Remote venting of a chimney


Postby gilesnz » Tue Dec 30, 2008 10:17 am

I have a fire place in the attic bedroom and would like to remove the surround and seal the chimney from the room(the wall is flat as other chimeny breasts from other fires). The neighbours either side have rooms also but they do not heat. So I am going to internally insulate these walls. I am planning to create a couple of grooves in the plaster (1"deep)and matching groove in the 50mm insulation(king span type) and run a couple of 1 1/4"pipes up the wall into the vented roof space both ends of pipe will point down to avoid blocking

Is this an adequate solution? its not an easy topic to find this kind of information on

Thanks Giles
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Postby stoneyboy » Wed Dec 31, 2008 4:21 pm

gilesnz,
Difficult to imagine what the pipes are for - if the bottom ends are open into the fireplace opening I don't think this will achieve anything. Suggest you instal a Hit & Miss vent to allow air into the fireplace opening and fit a pepperpot cap on the chimney. This will allow the chimney to remain ventilated - essential if you are to avoid damp problems
end
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Postby Perry525 » Sat Jan 03, 2009 6:00 pm

An un used chimney is frequently the weak link in a room as, it has but one brick between you and the sky.
And as such is more often than not the coldest spot in a room, attracting all the moisture/water vapour held in the air to condense on it, as it (the water vapour) makes its escape to the outside cold air. An open chimney makes this escape easy.
If you do block up the fireplace, then do insulate the whole chimney breast with at least 25mm thick polystyrne or similar, to keep the surface warm and move the condensation, probably to the nearest window.
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Postby the specialist » Tue Jan 06, 2009 7:39 pm

Hi gilesnz,

First point - if you want to block off the chimney do as stoneyboy says.

Second point - blocking off the chimney doesn't just cause condensation problems but also (and quite often more seriously) a bigger damp problem. Chimney's rely on ventilation internally to dry out the moisture within from all the rain that has fallen in over the years. Because there is an airflow the moisture dries out to the atmosphere. If you stop the airflow the moisture will eventually end up on the internal plaster bringing all the salts with it. Also do not fix a radiator to the chimney breast as this will draw moisture in from the chimney. I have come across this many times so trust me please.

Good luck.

aidan
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Postby gilesnz » Tue Jan 06, 2009 7:54 pm

Back to the remote ventation.. I want to seal the chimney opening from the room to stop the cold drafts but maintain some air flow to prevent damp, hence some ducted air from the the cold side of the insulation in the rafters. saving all the heat flowing up the chimney..
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Postby Perry525 » Wed Jan 07, 2009 2:11 pm

From what you write, am I to understand that the chimney is in the centre of two homes?
And that your neighbours have cold rooms backing onto your chimney?
And that while you wish to seal the chimney off from the room, to stop loosing heat up it, you wish at the same time to provide ventilation from the outside to the chimney via a pipe?
And that the chimney projects above the roof line and is not capped, nor is it insulated and that any rain beating on the chimney stack, will in part enter the brickwork and the open chimney top?
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Postby the specialist » Wed Jan 07, 2009 7:25 pm

Hi again gilesnz,

I dont think you will get enough throughput of air by doing what you suggest. A 9X3 vent low on the inside of the chimney once blocked off and a cowell on the chimney top are your best options. You wont notice that much heat escaping up the chimney. If your not having a window or velux it will actually benefit the room by changing the air regularly.

Aidan
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Postby gilesnz » Wed Jan 07, 2009 9:18 pm

Well thanks for the responses..

The chimney is capped in some fashion. I;ve not been out on the roof, but the pots have been removed..

So I suppose I need to know if I need warm air to stop the condensation forming in the chimney and in turn damp forming or can I duct cold air. and it will do the job. I can look at increasing the amount of ducting

I have 2 velux and a dormer window in the roof and there will be an ensuite with extracter.. I suppose I am trying to make the loft as air tight as possible.. The rest of the house just pours out heat out of every corner and I'm starting at the top.. the coldest room and working down..

I know its not the normal way.. but i'm willing to experiment and if I have cut a vent in in 6 months time dry thing out a bit I'm willing. just want to try something a bit different..
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Postby Perry525 » Thu Jan 08, 2009 10:34 am

OK, the best thing to do is to remove the chimney on the outside of the house.
If you cannot, because its shared.

Then capping and repairing the outside pointing and painting with silicone to shed water is a start.

The next thing is a cold chimney in a room will absorb all the excess water vapour in the air and become damp.
You can deal with this by running a dehumidifier, set at about 65% it will collect any spare water in the air during the winter and keep the room and chimney dry. Provided you live sensibly, ie; run your extractor fans while bathing, washing and cooking, keep bathroom and kitchen doors closed, do not dry things on radiators then, the dehumidifier will only need to cope with your breath and sweat during the spring, autumn and winter. It won't be on much.
Or, you can accept that water vapour will always make its way from hot to cold and that as next door will be colder, the water vapour will make its way to the top of the chimney via their side.
Perry
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Postby the specialist » Thu Jan 08, 2009 1:45 pm

Hi again, air temperature is not important. Flow rates are. Good luck and let me know how you get on.

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