kitchen fan causing smell from fireplace.

hi not sure if this is correct area but couldnt see a section where this question should go.

we have a detached house with an open fireplace which was recently swept.

In the kitchen i have recently fitted an extractor fan over the cooker which vents through an outside wall.
since this has been installed and since we have started to use the open fire in the last few weeks since it got colder, whenever the fan is on its maximum extraction setting it causes (after around 5 mins of use) a cold gust of air to come down the chimney. If there are still ashes there from last nights fire it then brings the smell from the fireplace into the living room.

If you have the door between the living room and the kitchen closed then it doesnt do it as much or if you have the back door in the kitchen open this also stops it from drawing air down the chimney.

i understand why it is doing it but the extractor is around 20 metrs away from the living room so i never expected it to be powerful enough to cause a downdraught. the only thing i can think of changing is the chimney pot as it is a very low, very wide one as i beleive it was originally for a gas fire. i would guess the pot is around 9" wide and only stands around 2-3" up from the top of the chimneystack.
if i put a taller tapered chimney pot on could this cure this odd problem ?

we used the fire all of last winter but we hadnt installed the extractor in the kitchen then so didnt have this problem.

i have also just bought an expelair extractor which i want to install in the downstairs bathroom which is about the same distance from the living room. this will be on for more of the day than the kitchen fan is so i want to sort this problem before the whole downstairs of the house smells of fireplace.

any ideas?

a fan will be removing say 10L off air from the house every minuet
if you do so the airflow coming down the chimnie will be the same assuming theres no easier path for the air

if you close the door inbetween the airflow will be reduced to what can pass around the door and any other small gap

The room with fireplace should have adequate ventilation so that the kitchen fan should not be capable however powerfull to cause a back draft, check with solid fuel advisory council for further info.

this is the problem nowadays..
when built, older houses leaked like a sieve and there were draughts all over the place..
now with double glazed windows and so on, many houses are fairly air tight.

you need to put in a vent or air brick in the kitchen to allow it to draw air into the kitchen without sucking it from the rest of the house..

that's the reason that new double glazed windows have trickle vents in them..

I agree with Coljack . You need to put additional venting in the kitchen to allow through flow of air within the room to avoid the extractor drawing air from your chimney . Some of the better quality hoods can pull 700 to 800 m3 per hour. Even wood burning or coal fires can produce toxic gasses, and you don't want those coming into your living space. For now open a window in the room or an external door until you get a vent in place.

I presume the trickle vents on your widows are open?

wow i never expected this many replys so quickly.

i have older style aluminium double galzing without trickle vents which we will be replacing next spring with upvc with vents so that may be enough to stop it.

i think i will look at adding a vent in the kitchen, but will it let a constant draught through it on windier days? as i presume it will need to be a constantly open vent like an airbrick?

also when i put the new extractor in the bathroom , will i need to put a vent in there as it is a small room and there arent too many places i could fit one.

thanks for the help

Kitchen and bathroom should already have permanent vents fitted, explains your problem with draw back.Kitchen is dangerous without vent if you have gas oven.