that.

The patio doors in particular are draughty anyway so I'd expect to see
improvement there. Also are any of the modern alternatives to hardwood
any good?

Draughtiness is a different issue altogether and not down to the number
of layers of glass... can't you fix the draughts with methods other than
replacing the windows?

uPVC windows etc are usually very effective at sealing the place up
though there are other considerations, eg aesthetics; also compared to
timber frames they are pretty hard to adjust if ever you do need to, in
that eg you can't plane them, plug old screw holes with filler etc

David