Ohhhh the draught !

[Nthkentman]

Cold air tumbling down the chimney through the flue is causing the room to be colder than I'd like it. Apart from lighting the fire, cutting things up with an angle grinder to plug the gap, or stuffing a chimney balloon up it (I really do like the fire you know)

1890 cottage, standard chimneys up through upper floor to roof . Only 1 with a "Real" fire all others blanked properly. Older type "Back boiler" multi-fuel fire with a plate inside at the top acting as a damper only (Fire was donated by a friend who didn't need it and it is only used as a secondary room heat source to the gas CH in cold weather and when "The Management" want to feel cosy ;-) . (and for roasting chestnuts or doing toast)

What can I do to reduce the downdraught?

[Andrew Gabriel]

I've never had a downdraught from a chimney. They tend to generate a small updraught even when no fire due to heat in the room and building fabric. Is there some reason you have negative air pressure in the house, such as extractor fan, or open-flued gas appliance? If it's due to wind in a particular direction, it may be that the chimney height is wrong relative to the building height, and/or an appropriate cowl might help, and you should get this investigated if you use the chimney for a fire.

[Nthkentman]

Hmmmm....... When I noticed it the air temp was minus 4 and no extractor on in house. Might have been a breeze helping it out, but the room always feels a little coler than the rest of the house.

[Weatherlawyer]

Down draughts are caused by the chimney being cooler than the house. This happens when they get damp. The flue gets lined with water absorbent chemicals dissolved in the soot including alkali ashes but ammonia is the favourite.

Also the other flues not in use will contribute to this as the chimney is not capped.

What may help if there are nearby buildings surrounding your home that are as high as, or higher than, your chimney is having a flue cap that turns away from the wind. I have no idea what they are called but unless you have the ladders to diy, it will be expensive.

I imagine such a cap will be hard to find these days -as well as expensive in itself anyway. (And to be honest, not all that effective.)

Your best bet is a daily fire in the hearth during winter when you are parked in the house. You only have to warm the flue so a very small banked fire will be adequate. When was the last time you had the chimney swept?

If it was not too long ago (Too many fires ago, that is) And you are sure there is no sooty or tarry build up, you might get away with burning a news-paper up the chimney every day or so.

If your chimney catches fire you will know why you were getting a problem in the first place. Putting a packet of salt on the fire is said to cure such a problem, don't ask me how.

[Andrew Gabriel]

Well, even an updraft will generate cold airflow into the house somewhere, to replenish the air which has gone up the chimney. When doing heatloss calculations to design central heating, you typically allow up to 1kW heatloss up an open chimney.

What you can do is provide an external vent near the fireplace (not in it). That means the path of the draft will be relatively short, and not across the whole room, and that works well when you have a fire going too. Otherwise, what's wrong with using a balloon?

[The Natural Philosopher]

IF fire aint lit bung a balloon up t'chimbley or shove a screen in front

[Chris Hogg]

As others have said, probably not downdraught but cold air being drawn into the room from outside, replacing the warm air that naturally convects up and out of the chimney. When working around a chimney pot, it's surprising how much warm air you can feel coming out even when there's no fire below.

We have a similar situation, although with a large open fire and a chimney that's considerably bigger than standard. Our has a very wide throat, and not too long after we moved into this place, I installed a large, hinged aluminium flap up inside the throat that can be closed when the fire isn't in use. A bit of a pain to open and close, but effective. But you absolutely must open it before lighting the fire as it's only accessible by putting your arm up the chimney. You only ever forget once.....

This probably isn't an option for you, but you mention a damper in the flue. Does this damper close the flue, or is it just to divert the hot combustion products away from or through the back boiler? If the former, keeping it shut when the fire isn't in use should make a difference to the updraught. Failing that, a tight-fitting plywood panel, suitably decorated, that fits into the fireplace aperture. Use standard foam pipe insulation pushed over the edges of the panel to act as a gasket and make a good seal, although a small amount of air movement is probably no bad thing to keep the flue dry. If that doesn't appeal, try a ball of tightly-crumpled newspaper stuffed up the flue. Always use it to light the fire with next time, so that you never forget it and leave it there when the fire is lit.

[Huge]

Why not in it? I've been umming and ahhing about installing a vent in the fireplace for ages.

[The Natural Philosopher]

Mine are all in the fireplaces for sure.

[Davey]

[Andrew Gabriel]

It can blow the fumes back into the room with the right wind direction. It could possibly blow ash and sparks in too if someone suddenly opens or slams a door.

[The Natural Philosopher]

It could, but it doesn't.

[Andrew Gabriel]

When I was doing the one in the living room, ISTR reading that a vent in the fireplace is forbidden, if the fireplace is still used for burning anything (including gas).

Nearest position allowed was in front of the fireplace in the hearth, which is what I did (it's well conceiled although not obstructed by the gas fire decorations). If you use a real fire, you need to consider fire risk if any embers fall through though.

[The Natural Philosopher]

Building inspector passed all mine.

Reading my 2000 building regulation it is merely stipulated that adequate ventilation exists. No direction is given as to where or how it should be supplied. Only its dimension is specified.

That's still *in* the hearth. Obviously is would be silly to put it where ash would block it.

All my ground floor solid fuel stuff has vents punched to the underfloor spaces.

In my (wood stove equipped) bedroom there is a 4" pipe going through the register plate and up into the loft space, that being 'well ventilated'.

Its perfectly fine and the BCO thought it was 'ingenious'

[Huge]

Good point. Looks like I have to tunnel under the hearth after all. :o(

It wasn't going to be located anywhere this could happen.

[RJS]

Grandfather of a friend was a fireman and attended many chimney fires. At the time of the fireman's strike he chanced upon a group of squaddies setting up their Green Goddess prior to tackling a chimney fire from the roof. He calmly pointed out that you need only a stirrup pump and a bucket of water to extinguish a chimmney fire and that their approach would flood the house. Apparently the steam generated when water is sprayed onto the fire in the hearth is sufficient to extinguish a chimney fire as it rushes up the chimmney.

Don't try this at home, kids.

Richard

[The Natural Philosopher]

I have. several times.

It works.

Unless the roof timber also have caught fire: the key thing is get cracking early - douse fire with water and block the chimney.

[David WE Roberts]

I have occasionally had chimneys 'reverse' on me - cold air flowing down.

Contemplating this, I can visualise that if there is somewhere (say an upstairs window) where warm air can escape then, once the chimney has been 'primed' e.g. by a door to the room being opened and causing a minor lowering of the room air pressure which in turn pulls some cold air down the chimney, the whole thing could work as a gravity circulation system with cold flowing down and warm flowing up. Could even work with two chimneys in different rooms - one being the down flow and the other being the up flow. This would have to be on a still, cold day where there wasn't enough wind past the chimney pot to generate an updraught in the chimney.

Burning a piece of newspaper in the chimney usually reverses the flow.

Cheers

Dave R

[grimly4]

A similar problem in my old cottage was easily remedied by cutting a square of plywood the size of the 'ole and putting it across the front when the fire wasn't in use. It did make a helluva difference.

[grimly4]

Indeed; it's the basis of the Chim-Safe chimney fire extinguisher. The makers also mentioned it was useful preventative maintenance to manually over-ride and give the chimney a squirt every so often to keep the soot levels down.