There is no regulation that tells you what diameter of gas pipe a commercial building needs. The law sets a duty to install and maintain gas fittings safely, and recognised technical standards give the method for sizing pipework to meet that duty. This article explains how commercial gas pipe sizing regulations fit together in practice, how the sizing calculation works in principle, why undersized pipework causes boiler faults, and what to ask your Gas Safe registered engineer before work begins.
It is written for property owners, landlords and facility managers across the North East and Northumberland who are replacing a boiler, extending a building or chasing poor heating performance. It is an explanation, not a design guide. Gas work of any kind, including sizing, alteration and testing, must be carried out by a Gas Safe registered engineer.
Two layers apply, and it helps to keep them separate.
The Gas Safety (Installation and Use) Regulations 1998 require that gas fittings are installed, maintained and serviced safely, and that anyone carrying out gas work is competent, which in Great Britain means being on the Gas Safe Register. Behind that sits the Health and Safety at Work Act 1974, which places general duties on employers, the self-employed and those in control of premises, including landlords, to protect people from the risks of the work and the workplace. Neither document contains a table of pipe sizes. For a wider overview of the duties involved, see our guide to commercial gas safety regulations in the UK.
Sizing is dealt with in standards. BS 6891 covers the installation of low-pressure gas pipework of up to 28 mm in size, and IGEM/UP/2 is the Institution of Gas Engineers and Managers standard for larger and commercial installations, including those involving bigger pipe sizes and higher pressures. Both are revised from time to time, and the scope of each depends on pipe diameter, operating pressure and the type of premises, so your engineer should confirm which edition and which standard applies to your site as of 2026.
This is why "regulations" is really shorthand. The law says the installation must be safe; the engineer follows the relevant standard to show that it is. If something goes wrong, working to a recognised standard is the most credible evidence that the duty was met.
The gas transporter or supplier is generally responsible for the equipment up to and including the meter. The pipework downstream of it, running to the plant room and the boilers, belongs to the premises and is what gets sized. That boundary matters because the meter and the supply feeding it have their own capacity limits, and those limits come into the calculation discussed next.
Sizing is an engineering calculation with a few clear inputs. Understanding them helps you judge whether a quote or design is realistic.
Gas loses pressure as it moves through pipe, and the loss rises with flow and with length. The test is that the pressure arriving at each appliance inlet stays within the range stated by the manufacturer, even when every appliance is firing at its maximum together. A design that works with one boiler running can fail when a full cascade calls for heat on a frosty morning.
Suppose, purely for illustration, that two plant rooms need the same total load. One sits close to the meter with a short, straight run. The other is at the far end of a building, with a long run and several bends. The second will need a larger diameter, or a different arrangement, to deliver the same pressure at the appliance. The load is identical; the geometry changes the answer.
Pipe material and supply pressure also affect the result. Internal roughness differs between materials, and an installation fed at low pressure behaves differently from one fed at medium or higher pressure, which is partly why different standards apply at different scales.
For these reasons no chart in an article, brochure or online forum should be used to pick a pipe size. Each site needs its own calculation by a competent, Gas Safe registered engineer who has seen the actual route and the actual load.
Undersized pipework rarely announces itself on the day it is installed. It shows up when demand peaks.
Typical symptoms include boilers that lock out or fail to reach high fire, burners that start and then drop out, and nuisance faults that cluster on the coldest mornings when every boiler is calling at once. The same boilers may behave perfectly well in October and struggle in January. Engineers often find that pressure at the appliance inlet falls sharply once several burners are running together. If you are seeing this pattern, our guide to a commercial boiler that keeps cutting out explains how to approach the diagnosis.
This is not only about comfort or running costs. Unstable inlet pressure can disturb burner performance and combustion, and poor combustion is a safety concern in any plant room. Modern boilers have safeguards that shut them down rather than run badly, which is why lockouts are common, but a safety shutdown is a warning to investigate, not something to reset repeatedly. Our article on the commercial boiler lockout reset procedure sets out what is and is not safe to do.
It is tempting to assume a new, larger boiler can simply be connected to the old pipe. It cannot be assumed. The existing pipework, and the meter and supply behind it, must be confirmed as capable of delivering the new total load before the boiler is specified. If a site is already showing lockouts on peak days, that is a prompt to have the supply assessed by a Gas Safe registered engineer rather than to keep resetting the plant.
Sizing is one part of a compliant installation. Several other requirements are assessed in the same project, and each can affect cost and programme.
Ask for commissioning records and, where sizing was carried out or revised, the calculation behind it. A competent engineer should be able to show you these, and keeping them on file helps you demonstrate that you have met your duties under the 1998 Regulations and the 1974 Act. Our guide to commercial gas safety record keeping requirements covers what to retain and for how long.
Check the engineer on the Gas Safe Register before work starts. Registration is divided into categories of work, and commercial gas work is not the same as domestic work, so confirm that the engineer's registration covers the work you are commissioning. The back of the Gas Safe ID card lists what they are qualified to do, and the Register can be searched online to verify it.
The order of work matters more than most project plans allow for. A sensible sequence looks like this:
Choosing the boiler first and checking the pipe afterwards is how projects end up with delays and expensive rework. A step-by-step view of the wider process is in our guide to commercial boiler installation.
If the meter or supply needs uprating to carry a bigger load, that work involves the gas supplier or transporter and not just your contractor. Lead times vary and are outside your engineer's control, so raise the question at the survey stage rather than after the boiler has been ordered. Ask what timescales apply to your site instead of assuming them. If you are weighing up budgets alongside this, our breakdown of commercial boiler installation cost in the UK shows what to plan for.
Many older commercial premises in Newcastle, Sunderland and across Teesside have been through decades of changes: former industrial units split into smaller tenancies, offices converted, plant added or removed. The result can be pipework that has been extended and modified several times without a fresh look at the whole system. North East winters expose those weaknesses, because the peak demand days are when everything fires together.
As of October 2026 the cold months are close. If you intend to replace or add plant this season, or you have had peak-time faults, book surveys promptly. Surveys, supplier enquiries and any pipework alterations all need to be finished before demand rises, and an emergency callout in January is a poor time to discover that the supply is inadequate.
You do not need to be an engineer to hold a contractor to account. These questions are reasonable to ask, and a competent firm will answer them without hesitation.
Finally, make sure everyone on site knows what to do about a suspected leak. If you smell gas, leave the area, do not operate light switches or electrical equipment, avoid naked flames, and call the National Gas Emergency Service on 0800 111 999. Do this from a safe distance and do not attempt to find or fix the cause yourself. It is also worth having a written plan in place, and our commercial gas emergency procedure template guide shows how to build one.
Commercial gas pipe sizing is a calculated, standards-based job. It depends on the load, the route and the supply, and it belongs with a Gas Safe registered engineer who can show their working. Treat any claim of a quick, one-size answer with caution, and never connect new plant to old pipework on assumption.
Commercial Boiler Solutions is Gas Safe registered and carries a 5-star customer rating, serving commercial properties across the North East and Northumberland, from Tyneside and Wearside to Teesside and North Yorkshire. We can survey your existing supply, advise on upgrades, and support your plant through maintenance and annual inspections, with emergency callouts available if something fails.