The Lemon Fool

A colleague having her CH boiler replaced is not able to use the chimney the old boiler uses – which is lined and has a cowl. She asked me how the existing round flue hole can be sealed to prevent the odd spots of rain dripping down while at the same time still allowing a flow of air to circulate upwards. Are there any proprietary blanking plates that also allow air ingress (almost an upside down version of a Durgo valve!) ?

Worcester Bosch do produce a boiler which can use an existing chimney.

I am interested in this topic because I am considering removing my existing boiler and gas fire,completely sealing the chimney in order to improve the thermal efficiency of the house,and using an alternative form of heating.

Google chimney capping cowl for starters.
I have an old chimney with a metal plate over the top which allows draughts.
Internally clamped like this

https://www.bes.co.uk/media/catalog/pro ... 61_P_1.jpg

Tnx. There are lots of different caps for the tops of chimneys but nothing for the bottom end.
The flue was built for an Aga and was lined later. At the bottom end there is a side access plate in the brickwork about 20 cm above the flue hole that was presumably there to allow the chimney to be swept and may have also had a damper (but this will have been removed when it was lined).
I may just have to completely blank off the hole, perforate the lining at the access plate, and fit a grille in place of the access plate, but was hoping that there was something specific that would allow the hole to be capped while at the same time allowing an upward draft of air - both for ventilation and to keep the chimney dry.