Cap Chimney Flue

listermint

Hi I need to cap a Chimney Flue on the roof. (traditional chimney stack circular flue) Anyone know where to get a cap ? has to be full seal as the chimney is not being used any longer - removed the a multi stove in a kitchen.

lgk

I used these.

Markcheese

lgk wrote: »

I used these.

I've seen something similar In a builders providers for about 40 / 50 quid

jack of all

If you decide to cap off an unused chimney you should provide a cap which will allow some trickle ventilation and a hit and miss vent grille at the fireplace opening, otherwise you run the risk of condensation within the flue, which can run down into your room, causing nasty smells and stains. Because a chimney stack penetrates the roof it will be cold and warm air (which is moisture laden) will rise through the existing flue, cool down and deposit the moisture vapour as condensation on the inside of the flue- thus it must be ventilated.

listermint

jack of all wrote: »

If you decide to cap off an unused chimney you should provide a cap which will allow some trickle ventilation and a hit and miss vent grille at the fireplace opening, otherwise you run the risk of condensation within the flue, which can run down into your room, causing nasty smells and stains. Because a chimney stack penetrates the roof it will be cold and warm air (which is moisture laden) will rise through the existing flue, cool down and deposit the moisture vapour as condensation on the inside of the flue- thus it must be ventilated.

The room side will be fully blocked off and plasterboarded. So can't provide ventilation from that end.

Any other choices,?

Markcheese

Aren't those chimney plugs slightly irregular, to allow a small amount of air movement.. Would usually still need a vent down the bottom as already mentioned..

jack of all

listermint wrote: »

The room side will be fully blocked off and plasterboarded. So can't provide ventilation from that end.

Any other choices,?

It's my understanding that unless the stack is partially removed/ demolished, ie so that the the remainder of the stack is within the heated building envelope you risk condensation unless you provide some minimal trickle ventilation at the base of the flue opening and at the top.

listermint

jack of all wrote: »

It's my understanding that unless the stack is partially removed/ demolished, ie so that the the remainder of the stack is within the heated building envelope you risk condensation unless you provide some minimal trickle ventilation at the base of the flue opening and at the top.

That was a concern i had, I suppose il have to open a vent into the stack then.

jack of all

listermint wrote: »

That was a concern i had, I suppose il have to open a vent into the stack then.

A small vent like this would be sufficient:

https://www.goodwins.ie/products/Louvre-Vent-9x3-.html?name=+vent&type=simple

Just cut a small hole in the wallboard with a pad saw, surface mount and you're done.