How would I know if I need a flue liner?

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angelahorn

New Member
Dec 23, 2009
9
United Kingdom
Hello - I am a newcomer to woodstoves and to this forum. I have a Clearview Vision 500 cleanburning stove and am in the UK. We have central heating and have installed the stove as supplementary heating for an open-plan area, and for FUN, because I think being able to see fire is a basic need - whenever I see a fire I feel that something has been missing in my life without it! While stove-shopping I read that all the manufacturers seem to recommend a lined, insulated flue, and found some good explanations online of the need to keep the flue warm and clean. On the downside, in our case because our chimney is very high (about 48 feet off the ground) it would have added about #1,200 pounds sterling to the installation (I got several estimates and would want it professionally done). The installer (who does a lot of woodstoves but specialises in gas) felt that we did not need to have our Victorian flue lined because: the brickwork was in good condition, the flue passed a smoke test (ie he put a smoke bomb in and checked through the house for leaks), and because the chimney was so tall he thought it would draw well enough without. He recommended we have the flue pipe exiting from the top of the stove and not the back, to get a better draw.

We decided to take his advice and go ahead and see if we could get away without this extra expense, albeit with some trepidation because there are lots of very convincing articles and opinions out there from knowledgeable people who make it clear that it is best practice to line the flue. So far it *seems* to be working out, but I wanted to ask how you would know if your flue needed lining. Our stove lights very quickly, blazes away well if we have good wood in there and reaches its efficient operating temperature of 200C - 260C after about 30 minutes - we have not, so far, been putting loads of wood on, just a couple of small logs or sawdust HeatLogs at a time. The glass stays clean. I have not so far seen *anything* coming out of our chimney, although it is rather high up!! But certainly no black or grey smoke. All this suggests to me that there isn't a problem, but is there anything else which would tell me if the flue is letting the system down? I think the extra costs of flue lining in this case are so high that the system would have to be much more efficient for me to see a real payback, when I don't know how long we'll stay in this house (we'll take the stove with us if we move).

I am aware that an unlined flue is harder to clean and more vulnerable to chimney fires. Slight digression here to show that I know chimney fires are a real possibility:- having grown up in a house heated solely by one massive open fire, with my dad's DIY chimney cleaning, and often burning green or wet wood - I have experienced chimney fires on a few occasions - twice as a teenager left house-sitting! I dealt with it by holding a blanket over the fireplace from below, if I remember right (or something like that that Dad had told me to do), and on one occasion by climbing up the giant logstack at the side of the house and directing the hosepipe at the chimney. That was very effective - it was a good job the logstack reached almost to the roof! But anyway, I know it could be much worse and intend to get the sweep round very regularly to avoid the same thing happening here. Am also being careful to burn only dry wood and to use the stove properly etc..

I would appreciate your thoughts on this flue liner question. Many thanks for your time,
Angela
 
The newer EPA stoves (you have that or similar in the UK, right?) are designed as an 'airtight' system with the appropriate 6" or 8" flue (6 or 8, depending on stove brand). While everything seems to be operating correctly in your current installation I would think you are burning more quantity of wood than you would if you had the 6" or 8" size appropriate liner. Specifically stated you are 'burning faster' not 'burning efficient'. More efficiency = less wood consumption.

Shari
 
Let's look at your question. First, safety and second operation. Safety is paramount. A liner gives an added measure of safety to a masonry chimney that may be compromised from years of use in wood burning. Many installers use a digital camera and drop it down the flue to examine the integrity of the current chimney. A liner is mandatory in Canada with a masonry insert but in the USA it is voluntary.

The other issue is operation. If a particular unit is designed to burn on a 6" or 8" flue but your chimney is 12" x 12" i.d., then it is unlikely the more efficient stoves would produce enough heat loss to create a positive draft.

The smart thing here is you are looking to have a professional do the job. I had a dealer install my stove and chimney where I live and I could have easily done it myself...I have the tools. But I did not have the experience.

These days people complain about the prices they have to pay retailers forgetting they are also paying for experience.

Merry Christmas to you in the UK and stay warm.
 
Shari said:
The newer EPA stoves (you have that or similar in the UK, right?) are designed as an 'airtight' system with the appropriate 6" or 8" flue (6 or 8, depending on stove brand). While everything seems to be operating correctly in your current installation I would think you are burning more quantity of wood than you would if you had the 6" or 8" size appropriate liner. Specifically stated you are 'burning faster' not 'burning efficient'. More efficiency = less wood consumption.

Shari

Thanks Shari. Yes, I think our 'smoke control' stoves are probably the same idea as your EPA stoves, ie they have to pass strict emissions tests and are allowed to be used in smoke control zones like London. I just wish there was some sort of meter so we could check the draft in a flue and decide whether it really needed that much money spent on it or not!
 
BigBlockChevy said:
Safety is paramount. A liner gives an added measure of safety to a masonry chimney that may be compromised from years of use in wood burning. Many installers use a digital camera and drop it down the flue to examine the integrity of the current chimney. A liner is mandatory in Canada with a masonry insert but in the USA it is voluntary.

The other issue is operation. If a particular unit is designed to burn on a 6" or 8" flue but your chimney is 12" x 12" i.d., then it is unlikely the more efficient stoves would produce enough heat loss to create a positive draft.

.
Thanks Chevy. The stove was already installed when I posted; I was curious really to find out how one would tell if it was burning efficiently or not, ie is there anything you look for apart from reaching the required temps and getting lots of pretty secondary combustion flames?

Our flues are quite small I think - they are Victorian flues designed for small coal fires so perhaps the discrepancy in size is not so great. The building regulations here state that a flue liner is optional depending on the condition of the existing flue - which seems to be fine as there is no leakage in the rooms which the flue passes behind. "We are getting through *plenty* of wood so what Shari said, above, makes sense.

I am planning to ask the chimney sweep to give it a very thorough check. I know ideally it has to be swept before installation but this wasn't possible because the flue was bricked in top and bottom, so the installer allowed enough time to fit a liner if the condition of the brickwork made it necessary, but we couldn't get the sweep in. Now I have another headache because the stove dealer had advised me that the sweep could put his brushes through the stove, but it turns out this was incorrect for the smoke control/cleanburning model, and we don't have a sweep's hatch in the register plate so that is going to have to be re-done. I have to say that the Clearview stove as a product seems great, but the customer service and information provided by the company is not so great :-(

Thanks again for your time.
 
Shari said:
The newer EPA stoves (you have that or similar in the UK, right?) are designed as an 'airtight' system with the appropriate 6" or 8" flue (6 or 8, depending on stove brand). While everything seems to be operating correctly in your current installation I would think you are burning more quantity of wood than you would if you had the 6" or 8" size appropriate liner. Specifically stated you are 'burning faster' not 'burning efficient'. More efficiency = less wood consumption.

Shari

Does that mean that he has too strong a draft and might benefit from a damper on his stovepipe?
 
angelahorn said:
I just wish there was some sort of meter so we could check the draft in a flue and decide whether it really needed that much money spent on it or not!

Ah, but there is just such a meter. In the US we call it a draft meter. Can someone else chime in here with any other name(s) for this item?

What size is your flue?

Shari
 
48ft tall flue? That sounds like it would draft insanely well... but without insulation might deposit some creosote due to its huge length and the fluegas cooling along the way. I'd imagine with Coal it's not such a big deal, but with Wood it could get touchy? Though the newer high-tech stove may minimize that a fair amount.
 
We have an external masonry chimney with a 44-foot terra cotta flue for the woodstove in our basement. The inside flue measurements are 11 inches x 11 inches. When we installed the stove about 3 years ago, we decided to try it without a flue liner and see how it performed for us. Our stove is a Jotul Oslo, which looks like it might be 50% larger than your stove, more or less.

We've burned the stove on weekends for two winters so far and have been happy with the results. The stove drafts well and doesn't over-fire. We always have a strong secondary burn. Our stove is a non-catalytic model, and whenever we have it burning, we run it hot. We typically have flue gas temperatures running around 1000 or 1100 degrees Fahrenheit (probe measured), which is above the recommended range. That means we're losing some efficiency by sending extra heat up the flue, but it also means we're depositing less creosote during hot burns.

Our sweep told us this year that there was such a small amount of creosote in the flue that he didn't think it needed to be cleaned every year if we continued the hot, clean burns as we have the past two years. Again, we only burn on weekends - perhaps a cord or two of seasoned wood.

You should consult your own expert professionals, of course. I just thought I would share our experience in our particular situation.

Zell
 
angelahorn said:
I was curious really to find out how one would tell if it was burning efficiently or not, ie is there anything you look for apart from reaching the required temps and getting lots of pretty secondary combustion flames?

Our flues are quite small I think - they are Victorian flues designed for small coal fires so perhaps the discrepancy in size is not so great.

Just thought I'd follow up on this in case anyone is interested - I phoned the stove manufacturer (Clearview) and (after a few tries) got someone who had the technical know-how and was prepared to spend the time to talk me through this. They said that if the stove would get to 500F then clearly the flue draft was sufficient and not to worry about that. The main benefit to a liner from our point of view, they said, would be a) to stop decorative problems in rooms which a chimney breast passed through, because of tars etc.. leaching through the bricks - apparently more likely to be a problem with a stove because the high flue temps will liquify deposits which have sunk into the bricks over the years, and b) ease of cleaning chimney. As it would cost a phenomenal amount to line our tall chimney, I'm happy to take the risk of decorative problems as I'm not going to skimp on having the chimney swept anyway. We've been very happy with the stove over the winter; our house is about 4,250 sq ft over 3 storeys and the one 8Kw stove has made an appreciable difference to temperatures - it does the entire ground floor and the bedrooms which the chimney passes through are warmer too (I suppose that's one benefit to having an unlined flue!). I guess I would be cautious about an unlined flue if the chimney was not as tall or narrow, but it all comes down to economics and the stove would have to be made hugely, hugely more efficient for this to be viable for us.

One other issue which has arisen and which I'll mention in case it benefits other newbies like me - the dealer said that the chimney could be swept through the stove, so we wouldn't need a register plate with a sweep's hatch. However, it turns out that this presupposes a fully lined chimney - I suppose it's obvious when you think it through, but it wasn't obvious before - otherwise when the chimney is swept, lots will fall onto the register plate and can't be removed through the stove. I have phoned round several sweeps and asked them what *their* preference was for access to an unlined flue with stove and they were very helpful - said that the sweep's hatches usually installed in register plates are often too small to work with and ideally a 9" square aperture is required.

Best wishes,
Angela
 
I would think if the flue gasses cool too much it could cause condensation. Which if you have a cleanout, could very well come out there. It would be difficult to keep a chimney that size warm. You need to get an inclined manometer to measure your draft speeds. We have a 35' 8x12 masonry chimney that when the fire is low the draft is very low, around .02-.03" When the fire is burning full bore, it can very well go over .1" of draft making it overdraft. Its hard to get good draft when the furnace is operating normally, so we need a liner. I know liners can be expensive, but if your chimney is oversized I would consider lining it. Here is what I bought to measure our draft.


http://www.drillspot.com/products/67993/dwyer_mark_ii_25_molded_plastic_u_inclined_manometer#
 
The reason that in the Colonies and Canada a flue liner is required in a brick only masonry chimney is that a "decorative" problem rapidly becomes a burn down your house problem when a chimney fire causes creosote that has seeped between the bricks to ignite and set fire to adjacent framing in the house. In the States and Canada you cannot have a brick chimney that does not at least have a fire clay tile liner and if the fire clay tile liner has any cracks or suspect mortar joints a stainless steel liner is required. The purpose being to contain a fire so that it does not ignite any wayward creosote in the the joints or crack.
 
laynes69 said:
I know liners can be expensive, but if your chimney is oversized I would consider lining it. Here is what I bought to measure our draft.
Thanks, I'll have a look at that meter - sounds interesting. Our chimney isn't oversized dimension-wise I think - it's a Victorian house so the chimneys are narrow, designed for coal fires - only about 6" internal diameter I think. The stove manufacturer said if the stove can reach optimal operating temperature then clearly draft is sufficient, but it may be burning more wood (I suppose to heat up the flue initially) and therefore less efficient. But at UK prices, to line and insulate a chimney this size, the best quote I've had so far is over £1200 - that is a **lot** of firewood which would need to be saved to make it worthwhile! I suppose it all depends on the initial construction of the chimney. A country house with a fireplace and flue designed to burn wood on an open fire would generally have a far larger flue than a town house with smaller fireplaces and flues designed for small coal fires. I can understand why it is possible to generalise about fire safety and ease of cleaning, but it seems that it's harder to generalise about performance. In terms of fire efficiency, both the height and the diameter of the flue will make a big difference, so the added value of the flue liner will vary in each circumstance.

I get the impression that this woodburning is going to be very educational - it already seems like we need Master's degrees in plant biology to season the wood, and then another in physics to run the fire!!

Thanks,
Angela
 
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