Flue Liner - necessary?

JohnB47

I thought I'd posted a thread similar to this but I can't find it.

We've had a wood burner for many years and there's never been any leakage from the chimney flue to surrounding rooms (chimney stack is fitted outside the house - no chimney breast inside), 1930s house.

I was researching types of liner and register plate adapter and came across some threads, on other forums, saying that a flue isn't necessary if there aren't leaks and fitting a liner just provides a failure point in future years.

Any thoughts? Just get the flue cleaned regularly and don't bother with a liner?

stuart45

You don't have to use a liner provided the flue is properly tested and found to be OK. 
Most HETAS fitters will only put in a stove with a liner, as it makes the wood burner more efficient, especially on an external flue like yours. 

JohnB47

stuart45 said:

You don't have to use a liner provided the flue is properly tested and found to be OK. 
Most HETAS fitters will only put in a stove with a liner, as it makes the wood burner more efficient, especially on an external flue like yours. 

Thanks. I'm interested in how a liner makes a wood burner more efficient. I'll do a search.

WIAWSNB

Hi John.
Necessary? Not as a rule. But yes if 'needed'.
Why are they often fitted as standard with new installations? I guess 'to be sure', and to provide a consistency of behaviour of that flue.
If a HETAS isn't 100% certain that the existing flue liner is in acceptable condition, or if there isn't an actual liner, or if the stack is of an age where it's likely the liner could be failing, then sticking in a SS liner prevents any risk, and also gives them a known 'draw' condition to work with. 
But if your stack already has, say a, clay liner in good order, then it should be fine. 
Any idea what lining your chimney currently has? Our late-30s house has clay liners. 
I presume you have it cleaned annually, and smoke-tested?
Do you need an additional liner? It depends on the condition of what's already there, and how well it works.
If your stack doesn't have liner at all - it's simply brick - then the answer is obvious.
How do flexible steel 'liners' make wood burners more efficient? They don't per se. Ie, not unless they are an improvement on what's already there - say smoother, more consistent sizing, condition, etc.
There was one aspect of a Flexi liner installation that I thought would make an immediate improvement, and also assumed for that reason would be standard, but it does not appear to be; adding vermiculite insulation betwixt liner and existing flue. But, no, seemingly not a standard feature.
I'd have thought that this would ensure a faster warm-up, and hence draw. Anyone know why this is not done? Just not needed?
Anyhoo, if you currently have a liner, and it's in good order, then you should be fine.

bjorn_toby_wilde

Not necessary, but may improve the draw of the chimney because 1. smooth flow of air through a regular circular profile liner vs. turbulent flow through a rectangular irregular chimney and 2. if insulated then the liner will be warmer and that will improve flow and reduce downdraught which often happens with cold external chimneys when the burner isn’t used every day (the chimney gets cold then, typically on a cold still day, the flow reverses).

stuart45

WIAWSNB said:

I'd have thought that this would ensure a faster warm-up, and hence draw. Anyone know why this is not done? Just not needed?
Anyhoo, if you currently have a liner, and it's in good order, then you should be fine.

It's not normally done because the liners are already insulated. If the flue.is internal it won't lose much heat anyway, and if it's got any mid feathers missing you'll be pouring vermiculite into next door's flue.
If it's an external flue, the vermiculite helps more, but has been found to get wet over time and cause damp issues.
It is also more work and expense getting it down the flue.
It's also a pain when you have to renew a liner and it runs out when you whip the closure plate off.

JohnB47

Thanks everyone.