- Understanding Renewable Heat Incentives in the UK
For anyone who works with heating systems, whether that’s an installer on site, a facilities manager responsible for energy costs, or a homeowner investing in efficiency, the words renewable heat incentive still carry weight. The UK Renewable Heat Incentive (RHI) changed the shape of the industry, forcing both manufacturers and engineers to rethink how buildings are heated.
This UK renewable heat incentive guide explains what the RHI was, why it mattered, and how its principles continue to influence the systems being designed and fitted today. Although the scheme is now closed to new applicants, the standards it set remain part of everyday engineering practice.
Why the Renewable Heat Incentive Mattered
Before the RHI appeared, low-carbon heating was seen as expensive and experimental. Gas and oil ruled the market, and most clients couldn’t justify the higher upfront cost of heat pumps or biomass boilers. The government’s plan was simple: reward households and businesses for generating renewable heat, and the industry would follow.
And it did. Thousands of engineers retrained, new product ranges appeared, and the sector began to understand that carbon reduction wasn’t just policy,it was future business. Payments were linked directly to performance, so design accuracy, correct commissioning, and proper maintenance suddenly became the difference between profit and loss.
Two versions of the scheme operated in parallel:
- Domestic RHI – covering individual homes and small landlords.
- Non-domestic RHI – focused on larger installations for schools, offices, and housing developments.
Both shared a single purpose: to make renewable heating financially competitive with traditional fossil-fuel systems.
RHI Eligibility in the UK
Understanding RHI eligibility in the UK was essential for anyone involved in installation or specification. The scheme demanded high standards to protect its integrity, and those requirements still guide current incentive programmes.
To qualify, five main conditions had to be met:
Certified technology. Only systems approved under the Microgeneration Certification Scheme (MCS) could be used. That list covered air and ground source heat pumps, biomass boilers, and solar thermal systems.
Qualified installation. The installer also needed MCS accreditation. This ensured competence and provided a clear chain of accountability.
Energy-efficient property. Applicants required a current Energy Performance Certificate (EPC) proving that basic insulation measures, such as loft and cavity, were in place before fitting renewable equipment.
Accurate monitoring. Where metering was needed, it had to meet MID Class 2 accuracy and be located as shown on approved schematics.
Sustainable fuel. Biomass boilers could only burn fuel from the official Biomass Suppliers List (BSL).
The combined effect of these conditions was a huge improvement in build quality. Installers had to think about system balance, pressure control, and documentation in a way that was rare before 2014.
How the Scheme Operated
The idea was straightforward but revolutionary: pay participants for every kilowatt hour of renewable heat produced. Domestic customers received payments for seven years, commercial systems for twenty. The funds came from the central government and were administered by Ofgem.
To make those payments, the system output had to be calculated correctly. For domestic jobs, this was usually derived from the property’s heat-loss data; for non-domestic projects, it came from actual heat-meter readings. That pushed engineers to take measurements seriously.
The tariff rates changed quarterly, but they all worked on the same principle: better performance equalled better returns. A well-designed system could recover a significant share of its installation cost, while an inefficient one could fall short of expectations.
Main Technologies Supported
Air Source Heat Pumps
Air source heat pumps absorb heat from outside air and use a refrigerant circuit to upgrade it to a usable temperature. Modern inverter models continue producing heat even in freezing weather, though system design makes or breaks the result.
If the unit is undersized, it will run flat out all winter. Oversize it, and you’ll get short-cycling, noise, and higher electrical use. Good engineers balance those factors by matching the pump to realistic heat-loss figures, choosing a high-quality circulator such as a Grundfos or Lowara model, and controlling it through reliable equipment from Honeywell or EPH Controls.
Ground Source Heat Pumps
Ground loops draw heat from the earth, where temperatures remain stable throughout the year. The pipework must be carefully sized; too small a loop and the ground cools down, cutting efficiency.
In a school project near Bristol, engineers found that increasing the loop length by just 15 % lifted seasonal performance by nearly one whole point of COP. It’s a reminder that design margins matter.
Choosing efficient circulation gear, again, Grundfos is a common favourite, keeping pumping power low and reliability high.
Biomass Boilers
Biomass systems burn organic matter, typically wood pellets, to generate heat. They’re ideal for large rural properties or district systems where fuel storage is practical.
Combustion safety and flue layout are critical. Every installation must comply with Building Regulations Part J and include proper pressure management. Expansion vessels from Altecnic Ltd are often specified because they hold pressure consistently through temperature swings.
Solar Thermal Systems
Solar collectors pre-heat domestic hot water or support space heating. They’re usually paired with a twin-coil cylinder; brands such as Gledhill or Kingspan are often chosen for their build quality.
Good installation practice includes a correctly rated expansion vessel, pressure relief valve, and non-return valve to prevent unwanted thermal siphoning. These details seem minor, but they make the system safe and reliable.
How Components Keep a System Alive
An expansion vessel is to a heating system what a shock absorber is to a vehicle. It cushions pressure spikes caused by temperature changes. Without it, pipes rattle, valves weep, and seals fail.
Renewable circuits can experience wider temperature swings than conventional boilers, so vessel capacity and pre-charge are crucial. The same goes for pump selection; a mismatched pump can cause noise and cavitation, cutting system life.
Choosing recognised trade brands, Altecnic Ltd for vessels, Grundfos for circulation, and EPH Controls for control logic, saves countless call-outs later on.
A Real-World Example
During a commercial retrofit in Leeds, a team swapped three old atmospheric boilers for a cascade of air source heat pumps feeding a buffer tank. Within weeks, the client complained about fluctuating temperatures.
On inspection, the lead engineer found the buffer volume was half what it should have been. The pumps were cycling rapidly, and the controls weren’t sequencing properly. A larger expansion vessel and a variable-speed Grundfos circulator solved the issue. The system settled at a seasonal COP near 3.8, comfortably beating its design target.
The lesson from that job mirrors the RHI philosophy: efficiency starts with design accuracy.
The RHI’s Legacy in Modern Standards
Although no new applications are accepted, the RHI left a permanent mark on the industry. It created a baseline for professional competence that remains embedded in regulation and training.
- MCS accreditation is now the default expectation for any renewable installer.
- Documentation of heat-loss and commissioning data has become normal practice.
- Quality assurance on fuel sourcing and component choice is far higher than a decade ago.
These improvements ripple through every renewable project. Engineers who once specialised in fossil-fuel systems now design hybrids, combining condensing boilers with solar thermal or heat pumps, using smart controllers to maintain efficiency.
From RHI to the Boiler Upgrade Scheme
In 2022, the Boiler Upgrade Scheme (BUS) replaced the RHI. The focus shifted from long-term payments to upfront grants.
Homeowners can now receive £7,500 for air or ground source heat pumps and £5,000 for eligible biomass systems in rural, off-gas areas. The grant is paid directly to the installer, reducing the client’s initial cost.
While the funding model changed, the underlying rules didn’t. MCS accreditation, correct design, and compliance with Part L remain compulsory. The BUS also demands accurate documentation at the design stage, proof that system sizing and building insulation meet modern efficiency targets.
For engineers, that means getting it right the first time. There’s no performance-based payment to fall back on; a poorly performing installation damages reputation as well as margins.
How the RHI Continues to Shape the Market
The RHI did more than hand out money. It proved that renewable heat could work at scale. Manufacturers responded by investing in better compressors, smarter controls, and improved refrigerants. Training providers expanded MCS courses, and merchants like Heating and Plumbing World began stocking an ever-wider range of renewable components.
Even now, when an engineer specifies a heat pump or biomass system, many of the design checks, load calculations, flow-rate verification, and insulation assessments stem directly from RHI documentation procedures.
The scheme also changed client expectations. Businesses now ask for predicted running costs, carbon savings, and maintenance plans before committing. That level of transparency builds trust and keeps the industry honest.
Key Lessons for Trade Professionals
Design comes first. Whether under the RHI or BUS, accurate design delivers efficiency. Estimate heat loss carefully, size the plant correctly, and match components to real-world conditions.
Use proven products. Reliable brands, Grundfos, Altecnic Ltd, EPH Controls, help maintain pressure, control temperature, and prevent breakdowns.
Document everything. Keep commissioning sheets, flow rates, and serial numbers. If a grant auditor ever asks, that paperwork protects both the installer and the client.
Educate the user. A ten-minute handover explaining control settings prevents months of confusion. Many renewable systems underperform simply because occupants don’t understand them.
Stay current. Regulations evolve; Part L, MCS, and manufacturer training updates appear regularly. Keeping certificates up to date is good business as well as good practice.
Supporting Professionals Through Reliable Supply
With renewable installations increasing, product reliability is non-negotiable. Heating and Plumbing World remains the main hub for all professional-grade heating and plumbing products, supplying everything from control gear to expansion vessels.
Installers can source advanced circulation systems from Grundfos, durable pressure equipment from Altecnic Ltd, and smart controls from EPH Controls, all in one place.
For bespoke advice on component compatibility or bulk trade supply, professionals can get in touch directly with the technical support team.
Looking Ahead: The Road to Net Zero
The RHI’s end wasn’t the end of renewable heat; it was the beginning of mainstream adoption. The government’s goal of 600,000 heat pump installations per year by 2028 shows how far the sector has come.
Engineers now play a direct role in meeting national carbon targets. Every correctly sized pump, every well-balanced circuit, every properly commissioned cylinder contributes to that progress.
The path to Net Zero will depend on collaboration between installers, suppliers, and manufacturers. It will also rely on the professionalism that the RHI helped to instil, a belief that quality design and workmanship deliver measurable results.
For anyone in the trade, understanding how the RHI worked isn’t just history; it’s a foundation for what comes next. The principles remain the same: build efficiently, document thoroughly, and use products that last.