Extract fans that lift air.
Discussion
I'm planning on puttinga kitchen extract in the roof of our two story house. It will extract through an exiting roof vent.
How do I size a fan that has to lift the air 9m? Presumably there's some 'chimney' effect once the column of air is moving?
I'm fitting a 150mm duct up from the hob hood into the ceiling void, where I want the fan mounted. The plan is to have an effective vent without the fan noise in my ear whilst I'm cooking.
How do I size a fan that has to lift the air 9m? Presumably there's some 'chimney' effect once the column of air is moving?
I'm fitting a 150mm duct up from the hob hood into the ceiling void, where I want the fan mounted. The plan is to have an effective vent without the fan noise in my ear whilst I'm cooking.
Paul Drawmer said:
How do I size a fan that has to lift the air 9m? Presumably there's some 'chimney' effect once the column of air is moving?
I think the opposite - drag from the walls of the tube. Plus if it's cold outside it has to defeat the column of cold air coming down.How about a second fan halfway up to make sure?
Paul Drawmer said:
I'm planning on puttinga kitchen extract in the roof of our two story house. It will extract through an exiting roof vent.
How do I size a fan that has to lift the air 9m? Presumably there's some 'chimney' effect once the column of air is moving?
I'm fitting a 150mm duct up from the hob hood into the ceiling void, where I want the fan mounted. The plan is to have an effective vent without the fan noise in my ear whilst I'm cooking.
You can get external/wall mounted extractor fans which will isolate you from the fan noise and allow you to just route the ducting out through the house wall.How do I size a fan that has to lift the air 9m? Presumably there's some 'chimney' effect once the column of air is moving?
I'm fitting a 150mm duct up from the hob hood into the ceiling void, where I want the fan mounted. The plan is to have an effective vent without the fan noise in my ear whilst I'm cooking.
e.g http://www.i-sells.co.uk/external-extractor-fans
GnuBee said:
You can get external/wall mounted extractor fans which will isolate you from the fan noise and allow you to just route the ducting out through the house wall.
e.g http://www.i-sells.co.uk/external-extractor-fans
But careful it's not going to be too near to any neighbours if noisye.g http://www.i-sells.co.uk/external-extractor-fans
Some input to try and help you out...
You say the room is 30m3 - how many air changes an hour do you want to achieve to collect the steam? This will allow you to roughly size the volume of airflow through the fan. Remember that you will need to allow replacement air into the room to replace the volume extracted.
You will need to work out the pressure headloss in your duct run - this will guide you on the pressure development needed from your fan to give the requisite suck to overcome the headloss.
As others have said that "steam" you are extracting will have all sorts of other grot entrained into it that will become more evident over time as they are deposited in your duct. You might want to consider some sort of carbon charcoal filter to catch that at the bottom of the duct but remember to add the pressure drop across the blinded filter to your headloss calculations otherwise as soon as the filter is lightly coated the fan will be incapable of sucking hard enough.
I'm more used to spraybooths in my day job but the principles are the same!
You say the room is 30m3 - how many air changes an hour do you want to achieve to collect the steam? This will allow you to roughly size the volume of airflow through the fan. Remember that you will need to allow replacement air into the room to replace the volume extracted.
You will need to work out the pressure headloss in your duct run - this will guide you on the pressure development needed from your fan to give the requisite suck to overcome the headloss.
As others have said that "steam" you are extracting will have all sorts of other grot entrained into it that will become more evident over time as they are deposited in your duct. You might want to consider some sort of carbon charcoal filter to catch that at the bottom of the duct but remember to add the pressure drop across the blinded filter to your headloss calculations otherwise as soon as the filter is lightly coated the fan will be incapable of sucking hard enough.
I'm more used to spraybooths in my day job but the principles are the same!
So..never having had an external cooker extract before, do domestic installations require regular duct cleaning?
My fan in roof plan was to move the noise source as far away as possible. It sounds as if it is going to be a 'must' to use rigid ducting, and to allow for access to clean it when the grot takes over.
Ok on the calcs - I'll be studying the specs of the filter manufacturers now.
My fan in roof plan was to move the noise source as far away as possible. It sounds as if it is going to be a 'must' to use rigid ducting, and to allow for access to clean it when the grot takes over.
Ok on the calcs - I'll be studying the specs of the filter manufacturers now.
A quick Google suggests an air change rate of 15/hour for a domestic kitchen.
So the fan have to extract 450m^3 per hour or 0.125m^3 per second.
As 'It's fixable' says you'll nee to consider how that air will be replaced or you'll quickly create a vacuum and get zero extraction.
What will the duct run be? straight up and out or will there be any 90 or 45 degree ends? From there you can work out what pressure you need on the fan. (You also need to know the pressure drop across any filters your proposing to use)
So the fan have to extract 450m^3 per hour or 0.125m^3 per second.
As 'It's fixable' says you'll nee to consider how that air will be replaced or you'll quickly create a vacuum and get zero extraction.
What will the duct run be? straight up and out or will there be any 90 or 45 degree ends? From there you can work out what pressure you need on the fan. (You also need to know the pressure drop across any filters your proposing to use)
Sounds like (a) a very complex, problematic and expensive solution to a very minor problem and (b) the sort of thing that will knock thousands off the value of your house as prospective buyers think "WTF did he do that for and how much is it going to cost to rip it all out and make good?".
Still, your home, your castle.
Still, your home, your castle.
Gassing Station | Homes, Gardens and DIY | Top of Page | What's New | My Stuff