Diagnosing Chimney Problems – Chimney Siphonage

One of the big problems with diagnosing chimney problems is that some problems mimic others, and if you rely on certain sources for your diagnosis and information, you may end up paying for an unnecessary and expensive solution that won’t even begin to address the problem.

Siphonage is a classic example.

What are the symptoms?

Normally speaking, the course of events is like this… Someone smells smoke in a room that has an appliance like an open fire, when there is no fire in the hearth.  Usually, this is due to the chimney being of Victorian construction, where its cement mortar lining has become corroded and pierced, leading to smoke passing from the flue serving the fire into an adjacent, cold flue where the smoke falls down the flue and into another room.  Do please follow this link to our article on the subject.

Serious cases require relining, but if the problem isn’t that, then you will be badly out of pocket if the chimney is relined and the problem persists.

What steps to take?

The first step is to call in a certified chimney sweep.  I say certified, because such a chimney sweep will belong to the Guild of Master Sweeps.  This means they have had to undergo training and assessment to a nationally recognised standard, not just in the physical act of cleaning the chimney, but also in the technological knowledge and the study of the Building Regulations and the British standards pertaining to chimneys, hearths, fireplaces, etc.

In short, a certified chimney sweep is the best person to advise you.  All too often, a less qualified person will have the attitude that you are a once off opportunity to earn money from you.  A certified chimney sweep wants to come back each year to sweep your chimney, and that won’t  happen if the advice he gives you isn’t up to scratch.

So, back to siphonage.  It usually happens when two rooms have been knocked together to make one, or when there is a large, loosely fitting set of doors between two rooms, where both rooms have their own fireplace.

The householder has been efficient with draught exclusion, because no one likes cold air streaming in from outside, and this means that there is not enough ventilation in the room for the fire to work properly.

Fireplaces exert a surprisingly high pull on the air in the room and if not enough air is available from the natural (or additional) ventilation in that room, then the fire will pull air from the adjacent room.  Naturally, if that room too has been well draught proofed, then the only way that the fire can function properly is to pull air down the chimney in the adjacent room.

Now this doesn’t matter until the wind blows the smoke from the fire across the top of the pot that serves the unused fireplace, whereupon that smoke is pulled down the chimney and into the room.

The cure is comparatively simple.  Both pots need to be removed, and a taller pot placed on the active chimney, which we will call ‘the Blower’.  The other pot which served the ‘Sucker’ should not be replaced, so as to maximise separation between the two, so that the blower vents the smoke as high as possible away from the sucker.

So to recap.

  1. If you have a smoke problem in your home, discuss it with your chimney sweep.
  2. Do make sure yours is a certified chimney sweep.
  3. If it turns out to be siphonage, remember the solution is to raise the blower, and drop the sucker.
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Wight Initiatives Ltd,
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Registered in the UK # 7725 203
VAT # 218 3459 04