WBS's over a certain size (5kw?) need a source of external air to promote efficient combustion - this in building regs. However, this of course wrecks your good work with air tightness, etc so you need a stove that can be fitted with an external air feed which is basically the same hole but vented into the back of the stove, rather than your room. We have a Clearview and an Esse 200 with these fitted and they do work well. You do run the risk of it being an air-filled 'cold' radiator when not in use though as I don't think the external air feed can be fitted with a dampener...

Not sure about the chimney / flue - ours 'slipped through the net' and needed some retrospective thinking-about.

Could you have an external masonry chimney with standard flexible flue liner? I presume the clay liner is basically to speed construction and provide a snag-free path for the liner?

Hi,
Sounds very strange to me.
In our first extension we had a clay lining and the clay "pots" could be heard cracking when the fire was on full blast - perhaps that's the reason for the flexible flue liner.

More recently we installed an isokern chimney, which comes in sections and is filled with a Lica type material. This is really good, well insulated, draws well and shows no sign of "wear" some 10 years on. It would seem to me to be very strange to fit a "consumable" part (liner) to a chimney which should last as long as the house.

Could be a cost thing I suppose, but over the life of the house I reckon it'll be cheaper to fit the best thing first!

Cheers

Y

I don't think I would want a flexible liner in a chimney that I was (or someone else was) going to stuff a sweeps brush pushed by hard rods up the thing periodically.
Are you sure the architect knows what he is talking about rather than doing a cut and paste job on standards he has used in the past? (Flexible liners are pretty standard for gas)
When talking about clay liners do you mean ceramic liners or clay. The difference being ceramic is fired at a higher temperature,is harder and more robust than clay. I have a ceramic liner and over the last 20 years and a couple of chimney fires later (learning curve, I now know better!!) I have had no problems. I would go for ceramic liner insulated with vermiculite between the liner and the brick.
You would need a stove with the capability of an external air feed as quoted above but remember there a difference between 'external air feed' and 'room sealed' I seem to recall that the building regs might have caught up with the difference, but not sure.

Following from Jamster's comment, note that even WBS below 5kW need a dedicated air supply if (IIRC) air-tightness is better than 5m3/m2/hr.