Chimney problems - help please!

[bonym]

Hoping someone might have a dh or dp who might know the answer to this question (don't mean to be sexist - if any mum knows the answer then suggestions gratefully received!) I have a property which I let out - every time the people next door light a fire, smoke comes down the chimney in the adjoining room in my property and fills up the room. I had a builder to look at it yesterday who said he thought it was a blockage and to get a chimney sweep in. I then rang a chimney sweep who said it didn't sound like a blockage! I am at my wits end with this as you can tell by the when I am posting this thread - woke up at 4am this morning and couldn't sleep for worrying about it! Any help/suggestions would be greatly appreciated.

Hi bonym,

It sounds like the flues in your chimney and the one next door share a chimney stack, and the isolation between the flues has broken down.

Chimneys work in two ways. Usually, when you light a fire, the hot air rises and creates a draft, drawing the smoke up the chimney. If there is a hole into another flue, smoke will go through and cool, dropping again.

The other way they work is by the "bernoulli effect". Those rotating wind fan caps you see on top of some chimneys are to boost this. Wind blowing across the top of the chimney makes the air pressure above the chimney slightly lower than the air pressure in the room. Air rushes in from the room to try equalize the pressure and takes the smoke with it.

Either way, the flues inside the stack should be separate from each other. It sounds like your chimney needs repairing. A simple blockage shouldn't cause this.

...suppose it could be blocked at the top where the flues join. hmm. I think they are supposed to be separate all the way up to the little pots though.

Oh - thanks tech - I guess if the chimney needs repairing it's job for a builder, or do you know if I would need a specialist chimney person? Thanks

This must be the only thread on mumsnet with the term 'Bernoulli Effect'

bonym, a decent builder should be able to repair it for you.

How come you know so much about chimneys Tech? Are you Dick Van Dyke???

To find out if its a blockage or a flue breakdown, wait until both fires are out. Hold a piece of burning newspaper in the grate and let go. If it flies up the chimney chances are there is a breakdown between the two flues. If it just falls to the grate you probably have a blockage, could be a dead bird, nest, dead rat, a bit of old flue, chimney pot moved etc.

If you have a flew breakdown you can reline the chimney, either with a flexible flulinner and cemment/vamiculite backfill (~£700 but all work done from roof)or inserting new pots from inside the house (cheaper but loads of mess)

Would get an expert to look at tho as the house is let. Would guess at flubreakdown or problem with chimney. The chimney option is going to be the easiest and cheapest to deal with.

Wow - thanks anteater - it never fails to amaze me how you can ask almost any question on mumsnet and get the answer you need! At least I've got idea of what my next step should be. Now all I need to do is get dh to cut out the expandable filler he put in the pipe last year in an attempt to solve the problem so I can do the burning newspaper test! (IDon't worry, the fireplace in my house isn't used!)

Hi,
the expandable foam will probably be compounding any problem you may have. As Tech says the chimney relys on wind speed over the pot to reduce pressure and thus draw the smoke up. If the bottom is sealed there is no pressure differential and therefore no draw. This means smoke from the adjacent fire may well be entereing at the chimney and dropping... this is good as will mean you MAY just need an air brick at the bottom of the flue.

Best talk to an expert tho...

Thanks for your advice Anteater - had a supposed expert round today but I think he mainly deals with stack problems and said he wouldn't be able to tell what the problem is until he gets up there which would need scaffolding (cost c£600 + £300 for work & materials). Said if it did need a new flue he could do it (and could get it done in next few days) but I don't think he's had much experience of this and he didn't instill confidence. I then spoke to another person who said straight away that the internal feathering must have gone but that probably both next door's and my chimney would need to be re-lined - also he couldn't do it until after Xmas - I can't let the tenants suffer the pollution that long. Really don't know what to do now - feel like I'm back to square one and feeling stressed!!! Any bright ideas anyone please?