How to cap a chimney?

On Thursday 07 February 2013 09:47 Paul D Smith wrote in uk.d-i-y:

The simple way would be a board in front or under the opening.

But *do* leave a 3x10" (approx) grill in the board for ventilation - you need *a little* air going up there or you risk damp problems.

In addition, you can put a vented cap on the chimney pot which will keep out birds and most of the rain.

For a quicky solution now, put a bit of scrunched up newspaper up there, but come back in spring and do it properly :)

Chimneys must remain ventilated top and bottom, so it's not a complete no-brainer getting this right.

How old is the chimney and is it just a plain brick one, or lined? Is the chimney on an outside wall, and/or how much is exposed?

Easiest is for a brick chimney on an outside wall. You block it off at the bottom (either brick up fireplace, or keep fireplace and block off flue above it with a piece of plasterboard with loft insulation on top). Behind the point where you have blocked it off, knock out a brick to the outside and fit an air brick, which ventilates the bottom of the flue, but without any draft in the room.

permanently? or temporarily?

if latter google "chimney balloon"

Jim K

In message , Andrew Gabriel writes

For the past 30 years, I've had scrunched-up newspapers stuffed up the chimney. Obviously, it's not a complete seal - and this is exactly what I want.

if using loft insulation and plasterboard as the room seal you may wish to do something about rain coming down from the top.

Jim K

I'd certainly pop a vented cap on, most of the commercial pottery ones are hidious but these are nice:

Or you can have a bit of cheap plastic or tin.

something about rain coming down from the top.

All you need to do is keep the flue ventilated top and bottom. If you cap off the top without ventilating it, then it will fill with moisture which can't get out, and you'll have damp problems.

Capping off at the top will prolong the life of the stack, but that's providing you cap it with a vent. Otherwise it will shorten the life of the stack due to damp buildup freezing.

BTW, the loft insulation is there for two reasons

1. to act as insulation as the flue will be open to the outside.
2. to cushion the fall of anything that comes loose and drops down the flue, hopefully preventing it breaking the plasterboard.

I wanted something almost invisible from the ground. I used these:

The top does not seal against the pot, and makes a vent.