4 inch flue...to small?

[Silas]

Hello all

I have just re-opened an old chimney in the hope of returning it to use as an open fire. I have had a HETAS fireplace installer
inspect the chimney and a smoke test has been done, the chimney passed both, however the inspector advised me that
the flue pipe was only approx 4 inches, apparently 6" is the minimum and 8" would be best.

I have since tested the fire myself, it lights well and it also pulls well however even after starting with a small fire to warm the
chimney flue and then building the fire, I am getting about 70% of the smoke up the chimney and the rest in the room!
The fireplace is a cast Iron Victorian repro with basket and brick K back, the Chimney is external and I have added a rotating anti down draft cowl to the pot,
is there anything else I can do? or is it a case of taking the chimney down and re-building the stack incorporating an 8" liner
I have been quoted between £5-6000 for this! any advice would be great.

Thanks all

 

[Lime]

I have added a rotating anti down draft cowl

What type?
~One that resembles a 90 degree bend or one like the top of a fairground merygoround/carousel?

Do you suffer from downdraughts?
There is a difference between a fire that doesn't draw and one that puffs out smoke.

 

[Flyfisher]

Do you know the rough age of the chimney? It does sound odd for it to be built with only a 4-inch flue. When you say 'flue pipe' do you literally mean there is a pipe within the chimney stack, or is the actual chimney inside dimension 4 inches? What sort of fire/appliance was installed before you opened it all up? I'm wondering if in 'opening up' the old chimney you might not have removed as much as possible and that there is a much bigger flue still lurking inside.

 

[Penners]

I think Flyfisher is on to something.

In a previous house we had a porous dining room chimney - when we lit an open fire, smoke seeped out of the stack in the bedroom above. So I put a 4" flexible liner down the chimney (it was the biggest that would fit in the rectangular-section flue), and fixed it to a register plate above the fireplace.

The result was smoke pouring out into the dining room, because the liner was too small to carry it all away. We live and learn!

The corollary of this is that removing the liner from your chimney should restore it to the correct volume to cope with the fireplace. The only thing is that you may also discover why the liner was put down it in the first place!

 

[Silas]

Thank you all for your replies, after further investigation and talking to neighbours the reason the liner is so small
is due to the chimney being a DIY self build job, built in the 70s by Victor a former owner, it seems he used 4 inch
drain pipe as the chimney liner, I'm going to guess that this is not best practice. I added a rotating (merry-go-round style)
cowl to get as much pull as possible, but I suspect that the pull isnt the issue. Im told that originally it had a 'closed fire'
or a fire in the wall with a door on the front similar to a modern jetmaster. Whether it ever worked properly I dont know.
The fireplace company who carried out the chimney smoke test told me that modern regulations would not allow a wood burner
or a jetmaster with such a small flue. I'm told my only option is to stand candles in the grate as a feature or rebuild the chimney,
guess Ill start saving my pennies. :roll:

 

[Flyfisher]

Such a shame not to have used a correct diameter flue in the first place - it surely wouldn't have added much extra to the cost. Perhaps there was a space constraint? Still, all a bit academic now, unfortunately.

Powered chimney fans are available, which would presumably give a lot more 'pull' than a passive rotating cowl, but I'd hesitate to use one as a substitute for a basically inadequate chimney.

It might be worth phoning around to see if any dealers know of fires or stoves that could safely operate with a 4-inch flue. The flue pipe on our old Rayburn looks about 4-inches diameter, and that was a solid fuel model before its conversion to oil (available for sale incidentally!), so perhaps there are other fire appliance out there that can operate safely with a 4-inch flue.

 

[Lime]

Such a shame not to have used a correct diameter flue in the first place - it surely wouldn't have added much extra to the cost

It's easy to forget but having access to things out of the ordinary back in the 70s was not easy for the do-it-yourselfer.
Back in the 70s builders merchants didn't like serving the public.
Many shops that once sold "everything" had closed or contracted down to mere shadows of their former selves.
On top of that imperial was being replaced by metric and accompanying all that was rationalisation of stock and less choice by default.


The internet and speedy delivery has changed all that.

It is ironic that in those days householders were allowed to do anything they wanted to do to their houses if they could get hold of the materials.
(But often couldn't, hence a lot of bodging went on.)
Now, when the materials ARE freely available, householders are not allowed to do the work!

 

[Tom]

It might be worth phoning around to see if any dealers know of fires or stoves that could safely operate with a 4-inch flue. The flue pipe on our old Rayburn looks about 4-inches diameter, and that was a solid fuel model before its conversion to oil (available for sale incidentally!), so perhaps there are other fire appliance out there that can operate safely with a 4-inch flue.

I have a multi-fuel burner with a 4" flue, which is being fitted at the end of this week

Jaqy

 

[Flyfisher]

Very interesting Jaqy. Do you know if the chimney liner will also be 4-inches all the way to the top? If so, Silas' problem might be solved!

Lovely stove by the way. I can just see a kettle merrily boiling away on it. What make/model is it?

 

[Tom]

As far as I'm aware the flue will be 4" all the way but it is in a first floor bathroom, so the rise isn't as far as a ground floor one would be. Once it's fitted, I'll let you know.

I bought it 4 years ago off eBay. MachineMart do one almost the same but their flue is 5".

Jaqy

 

[Andrew Bodenham]

Dimensions for flues are given in Building Regs Approved Doc J for various configurations and fuel types. Essentially the minimum size for a stove flue is 150mm dia. or 200mm dia. for an open fireplace. Of course the flue size is not the same thing as the size of the stovepipe that connects the applicance to the flue.

 

[Silas]

Thank you all for your replies and advice, we have decided to rebuild the chimney
after a few years of saving, I think this is the best idea and worth waiting for.

 

[Flyfisher]

Dimensions for flues are given in Building Regs Approved Doc J for various configurations and fuel types. Essentially the minimum size for a stove flue is 150mm dia. or 200mm dia. for an open fireplace. Of course the flue size is not the same thing as the size of the stovepipe that connects the applicance to the flue.

I wondered about the point of a 6-inch flue when the stove outlet pipe might only be 4-inches. I found the following advice at:
http://server.iad.liveperson.net/hc/s-4653057/cmd/kbresource/kb-1758929904310781165/view_question!PAGETYPE?sf=101133&documentid=56973&action=view

What diameter multi fuel chimney liner do I need ?
The diameter of the chimney liner required depends on many things including the type of appliance and fuel/s which you are using, current building regulations, the fireplace opening size and the chimney stack height.

We'll start with chimney liners for multi fuel stoves as this is fairly straightforward. By multi fuel we mean any or all of the following fuels; cured dry logs, coal, coke, peat and smokeless fuel.

The diameter of the chimney liner will normally be the same diameter as the outlet from the stove. An average sized multi fuel stove will have a 6" (150mm) diameter outlet and the chimney liner and stove pipe will nearly always be 6" (150mm). There is an exception to this rule as follows:-

1. Building regulations state that if you are burning cured dry logs only, then the minimum diameter for a chimney liner should be 6" (150mm). So if the outlet from your stove is 5" (125mm) and you burn only wood, then you'll need to increase to 6" diameter chimney liner. This can either be achieved directly from the stove with an increaser in vitreous enamel stove pipe, or you can use 5" diameter stove pipe and then use an increaser liner to pipe to connect to the liner. The reason for this regulation is to try to minimise the chances of the flueway becoming blocked with tar deposits.

This seems to be saying that a 6-inch flue will probably be fine for any stove but also seems to allow that a smaller multifuel stove could be OK with a 4-inch flue if the stove outlet itself is 4 inches and you don't only burn wood. In other words, you probably can't go wrong with a 6-inch liner but that a 4-inch flue could be OK in certain circumstances as well, even though a wider flue to allow for tar build-up sounds like a sensible idea.

All a bit academic, though, if you can't get anyone to sign-off the installation as compliant.

Anyway, I think Silas' decision to rebuild a 'proper' chimney sounds like a sensible way forward. Where a new chimney is built with a modern (terracotta?) lining then presumably there will be no need for a chimney liner at all, which could be an immediate saving of around £800-£1000 towards the cost of the new chimney.