Extraction Fan Drawing Smoke out of the Chimney

jonski

Hi ,


Anyone have a cure for this , the extraction fan over the cooker , when turned on , draws the smoke back down the chimney . The chimney is in the sitting room but it is open out to the kitchen . We have to open a window in the kitchen when the fan is on . Even if the fire isn't lighting , say during the summer , the fan still draws the smell down and out around the sitting room . Should the draw from the chimney be strong enough to counteract this ? or is this normal for anyone else whose kitchen opens out to the sitting room ?

Any advice welcomed

John .

listermint

Have to be honest this is the first ive heard of this. Must be some powerful Hood youve got there

Its there any blockage in the chimney? Anything that would affect the Draw.

Even still ive yet to see a household extractor that would perform such feats

Victor

If the chimney is meant to remove air and the fan is meant to remove air, that air needs to be replaced somehow, so yes, you need to open a window.

But do check the chimney for obstructions and make sure the filter is fitted to the extractor fan.

MicktheMan

jonski wrote: »

Hi ,


Anyone have a cure for this , the extraction fan over the cooker , when turned on , draws the smoke back down the chimney . The chimney is in the sitting room but it is open out to the kitchen . We have to open a window in the kitchen when the fan is on . Even if the fire isn't lighting , say during the summer , the fan still draws the smell down and out around the sitting room . Should the draw from the chimney be strong enough to counteract this ? or is this normal for anyone else whose kitchen opens out to the sitting room ?

Any advice welcomed

John .

John, this means that you have a reasonable airtight house and as another poster has said, the air you are extracting needs to be replaced from somewhere.
Advice is to continue to open the window when extractor is on as this will not only replace the air being extracted but also draw in nice dry air (when colder outside) which aids the extraction of the moisture generated.

jonski

The chimney was only cleaned about 8 weeks ago and without the fan on there is usually no problem with the draw . I kinda figured the same as the answers above but I wanted other peoples opinions in case there was another reason .

Thanks all

John

Carlow52

where does the air come from when fire is lit?

Are all the wall and window vents sealed?

If you have an external wall may be better to provide an external air supply on a shutter controlled vent

bette

I would be concerned with carbon monoxide with an arrangement like this! You should have a direct passage out through a wall and this firestack arrangement seems bizarre to say the least. If it were up to me I would blank off the exhaust hole and put in a filter instead.

DoneDL

You will most likely find in the manufacturers instructions that permanent air supply is required or a minimum amunt of air is required, it is definitely in the building regs. This topic has come up in previous posts and it would seem that solid fuel heating and mechanical ventilation are not permitted in the same room because of the very problem that you are experiencing.

jonski

bette wrote: »

I would be concerned with carbon monoxide with an arrangement like this! You should have a direct passage out through a wall and this firestack arrangement seems bizarre to say the least. If it were up to me I would blank off the exhaust hole and put in a filter instead.

Sorry , you lost me there .

1 : I would be concerned with carbon monoxide with an arrangement like this!
Understood this and it is the main reason why I am asking for advice here

2 : You should have a direct passage out through a wall

Do you mean a vent ?

3: firestack arrangement

Don't understand

4: I would blank off the exhaust hole and put in a filter instead


Blank off the exhaust hole from the extractor fan ? ? put a filter in where instead ??

Sorry I just don't understand your post .

John

bette

jonski wrote: »

Sorry , you lost me there .

1 : I would be concerned with carbon monoxide with an arrangement like this!
Understood this and it is the main reason why I am asking for advice here

2 : You should have a direct passage out through a wall

Do you mean a vent ?

3: firestack arrangement

Don't understand

4: I would blank off the exhaust hole and put in a filter instead


Blank off the exhaust hole from the extractor fan ? ? put a filter in where instead ??

Sorry I just don't understand your post .

John

John

Try to curb the antagonism a little! You need to seek the advice of someone who deals with these issues. I won't discuss your points because I believe you are into point scoring instead of trying to solve your problems.

Try to be a little more objective and hopefully you won't be another statistic of "the silent killer"...

jonski

bette wrote: »

John

Try to curb the antagonism a little! You need to seek the advice of someone who deals with these issues. I won't discuss your points because I believe you are into point scoring instead of trying to solve your problems.

Try to be a little more objective and hopefully you won't be another statistic of "the silent killer"...

Thats the problem with posts on forums , people read things into them that aren't there . I genuinely do not understand what you mean , you are using terms and phrases that I have never heard of . You would have been better off reading ignorance into it than antagonism or point scoring .

Go back and read my post again and this time use a goofy stupid voice for my parts .

PeteHeat

Hi,

Your chimney needs to take air from the room to work properly, it appears from your post that you do have enough ventilation for the chimney to work on its own but not enough for both the fan and the chimney.

When the fan is on it is extracting so much air from the room that the chimney can't get enough to work properly, it is also possible that the fan is pulling more air out of the room than your ventilation allows in so the force of the fan is pulling air from the only other open source which is the chimney.

You need to provide more ventilation to the room, if you are concerned this would create draught problems you might consider fitting a vent that you open when the fan is on, similar to opening the window.

The information you need is the amount or volume of air the fan extracts to correctly size the ventilation for the room.

Carbon monoxide is the product of poor combustion, I wouldn't be worried from what you describe because the source of the problem has been identified and all you have to do is not use the fan.

Stack arrangement describes the flue working the way it does when the fan is on, that is working in reverse.

Some fans can work with a filter to clean the air from cooking smells etc instead of actually extracting air from the room.

It is possible that the vent for the fan is actually providing the air for combusion when the fan is not switched on.
.

cnocbui

I have exactly the same situation.

I have a stove in the siting room adjacent to the kitchen. The extractor hood I installed is very capable (required 150mm ducting). It has 5 speeds, any speed higher than the lowest one will cause a backdraft in the stove so smoke comes out the air inlet (on calm days when the draw is a bit less). This is despite the fact that the house is well provided with 100mm, unblocked, wall vents.

In my case I have two solutions for when I need a high speed on the hood. I crack a window open slightly or close the door between the kitchen and sitting room.

An extractor hood should exhaust to the outside. Fitting a hood with just a filter is a poor joke and would not be a tolerable solution to me.

This situation is not indicative of any problem with the flue or air vents, it is just a consequence of well sealed housing and an adequate kitchen extractor fan.

In a perfect world I would have a dedicated ducted air supply from outside to the stove, but really only continental Europeans are that advanced and have post neolithic standards of house construction.

heinbloed

...post neolithic standards of house construction

Well formulated, cnocbui (smiley).

" Pressure differential guards " the devices are called which could safe lives. Try google or similar.

A simple warning device ( a legal requirement in European post neolithitic house constructions) can be seen here:

http://www.marley-germany.com/en/products/ventilation/exhaust_air_control/index.htm

or this one:

http://www.siegenia-aubi.de/en/products/building_technology/aerocontrol/index.html

PeteHeat

This is despite the fact that the house is well provided with 100mm, unblocked, wall vents.

100mm intake versus 160mm outlet could be the answer the OP's question

An extractor hood should exhaust to the outside. Fitting a hood with just a filter is a poor joke and would not be a tolerable solution to me.

I agree never saw the filter type work to any level of satisfaction.

In a perfect world I would have a dedicated ducted air supply from outside to the stove, but really only continental Europeans are that advanced and have post neolithic standards of house construction.

Stoves with external air intake are available in Ireland and have been for a long time, there are even stoves designed for air tight houses available here sadly consumers spend a fortune on mechanical ventilation and are not advised properly even though the contractors can see the fireplace being built.

They have very similar problems in the more advanced countries that is how they came up with the answers.

heinbloed,

I do agree we need proper enforced standards for the construction industry here for everything from the new build to the small jobs that many consider DIY.

When the chance (money) was there it can be seen as a missed opportunity, today there are many consumers who either don't have the money to get the job done properly or believe the standards are not necessary and anyone working to high standards are ripping them off.

No enforced regulations lead to problems described by the OP.

.

jonski

Thanks for the extra information people . Just while I have ye here are there any other downsides to having a " reasonable airtight house " as MicktheMan put it .

Reading back through the thread I see a mention of window vents ....... there are no vents in my windows and there is only one wall vent , about 4" by 8" low down in the wall of the front room . I know that it is hard to give exact advice without knowing the house and the dimensions of the rooms but it does seem obvious from reading the replies that I should continue to open a window when needed but also consider fitting a shuttered vent . This is an old mass concrete walled house and it is hard enough to heat it as it is and I am worried that the vent would be another source of cold to deal with in the winter . It should be said that my experience with vents is not very up to date .


Thanks again .

John

Carlow52

the vent in front room may have been for an open fire.

Based on what you have written thus far it seems to me that your house does not meet what might be called minimum ventilation, not to mnd the reg as per the building standards which can be found here
http://www.environ.ie/en/TGD/#Individual%20Technical%20Guidance%20Documents

Part F

Relying on opening a window is not the right solution, long term.

What happens if the occupants become unable to open windows?

heinbloed

As Carlow52 mentioned: the window or wall vent isn't the best solution.
During windy weather the suction created at the lee side of the house could suck the smoke from the chimney into the house - if the window or vent is there at the lee side.

Only a " pressure differential guard " can avoid in a situation like this severe risks.
But these devices are expensive, cost more than a stove and require regulare calibration and maintenance by a specialist.

The suction force on the lee side could be twice (?) as strong as the pressure on the luv (wind-exposed) side.
This would create a downblow of smoke from the chimney into the house combined with an underpressure/suction at the wall vent or window, at the lee side of the house.
Not only a health and safety risk but also an increase in maintenance and renovation costs !

There are hardly any savings on money or energy consumption to be expected with the combination of fire and extractor in one and the same unit/house.

Victor

cnocbui wrote: »

I have a stove in the siting room adjacent to the kitchen. The extractor hood I installed is very capable (required 150mm ducting). It has 5 speeds, any speed higher than the lowest one will cause a backdraft in the stove so smoke comes out the air inlet (on calm days when the draw is a bit less). This is despite the fact that the house is well provided with 100mm, unblocked, wall vents.

One 150mm extract , close tot he fan, can be the equivalent of 3-4 passive vents. If the vents have substantial grilles on them, that further reduces the flow of air through them.