Thanks for all the replies.

What type of flue system do you have? If it's an old chimney, then have
it
smoke tested to see if it leaks anywhere other than the top pot. If it
leaks, get the chimney re-lined. If it shows no signs of leakage, then
leave it alone.

I took Yekal's advice and phoned Aga-Rayburn - and their advice was
precisely that! The chimney dates from 1925. No obvious leaks when it was
used earlier this year

If you are connecting directly to a flue outlet on the Rayburn, then the
need for a small section of flue pipe from the appliance to damper shelf
of
the chimney is needed, but you may also need a draw hood just before the
final sealed plate at the damper shelf. The draw hood is like a small
break
with a cowl in the flue pipe. It allows air from the room to be drawn up
the chimney when the Rayburn is either in use or not. If the Rayburn
you've
chosen has a sealed burner chamber, with a door, then a draw hood should
really be used to keep air circulating up the chimney all the time. This
is
better for your house ventilation as well as your general health.

What we will have is a Rayburn (Heatranger 216M) which has a sealed chamber.
The smoke exits the Rayburn at a chamber which has a controllable vent to
draw in air, and immediately before that a slide to restrict (or choke if
you like) the flue opening. The flue itself rises about 12" and then takes a
135 degree elbow and other 12" before it goes into the chimney breast. This
section of flue has a removable aperture for cleaning the chimney. Does that
sould like what you were describing?

The Rayburn will be a direct replacement for a old Rayburn MF, and I
understand that the 216M is virtually identical. Interesting what you say
about keeping air flowing up even when not used, we will take that on
board - thanks.

If you think that the system is better to have a complete flue from
scratch,
then go with your feeling about it. A completely new flue that you know
is
working and is healthy for you and the house is the best way to go with
it.

Ok, we'll see what the cost is. If it isn't that much, then we probably
will. But I don't want to spend £££ on something that's unnecessary.

Regards,

Paul.