Facebook pixel
new boiler

Get a new boiler

Fixed price boilers, next day

See boiler prices
new air conditioning

Air Conditioning

Get a quote
new heat pump

Heat Pumps

Coming soon

new ev charger

EV Chargers

Get a quote
boiler servicing

Boiler Servicing

Get a quote

Last updated: 12th February, 2024


This Valentine's Day we’re asking - Does the size of your pipe really matter?

This Valentine's Day we’re asking - Does the size of your pipe really matter?

Key takeaways

  • Combi boilers deliver water instantaneously, therfore need pipwork that can withstand the pressure.
  • Gas Safe advise all modern boilers, especially combis, require 22mm gas pipes.
  • iHeat will replace any 15mm pipes with 22mm on installations and conversions when possible, for free.

This Valentine’s Day we want to let you in on a dirty little secret…

It’s true, size does matter, especially when it comes to getting you hot this February.

In this blog we’ll be exploring new size regulations for boiler gas pipes, and telling you how if the job needs it, our engineers can lay some pipe, no problem at all.

Valentine’s Done Right

The sensory rush of hot water dancing down the back of your neck, soothing steam matching the temperature of your skin, the cool sting of the shower glass on the palms of your hands…

Not quite the same if you both have chattering teeth and the water is half frozen.

You may need a thicker pipe to finish the job.


What is a Gas Pipe?

A gas pipe or ‘boiler gas pipe’ is a branch line from the mains building line or ‘gas supply pipe’.

Boiler gas pipes split off from this mains connection and run to the gas powered appliances around the home, i.e. a boiler.

Gas pipes deliver gas from the meter to be used as fuel by the boiler to generate central heating and domestic hot water.

Boiler gas pipes are commonly constructed from copper or alternatively some types of pipework can be constructed of steel, brass or aluminium.

Why Does Size Matter?

Gas pipes can vary in size (inc. 15, 22, 28 or 35mm) often depending on the distance between the gas meter and the boiler, the boiler’s brand/model and the size of the boiler.

Petite Combis Need Big Pipes

Older properties have usually been fitted with 15mm diameter pipes, newer combis may be more compact but require a larger deposit of gas in a less amount of time than most traditional boilers.

Combis have a more substantial gas demand due to their instantaneous hot water delivery as opposed to cylinder storage. This hot and fast delivery means a combi is suited to being filled by thicker pipes, to supply as much gas as possible.

System or regular boilers heat water in a slower process involving a hot water cylinder, not needing high volumes of gas in as short a space of time as a combi, meaning often 15mm can be sufficient.

For a combi to be operating as optimally as it should, providing you with central heating and hot running water, Gas Safe states its pipes should be no smaller than 22mm.

If the pressure is too much for the pipe it could burst or leak, leading to more serious plus potentially dangerous problems.

Let’s face it, bigger pipes can heat up your bedroom and make those shared showers truly tingle on February the 14th.

How iHeat’s Engineers Can Plug the Gap

Changing or upgrading any gas pipes on your boiler should be left to the experts, all of our engineers here at iHeat are Gas Safe registered and pack the tools to finish the job.

During a boiler installation or conversion, If the run (length of fitted gas pipe) that needs replacing is a standard length, our engineers will replace any 15mm pipe with new rock hard, rigid 22mm piping, and at no extra cost!

(In some cases if the pressure is fine with lower sized piping there is no need to change from a manufacturer warranty side of things, but Gas Safe may still advise an upgrade.)

iHeat's approach to gas pipe upgrades during new boiler installations is precisely targeted to meet the system's specific needs. They will replace 15mm gas pipes with the recommended 22mm diameter, but only if the millibar pressure in the existing pipe is too low for the boiler to function optimally.

This policy ensures that pipe replacements are carried out solely when essential for improving the system's efficiency and safety, following detailed assessments of gas flow and pressure requirements

New Boiler Costs

Boilers can be a daunting purchase for many people as they’re an appliance with a lot of responsibility, providing heat for you and your family is something you want to get right. Boilers aren’t exactly a quickly disposable item either, potentially lasting you a decade.

Effectively, new boiler cost can be split into two segments: the first is the actual boiler itself (unit price), and the second is the cost of the boiler being installed (set up) in your property by an expert engineer. 

Here at iHeat, we want to remove all of this undue stress and make the decision making process of upgrading to a new central heating system, as easy as possible.

Boiler costs can vary depending on a number of factors including their brand, model, fuel, output, warranty, labour and installation type. Typically a new boiler will cost between £1,845 and £3,500, below is a list of average boiler installations offered by iHeat (guide only).

Installation Type

Price (inc VAT)

Combi to combi swap


Get a quote

System to combi conversion


Get a quote

New boiler install


Get a quote

Back boiler to a combi


Get a quote

System to system


Get a quote

Frequently Asked Questions

Why Is Choosing the Right Gas Pipe Diameter Critical for Boiler Efficiency and Safety?

The correct gas pipe diameter is crucial because it directly impacts the efficiency and safety of your boiler. Opting for larger diameters facilitates improved gas flow, which is essential for the optimal performance of modern boilers.

What Gas Pipe Diameter Is Recommended for Modern Combi Boilers?

For modern combi boilers, Gas Safe recommends a minimum pipe diameter of 22mm. This size ensures that the boiler receives adequate gas pressure and flow, which is vital for efficient operation.

Can a 15mm Gas Pipe Be Used for New Boiler Installations?

Although a 15mm gas pipe might suffice for some systems, upgrading to a 22mm diameter is highly recommended to achieve the best performance from your new boiler.

What Are the Consequences of Using a Gas Pipe with Insufficient Diameter?

Utilizing a gas pipe with a diameter that's too small can lead to a reduced gas flow, which may impair the boiler's efficiency and pose potential safety risks.

Is Professional Installation Necessary When Upgrading My Gas Pipe Diameter?

Absolutely, any modifications to your gas piping, including upgrading the diameter, should be conducted by a Gas Safe registered engineer to ensure adherence to safety standards and regulatory compliance.

How Does iHeat Ensure Optimal Gas Pipe Diameter During Boiler Installation?

iHeat is committed to ensuring your boiler operates efficiently and safely. They offer complimentary upgrades from 15mm to 22mm pipes during boiler installations and conversions, when feasible, to meet current standards.

Why Might Replacing My Gas Pipe Be Necessary When Installing a New Boiler?

Replacing your gas pipe during a new boiler installation might be necessary to conform to the latest standards for gas pressure and flow, thereby enhancing the system's efficiency and safety.

Stephen Day profile photo
Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.