Nasty (very) odour from Wood Burner - resin/ tar forming at stove to flue union

[Sulloir]

We have 2 wood burning stoves (Hunter Stoves Aspect 4 and 5).  Both burn using seasoned beech or ash, same wood source, same wood.  The larger stove works like a dream, the smaller one intermittently creates a 'really nasty' smell.  Nothing like wood smoke etc., more a foul burning plasticy, even bakelite (if you cam remember that) and it permeates the whole house.  Any thoughts on what it could be?  Both chimneys were swept mid November.  I can occasionally hear a crackling/ fizzing sound from the flue pipe immediately above the stove, and I noticed last night that there is a small amount of black tar/ resin forming around the union between the flue and stove.  Any ideas what could be the cause?  Both stoves burn using seasoned beech or ash, same wood source, same wood.

 

Cheers

 

Chris 

[Squaredy]

21 minutes ago, Sulloir said:

We have 2 wood burning stoves (Hunter Stoves Aspect 4 and 5).  Both burn using seasoned beech or ash, same wood source, same wood.  The larger stove works like a dream, the smaller one intermittently creates a 'really nasty' smell.  Nothing like wood smoke etc., more a foul burning plasticy, even bakelite (if you cam remember that) and it permeates the whole house.  Any thoughts on what it could be?  Both chimneys were swept mid November.  I can occasionally hear a crackling/ fizzing sound from the flue pipe immediately above the stove, and I noticed last night that there is a small amount of black tar/ resin forming around the union between the flue and stove.  Any ideas what could be the cause?  Both stoves burn using seasoned beech or ash, same wood source, same wood.

 

Cheers

 

Chris 

Is it a new installation?  If so have you spoken to the installer?

[trigger_andy]

15 minutes ago, Sulloir said:

We have 2 wood burning stoves (Hunter Stoves Aspect 4 and 5).  Both burn using seasoned beech or ash, same wood source, same wood.  The larger stove works like a dream, the smaller one intermittently creates a 'really nasty' smell.  Nothing like wood smoke etc., more a foul burning plasticy, even bakelite (if you cam remember that) and it permeates the whole house.  Any thoughts on what it could be?  Both chimneys were swept mid November.  I can occasionally hear a crackling/ fizzing sound from the flue pipe immediately above the stove, and I noticed last night that there is a small amount of black tar/ resin forming around the union between the flue and stove.  Any ideas what could be the cause?  Both stoves burn using seasoned beech or ash, same wood source, same wood.

 

Cheers

 

Chris 

Do you use a moisture meter on your firewood? Even if you do its worth re-splitting a piece you intend to put in the Stove and re-measure to get an accurate reading of the actual MC of the wood you're putting in your Stove. 

 

It certainly looks like you're getting a build up of Tar in there.

Could it be that you're slumbering the smaller stove more?

Do you ever let the Stove get up to a good roar to help clear the flue out? My Stove manufacturer recommends a 20 minute high temp burn twice a day to keep everything clean. 

Is one stove older then the other? 

The bigger stove might be getting a more efficient burn and therefore not facing the same tar/creosote issues.

Whats the positioning of each Stove? Both on Ground floor level? One upstairs and potentially a shorter Flue and therefore less draw? Prevailing wind direction and obstructions from the house or trees etc. 

I dont tend to put much trust in Sweeps either. They seem to be in and out fairly fast. Running up your own brush after and spending some extra time on it could well result in a better clean.

[Sulloir]

ThanQ both.  Both stoves were installed brand new about a year ago.  I will be calling the installer this morning 😉   Each stove is on the ground floor so floor to the roof ridge line is pretty much exactly the same.  There are no obstructions near to the cowls.  For the high temp burn, I'd say yes they do get that, though they mainly run at a slow burn.  One thing I do remember now I write this, was that the chimney where the smaller stove is wasn't 100% vertical, there was a bend/ crook in it.  Could this be constricting the liner?

 

Comments and advice is much appreciated.

 

Cheers

 

Chris 

[trigger_andy]

1 minute ago, Sulloir said:

For the high temp burn, I'd say yes they do get that, though they mainly run at a slow burn. 

Define a 'slow burn'. I'll assume being so new they will have all the new anti-slumber gubbins attached stopping them going into a full slumber but regular 'slow burning' will not be helping matters IMO. 

 

Id also look to mix in some softwood with your hard. Ash and Beech are great for long slow burns but softwood will burn nice and hot. Id recommend burning that problematic stove hot and hard for a few days and see if that clears your issues. Then Id not 'slow burn' them nearly as much. 

[Sulloir]

ThanQ, will do, and I'll what the installer's thoughts are.  

[devon TWiG]

my first thought was that it is the sealant melting , but it really should not if fitted properly using suitable stuff ..

[sandspider]

One of our burners was installed with the wrong sealant in that flue to stove join. Melted every time the stove got hot and seeped out like that, and it smelt horrible when it burned on the stove. Installer came back out and replaced it, blamed it on a bad batch of sealant and it was fine after that. But it melted and smelt grim every time, not just occasionally.

[teepeeat]

I'd go with Sandspider - think the sealant was missed or badly done or incorrect type used.

 

That said the products of combustion are a nasty cocktail and can smell quite bad. They tend to settle out if cooled and this can be happening locally to the flue join if air is getting in as I suspect it is so the smell could just be the tar in the join cooking.

 

More generally, 'slow burning' should be confined to the history books as it massively increases emission of particulates as well as gumming up the flue.

To maximise efficiency of your wood, burn smaller amounts at a time - the more you put in the more heat gets pushed up the chimney as the stove can only transfer a certain proportion of the heat to the room at any one time.

That said a good bit of heat up the chimney now and then does help to keep it clear as has been mentioned already, but using well seasoned wood also helps to minimise build-up.

A key part of seasoning in my view is to have a good few days of wood stacked near the fire (space permitting) as this brings the moisture content right down over a few days prior to burning. 

 

[Steven P]

I'll also go for the sealant melting. Very unlikely with a chimney swept in November to be getting tar leaking down like that - unlikely if it was 3 years ago too! Even more if the liner was brand new, and clean a year ago.

 

As far as I can tell the tar kind of settles on the chimney, all the way up, doesn't drip down, so if you get a chimney fire the fuel is all up the chimney. which is where the problems start. Have to get it proper hot for it to melt in this kind of quantity and you'd notice it on the register plate, and also into the fire which would be doing funny things too.

 

Going by your history, installed about a year ago so this is probably the first winter when you have been using them fully? and the first winter when they have been getting proper... and so the first winter you will have noticed this going wrong. Ask the same question this time last year and everyone will be saying sealant.