Gas Water Heating for Schools: What You Actually Need to Know 

A practical guide for school business managers, local authorities, installers, and contractors. 

Schools burn through enormous amounts of gas. That’s not an opinion. On average, heating and hot water account for 40% of a school’s overall gas consumption (Energy Sparks). Water heating alone can consume 30% of a building’s energy demands (Adveco). Those are big numbers. And yet in most schools, the hot water system sits in a plant room nobody visits, running on equipment that’s been there since the building went up. Given that the National Audit Office notes the estimated initial design life of school buildings is 60 to 80 years for non-system-built and 30 to 40 years for system-built (NAO), you can guess how old some of this kit is. 

The money side makes uncomfortable reading. Average annual energy costs for 2023/24 were £38,214 for primary schools and £190,897 for secondary schools (UK Parliament). Those figures have climbed sharply, up from £33,078 and £169,338 respectively the previous year. When 40% of your gas bill is going on heating and hot water, even modest efficiency improvements translate into real savings. Savings that could be going toward teaching, staffing, or facilities instead of feeding an aging boiler. 

What the Data Actually Shows 

The evidence base here is solid. A study analysing 13,569 schools, representing about 69% of primary schools and 58% of secondary schools in England, gives us a proper picture of energy consumption patterns across the education estate (Applied Energy). The DfE issued an energy survey to all schools and trusts in May 2022 asking about gas and electricity contracts, including prices and consumption (DfE). The ND-NEED 2024 report provides further insight into electricity and gas consumption of non-domestic buildings in England and Wales (ND-NEED). We’re not short on data. We’re short on action. 

Schools that do act see results quickly. During the 2023/24 academic year, the average reduction in energy use achieved by Energy Sparks schools was 10% versus the previous academic year (Energy Sparks). Average emissions reduction for primary schools was 7 tonnes CO2, with an average cost saving of at least £5,000. Secondary schools achieved average savings of 26 tonnes CO2 and £21,000 (Energy Sparks). One case study school reported a 48% reduction in out of hours gas use since joining the programme (Sheffield Hallam University). That last figure is particularly telling. Schools empty out at 3:30pm and often don’t reopen until 7:30am. If your system is burning gas throughout those hours without producing useful hot water, you’re wasting money every single night. 

School Energy Savings: The Numbers 

At a programme level, the Carbon Trust’s Collaborative Low Carbon Schools Service aimed to help local authorities identify £40 million of annual energy savings across their regions’ schools, supporting over 400 pilot schools to implement cost effective energy saving measures (The Carbon Trust). That’s a national scale acknowledgement that school energy efficiency is a serious budgetary issue, not a nice to have. 

Legionella, Storage Temperatures, and Compliance 

Schools can’t just think about efficiency. They’ve got a legal obligation to manage Legionella risk, and hot water systems are right at the centre of that. The Health and Safety Executive is clear: hot water should be stored at least at 60°C and distributed so it reaches 50°C within one minute at the outlets (HSE). Legionella bacteria multiply between 20°C and 45°C and do not survive above 60°C (HSE). 

This matters enormously when you’re upgrading or replacing water heating systems. Any new system must maintain these temperatures reliably. It’s not negotiable. Schools that have moved to heat pump-based systems, for example, have found creative solutions. One case study notes booster heaters pasteurising stored hot water at 70°C two or three times a week using 9kW electric heaters in cylinders (CIBSE Journal). Gas water heaters handle this naturally because they produce water at these temperatures as standard. That’s one of their practical advantages in a school setting. No supplementary pasteurisation needed. No complex controls to manage bacteria risk. The system just works at the right temperature. 

For installers and contractors working on school projects, always verify that any new or replacement system meets HSE Legionella guidance. It’s one of those things that’s easy to tick off at the design stage but causes real problems if it’s missed. A school’s duty holder should have a Legionella risk assessment in place, and your system needs to demonstrate compliance with it. 

What Schools Are Actually Doing Right Now 

The Public Sector Decarbonisation Scheme has been the main funding driver for school heating upgrades. The numbers are significant. Around 60 schools are being equipped with more than 180 air-to-water heat pumps through one programme alone (Carrier). A £5 million grant-funded programme replaced existing gas boilers in five schools with heat pump-based systems (CIBSE Journal). Schools Week reported that 222 projects won funding in one tranche, with 47 projects worth £37 million listed as schools (Schools Week). 

Individual school case studies show the range of approaches being taken. A primary school secured a £170,920 PSDS Phase 3a grant to install a ground source heat pump as the preferred heating and hot water solution (Salix Finance). Another school retrofit achieved a 77% reduction in emissions from heating and hot water after replacing aging gas heating with ground source heat pumps and solar PVT, an installation that included 18 boreholes, each 127 metres deep (Kensa). A £120,000 grant-funded education project reported 15 tonnes of CO2 saved per year and annual energy savings of £4,000 (Mitsubishi Electric). 

Heat decarbonisation planning is also gaining traction at a local authority level. Lambeth Council commissioned a heat decarbonisation plan for maintained schools in June 2022, funded via Salix’s Low Carbon Skills Fund (Lambeth Council). One school’s plan delivered 10 Category 2 and Category 3 energy-saving projects across two buildings (Maple Project Solutions). DfE guidance explicitly focuses on reducing energy use for heating and hot water across the school and FE college estate (GOV.UK). 

Where Gas Water Heating Still Makes Sense in Schools 

There’s an obvious push toward heat pumps in the education sector, driven largely by PSDS funding. But that doesn’t mean gas water heating has become irrelevant overnight. Far from it. The reality on the ground is more complicated than the policy direction suggests. 

Plenty of schools aren’t eligible for PSDS funding, can’t afford the capital outlay for a full heat pump conversion, or have buildings that aren’t suitable for the technology. System-built schools from the 1960s and 70s with limited external space, poor insulation, and ageing infrastructure often need the existing gas system replaced or upgraded before any longer-term decarbonisation work can happen. You can’t install a heat pump system in a building that needs a new roof first. 

Modern condensing gas water heaters offer a practical middle ground. They meet Part L minimum efficiency requirements, deliver reliable hot water at Legionella safe temperatures without supplementary equipment, and have lower capital costs than heat pump alternatives. For a school that needs its hot water system replaced this year rather than in three years when funding might become available, a condensing gas unit is a sensible, compliant, cost-effective choice. 

There’s also the hybrid approach. Some schools are installing condensing gas water heating alongside heat pumps, using gas for domestic hot water where the temperature requirements make it the more straightforward technology, and heat pumps for space heating where lower flow temperatures work well. This isn’t an either-or conversation. It’s about choosing the right technology for each application within the building. 

Consider the numbers honestly. A ground source heat pump installation with 18 boreholes at 127 metres deep is a major civil engineering project for a school site. It works brilliantly when the funding is there and the site conditions suit it. But a condensing gas water heater replacement can be done during half term with minimal disruption to the school. For many school business managers juggling tight budgets and tighter timescales, that practical reality matters as much as the long-term carbon ambition. The right answer depends entirely on your school’s specific circumstances, its building condition, its budget, its timeline, and its access to funding. 

Practical Steps for Schools Considering an Upgrade 

Start with your data. If your school doesn’t have sub-metering on its hot water system, you’re making decisions blind. You need to know how much gas you’re using for hot water specifically, when you’re using it, and crucially, how much you’re using outside of school hours. That 48% out of hours reduction one school achieved tells you there’s probably waste in your system right now that you don’t even know about. 

Get a heat decarbonisation plan. Even if you’re not ready for a full system replacement, understanding your building’s energy profile and the options available helps you plan capital expenditure properly. Salix’s Low Carbon Skills Fund can help cover the cost of these plans for eligible schools. Having a plan in place also positions you to move quickly when PSDS or other funding rounds open. 

If you’re replacing a gas water heater now, specify condensing. The efficiency gain over a non-condensing unit is roughly 20%, which on a secondary school’s energy spend could mean several thousand pounds a year. Make sure the replacement system maintains water at 60°C minimum for Legionella compliance. Factor in ancillary works like flue upgrades and condensate drainage. And consider smart controls and metering from the outset rather than retrofitting them later. 

For local authorities managing multiple school sites, the coordinated approach matters. Lambeth’s portfolio-wide heat decarbonisation plan is the right model. You get economies of scale on procurement, you can prioritise buildings by age and condition, and you avoid the piecemeal approach where each school makes isolated decisions that may not align with a longer-term estate strategy. 

Installers and contractors should be proactive here, too. If you’re already working in schools on general maintenance or other building services, flagging the condition of ageing water heating equipment adds value to the relationship. School business managers are often not heating specialists. They rely on the trade to tell them when something needs attention. Offering an energy audit or pointing out that a 25-year-old non-condensing water heater is costing the school thousands more than it needs to is the kind of advice that wins long-term contracts. Pair that with knowledge of PSDS funding rounds and Salix grants, and you’re positioning yourself as a genuine partner rather than just someone who fixes things when they break. 

The NEED dataset, last updated June 2025, provides the broader data framework for understanding energy use and efficiency in Great Britain’s non-domestic buildings (data.gov.uk). Schools sit within that picture, and the trajectory is unmistakable. Buildings that improve their energy performance now will face lower costs, easier compliance, and better outcomes for years to come. 

The bottom line for schools is straightforward. Energy costs are rising. The existing systems in most school buildings are inefficient by modern standards. Whether you’re heading toward heat pumps, upgrading to modern condensing gas, or implementing a hybrid approach, doing nothing is the most expensive option. The schools that have already acted are saving thousands of pounds annually and cutting tonnes of CO2. The data is clear. The funding mechanisms exist. The technology works. It’s a question of when, not whether.