Heat Pump for New Build vs Retrofit Decisions UK 2026

Heat pump new build vs retrofit UK 2026: design integration, Future Homes Standard, sizing for excellent insulation, install cost differences.

Modern UK new build house representing heat pump install in new build vs retrofit decisions
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By Rob Griffiths15 June 2026 · 6 min read

UK new build vs retrofit heat pump installs face different design constraints, regulatory requirements, install costs, and achievable SCOP. This guide covers the structural differences + what to prioritise in each context.

Future Homes Standard - new build context

What the regs require from 2025.

The Future Homes Standard applies to new UK builds from 2025:

  • Gas boilers banned in new builds. All new homes must use low-carbon heating - effectively heat pump (some new builds use direct electric or district heating but heat pump dominant).
  • SAP 10 calculation - updated Standard Assessment Procedure includes heat pump efficiency calculations + lifecycle carbon assessment.
  • Fabric First standards - U-values for walls, roof, floor, glazing significantly tighter than 2013 Part L baseline.
  • Air tightness - 5 m3/h/m2 vs older 10 m3/h/m2; combined with MVHR (Mechanical Ventilation Heat Recovery) for ventilation.
  • Photovoltaics + renewables - heat pump often paired with rooftop PV by design.

Result: new build heat pump installs designed into the property from day one, with envelope tuned for heat pump efficiency. Very different starting point from retrofit.

Sizing differences - new build vs retrofit

Heat loss differences drive heat pump size.

Typical UK 3-bed semi heat-loss comparison:

  • Future Homes Standard new build (2025+): ~3.5-5 kW heat demand at design conditions. Heat pump 5 kW typical.
  • Modern build 2013+ (Part L 2013): ~5-7 kW heat demand. Heat pump 5-7 kW typical.
  • 1990s-2010s build: ~6-8 kW heat demand. Heat pump 7-9 kW typical.
  • Pre-1990 build (uninsulated cavity / solid wall): ~8-12 kW heat demand. Heat pump 9-12 kW typical.

New build heat pump sizing typically 30-50% smaller than retrofit equivalent for same property size due to better insulation. Smaller heat pump = lower unit cost (GBP 1,500-3,000 difference) + lower running cost + simpler install.

Cost comparison

What you actually pay in each scenario.

New build heat pump install (typical UK 3-bed):

  • Heat pump unit (5-6 kW R290): GBP 4,500-7,000.
  • Indoor cylinder + UFH integration: GBP 2,000-3,000 (UFH cost spread across general construction).
  • Electrical + commissioning: GBP 800-1,500.
  • BUS grant: typically NOT available for new builds (rule check current eligibility).
  • Total: GBP 6,000-11,500 - paid by developer or builder, not homeowner directly.

Retrofit heat pump install (typical UK 3-bed):

  • Heat pump unit (7-9 kW R290): GBP 6,000-9,000.
  • Indoor cylinder + plumbing: GBP 1,500-2,500.
  • Radiator upgrades: GBP 500-1,500.
  • Pipework + electrical: GBP 1,500-2,500.
  • BUS grant: -GBP 7,500.
  • Net: GBP 2,000-7,000.

New build homeowner doesn't pay heat pump separately (built into property price), but is essentially buying a higher-spec house. Retrofit homeowner sees direct out-of-pocket cost reduced by BUS.

SCOP performance differences

Why new builds run more efficient.

New build SCOP (4.0-4.8 typical):

  • Excellent thermal envelope = low heat demand = heat pump rarely runs at peak capacity.
  • UFH enables low flow temp (28-35C) = highest SCOP operating point.
  • Low ventilation losses (MVHR) reduce overall heat demand.
  • Often paired with solar PV = direct self-consumption boosts effective economics.

Retrofit SCOP (3.0-3.8 typical):

  • Variable thermal envelope = higher heat demand at design conditions.
  • Radiators (vs UFH) require higher flow temp (40-50C) = lower SCOP.
  • Older buildings often have air infiltration + draughts = more heat needed.
  • Less likely to have integrated solar PV.

Gap of 0.5-1.0 SCOP points = ~15-25% lower annual electricity cost for new build vs retrofit on identical property size. Material lifetime difference.

Self-build + new build planning

Specific considerations for self-builders.

UK self-builders gain significant control over heat pump install via architectural design phase:

  • Architect-led heat pump design. Heat-loss calc + system design done at architectural stage; ensures correct sizing + emitter design for the property's actual envelope.
  • UFH integration in slab. Underfloor heating designed into concrete pour or screed install; no retrofit complications.
  • Outdoor unit siting at design stage. Sympathetic to property design + neighbour relations; no retrofit pipe-routing issues.
  • Cylinder location optimised. Plant room or airing cupboard designed for the cylinder + buffer + DHW circulation.
  • Solar PV ready. Roof orientation + structural reinforcement for solar at design stage; inverter siting next to heat pump electrical.
  • SAP calc gives accurate baseline. Performance prediction matches reality more closely than retrofit.

Self-build heat pump installs routinely achieve SCOP 4.5+ - significantly above retrofit averages. Self-build BUS eligibility currently differs from retrofit BUS - check current rules.

Retrofit-specific decisions

What to prioritise when existing property.

Retrofit heat pump install (existing property):

  1. Heat-loss calc first. Get MCS-certified survey to establish actual property heat demand. Don't assume; measure.
  2. Insulation upgrades second. Loft + cavity insulation typically pays back faster than radiator upgrades + makes the heat pump install economics work better.
  3. Radiator upgrades third (selective). Replace single-panel radiators in the highest-demand rooms with oversized double-panel for low-temp operation. Not every room needs upgrading - the heat-loss calc identifies which.
  4. Heat pump install fourth. Sized to the post-upgrade property; correctly tuned weather compensation; UFH retrofit only if doing major renovation anyway.
  5. Smart tariff fifth. Octopus Cosy or similar at install commissioning; tune heat pump schedule to off-peak windows.

Retrofit projects often need 2-4 weeks of envelope improvements + radiator work before the heat pump install starts. Bundle into a single project for cost efficiency (shared trades, scaffolding, etc.).

Q01Are heat pumps mandatory in UK new builds?
Effectively yes from 2025 Future Homes Standard. Gas boilers banned in new builds; low-carbon heating mandatory. Heat pump dominant choice; some new builds use direct electric or district heating. Designed in from architectural stage with property envelope tuned for heat pump efficiency.
Q02What size heat pump for a new build vs retrofit?
New build 3-bed (Future Homes Standard): ~5-6 kW. Retrofit equivalent: 7-9 kW (1990s build) or 9-12 kW (pre-1990 uninsulated). New build sizing 30-50% smaller due to better insulation = lower install cost + better SCOP.
Q03Does BUS grant apply to new builds?
Typically NO for new builds - BUS designed for retrofit installs replacing fossil fuel heating. New builds already required to install low-carbon heating from 2025; no grant needed because no fossil-fuel alternative. Check current BUS eligibility rules for self-build scenarios.
Q04Why do new builds achieve higher SCOP than retrofits?
Better thermal envelope = lower heat demand; UFH (standard in new builds) enables 28-35C flow temp; MVHR ventilation reduces losses; often paired with solar PV. Typical new build SCOP 4.0-4.8; typical retrofit SCOP 3.0-3.8. Gap of 0.5-1.0 points = 15-25% annual electricity cost difference.