StoveFitters > DIY Articles
A flexible chimney liner (or “flexi” or “liner”) is a flexible stainless steel tube that is connected to the top of the pipe protruding from your wood burning stove and at the other end within the chimney pot (or attached directly to the cowl).
It can be seen from this that smoke (and property damaging acids and tar) never come into contact with the inner walls of your chimney (and can therefore also not escape through old/damaged building material and into the property). A chimney liner may benefit from insulation (see below).
There are other methods of lining your chimney other than to fit a chimney liner but to fit a chimney liner is by far the cheapest and most common.
A chimney liner is not supposed to be in place of a suitable chimney or used if a chimney has fallen into a poor state of repair (if the chimney has faults they should be repaired professionally before lining).
Building regulations do not insist that you fit a chimney liner. If a chimney can be proven sound (using a set smoke test procedure), AND is of a diameter suitable for the stove, AND the stove-fitter can connect to the chimney in a way that satisfies the regulations, AND the end result is that the stove draws within the parameters laid down by the stove manufacturer, AND it can be swept, AND every building regulation is followed then you do not have to fit a chimney liner – a tough call for even an experienced stove fitter and many will not even consider it.
STOVES WORK BEST WITH A FLUE DIAMETER AS CLOSE AS POSSIBLE TO THAT SPECIFIED BY THE STOVE MANUFACTURER OR BUILDING REGULATIONS.
I have shouted that last sentence to really try to put you off from choosing to not fit a chimney liner. A stove designed to work with a 6″ flue will not perform so well if attached to a chimney with an 11″ diameter! Fit a chimney liner properly, insulate it if required, and there should be no reason for a stove not to perform perfectly: happy dreams for the fitter.
I generally only do not fit a chimney liner if the chimney is new or pot-lined and of a narrow enough diameter.
1. If the chimney is not sound then smoke and Carbon Monoxide can travel into your (or next door’s) property and it can and does kill. I was told the story of a stove fitter who chose not to fit a chimney liner in a terraced property. The fitter smoke tested the chimney but did not seal the chimney for the test (the smoke floated off out the pot). One weekend, whilst the owners were away, Jackdaws built a nest in that pot. Later on the customer lit the stove. Smoke could not escape. Smoke found a hole in the chimney flue and made its way into next door’s chimney. Next door’s chimney was not being used and was blocked at the top to prevent rain ingress. The smoke exited via a vent (designed to air the chimney) in next door’s bedroom. The Carbon Monoxide killed the sleeping neighbours in their beds. Note: that’s why a CO detector in all bedrooms as well as the stove room is a good idea.
2. Hot air (smoke) rises because it is hot – cool it down and it will slow, stop or sink. It does not rise well in cold chimneys, especially where heat-stealing voids, or non-smooth surfaces are present as these steal heat and slow down the combustibles. These combustibles, when slowed, deposit tar and condensation both of which can damage properties (in brick/stone chimneys tar eventually bleeds through the mortar into the house, staining wall papers etc. and is almost impossible to do anything about unless demolition is the tactic). If smoke slows down too much then the smoke behind dams up underneath and the stove burns poorly. Smoke can exit out of stove doors when they are opened to add fuel, and exit the stove via intakes designed to let air into the stove (adding dangerous gases to the room).
3. A chimney fire is more likely (far less likely if lined and would also be contained within the metal tube) if you do not fit a chimney liner.
Sometimes people say “but I have had an open fire in this chimney for years and no problems”. Open fires are very inefficient compared to stoves and have a very large amount of heat going up the chimney: the heat in most open fires travels fast and out the pot before it has chance to cool and deposit tars etc. With an open fire 70% or more of the heat generated by the fire goes out the top of the chimney. Modern solid fuel stoves are highly efficient with only 30% or less heat going up the chimney (more heat for the room with less out of the chimney). Solid fuel stoves need all the help they can get in keeping that rising air nice and hot (hence liners and sometimes even insulated liners).
A 115mm angle grinder with metal 1 or 2mm cutting wheels (you can use a hacksaw or tin snips).
A length of rope longer than your chimney is tall, twice as long ideally.
A nose cone.
Gloves, mask, googles, suitable clothing.
Depends on many factors in particular: the design and height of the property and whether scaffolding is in place/tightness of chimney etc. Brains, brawn and bravery all help.
There are also safety issues due to “working at height” – I’m not going to get into this can of worms so here’s a link: www.hse.gov.uk/pubns/heightsafeleaflet.pdf. Suffice to say it always looks a lot easier from the ground than it feels when you are up there.
(Or get a local roofer to fit your liner and cowl: you can save yourself a few hundred pounds when compared to many specialist companies.)
You can purchase liner in two grades: 316 grade and 904 grade. The 904 is the better and has the longer guarantee but is more expensive. Use 904 if you plan on burning coal on anything other than an occasional basis. If burning good quality wood only 316 is fine. If you can afford it go the 904. If your stove has a back boiler go for 904. Or Google it and make your own mind up!
Liner for gas stoves is completely different and should NEVER be used for solid fuel.
Liner can be purchased in a variety of diameters: 5″, 6″, 7″, 8″, 9″. Rarely will a fitter be fitting anything other than 5″ or 6″.
2. A liner must never be of a lesser diameter than the flue size requirement stated by the manufacturer. So if a stove manufacturer states that the stove requires a flue diameter of 7″ then a 7″ liner must be fitted. When buying a stove you will soon see that the flue size requirement (or flue collar size” is stated). NEVER STEP DOWN IN SIZE ANYWHERE ON THE FLUE ROUTE.
3. As stated in (1) above the minimum liner size one can fit is 6″. UNLESS the stove is DEFRA-approved to be used in a smoke control zone. If this is the case AND rule 2 can still be followed then a 5″ liner can be fitted. In other words if the stove is DEFRA APPROVED and the stove manufacturer permits it then a 5″ liner can be fitted.
Many manufacturers will recommend 6″ even though the stove is DEFRA-approved and the flue pipe connector is 5″ and therefore can legally be fitted. They will often do this because there is more room for error if a person does not have their chimney swept as often as they should (a heavily soot coated liner obviously loses internal diameter).
Tip: Unless your chimney is obviously large enough for a 6″ (some chimneys are huge and some you can even see bottom to top) then I suggest you consider the 5″ DEFRA route if possible – especially if the flue is narrow with bends. In these circumstances 5″ liners arer much easier to fit than 6″ liners. i have never had to break open a chimney to assist a 5″ liner round a bend but have done many times with 6″. BUT CHECK FIRST THAT YOUR STOVE MANUFACTURER ALLOWS IT.
One can insulate a flexi liner by blanket-wrapping it with a suitable material before inserting it (Chimwrap etc.) or by pouring Vermiculite into the gap between the liner and flue after fitting.
But do we need to insulate when we fit a chimney liner?
If the chimney is exposed (on an outside wall), or the stack is particularly tall, or the flue is of a large diameter then the answer to the proposed question above is a definite YES! Insulated liners keep the flue gases warmer, increase the upward speed of those gases and help prevent condensation.
Otherwise it is not necessary. The air between the liner and the flue will insulate the liner. However, it is not difficult to insulate a liner (just adds cost) so it is up to you. More information on the insulating methods to follow.
Link (discussion on this issue): http://w.thegreenlivingforum.net/forum/viewtopic.php?f=21&t=11626
You have swept the chimney haven’t you? This is a MUST. Otherwise the loose soot is still a fire hazard and the person helping fit a chimney liner from inside the property will be covered in soot. The room may also fill with billowing soot dust.
Sweeping from bottom to top also tells you which pot belongs to your fireplace, something you obviously need to know. Shortly you will be dropping a weight attached to a rope down the chimney; you do not want this knocking loads of soot off the walls of the flue and into the fireplace of another room (likely with a beige carpet!).
One stove fitter I heard about swept a chimney from the top down. Trouble was he got the wrong pot and the customer’s lounge was filled with a layer of soot. Full re-decoration and all new soft furnishings was the result (and a new TV).
Before we go any further let’s do a quick overview of what is going to happen. You are going to drag a 10 metre (or whatever) stainless steel tube to the top of your chimney stack. You are going to drop a rope down the chimney (with a weight on the end) so your helper can grab it from within the fireplace (other end secured to one end of liner). You are going to use both hands to feed that liner down the chimney whilst your helper pulls down with the rope. The liner might get stuck on a bend. Then you have to pull it back up a bit, then push it down a bit and even maybe spin the whole lot 180 degrees (remember you might have X metres of the liner being dragged around your roof at this stage). Likely you’ll have a TV aerial trying to take your eye out whilst the liner plays rough with one of your nipples.
TIME TO STEP BACK AND THINK OF SAFETY. CAN YOU ARRANGE FOR SCAFFOLDING? WILL A CHERRY FITTER REACH? HOW ABOUT A PLATFORM?
It’s your call. I am happy in some circumstances to use ladders and cat ladders). However I always wear a professional harness and associated safety equipment.
The liner will likely arrive in a coil. Uncoil it. You will notice that it has arrows printed on it. These arrows should always point to the sky when the liner is fitted (they show the smoke direction). DO NOT fit the liner upside down. Some brands can be fitted either way.
Fit the end cone to the liner (you did order one didn’t you?) using strong tape (gaffer tape) lots of it or self tapping screws. If the cone has no “tie off handle” then you need to drill a hole in it and slip a short length of rope through, tying a large knot inside the cone. See pic “Nose cone”.
ARROWS POINTING UP TO THE SKY?
YOUR HELPER DOWN IN THE FIREPLACE AREA SHOULD NOW PUT ON HIS MASK, GOGGLES AND HARD HAT. YOU SHOULD NOT BE PROCEEDING WITHOUT ENSURING THE FIREPLACE LINTEL IS IN PLACE AND SUITABLE.
Connect your long rope to the short rope connected to the cone. Connect a weight to the other end of that long rope. Take the weight to the top of the chimney and lower it down slowly until your helper has it.
Feed the liner down the chimney. Your helper is pulling and you are pushing. Hopefully the liner will slip easily down the chimney and within minutes your helper is shouting “yeeeeehaaaaaa!” as he spits soot from his mouth and the cone enters the fireplace (more likely a swift outcome with a large chimney or a 5″ liner). It is often good to have a third person running in and out of the house passing messages from you to your helper.
But if the liner stops and will not feed further then stop and take a breather. When ready pull it back and try again, hopefully after a few attempts it will go.
If it will not go then you have to start thinking why? If it is in the first few metres then it will likely be getting stuck in the loft area (where chimney flues often split away from each other and run off to their various rooms).
If the liner does get stuck here then you can try the following to fit your chimney liner:
Try “turning the liner 90 degrees” whilst you and your helper attempt to pull push as before. This works if the liner has turned one bend and is not set up for the next bend (has bent itself to point the wrong way). Then try 180 degrees. Any “spinning” is a lot easier for a double bend lower down in the chimney than this high up though; due to the sheer amount of liner sticking out of the chimney and lying on the roof.
Most likely you will have to break into the chimney from the inside or outside of the house and help the liner on its way. If stuck in the loft then this can be easy due to “making a mess in the attic who cares syndrome”. It will be a differnt matter if the attic is a loft conversion with the liner stuck behind little Charlotte’s Princess Pony wallpaper.
Another option is to withdraw the liner and try pulling it up from the bottom to the top (some bends are easier one way than the other). I suggest that this is only a remote possibility and do not really recommend this option except as a last resort. If you do try this remember that any ARROWS MUST POINT SKYWARDS.
You are warming towards the DEFRA approved stove with the 5″ liner now I guess…? As a guide, out of all the 6″ liners I have fitted I would say 60% give no problem, 25% are a fight but we get there without breaking through walls, 10% we break through the wall somewhere and 5% we give up. With 5″ liners: we have never had a problem fitting a 5″ liner (say 10% a bit of a grunt).
Note that it may not be possible to break into the chimney in some stone or rubble built properties. Luckily these usually have large diameter chimneys (we get a lot of these in North Wales).
If you cannot get the liner down the chimney and cannot break through the wall? You may need to put the liner on Ebay and look at having the chimney concrete lined.
Anyway, enough of the doom and gloom. Hopefully you arrive at the stage where you have a little liner sticking out the fireplace and a little sticking out the chimney stack or pot.
What you do next depends on whether you are pouring Vermiculite around the liner or not pouring Vermiculite around the liner. Scroll down to “Time to look at your chimney pot”.
I recommend Chimwrap as it is easy to fit and lighter than some others. It is supplied ready to go with the proper connectors.
I tried Rockwool once and never again. I itched and scratched like a farmer’s dog and it was extremely heavy.
Fitting is straightforward. Instead of feeding it down the chimney you haul it up the chimney. The person at the top has to have a very secure platform (e.g. scaffolding). A cherry picker might work but add the liner and Chimwrap weight to the maximum allowed by the cherry picker. I managed this once on a very sturdy stack that I could sit atop of and strap myself to. For connection at the top refer to the “inside chimney pot method”.
Your liner needs to be connected at the chimney pot. There are two standard methods of achieving this: 1. Hanging cowl method (no insulation). 2. Inside chimney pot method (with Vermiculite or blanket wrap). A third method can be used when you wish to add Vermiculite but wish to use your existing pot: 3. Vermiculite via existing pot.
Hanging cowl method (no insulation)
This is a very simple method with many advantages and some disadvantages. Essentially you hang your liner from the cowl, the cowl having a male tube that inserts into the female liner with a Jubilee clip clamping the female liner around the male tube.
Tip: The Jubilee clip pictured will only tighten with a screw driver with the “bolt part” flat against the liner.
The cowl pictured, available from our online store, is the “Hanging AD Cowl”. It is anti-bird, anti-downdraft and anti-rain.
As can be seen the liner is now “hanging” from the cowl. I fit these very often as they are swift and effective. In practice the liner is usually well-supported by the tightness and various bends in the chimney flue (unless in a larger chimney and in this case the “within pot” is generally considered the better option especially if the liner has heavy insulation).
The hanging cowl has three key advantages:
The hanging cowl has two key disadvantages:
Note: As long as your liner will fit down the pot then many pots will be okay for the hanging cowl – it all comes down to aesthetics. However, anything that it is very tall or with an ornamental top can be cropped to make life easier when fitting or improve the aesthetics. I often crop pots.
To cut a pot down you need an angle grinder with a suitable 115mm cutting disc (I use general purpose diamond tipped blades).
WARNING: Chimney pots are very heavy and the part you cut off can be very heavy. The weight of the top part, when it comes away from the bottom part, can trap your cutting blade causing your angle grinder to to spasm and jump. This is not a nice operation. Only attempt this if you are using a cherry-picker or have a suitable platform or scaffolding or a suitable base on which to work. NEVER attempt this from a ladder.
Fit a liner: Inside chimney pot method (with Vermiculite or blanket wrap)
Top Plate And Top Clamp: The top plate and top clamp are used together as one a method of fixing the chimney liner at the top of the stack. It is necessary to remove the chimney pot, fit the chimney liner in place with the plate and clamp, and then refit the chimney pot once installed. The chimney liner passes through the hole in the plate and is gripped in place above this with the top clamp. For a secure fixing, it’s recommended to use a top sleeve. The top sleeve fits inside the top of the chimney liner and gives a solid inner for the top clamp to grip against. Fill the gap between the liner and the pot with a sand/cement mix.
Add a cowl that will prevent bird and rain egress. Cowls (must be for solid fuel as some are for gas and oil).
Note: If adding Vermiculite follow the instructions as detailed below but adapt as required: obviously you will pour the Vermiculite in before the plate goes on.
Vermiculite via an existing pot
Firstly, you will not add your Vermiculite until the stove is fitted and the closure plate above the stove is fitted (otherwise it will just pour out of the chimney and into the room!). So you need to check out the stove fit section and come back here afterwards. Best to read it now to get an idea of what is to come later.
You will be in the position as seen in the picture on the left (unless pouring Vermiculite PRIOR to the pot going on and then you will find it even easier – just fill that chimney up).
Vermiculite cannot catch fire and is used to insulate around chimney liners. It is poured into the top of the chimney and will cascade down the chimney onto the closure plate, filling the gap between the liner and the chimney itself all the way to the top.
Vermiculite is only suitable for chimneys with a few inches of air gap. If your liner has more than a few inches of air gap you are going to use a heck of a lot of Vermiculite. To be safe allow 1 bag for each metre of chimney you need to fill. If you really hate the idea of having any left over you can budget for 0.8 bags per metre and hope you do not run short.
The simplest method of filling is to obtain one of those “Gorilla buckets” as favoured by builder’s or horsey folks. Cut a hole in the bottom just slightly smaller than the hole at the top of your pot then slip it over the bit of liner sticking out of your chimney pot. Tape it to the pot using Gaffer tape or similar. Passers by love to shout comments at this stage but just ignore them. If the protrusion of liner is “inside the bucket” then stuff a rag in the end to stop Vermiculite going down the liner.
Pour Vermiculite into your new “funnel” (the bucket”) and keep doing so until your chimney is full.
You want to end up with a picture that looks like so:
Note that this method of attaching liner to pot is not to be used if your liner is wrapped (rather than Vermiculite).
You will need to cut the liner just above the top of the pot (1-2cm) using an angle-grinder, hacksaw or tin snips. I like this 1 cm as it allows the sand cement mix to overlap onto the top of the pot, this all asisting its grip on the pot itself.
The Vermiculite will provide a base for the mix(you will of course have to extract some Vermiculite (wriggling the liner will “settle” the mix and this also works).
A 3:1 sand cement mix will do here.
Are you off to fit a chimney liner now?
By Julian Patrick