Condensation in a chimney

[Vir Campestris]

We've got an old chimney in our kitchen. The bottom has been removed, and the stack is held up on an RSJ. It's lined with what look like ceramic drain pipes. At the top used to be a cowl, but as it looked horrible (and doubtless sucked lots of heat out) I replaced it with a cap which has a much smaller opening. At the bottom is a hit-and-miss grill. We've tried the grill both open and shut - and we're suffering from condensation dripping down onto the worktop beneath. It's much worse without the cowl :(

It's worse after rain. This may just be due to higher humidity, or it could be soaking in - the pointing isn't wonderful.

What should we do?

Andy

[Tim Watts]

Is the chimney capped off at the top (to allow ventilation but prohibit rain entering directly)?

Next thing that might be worth a shot is painting water repellent on the bricks above the roof line (I did with one defunct stack).

[Brian Gaff]

[Tim Watts]

That's a really good idea!

If the stack is on the outside wall, put an external vent in and close it off completely inside.

[stuart noble]

Or having the stack taken down to roof level, which is a job I'm resigned to. It's leaking somewhere but not obvious where, and that's a hell of a lot of re-pointing

[Vir Campestris]

OK, answering all at once, inline (Sorry Brian)

Sadly the bottom of the outside is inside a roof - part of the kitchen has a lean-to type roof.

Yes, I did mention that - it used to have a cowl, but now has a cap.

That had crossed my mind. I'll attack the pointing and paint something on it next summer.

We're listed. They were difficult about us having a new chimney pot on the other one; they'd never allow that. (The new pot was to keep the heat from the wood burner well away from the thatch, which the insurance co. wanted)

Andy

[Tim Watts]

Isn't that just totally insane...

[DICEGEORGE]

ventilation must be with a hole top and bottom so it works, or warm moist air will condense inside and rot the brickwork. But the bottom ventilation lets lots of warm moist air into the chimney.

The only solution I can think of is to fill the air gap with concrete or kingspan and foam, firefoam not flammable foam. Then air wont infiltrate and condense. Concrete might be too heavy!

[george]

[DICEGEORGE]

but if its listed they maybe wont let you pour concrete or foam down the chimney as thats not irreversible.

So maybe get the chimney lined properly? or diy from inside and use it as part of a new improved kitchen ventilation system? Maybe blocking an existing out-vent when this is working?

[george]

[DICEGEORGE]

can you drill out a few bricks in the attic into the chimney for inspection?

(and maybe eventual use in air ventilation system)

[Vir Campestris]

I'd be cautious about pouring _anything_ down it, when there's only plastic grill stopping anything from ending up in the kitchen...

We're considering a new kitchen. Putting a sleeve in it and using it for the cooker hood is one possibility - with the risk that we'd get condensation inside the sleeve instead...

Andy

[David]

Lack of airflow up the chimney? Worse after replacing the cowl seems to confirm this. There has to be enough flow of dry(ish) warm(ish) air to absorb any moisture within the chimney and then carry it to the outside through the top vent. So perhaps a ventilation fan to push air up the chimney and/or replace the original cowl as that seemed to be doing the job better than the current arrangement.

From information within this thread, getting a good external airflow into the chimney doesn't seem to be an easy option so to combat the damp you probably need to accept that you will have to lose some heat to shift it.

There have been loads of posts about tenants and damp houses, almost all due to the tenants closing all the windows to keep the heat in and thus trapping all the moisture as well. Ventilation (in moderation) is a very good thing but does involve some heat loss.

Cheers

Dave R

[Vir Campestris]

One of the possibles is to route an extract from the cooker hood up there.

Of course that would be warm, but not dry.

Andy