What is the vertical height of gas cooker hot zone?

[XEman]

Our kitchen rip out starts on Monday, following four week kitchen update at our daughter's house. We are scrapping the cooking range and going to a more normal sized gas four burner cooker. The plan is to install an angled extractor above the hob. But like most things its not a simple "just do it". Our installer says that the extractor must be 800mm above the level of the hob burner. Nothing I have seen has equalled 800mm for the vertical height of the hot zone for gas cooker/hob installations. Many seem to quote 750mm on various websites. and appliance suppliers but without reference to a source reference. The AEG cooker installation instructions say 650mm, and the Franke hood say 650mm too. On that basis both are okay for a 650mm minimum height separation. So I looked at the Gas Safe website, but it doesn't give a lot of insight as I am not registered for it. However, I found Technical Bulletin 005(A) dated July 2015 which deals with ventilation requirements for gas cookers in internal kitchens.The only information that was relevant was:

"If the extraction is via a cooker hood, it should be installed paying due regard to both the hood and cooker manufacturers installation instructions" There is reference to a Gas Safe TB 095 dealing with extract fans and open fluid appliances, but I can't find anywhere to view it.

I then went to the Health and Safety Executive website, but their gas safety helpline wasn't available. However, reading the most recent guidance "HSE Safety in the installation and use of gas systems and appliances, Gas Safety (Installation and Use) Regulations 1998 as amended July 2018 L56." the advice guidance was in Part E Gas Appliances Regulations 26 and 27. It stated:

"261 Minimum clearance distances for operation, inspection and maintenance purposes are normally specified in manufacturers’ instructions for the installation of appliances."

And that's it in a nutshell. I am none the wiser as to where the "trade" get their 750mm vertical height separation between gas hob and hood. Per se it's not gas safety installation issue, more one of fire safety. But does anyone know why the 'trade" use 750 mm, or more when two authoritative bodies advise to align with alliance makers recommendations?

So what is the basis for the often quoted 750mm distance? Is there a minimum legal requirement specified anywhere?

 

[JohnD]

If the cooker hood is placed lower than your height, you will bang your head on it.

I can't see any benefit in putting it lower.

 

[XEman]

The benefit is that it will work more efficiently and require a lower fan speed than if its height is so much higher than either manufacturer specifies. At 6ft 4 inches I am used to knocking my head, but the 5ft 2 inch prime user doesn't have that problem. The angled extractor hobs don't extend outwards as far as a conventional horizontal hob does.