Gas Cooktop Clearances and Connections: What the Standard Actually Requires

Most gas cooktop problems we get called to are not faults. They are installations that were never right, usually because somebody fitted an appliance without checking what has to sit around it and how it is allowed to be connected.

Gas cooktop installation in New Zealand is governed by AS/NZS 5601.1, the gas installations standard. Here is what it requires, in plain terms, so you know what to ask for.

The clearances around a hob

The manufacturer’s specification comes first. Where they do not specify, and always for overhead clearance, the standard sets minimums. Clause 6.10.1.1 is the one.

Our own sketch of the requirement, not to scale. A is measured to the surface the pots sit on, B from the edge of the nearest burner, and C is the height the wall has to be protected to. The manufacturer's specification takes precedence, and where two figures apply the greater clearance always wins.

Overhead (A). At least 650 mm from the hob surface to a rangehood, and at least 750 mm to an exhaust fan. Where the manufacturer of either the appliance or the rangehood specifies more, the greater figure wins.

Replacing an existing hob. The standard allows 600 mm from the highest part of the highest burner to the rangehood when an appliance is being replaced in an existing installation, unless the manufacturer’s instructions require more. This matters in older kitchens where there is simply not 650 mm available, and it is worth knowing before anyone tells you the whole rangehood has to move.

Any other surface overhead. A downward-facing combustible surface closer than 650 mm has to be protected across the full width and depth of the hob, and in any case cannot be closer than 450 mm.

To the side (B and C). If the distance from the edge of the nearest burner to a vertical combustible surface is less than 200 mm, that surface must be protected to a height of at least 150 mm above the burner, across the full width or depth of the cooking area.

Oven flue. On an elevated cooking appliance, at least 200 mm from the oven flue outlet to any surface above it.

The splashback question

This comes up on nearly every kitchen, so it is worth being precise.

If the appliance comes fitted with its own splashback, you do not need to separately protect the rear wall, provided that splashback actually covers what needs covering: any combustible surface within 200 mm of the nearest burner, up to at least 150 mm above the burner.

A separate glass or tiled splashback installed by the kitchen company is a different thing from an appliance splashback, and whether it satisfies the requirement depends on what it is made of and how far it extends. Tiles and toughened glass are the usual answers in an Auckland kitchen. The standard has a whole appendix on acceptable facing and backing materials, and the detail matters more than people expect, so the time to confirm it is at design stage rather than after the tiler has finished.

How it is allowed to be connected

This is where we most often find existing work that is not compliant, and the rules differ by the type of appliance.

Under-cooker connection point: no hose, no semi-rigid connector. Where a freestanding cooker has its connection point underneath, clause 6.10.1.10 prohibits connecting it with a hose assembly or a semi-rigid connector outright. There is no “as long as it is short” version of this. If you look under a freestanding cooker and find a yellow flexible line going into an under-cooker connection point, that installation is not compliant, and it is one of the more common things we find.

Elevated freestanding cookers may be connected with either annealed copper pipe or a hose assembly, provided the connection is long enough that the appliance can be pulled out to disconnect it.

Inbuilt ovens must use annealed copper for the final connection, unless the oven is specifically certified for a hose connection in the manufacturer’s instructions. Again it has to allow the oven to be withdrawn from the recess.

Indoor LPG cylinders feeding a cooktop have their own set of conditions under clause 6.10.1.8: a hose assembly no longer than 1 m, no jubilee clips, copper piping wherever the line passes through a wall or a cupboard, a cylinder no larger than 9 kg, not in the same compartment as a power point or an appliance like a dishwasher or waste disposal, and a low-level vent to outside of at least 1000 mm². The standard’s own note says it plainly enough: cylinders are better outside.

Replacing a cooktop: get the model number first

The practical problem with a like-for-like replacement is not gas. It is the hole in your benchtop.

Cut-out dimensions vary between models, and a replacement with a different cut-out means either altering a benchtop or replacing it. On a rental in Unsworth Heights we found the existing cooktop was an older model with no parts available, so repair was not an option. Rather than guess, we went back to the manufacturer, confirmed the cut-out size of the existing unit, and then put up replacement options that fit that opening. The bench never had to be touched.

So when you ring us about replacing a cooktop, the most useful things to have are the model number of the existing appliance, whether it runs on natural gas or LPG, and a photo of the installation. That is usually enough to tell you whether a straight swap is available.

Planning a cooktop, or suspicious about one that is already in? Send us a photo of the hob and of what is underneath it.

Common questions

My rangehood is lower than 650 mm. Does it have to move?

Not necessarily. If you are replacing the appliance rather than doing a new installation, the standard allows 600 mm from the highest burner to the rangehood, so long as the appliance manufacturer does not require more. Below that, something has to change, and moving a rangehood is usually cheaper than it sounds because the ducting is generally the hard part rather than the unit.

Can I use a flexible hose behind my freestanding cooker?

It depends entirely on where the connection point is. A connection point on the wall behind the appliance, at an appropriate height, can use a hose assembly within the rules in clause 5.9. A connection point underneath the cooker cannot use one at all. Those look similar to a homeowner and are completely different in compliance terms, which is why a photo is worth more than a description.

Does my gas certificate depend on the tiling?

On a cooktop, partly yes, because certification covers the installation as a whole, and the surfaces around the hob are part of what makes it compliant. That is why we ask for a photograph of the finished installation showing the wall surfaces behind the hob and the rangehood above it before the certificate is issued. Those usually go in after we leave.

I bought the cooktop myself. Will you install it?

Yes, and it is common, but check two things before it arrives: that it is the right gas type for the property, since natural gas and LPG appliances are not interchangeable without conversion, and that the cut-out matches. An appliance in a box on the day that turns out to be the wrong gas type or the wrong size is the most avoidable delay in this work.

Who is responsible if an existing installation turns out to be non-compliant?

If we find something like a hose on an under-cooker connection during other work, we will tell you and put it in writing, because it is a safety issue rather than a preference. Fixing it is usually a small job. Where a property is being sold or has changed hands, this is exactly the sort of thing a building inspection picks up, so it is better found by us than by a buyer’s inspector.