Kitchen fan airflow

[svouts]

I want to install a bathroom fan in the kitchen to control humidity when I leave the clothes to dry and when I cook since the cooker extractor is not ducted to the outside.

I will install it behind the air brick.

Shall I get one with 170 l/h or 95 l/h airflow?

Will it be a problem if the holes on the airbrick are not enough so I better opt for the small fan or the bigger the better?

 

[ban-all-sheds]

DO NOT FIT A FAN IF YOU HAVE A CONVENTIONAL FLUE GAS BOILER IN THE KITCHEN.

Assuming you don't have a boiler in there, or if you do have one it's a balanced flue or room-sealed one, then go ahead.



Size definitely matters.

Get the highest performing fan you can.

Ideally replace the air brick with a proper outlet - as it stands it will slug the performance of the fan.

Not thought about putting an extract cooker hood in?

 

[svouts]

I do have a combi boiler in the kitchen, it is in a cupboard and the doors have a vent. Does this mean that if I put a strong fan flowing outside it will turn the boiler fumes inside?

 

[ban-all-sheds]

No - that's not the issue. Conventional flue appliances draw their air from within the room, so if you have a fan sucking it out at the same time they can be starved of oxygen, then you get incomplete combustion and CO rather than CO2 produced, and possibly drawn into the room.

This is a Bad Thing.

Room sealed aka balanced flue appliances draw their combustion air from outside, so fans are not a problem.


I'm pretty certain that a combi will be too recent to not be a balanced flue type, but please make sure - getting it wrong can be fatal. Your boiler installation instructions or manual will say.

 

[viewer]

Even if it is a balanced flue boiler, bear in mind that to work properly there needs to be an inflow of air to the room equivalent to that expelled. With no inflow you could install the biggest fan in the world and it wouldn't work.

 

[bernardgreen]

Shall I get one with 170 l/h or 95 l/h airflow?

The air flow rates given by manufacturers are for the fan working without any obstruction to the air flow to an from the fan. They are the maximum flow rates. Ducting offers resistance and reduces air flow,corrogated fleexible being the worst for turbulance. Anything that creates turbulance and/or change of direction further reduces air flow.

Bite the bullet and get a properly installed outlet installed. If you have a cavity wall the air brick may vent into the cavity and pushing damp air into the cavity will create damp. ( Even if there is a matching air brick on the outer wall there is every possibility they have no connection between them through the cavity. )

 

[svouts]

The wall had two air bricks, from inside and outside, so I think will be no issue with damp. The previous owner removed the inside air brick and installed a fan that has so much dirt that I doubt it is working at all.

I think the big issue is the boiler. I am thinking to install a special fan that works in constant mode with very small airflow of 25l/h,
Or what if I install in parallel behind the air brick two fans, one blowing inside and one outside?

 

[ban-all-sheds]

The wall had two air bricks, from inside and outside, so I think will be no issue with damp.

Think again.

The whole purpose of a cavity wall is to insulate the interior of the building by creating an air gap, as air is a pretty good insulator. Other materials are better which is why the cavity is often filled with them, but the point is that the outer leaf will be cold.

If you pump warm moist air from the kitchen into the cavity you WILL get condensation in there, and that WILL be an issue. If yyou have a cavity wall then your ONLY option is to properly duct the fan to a proper outlet terminal.

I think the big issue is the boiler.

Why? Have you established that it is not a room sealed one?

If so, then...

I am thinking to install a special fan that works in constant mode with very small airflow of 25l/h,

No, not without taking expert advice first. If you get it wrong you and everyone else in the house could die.

Or what if I install in parallel behind the air brick two fans, one blowing inside and one outside?

I don't know.

Do you?

If you get it wrong you and everyone else in the house could die.


But if it is a room-sealed appliance you don't need to worry.

So as I said - your boiler installation instructions or manual will tell you what it is.

 

[svouts]

I am back home now and i can see the details for my boiler.
Ariston Microgenus 23 MFFI Non-Condensing Gas Combination (Combi) boiler:
Boiler type: Combination (Combi) / Non-Condensing
Boiler fuel: GAS
Boiler mounting position: Wall mount / Indoors
Boiler flue: Room-sealed
Boiler ventilation: Fan
Boiler ignition: No permanent pilot light
Boiler burner control: Variable
Electric power consumption during startup: 130 Watts

Does this mean I can install a strong bathroom fan in my kitchen?

 

[ban-all-sheds]

I am back home now and i can see the details for my boiler.
.
.
Boiler flue: Room-sealed
.
.
Does this mean I can install a strong bathroom fan in my kitchen?

Assuming you don't have a boiler in there, or if you do have one it's a balanced flue or room-sealed one, then go ahead.

But if it is a room-sealed appliance you don't need to worry.

 

[bernardgreen]

Boiler flue: Room-sealed
Does this mean I can install a strong bathroom fan in my kitchen?

It means the fan will not affect the boiler's operation.

Assuming the boiler's flue was correctly placed in relation to windows, doors and other openings in the wall then the lowered air pressure in the kitchen due to the fan will not ( should not ) cause fumes to be sucked into the kitchen from outside.