Recommended Cooker Hood Rate

[MortarThePoint]

Building regs require only 30 L/s if an externally venting cooker hood. Cooker hood manufacturers recommend 10 air changers per hour though which for a large room results in a much higher flow. Our kitchen/Diner is going to be 81m3 volume, so that advice would suggest a requirement for 810m3/h = 225 L/s which is 7 times the building regs requirement so seems silly.

 

I am contemplating going smaller than that and having a max flow rate of 500 m3/h = 140 L/s which would be only 6 air changes per hour. Will I regret that or are the cooker hood sellers over egging it? What have others done here?

 

 

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1045918/ADF1.pdf

 

https://www.faberhoods.co.uk/extraction-rate-calculator/

 

[JohnMo]

Do you or are you having MVHR?

Edited September 2, 2023 by JohnMo

[MortarThePoint]

2 minutes ago, JohnMo said:

Do you or are you having MVHR?

 

No so it's straight extract

[JohnMo]

Those rates may apply to a commercial kitchen, but why you would need them in a domestic house is questionable.

 

The further the extractor is away from the hob the less effective it is at taking away the smells and grease, so manufacturer quote stupid flow rates to get around it. 10x kitchen volume is the whole house volume or more every hour.

 

Passivhaus did a test on extract hood flow rates and effectiveness, basically the conclusion was min allowed distance from source to fan was best and required least flow. 

[MortarThePoint]

It feels wrong that there was no upper limit to the flow rate. If you had a cooker hood in a warehouse you'd need a tornado of flow rate.

 

I expected then to have a more appropriate formula for open plan living.

[Conor]

38 minutes ago, MortarThePoint said:

It feels wrong that there was no upper limit to the flow rate. If you had a cooker hood in a warehouse you'd need a tornado of flow rate.

 

I expected then to have a more appropriate formula for open plan living.

BCO said it was the actual working area of the kitchen within the open space. We still went with a beast in our last place at 800m³hr. For that flow rate you need mim 150mm ducting and a short run at that.

 

New house, MVHR. Hardly ever use the (recirculating)  hob extractor, not really needed.

Edited September 2, 2023 by Conor

[Mr Punter]

I have a TD 800/200 mounted in a store room on the roof terrace and connected to a hood above the cooker with 6" duct.  It can extract 300l/s and is really quiet.

[MortarThePoint]

1 hour ago, Mr Punter said:

I have a TD 800/200 mounted in a store room on the roof terrace and connected to a hood above the cooker with 6" duct.  It can extract 300l/s and is really quiet.

 

Sounds good, how often do you turn it up that high?

[MortarThePoint]

2 hours ago, Conor said:

For that flow rate you need mim 150mm ducting and a short run at that.

 

I've been trying to sort 150mm but think it's too tricky so am going with 125mm

[MortarThePoint]

15 hours ago, Mr Punter said:

I have a TD 800/200 mounted in a store room on the roof terrace and connected to a hood above the cooker with 6" duct.  It can extract 300l/s and is really quiet.

 

To use the TD 800/200 with 6" ducting you must be using reducers. I was wondering about doing the same with a Manrose MF150T which can achieve a more modest 855 m3/h = 238 L/s.

 

Really, I'd like a blower that has more flow settings that can ideally be remotely controlled. Is that what the TD 800/200 allows?

Edited September 3, 2023 by MortarThePoint

[Mr Punter]

17 hours ago, MortarThePoint said:

 

Sounds good, how often do you turn it up that high?

 

I tried it with the REB speed regulator but it tended to stall.  I just use it on full as it is very quiet.  Just on/off wall switch.  Reducer either side.