Stove pipe to flue increasing

[1867_owl]

Hi all, 

 

I'm looking for some advice on installing a multi-fuel stove in my house.

 

The house I just moved into comes with an open fire with a relatively modern 7 inch flue pipe. When providing me with a quote the other day, a salesman/ fitter for a stove company asked for £600+ to install a flue pipe. His recommendation was that we should buy a stove with a 5 inch pipe and that out chimney would likely have an 8 inch flue (turns out its 7 inches) and that it was not possible to convert from 5 inch to 8 inch.

 

However, the stove I have my eye on has a 6 inch outlet which i'm hoping will function more or less fine when converted to out existing 7 inch flue pipe. There are many such increasers/ converters on the market. This being the case, I would hope to be able to do the job myself.

 

So a few quick questions:

 

1. Is it building regs compliant to convert this way? I'm read that it is not ok to decrease from stove to flue but can't find anything conclusive for the other direction

2. What are the downsides? I've ready that there can be a drop off in efficiency which might lead to the chimney sooting up slightly quicker and obviously slightly more heat/ money 'going up the chimney'

3. to avoid the need to apply for building regs, would a Heatas approved installer be able to do part of the installation, for example fitting the collar/ cowl and thereby make the whole thing cosher?

 

Thanks in advance everyone.

 

[Steven P]

When we got our stove - 8 years ago and rules might be different, the option was to have a chimney liner / flue pipe or a short stretch of pipe into the existing chimney, and based on that I would say it is OK to go from small flue to larger flue.

[openspaceman]

39 minutes ago, Steven P said:

When we got our stove - 8 years ago and rules might be different, the option was to have a chimney liner / flue pipe or a short stretch of pipe into the existing chimney, and based on that I would say it is OK to go from small flue to larger flue.

Yes I think so if we are talking about a chimney with a flue up to 9". The building regulations only specify minimum sizes and not to discharge a lager outlet into a smaller flue.

 

There is a stipulation that it can be unsafe to discharge into an oversized flue, so don't exhaust a pipe through a register plate and then direct into a chimney of an inglenook for instance

[Guest Gimlet]

12 hours ago, 1867_owl said:

Hi all, 

 

I'm looking for some advice on installing a multi-fuel stove in my house.

 

The house I just moved into comes with an open fire with a relatively modern 7 inch flue pipe. When providing me with a quote the other day, a salesman/ fitter for a stove company asked for £600+ to install a flue pipe. His recommendation was that we should buy a stove with a 5 inch pipe and that out chimney would likely have an 8 inch flue (turns out its 7 inches) and that it was not possible to convert from 5 inch to 8 inch.

 

However, the stove I have my eye on has a 6 inch outlet which i'm hoping will function more or less fine when converted to out existing 7 inch flue pipe. There are many such increasers/ converters on the market. This being the case, I would hope to be able to do the job myself.

 

So a few quick questions:

 

1. Is it building regs compliant to convert this way? I'm read that it is not ok to decrease from stove to flue but can't find anything conclusive for the other direction

2. What are the downsides? I've ready that there can be a drop off in efficiency which might lead to the chimney sooting up slightly quicker and obviously slightly more heat/ money 'going up the chimney'

3. to avoid the need to apply for building regs, would a Heatas approved installer be able to do part of the installation, for example fitting the collar/ cowl and thereby make the whole thing cosher?

 

Thanks in advance everyone.

 

What is your existing flue? You say you have a 7" flue "pipe" but if the house was built with an open fire it presumably hasn't got a flexi-liner, so is yours a vitreous enamel steel liner or built in-situ sectional concrete rings?

 

If it's the latter, the problem you have in going from 6" to 7" that openspaceman refers to, is that you will have a 1" void on top of the register plate between the 6" stove pipe and the 7" flue which can't be swept and in which combustible deposits will build up creating a fire hazard. That void somehow has to be eliminated.

 

If you have a 7" vitreous liner, firstly has it been fitted with poured back-fill insulation, such as vermiculite, lime putty, ceramic beads etc? if it has, replacing it will be a PITA and I'd live with it and try and source, or even have made, a reducer fitting that takes you from 6" to 7" without leaving a length of 6" sticking up inside the 7" creating a debris trap that can't be swept. 

If it's an uninsulated stand-alone steel line inside the brick flue, I'd bite the bullet and replace it with a fully insulated 6" flexi. But you won't be doing it for £600. More like three times that. 

 

Bear in mind that vitreous enamel pipes (and sectional concrete rings come to that) and any adapter fitting attached to them must be installed with the female end uppermost and the male down, otherwise hot tar and dirty rain water will leach out of the joint and dribble down the outside of the liner onto the top of the stove. If fitted female up/male down, flue effluent will stay within the liner and get burned away cleanly by the stove. 

If you have an enamel liner and it has been fitted upside down, and I've seen a few that have, that's another reason to replace it. 

Edited June 1, 2021 by Gimlet

[Stubby]

I have 7" clay liner and a 6" stainless steel liner fits snugly inside that . The stove has a 6" outlet  and everything works fine .  The liner goes from the stove ( inside the short piece of stove pipe ) right up to the cowl on the roof . Jobs a goodun .

[Alycidon]

I assume you have a 7"clay lined flue,  that being the case no way will a 6" flex liner go down it, gobs of mortar between the sections will stop it.   A 5 inch liner should be fine.

 

Legally you dont need to fit a liner but if you use a clay liner adaptor instead it needs to be able to be sealed airtight to the base of your chimney.     That needs a flat concrete slab and you need the height above the stove to get the adaptor in. 

 

The installations needs to comply with the building regs and needs to be signed off post install as being safe to use,  a copy of that sign off is lodged with your local building control office.    No sign off and your insurance company will pull their cover in the event of a fire or other claim.

 

While you can do the installatio yourself you will then need to bring in a building inspector to check and certify the work,   a registered installer will not sign off work of others especially untrained others.

 

My advice is to measure that chimney ID accurately,  then get a qualified installer involved.  Stoves fitted with a flue liner work better than if not so fitted,  they pull harder.

 

A

[Stubby]

57 minutes ago, Alycidon said:

I assume you have a 7"clay lined flue,  that being the case no way will a 6" flex liner go down it, gobs of mortar between the sections will stop it.  

 

A

Well , " yes way " . The ID of a 7" clay liner is just a bit more than the OD of a 6" SS liner  and that's what I have got .  I know coz I helped install it .

Edited June 1, 2021 by Stubby

[Alycidon]

20 hours ago, Stubby said:

Well , " yes way " . The ID of a 7" clay liner is just a bit more than the OD of a 6" SS liner  and that's what I have got .  I know coz I helped install it .

You were lucky that there were no snots of mortar on the inside of the liner,  we wont even attempt to put a 150mm liner down a 175mm clay lined these days as it always ends in tears.

 

A

Edited June 2, 2021 by Alycidon

[Guest Gimlet]

4 hours ago, Stubby said:

Well , " yes way " . The ID of a 7" clay liner is just a bit more than the OD of a 6" SS liner  and that's what I have got .  I know coz I helped install it .

I built chimney stacks that incorporated sectional pumice liners. Nowadays they are bonded with fireproof resin, not mortar, and the joint should be rubbed clean as you go, so there should be no mortar snots to snag on. 

 

Your post has remonded me, I should have said that if the OP has got clay or pumice, and he can get the flexi up inside it like you have, the clay/pumice will act as an insulation jacket. 

I'd still want to be filling any gap between the liner and the pot with insulation or fire foam or something, so that smuts and embers can't fall back down the void.

[1867_owl]

Thank you everyone for all the incredibly informed replies..

 

To provide a little more detail. The house is an Edwardian terrace c1908. The flue was lined by the previous owner 5/6 years ago. I'm not sure if it was lined with the intention to enable a stove at a later date or if it was just to improve the safety/ efficiency of the existing open fire. I took the following picture up the chimney just now.

 

so is yours a vitreous enamel steel liner or built in-situ sectional concrete rings? - I'm not sure if this answers the question but it looks like flexi liner to me?

 

My 'plan' is to use something like this to adapt between the 6 inch stove pipe and 7 inch chimney.

 

 

 

Not the best picture i know but the internal diameter of the existing flue pipe appears to be 7 inches

 

a registered installer will not sign off work of others especially untrained others - Given adequate inspection of the existing flue and the ability to fit the stove/ adapter themselves do you not think a Hetas installer would 'sign it off'? I may also be able to get some certification/ proof of purchase from the previous owner of the house.

 

I'm not sure if there is any way for me to tell whether or not the flue has been backfilled with insulation material so i'm open to suggestions with regards to how I could find that out?

 

Finally, here is a view of the chimney. It looks like cowl is relatively new. Would this be adequate for the multi-flue stove that I am hoping to have installed?

 

  

 

Thanks again everyone!