Heating upgrades should be sequenced around the completed building, not around a generic heat-pump specification. Before selecting a system, establish the likely heat demand, fabric condition, emitter performance, hot-water needs, electrical capacity, siting and the specialist design or funding route that will apply.
Competence boundary: heat-pump system design, MCS certification, refrigerant work, electrical work and BUS applications require the appropriate competent or registered provider. TCM can undertake or coordinate building work related to the project, but this page does not claim that TCM itself is the MCS-certified BUS installer.
The Fabric-First Principle: Why Insulation Comes Before the Heat Pump
Fabric condition matters because heat demand affects the heating-system design, but "fabric first" is not a universal instruction to complete every insulation measure before a heat pump can be considered. Assess the actual building and planned works, then coordinate useful fabric improvements with the heating design.
Heat-loss assessment
Assess the completed property's room-by-room heat demand rather than selecting capacity from floor area or an old boiler size.
Building fabric
Review insulation, windows, airtightness, ventilation and moisture interactions as part of the wider refurbishment or extension design.
Emitters
Check existing radiators or underfloor heating against the proposed system conditions; retain or change them according to the actual design.
This page does not publish generic insulation costs, percentage heat-loss reductions, CoP ranges or payback periods. Those figures depend on the existing property, selected measures, installed system and current energy prices.
Radiator Sizing: Why Your Existing Radiators May Need Changing
Emitter suitability depends on room-by-room heat loss and the output each radiator or underfloor-heating zone can provide at the proposed system conditions. A lower design flow temperature can change the required emitter output, but there is no universal radiator-upsizing percentage that applies to every property.
During an extension or refurbishment, the design can coordinate retained radiators, new emitters, underfloor heating and pipe routes before finishes are complete. The responsible heating designer or installer should confirm the final emitter and hydraulic design.
The Boiler Upgrade Scheme (BUS) in 2026: What You Need to Know
| Current category | Current grant evidence | Important qualifier |
|---|---|---|
| Air-to-water heat pump | £7,500 standard; £9,000 for eligible off-gas-grid oil/LPG replacements | Eligibility is scheme- and property-specific |
| Ground-source / water-source heat pump | £7,500 standard; £9,000 for eligible off-gas-grid oil/LPG replacements | Ground/source and scheme requirements still apply |
| Air-to-air heat pump | £2,500 for eligible residential installations | Not all properties or installations qualify |
GOV.UK updated BUS grant categories on 21 July 2026. The £9,000 off-gas-grid uplift is time-limited to 31 March 2027. Grant values and eligibility can change, so verify the current GOV.UK grant notice and Ofgem BUS guidance before budgeting the grant.
BUS is installer-led. The applying installer must be MCS-certified for the relevant technology, and product-list inclusion alone does not prove the whole installation is eligible. Treat grant funding as conditional until the responsible installer has confirmed the current route.
Illustrative Project-Planning Pattern: Coordinating a Heat Pump with a Rear Extension
A useful planning sequence is to establish the extension/refurbishment brief, assess the completed building's heat demand, coordinate fabric and emitter decisions, reserve service routes and then obtain the specialist heat-pump design. This is an illustrative workflow, not a TCM case study or a claim that every project follows the same order.
The current Experience Inputs Register contains no approved TCM heat-pump project, measured saving or grant outcome for publication. Any future first-party example needs source, methodology and permission before it is presented as TCM experience.
When to Time a Heating Upgrade: The Building Project Window
A building project can make heating work easier to coordinate because floors, walls, ceilings or service routes may already be accessible, but the cost and disruption benefit is project-specific. Do not assume that a heat pump is automatically cheaper simply because an extension is underway.
- Resolve heat-loss and system-design information before closing up affected service routes.
- Coordinate emitters and underfloor-heating interfaces with floor and room finishes.
- Confirm electrical, hot-water and external-unit requirements before finalising the wider building programme.
- Keep the MCS/BUS installer role separate from general building-work coordination.
Upgrading Windows During an Extension: The Overlooked Opportunity
Window replacement can be considered alongside an extension where the existing units, comfort, airtightness or refurbishment brief justify it. Current Building Regulations apply to the relevant new or replacement elements, but this page does not prescribe one glazing type or claim a universal percentage reduction in heat loss.
Compare actual product performance, solar gain, ventilation, overheating, acoustic needs, frame condition and project cost. Any effect on heat-pump capacity or EPC rating should come from the project-specific assessment rather than a standard saving figure.
Frequently Asked Questions
Yes. An extension or refurbishment can be a useful time to coordinate heat-loss assessment, insulation, emitters, hot-water provision, electrical capacity and pipe routes. The heat-pump system should be designed for the completed property rather than sized from a generic house type. TCM can coordinate relevant building work, while heat-pump design and BUS eligibility remain with the appropriate specialist route.
Yes. An extension or refurbishment can be a useful time to coordinate heat-loss assessment, insulation, emitters, hot-water provision, electrical capacity and pipe routes. The heat-pump system should be designed for the completed property rather than sized from a generic house type. TCM can coordinate relevant building work, while heat-pump design and BUS eligibility remain with the appropriate specialist route.
Current BUS values depend on the technology and, for some off-gas-grid properties, the heating system being replaced. Standard grants include £7,500 for eligible air-to-water and ground-source systems and £2,500 for eligible air-to-air systems; eligible off-gas-grid oil or LPG replacements can receive £9,000 for air-to-water or ground-source systems until 31 March 2027. Check current GOV.UK/Ofgem guidance before budgeting a grant.
Current BUS values depend on the technology and, for some off-gas-grid properties, the heating system being replaced. Standard grants include £7,500 for eligible air-to-water and ground-source systems and £2,500 for eligible air-to-air systems; eligible off-gas-grid oil or LPG replacements can receive £9,000 for air-to-water or ground-source systems until 31 March 2027. Check current GOV.UK/Ofgem guidance before budgeting a grant.
Not automatically. Emitter suitability depends on room-by-room heat loss, the proposed flow temperature and each emitter's output under the designed conditions. Some existing radiators can be retained; others may need changing. The answer should come from the project heat-loss and emitter design rather than a universal upsizing percentage.
Not automatically. Emitter suitability depends on room-by-room heat loss, the proposed flow temperature and each emitter's output under the designed conditions. Some existing radiators can be retained; others may need changing. The answer should come from the project heat-loss and emitter design rather than a universal upsizing percentage.
Fabric improvements can reduce heat demand, but there is no universal upgrade order or payback rule. Assess the existing insulation, windows, airtightness, ventilation, moisture condition and planned building work, then decide which improvements make sense alongside the heating design. The goal is coordinated whole-building performance, not completing a fixed checklist before a heat pump can be considered.
Fabric improvements can reduce heat demand, but there is no universal upgrade order or payback rule. Assess the existing insulation, windows, airtightness, ventilation, moisture condition and planned building work, then decide which improvements make sense alongside the heating design. The goal is coordinated whole-building performance, not completing a fixed checklist before a heat pump can be considered.
Not by a guaranteed number of bands or percentage. EPC outcomes and running costs depend on the completed property, assessment method, seasonal system performance, heating demand, tariffs, controls and household use. Treat any modelled saving or EPC result as property-specific evidence rather than a standard TCM promise.
Not by a guaranteed number of bands or percentage. EPC outcomes and running costs depend on the completed property, assessment method, seasonal system performance, heating demand, tariffs, controls and household use. Treat any modelled saving or EPC result as property-specific evidence rather than a standard TCM promise.
BUS is installer-led. The installer applying for and redeeming the voucher must be MCS-certified for the relevant technology and meet the scheme requirements. TCM's building-related heat-pump scope does not itself establish MCS installer status, so the responsible BUS installer must be confirmed for the individual project.
BUS is installer-led. The installer applying for and redeeming the voucher must be MCS-certified for the relevant technology and meet the scheme requirements. TCM's building-related heat-pump scope does not itself establish MCS installer status, so the responsible BUS installer must be confirmed for the individual project.
Related Guides & Articles
Heating Upgrade Enquiries
Contact TCM to discuss building or refurbishment work around a heating upgrade. Heat-pump design, MCS/BUS responsibility, electrical work and grant eligibility remain on the appropriate specialist route.
Contact TCM