Mechanical Extraction in Kitchen

[studioreno]

I am having a remodel done to my studio flat, and planning to bring the kitchen into the main studio room and turn the existing kitchenette into a small bedroom.

The new bedroom room (former kitchenette) has an external vent, which thiis ducted to the bathroom to extract the air from there.

The new layout (and the ceiling jousts) do not really allow for me to duct mechanical extraction fan from the new kitchen through the bedroom to the existing vent. To do so would require lowering ceilings below the window line, which is not ideal and also costly.

Would having a circulating hood and then fitting a 60l/s mechanical vent to the window in the kitchenette solve this problem? Or would this not be building regs compliant? I've seen mixed advice about whether the mechanical extraction needs to be separate/at a distance from the window.

Thanks all!

 

[noseall]

Would having a circulating hood and then fitting a 60l/s mechanical vent to the window in the kitchenette solve this problem?

Yes.

Reg's asks for a more powerful rate, if remote from the hob. You'd have to look up the rate, but yes, it's doable.

 

[stevie888]

Put in your drawings showing what you want to do then discuss if they query.

 

[JuddlyFire]

Based solely on the Source File: The_Merged_Approved_Documents_Oct24.pdf, your proposed solution (recirculating hood + 60l/s window vent in the kitchenette) is not Building Regulations compliant for the following reasons:

• Kitchen extraction must be ducted externally – Document J requires retained or replaced extraction for kitchens during building work, and recirculating hoods do not satisfy this as they do not extract air outside the dwelling ↗ (Section 3, paragraph 3.30, page 631).
• Window vents cannot substitute for mechanical kitchen extraction – Part F explicitly states that window-based ventilation (purge ventilation) only applies to sanitary accommodation (bathrooms/toilets), not kitchens ↗ (Section 1, paragraph 1.49, page 618). Kitchen extraction requires dedicated ducted systems.
• Extract fans must be ceiling-mounted – Part F mandates extract ventilation terminals (including cooker hoods) be installed "as high as practicable" and "a maximum of 400mm below the ceiling" ↗ (Section 1, paragraph 1.20, page 612). A window-mounted vent violates this height requirement.
• Combustion safety risk – Extract fans depressurize the dwelling, which can cause dangerous spillage of flue gases from any open-flued appliance (e.g., boiler, fireplace) elsewhere in the flat—even if in a different room ↗ (Section 1, paragraph 1.20, page 842). A window vent would create this risk.
• Ventilation cannot be reduced below pre-renovation levels – Converting the kitchenette to a bedroom while removing its extraction system worsens ventilation. Part F requires post-renovation ventilation to be "no less satisfactory than before the work"↗ (Section 3, paragraph 3.2, page 625) or meet current standards ↗ (Section 3, paragraph 3.11, page 628). Your proposal fails both tests.
• Recirculating hoods are non-compliant for kitchens – Snippet 2 confirms recirculation systems have strict fire-safety constraints (e.g., rigid steel ducts, no transfer grilles), but crucially, they do not provide extraction—only air filtration within the room. Kitchens require extract ventilation to remove moisture, grease, and combustion byproducts ↗ (Section 3, paragraph 3.23, page 109).

Required Solution​

To comply:

• Ducted extraction is mandatory – The new kitchen must have a mechanically ductedextraction system venting directly outside (not through the bedroom). If ceiling constraints prevent routing through the bedroom, alternatives include:
  • External wall ducting via the kitchen studio room (avoiding bedroom penetration) ↗ (Section 4, paragraph 4.46, page 577 requires ducts through floors to be enclosed, but wall routing may avoid this).
  • MVHR (Mechanical Ventilation with Heat Recovery) system meeting Part F flow rates [14b] (Section 3, paragraph 3.11, page 628).
• Expert assessment needed – If airtightness increases (e.g., from new windows), Part F requires either MVHR installation or expert advice to ensure ventilation isn’t compromised [11a] (Section 1, paragraph 1.46, page 618).

Do not proceed with the window vent solution—it violates combustion safety ↗, height requirements ↗, and core ventilation principles for kitchens [3, 15]. Consult a Building Control Officer to approve duct routing alternatives.

 

[Scally-Ho]

Do you own the studio flat (mortgaged or otherwise) or are you a tenant?

 

[mrrusty]

@JuddlyFire - first, really good to see a knowledgeable fire safety person here. Second, can I just take issue with your point about extract fans must be ceiling mounted - I just checked the approved doc for my own interest and circumstance (OT for this thread) and it actually says:-

1.20 Extract ventilation terminals and fans, not including cooker extract hoods, should be installed to
comply with both of the following conditions.
a. As high as is practicable in the room.
b. A maximum of 400mm below the ceiling.

whereas your comment implies that cooker hoods are included.

Cheers.

 

[JuddlyFire]

@JuddlyFire - first, really good to see a knowledgeable fire safety person here. Second, can I just take issue with your point about extract fans must be ceiling mounted - I just checked the approved doc for my own interest and circumstance (OT for this thread) and it actually says:-



whereas your comment implies that cooker hoods are included.

Cheers.

Apologies my mistake.

I am a career Fire Fighter with >20 years experience, however my transition into Fire Safety is relatively new so I am going to frequent the forums to hone my advisory skill set before release into the wild. Thanks for the correction, I think I was incorrectly extending (and interpreting) Section 1.20’s height requirement to cooker hoods, contrary to Part F’s explicit exclusion. Perhaps cooker hoods also fall under Document J’s combustion safety rules, not just Part F’s general extract-fan height criteria?

Potential grey area as there are specific requirements for "Extract ventilation terminals and fans, not including cooker extract hoods" (as you pointed out) but no compliance conditions for cooker extract hoods... seems strange.

 

[noseall]

Apologies my mistake.

Also, look to separate out or not to confuse commercial with domestic. Whilst I agree there is some overlap, the two are distinct.