Placement of Stove Flue Pipe

BarneyMc

My blockwork (walls) is about to begin next week and my project manager has asked me where to leave a space in the wall for the flue pipe from the wood burning stove I hope to fit.

As I haven't decided on a specific stove yet, is there a 'standard' position for this or can it be adjusted with fittings to reach any space left for it? It will probably go straight out horizontally rather than up vertically for a bit.

martinn123

BarneyMc wrote: »

My blockwork (walls) is about to begin next week and my project manager has asked me where to leave a space in the wall for the flue pipe from the wood burning stove I hope to fit.

As I haven't decided on a specific stove yet, is there a 'standard' position for this or can it be adjusted with fittings to reach any space left for it? It will probably go straight out horizontally rather than up vertically for a bit.

Remember something like 1/2 the heat can be radiated from the Flue, so if it goes straight our horizontally, you are loosing the benefit of that.

Mine goes vertically and through the roof of a single storey ext, and the heat from the flue is substantial.

BarneyMc

Is this the same for all stoves? When the stove is not lit then is there a cooling effect on your room?

martinn123

BarneyMc wrote: »

Is this the same for all stoves?

Free standing stoves, yes as far as I know, inset stoves which are fitted into a fireplace and use the chimney, obviously no.

BarneyMc wrote:

When the stove is not lit then is there a cooling effect on your room?

No not at all.

BarneyMc

So I could possibly bring it vertical for a bit, e.g. head height, and then out at any point into my chimney?

martinn123

BarneyMc wrote: »

So I could possibly bring it vertical for a bit, e.g. head height, and then out at any point into my chimney?

Not sure what you mean by this.

Is it a free standing stove, or inset into a fireplace, and a chimney??

Assuming its free standing, as you posted

where to leave a space in the wall for the flue pipe from the wood burning stove I hope to fit.

you should visit some retailers who can advise the fittings available.

Or '' Google '' it

I would assume you could go vertically as you say to head height, and then a 90deg. bend out through the wall.

Eoghan Barra

To achieve the best performance, the ideal set-up is to have the stove in the middle of the space it is to heat, and to have the flue go straight up through the roof, emerging as close to the ridge as possible. I would avoid running the flue out through a wall at all costs.

See here for excellent advice and explanations of how to get the most out of your stove: http://www.woodheat.org/all-about-chimneys.html

To quote:

Summary of design guidelines

1. Put the chimney inside the warm building environment
2. Go straight up, no elbows or offsets
3. Insulation around the flue liner
4. Flue sized to match stove

BarneyMc

Eoghan Barra wrote: »

To achieve the best performance, the ideal set-up is to have the stove in the middle of the space it is to heat, and to have the flue go straight up through the roof, emerging as close to the ridge as possible. I would avoid running the flue out through a wall at all costs.

See here for excellent advice and explanations of how to get the most out of your stove: http://www.woodheat.org/all-about-chimneys.html

To quote:

Summary of design guidelines

1. Put the chimney inside the warm building environment
2. Go straight up, no elbows or offsets
3. Insulation around the flue liner
4. Flue sized to match stove

Thanks for this advice. Unfortunately my plans were drawn so that an outside chimney would take the flue immediately out - see the attached.

My ground floor slabs have just been laid so I assume I can't now build an internal chimney. Can I still create an internal flue without a block chimney surrounding it and bring it straight up through the building? Alternatively, can lite blocks potentially be used to create an internal chimney?

bakerbhoy

Free standing stove internal flue to chimney

Eoghan Barra

BarneyMc wrote: »

My ground floor slabs have just been laid so I assume I can't now build an internal chimney. Can I still create an internal flue without a block chimney surrounding it and bring it straight up through the building? Alternatively, can lite blocks potentially be used to create an internal chimney?

Why do you want to construct a masonry chimney at all? What is the advantage? A masonry chimney will:

1. Cost extra in materials and labour
2. Take up internal space
3. Become a substantial cold bridge where it exits the roof
4. Reduce draught by taking heat out of the gases exiting the stove
5. Require reinforced slab/founds underneath to carry the weight

Do it the simplest way, with a twin-wall insulated steel flue pipe going straight up through the internal space.

BarneyMc

Eoghan Barra wrote: »

Why do you want to construct a masonry chimney at all? What is the advantage? A masonry chimney will:

1. Cost extra in materials and labour
2. Take up internal space
3. Become a substantial cold bridge where it exits the roof
4. Reduce draught by taking heat out of the gases exiting the stove
5. Require reinforced slab/founds underneath to carry the weight

Do it the simplest way, with a twin-wall insulated steel flue pipe going straight up through the internal space.

I don't see why not although I would need to make sure it fits in upstairs! Are we talking about free standing stoves with no back boiler here? I intended using a back boiler but maybe a room only stove would be ok.

Thanks for all your help on this by the way, very much appreciated!

Eoghan Barra

BarneyMc wrote: »

I don't see why not although I would need to make sure it fits in upstairs! Are we talking about free standing stoves with no back boiler here? I intended using a back boiler but maybe a room only stove would be ok.

A free standing stove works better in terms of heating a space efficiently - the more centrally placed the stove is the better, but you'd have to figure out where to run your water pipes if it had a back boiler. There shouldn't be any difference as regards the flue set-up though.

The disadvantage of running a back boiler off a stove is that the continual stream of cold water leaving as heated water is constantly lowering the temp. in the firebox, with the result that the stove burns less efficiently (they are at their most efficient in terms of heat output for a given quantity of fuel when operating at a high temp.), with the resulting problem of increased deposits of tar in your flue etc.

I would invest a little time in going through the woodheat.org website, it was the best source of technical info. on stoves I was able to find.

BarneyMc

I've spoken with a retailer about this and am thinking the following now:

1. Build the external chimney as planned
2. Have a back boiler so a lot of the heat will be saved before flying up and away
3. Have the twin wall flue pipe exposed on the ground floor but bring it out to the external chimney just before it hits the 1st floor slab (at least I'll get the benefit of the extra heat from the flue for that stretch)

If I were to bring the flue pipe straight up through the house it would appear on a corridor upstairs which could be very awkward (see my attached sketches in an earlier post). The retailer also said that the flue pipe had to be boxed in on the 1st floor - is that the case? It would also break out of the roof at the lower side and it might be difficult to bring that flue pipe up significantly anyway.

I should explain that I've just laid the ground floor slabs and have installed a pipe to supply the external air for combustion so I can't really change the position of the stove now anyway.

Eoghan Barra

Just my opinion, Barney, but I think you will be making a mistake.

An external chimney is unlikely to have good draught because it is outside the thermal envelope of the house, and hence cold, and hence cools the gases exiting the stove. This problem may be augmented by the back boiler.

You seem to feel restricted r.e. the position of the stove because of the outside air supply pipe position, but to me that should not be your main concern, or anything like it. The most important thing (again, my opinion only) is to have a chimney that produces good updraught; otherwise you risk having nothing but problems, with a system that is unsatisfactory and frustrating.

To quote woodheat.org again: 'The chimney is the engine that drives a wood heat system.'

(By chimney they mean whatever takes away the gases exiting the stove, incl. a simple flue pipe.)

I would try to make all decisions based on what is most likely to deliver an efficient and satisfying performance, and make all the other issues have to tie in with that.

Anyway, whatever you decide, best of luck with it.

BarneyMc

Thanks very much Eoghan for all your advice. I'll have to get some more opinions and advice and think about this again before making a final decision. Anyone else out there with any ideas?

BarneyMc

Just an idea if I were to move the location of the stove to a more central location in the house and bring a twin-wall insulated steel flue pipe up and through the roof. Would it be possible to get an external air supply to this by drilling a hole through the ground floor slab (is this practical?) and sliding a pipe into it? The pipe would extend under the ground floor slab where there's about a 2 foot drop to the hardcore. This void is vented in numerous areas to the external air around the dead build so there would be a fresh supply of air. Does this sound practical?

Eoghan Barra

BarneyMc wrote: »

Just an idea if I were to move the location of the stove to a more central location in the house and bring a twin-wall insulated steel flue pipe up and through the roof. Would it be possible to get an external air supply to this by drilling a hole through the ground floor slab (is this practical?) and sliding a pipe into it? The pipe would extend under the ground floor slab where there's about a 2 foot drop to the hardcore. This void is vented in numerous areas to the external air around the dead build so there would be a fresh supply of air. Does this sound practical?

Not sure I understand, Barney, how come there's a void between the slab and the hardcore? Normally wouldn't the one be on top of the other, with insulation, a dpm, and some sand blinding in between?

BarneyMc

It's not a poured floor Eoghan. The ground floor came in slabs on a lorry and were placed on the rising "walls" - i.e. dead build (wide mass of blocks).

However inside the deadbuild was filled with some hardcore but not to the top - it's the walls that take the pressure of the slabs. Anyway there is a void below the slabs that's vented at the sides in numerous places.

See some photos on the last post #1675 here: http://www.boards.ie/vbulletin/showthread.php?t=2055036901&page=112

Eoghan Barra

Thanks Barney, never come across this before.

Anyway, yes, without being familiar with this floor set-up, can't see any reason why your stove can't take its outside air supply from the under-floor void as you suggest.

As a matter of curiosity, how do you insulate this type of floor?

BarneyMc

I wish I hadn't have heard or seen it either Eoghan as it's bloody expensive! :eek:

To insulate my understanding is: Firstly a dpc/radon barrier is laid. Then I'm getting 1 course of Quinn Kite blocks on all internal rising walls to help deal with the cold bridge from these slabs. Then the walls will be built with normal blocks.

Then when the finished floor is ready to go in a radon barrier/dpc (or some sort of barrier) is laid. Then 150mm of rigid PIR insulation, then the screed with the UFH pipes. There will be 50mm or so of rigid insulation along the perimeter walls as is the normal case with UFH.

If this is not the right sequence then somebody please shout!

Here's a technical drawing showing it: http://www.quinn-lite.com/downloads/drawings/pdf/QL-TD-002.pdf

Image 4270 shows the cement foundation (in the hole) where the chimney is planned to be built with the air supply pipe for the stove.

Image P1010836 shows the slabs being laid and the void that sits under them.

BarneyMc

If anyone knows of a qualified professional I can hire to look into this issue for me then please PM me their details ASAP. Thanks.