Stove got really hot

DocQuincy

I have a small multi-fuel stove in a Victorian house.

It has a liner and is swept every year. It was swept in October. I got a delivery of wood and coal yesterday and had my first fire since it was swept. I am very strict about what I burn — only HETAS-approved smokeless coal and kiln-dried hardwood.

I normally get ash but they had run out so they gave me a mix of kiln-dried oak and birch. I got the fire going, I run it with the door slightly open for the first half hour to get it roaring and clear away anything from the previous burn.

While bringing the wood inside I collected a carrier bag of small bits that I didn't want to waste. They weren't full logs just bits of bark and smaller bit broken off. The fire was burning fine but seemed hotter than usual so assumed maybe oak and/or birch burn hotter than ash. Anyway, all was good and as it started to die down a bit I chucked all the small bits from the carrier bag on the fire and closed the door. It burned really hot but I noticed in the dim light the bottom part of the flue, where it connects to the stove was ever so slightly glowing red (if the main light was on you wouldn't have noticed). But it was kicking out a lot of heat. I panicked and closed the vents down fully and it quickly went back to normal — within maybe 30 seconds to a minute.

Seeing as we are careful about what we burn and how we burn it and that we had just had it swept (the sweep has a device that is meant to remove creosote) and that it didn't burn too brightly, I am hoping it wasn't a small chimney fire and was just a result of the rapid increase in temperature as all that dry hardwood ignites quickly a the same time. I checked outside and couldn't see any smoke or fire coming from the chimney.

1. I'll be careful in future and not put so many small bits on at any one time but just wanted to check if there was any chance I'd done damage to the stove. It looks fine from the outside. I am assuming if stoves are made of iron and steel they have a really high melting point. Do you think I'm right that it just got too hot?
   
2. As an aside if there anything I can get in the event of a fire that will put a stove fire out but not cause loads of smoke?
3. Does oak and/or birch burn hotter than ash?

Bendy_House

DocQuincy said:

It burned really hot but I noticed in the dim light the bottom part of the flue, where it connects to the stove was ever so slightly glowing red (if the main light was on you wouldn't have noticed). But it was kicking out a lot of heat. I panicked and closed the vents down fully and it quickly went back to normal — within maybe 30 seconds to a minute.

You mean the outside surface of the flue? In which case, I suspect it was all just a tad too hot. It should cope, but, as with all things, if you drive them hard, they'll suffer longer term.

Your vents seem to work well - if it calmed things down in under a minute, then we can assume it shuts the air supply off quite well.

Just keep things under control!

I don't know about these respective timbers, but obviously some will burn hotter than others, as will 'dry' vs 'moist'.

You must monitor these fires - or shut the vent down if you can't. Don't let it get to the point where it's too hot.

Can you see that part of the flue from the inside if you look upwards through the door? Any actual burning residue or coating on the inside of the flue would be pretty obvious, I think.

DocQuincy

Thanks @Bendy_House.

Yes, the outside of the flue. I Googled chimney fires last night and from what I can tell it burns so hot it almost looks translucent; mine was nothing like that.

Because we have a small stove but our chimney is quite high (very high rooms in our style of house) we need to be careful not to burn the fire too “cold” because it means everything cools too much as it nears the top. We actually had problems with our first liner because of this. The advice I got — which seems sensible — is to burn it at full pelt for half an hour or so once it starts to clear any settled gases out. I've done this hundreds of times and never had a glow on the flue.

If I put a bed of coal down and then one big log on top I can have all the vents open and never get the problem I had last night. But in hindsight what I added burned so hot so quickly I think it really pushed the stove to its limit for this fuel type. Lesson learnt, I won't do that again.

I will certainly check the flue when I get home.

Stoves (mine at least) don't let you fully starve the fire of oxygen — even when fully closed air gets in. According to this page https://www.fireprotectiononline.co.uk/info/firefighter-warn-wood-buner/:

For when small fires break out, having a small powder extinguisher to hand can quickly prevent it from escalating.

I think I'll order one just in case.

Bendy_House

I don't think it was anything unusual, just a stove being run slightly too hot. Yes, when you turn the room light off, it's not unusual to see a dull red glow coming from the flue or stove top - I think a lot of people would be surprised!

You also threw on the fire a pile of small pieces, and these will always burn more quickly as the air can get to lots more burning surfaces at the same time. Larger logs will always burn more slowly.

Just a combination of events. But I doubt anything was actually 'out of control' - all within normal running ability, but best not to have it 'glowing'...

There is also the matter of getting the flue to 'draw' properly when you begin a fire. Some flues will only draw properly when they have warmed up, since the hot air is much lighter and therefore 'draws' up the flue more rapidly. My sis-in-law's stove is like this - it takes a while to 'get going'.

However, if your flue is already quite a good sucker, there will be less of this required. You still want the flue 'warm', tho', as this will help prevent moisture from the logs and combustion process condensing on the inside, and making the soot more like 'tar'.

I presume, tho', that your flue turns into twin-wall at some stage? This is better insulated, so should have no difficulty at all in keeping nicely warm.

The next time you have it swept, have a good chat with the sweep about what they've removed - ask their thoughts on its 'quality'. Is it a dry, dusty crumbly soot, or what?

DocQuincy

Thanks for putting my mind at rest.

Bendy_House

You are welcome.

But don't come crying on here if your house goes up...

(Soz - my bad :-(  )

DocQuincy

Sorry, I missed the last bit of your message as it didn't show in the email.

I'm not sure what you mean about the “flue turns into twin-wall at some stage”. It goes into the chimney breast. I think this then goes diagonal towards the centre of the house and joins the part from the (blocked off) fireplace in the kitchen. Regardless it is definitely a good “sucker” and draws up even before it's really warmed up.

My chimney sweep is really fastidious about his job and would always tell me if there were any issues so I'm satisfied based on that and your helpful responses that it's all good.

Bendy_House

Almost certainly everything is absolutely fine, and the stove just got a bit too hot, most likely due to the small pieces of timber being used.

Sorry - by twinwall I was referring to how new installations are usually made, ones that don't use an existing chimney stack. There's usually a short length of standard flue pipe coming out the stove, and then this turns to twinwall before it goes through the ceiling, outer wall or roof.

Your stack will have a natural level of insulation due to the lining and surrounding stack, so it should warm up quite niecly and work fine.

It's good to have an experienced and knowledgable 'sweep :-)

FreeBear

DocQuincy said: It burned really hot but I noticed in the dim light the bottom part of the flue, where it connects to the stove was ever so slightly glowing red (if the main light was on you wouldn't have noticed).

Have a look at this - https://en.wikipedia.org/wiki/Red_heat

A dull red colour barely visible under low light would equate to around 500°C (give or take). Yes, hot enough to take the skin off your hands and give a very nasty burn. But for a steel flue, nothing to worry about. If you have a chimney thermometer mounted on the flue a little higher, it would have probably registered around 400°C.

DocQuincy

Wow, interesting.

What would you expect/be an ideal temperature for a multifuel stove? According to Google “A household wood fire burns at around 600°C”. I have smokeless coal in there as well, which I always assumed burned hotter.

I don't have a thermometer but may get one. I wonder it's worth it to keep the temperature within a particular range.

alleycat`

Umm - most Stove thermometers recommend a "burn" of around 300 to 400F Not C!!

If my Stove gets to 550F it starts to smell quite bad and I'm well aware it's running too hot.

Thankfully the only times I've had that were with wood "briquettes" and a very , very windy day.

I tend to find smokeless burns cooler than wood - obviously your stove and experiences will differ.

I also have a "dunbrik" chimney - which is of some form of concrete construction - so it's hard to comment on "metal" liners heat tolerance properties but i'd be surprised if it was materially ruined by a single incidence with a very light red glow.