Interior flue pipes on a multi fuel stove.

[ianaitkensmith]

I thought I would try to get an opinion on the flue pipes and the covering that was installed on my Stovax Riva stove. I had the stove put in, and the flue pipes done by a local Jersey firm. I did not buy the stove from them, and when they agree to do the installation I was relieved that they would do the job, as many firms insist you buy the stove off them. I was expecting a black metal pipe  from the top of the stove to go up through the ceiling snd then out to the external flat roof, and would pass through the ceiling space above with a suitable protective heat insulating sleeve. It wa bit of a surprise when the shiny metal pipe was used from the stove and upwards via the ceiling and to the outside where it went up another four foot. Total length about 6.5 foot. I did not query this, and thought they must know what they are doing, and it seemed to look different and quirky. I had and still have no idea if this is a common way of putting a pipe through the ceiling to the outside flat roof. It works, My question is this: Does the insulation and metal cladding around this type of pipe suppress the amount of heat emitting from the pipe to the inside of the room to my loss? The temperature on the metal sleeve at the top of the stove was 295 celsius just now, after a good three log burn, and the temperature on the shiny metal pipe's exterior was about 62 celsius, which is quite a lot lower. So can anyone tell me if this set up I was given, is efficient or not so? Thx.

Edited January 31, 2021 by ianaitkensmith
spelling

[openspaceman]

2 hours ago, ianaitkensmith said:

My question is this: Does the insulation and metal cladding around this type of pipe suppress the amount of heat emitting from the pipe to the inside of the room to my loss? The temperature on the metal sleeve at the top of the stove was 295 celsius just now, after a good three log burn, and the temperature on the shiny metal pipe's exterior was about 62 celsius, which is quite a lot lower. So can anyone tell me if this set up I was given, is efficient or not so?

It does reduce the amount of heat lost from the flue gases to the room compared with an uninsulated flue pipe. Whether that is to your loss or not is debatable.

 

Consider the same stove fitted in the recess of a normal fireplace and then into an insulated chimney, the same hot flue gases would be going up the chimney without getting into the room.

 

Also consider if your flue were not insulated it would be too hot for safety without guards and you would need all combustible material to be kept suitably distant from it.

 

Most stoves will have a design temperature at which the flue gas will be entering the chimney when the stove is emitting its maximum heat into the room. Mine is 400C according to Morso, in fact I never see this and aim for it to be around 120-180C to get the most heat out of my wood. Any higher and the heat is being wasted even if more heat is getting into the room from a hotter stove.

 

The intent is that the flue gases leaving the top of your chimney to be above 100C to prevent condensation in the chimney, which is why chimneys are insulated, however mine isn't.

 

I have about 400mm of exposed  metal flue pipe between my stove and the register plate of the chimney and read my temperatures near there so my flue pipe is more exposed than yours and must put some heat into the room.

[carbs for arbs]

Hi

 

I'm no expert.  But we're soon having a stove fitted and so I've been reading a lot about the subject.  

 

I totally agree with @openspaceman RE combustibles.  An uninsulated flue needs to be three times it's diameter away from any combustible, and perhaps that's why they've done it that way?  It's more normal to see an uninsulated flue for a longer run, going into an insulated flue as it gets close to the ceiling.  That allows it to pass through the ceiling, wood in the ceiling, etc. safely.  

 

On the one hand you lose heat output from the flue, but on the other you gain a flue that heats up quicker and stays nice and hot, which in turn improves draw and stove efficiency.  A lot of people insulate their flue liners (in chimneys) for this very reason. 

 

What is more concerning though is the overall length of flue.  Are you saying the whole thing from stove top to cowl is 6.5 foot?  If so that sounds well too short.  4m (or 4.5m; can't remember which) is regarded as a minimum, and I **think** that's in the regs.  So unless there's something specific about your stove that allows for a shorter flue (not something I've come across), then that's definitely something to look into.  If I've misunderstood you, I'll go grab my coat!  

 

Cheers

[Steven P]

Looking at the photo, from the stove top to the cowel must be more than 6.5 ft, 4ft outside leaves about 2.5 ft insde above the stove - the poster is a hobbit! I suspect he means from the ceiling to the cowel is 6.5 ft

[carbs for arbs]

Haha - good thinking!  Maths was never my strong point.  It will be interesting to hear what the overall flue length is when the OP returns...

[slim reaper]

Whats the exact model of that stove . It looks like either  a cassette / inset model which should be fitted in a hole in a wall , in a fire place or it a free standing stove with some convection covers missing .

Edit:

Found its a Stovax  Riva Avanti F40 . .. I cant believe how unfinished they look 

 

 

Edited February 2, 2021 by slim reaper

[carbs for arbs]

I hadn't noticed that, but I see what you mean...  I think I was distracted by the overloaded sockets and the telephone.  I'm always making a mad rush to get to mine before it rings off, but I think I'd take a slower approach to answering that one!

[BARNSLEY BOB]

Looks stupid.

[bilke_user]

1 hour ago, BARNSLEY BOB said:

Looks stupid.

It does, and that's being polite

[Danny Boy]

Your primary source if heat is the wood burner. I wouldn't worry about what you're losing from a few foot of flue.
Any flue going thru ceilings or roofs etc has do be twin walled & I'm not sure if strictly speaking you can get away with having the length between the top of the stove & the approach to the ceiling as single flue.

Either way having a twin walled flue all the way up improves the draw so I'd say everything seems ok.