Ventilation, Building Regs and Chimneys

[WhitePJ]

Hi All,

I am part-way through a major refurb. Solar is progressing, insulation and UFH are being done, and I am now looking at ventilation.
The property is an old semi in the city outskirts, and comes with a large chimney, which is now unused. Using any of them for the original function (especially in the bedrooms) is highly unlikely!
However, I do need to think about:
1) the flue from the gas boiler (which currently has a metal pipe sticking through the roof); and
2) Ventilation air flow.

Therefore, the question is, can I put the chimney to some use here? I can't instantly see any problem with the gas boiler exhaust, but am I likely to encounter any difficulties with building regulations if I use one of the other flues as a ventilation exhaust?

Thanks,

Phil

[pb]

Therefore, the question is, can I put the chimney to some use here? I can't instantly see any problem with the gas boiler exhaust, but am I likely to encounter any difficulties with building regulations if I use one of the other flues as a ventilation exhaust?

Talk to your BCO I guess.  I don't think there is anything in the regs that forbids this, as such, but he might have other concerns.  The obvious one that comes to mind (for both your gas boiler and the ventilation system) is that, if the old flues are uninsulated, you might encounter severe condensation if you start exhausting warm, wet air at relatively low temperatures into them since the temperature will probably drop below the dew point before the flue terminal.  That in turn might make all the surrounding masonry damp which would probably not be a good thing.

What gas boiler are you using?  A non-balanced flue is relatively rare for domestic gas nowadays.

[dhaslam]

It could be useful to route ducting for a ventilation system  if there are  openings into  most of the rooms.  Usually chimneys have such thick walls that it would  be a lot of work  but it could make a neat job. 

[wookey]

You aren't allowed to put balanced flues up chimneys any more - the whole pipe has to be inspectable is the reason given, I believe. Not sure about simple exhaust flues (is your boiler old enough to be unbalanced?)

Best thing to do with unused chimneys is remove them completely. If that's too much trouble, then fill them with insulation is next best. People are normally advised not to do this, and to leave the chimney as a gert big, ventilated, thermal bridge sucking the heat out of your house. That seems like a really bad plan if you are trying to be efficient.

[derekmt]

I have an unbalanced flue old style boiler in the kitchen - why does everytime it gets inspected I am asked to provide ever larger ventilation for it.
The boiler hasnt changed, it passes all the tests just the same as last time. Its just like gas fire with flue so why does it get this "you must increase amount the ventilation" change in the regulations. Surely if it was safe with x area ventilation last year why does it need X+Y   now?
From a practical point of view the CO monitor has never gone off, and the amount of venting in the kitchen is enormous (you can feel the draft!)

[desperate]

I have an unbalanced flue old style boiler in the kitchen - why does everytime it gets inspected I am asked to provide ever larger ventilation for it.
The boiler hasnt changed, it passes all the tests just the same as last time. Its just like gas fire with flue so why does it get this "you must increase amount the ventilation" change in the regulations. Surely if it was safe with x area ventilation last year why does it need X+Y   now?
From a practical point of view the CO monitor has never gone off, and the amount of venting in the kitchen is enormous (you can feel the draft!)

Has anything else changed in your house, IE new extractor fans, extensions, lean-tos, anything that may affect the original ventilation that was presumably installed with the boiler? As far as I know there haven't, been any changes to the vent sizing for open flued boilers for some time now. Ask you gas man to show you why the vent needs increasing.

If you let me know the power input of your boiler and the details of its location I can check on the size of the vent you need, I am a gassafe monkey
 

Sorry to trample your thread whitepj, if your boiler is an open flued type then yes you can drop a liner down and connect up , but if it is a fanned or balanced flue AKA room sealed, then no you cant use a chimbley, again if you post a few specs I can advise about vents. As for using a redundant chimney for ventilation, yes why not? as long as it doesn't impact on the gas boiler flueing performance, which would only happen if it is an open flue appliance.

Desperate

[qeipl]

Best thing to do with unused chimneys is remove them completely. If that's too much trouble, then fill them with insulation is next best. People are normally advised not to do this, and to leave the chimney as a gert big, ventilated, thermal bridge sucking the heat out of your house. That seems like a really bad plan if you are trying to be efficient.

+1

[derekmt]

[...Has anything else changed in your house, IE new extractor fans, extensions, lean-tos, anything that may affect the original ventilation that was presumably installed with the boiler? As far as I know there haven't, been any changes to the vent sizing for open flued boilers for some time now. Ask you gas man to show you why the vent needs increasing.

If you let me know the power input of your boiler and the details of its location I can check on the size of the vent you need, I am a gassafe monkey
 
...Desperate

I'll get the details tonight. I gone to extremes removing grills from vents, removing doors, windows. There are two very  large vents behind  fitted cupboards which are open via apppliance openings . That they say dont count because they cant get to both sides.  There are also two 200x 90 through door vents, 10mm gap under the door. This boiler was installed in 1970s its a bungalow... is a conspiracy to get a new boiler sale from british gas?
My solution to this may be seal the boiler alcove with a full door and put in a large vent to the roof space.

[derekmt]

tis an old glow worm 60/80 23kw, likely to outlast me. That means 460 sq cm bottom 230 sq cm top in an enclosure, if i read the training material correctly. Efficiency? not worried about that as there is going to be 120 58mm x 1.8m evac tubes on the roof.

[mistadave]

I ended up getting rid of a chimney - it was last used as a flue for a gas fire and had already been taken down to roof level and replaced with a metal flue pipe. Like you I pondered using it to run ducting down but since I was to insulate the house on the inside I found it would either waste heat from the intake air or more of a problem, cause condensation in the ducting of any extract air.

In the end we decided to take it down and it was one of the most fun demolition jobs I have done on the house (of which there were quite a few), taking off bricks from the top and "posting" them down the chimney into a barrow downstairs  . It was then rebuilt as a normal cavity wall.

It actually feels like we have gained a good amount of space in both rooms too and gives far more options for furniture positioning!

The second chimney we kept but actually rebuilt the bottom half to make it come out further around our new woodburner, however we lined the chimney and back filled it with vermiculite insulation to ground floor ceiling level, and then below that the outside skin is lined with celotex and then a couple of layers of fireboard.

If you are worried about backfilling the chimney with insulation because of damp etc you should use silvapor - its a form of vermiculite but is treated so that it repels water but water vapour can obviously still pass through it to escape if needed.