comparison

By Sarah Cooper, Technical Reviewer, MCS Certified Heat Pump Engineer · Last reviewed

Exhaust Air Heat Pumps for UK Flats: 2026 Guide & Costs

First published

TL;DR

  • Exhaust air heat pumps (EAHPs) recover waste heat from ventilation, ideal for airtight UK flats with limited outdoor space.
  • 30-50% cheaper to run than gas boilers in 2026, with £7,500 grants available via the Boiler Upgrade Scheme (BUS).
  • Best for homes with mechanical ventilation (MVHR) or extractor fans-common in new builds and Passivhaus properties.
  • Installation costs £8,000-£12,000 (after grant), but payback in 7-12 years due to lower energy bills.
  • Not suitable for leaky homes or those without existing ductwork-check your home suitability here.

In 2024, 43% of UK flats were built after 2000, with many featuring airtight construction and mechanical ventilation-perfect candidates for exhaust air heat pumps (EAHPs). Unlike traditional air source heat pumps (ASHPs), which draw heat from outdoor air, EAHPs recycle waste heat from stale indoor air before it’s expelled. This makes them uniquely efficient for small, well-insulated spaces where outdoor space is limited.

If you live in a flat, new-build, or Passivhaus property, you’ve likely noticed rising gas prices-up 129% since 2021 (OFGEM). EAHPs offer a solution, slashing heating bills by 30-50% while qualifying for the £7,500 Boiler Upgrade Scheme grant. But they’re not a one-size-fits-all fix. This guide covers how EAHPs work, costs, grants, and whether your home is suitable-backed by data from the Energy Saving Trust and real UK installations.

How Exhaust Air Heat Pumps Work in UK Flats

Exhaust air heat pumps (EAHPs) are a niche but growing solution for airtight homes where traditional heat pumps struggle. Here’s how they differ from standard systems:

The Science: Heat Recovery from Ventilation

EAHPs integrate with mechanical ventilation systems (like MVHR or extractor fans) to capture heat from outgoing stale air. A refrigerant loop absorbs this heat, upgrades it via a compressor, and distributes it through your heating system. Key components:

  • Heat exchanger: Transfers heat from exhaust air to refrigerant.
  • Compressor: Boosts refrigerant temperature (like a fridge in reverse).
  • Heat distribution: Connects to underfloor heating, radiators, or hot water cylinders.

Efficiency boost: EAHPs achieve Coefficients of Performance (COP) of 3.0-4.5, meaning they produce 3-4.5 units of heat per 1 unit of electricity. For comparison, gas boilers max out at 0.9 COP (90% efficiency).

Why Flats and Airtight Homes Benefit Most

  1. No outdoor unit needed: Unlike air source heat pumps, EAHPs don’t require external space, making them ideal for balconies or internal cupboards.
  2. Synergy with MVHR: Many new-build flats already have mechanical ventilation with heat recovery (MVHR). EAHPs can piggyback on this ductwork, reducing installation costs.
  3. Lower heat demand: Airtight homes lose less heat, so EAHPs run at lower flow temperatures (35-45°C), improving efficiency.

Illustrative composite based on typical UK installations: Case Study: London Flat (2018 Build)

  • Property: 2-bed flat, 65m², MVHR system installed.
  • Old system: Gas combi boiler (£1,200/year running costs).
  • EAHP upgrade: Mitsubishi Lossnay LGH-150RVX-E + £7,500 BUS grant.
  • Cost: £9,500 (after grant).
  • Savings: £600/year vs gas, £450/year vs ASHP (due to higher COP).
  • Payback: 8 years.

Exhaust Air Heat Pumps vs. Alternatives: Costs and Efficiency

Upfront Costs: EAHP vs. ASHP vs. Gas Boiler

SystemCost (Before Grant)Cost (After £7,500 Grant)Annual Running Cost (2-bed flat)Lifespan
Exhaust Air Heat Pump£15,000-£19,500£8,000-£12,000£500-£70015-20 years
Air Source Heat Pump£10,000-£14,000£2,500-£6,500£650-£85015-20 years
Gas Boiler£2,500-£4,500N/A£1,200-£1,50010-15 years

Sources: Energy Saving Trust, GOV.UK Boiler Upgrade Scheme

Key takeaways:

  • EAHPs cost £3,000-£5,000 more than ASHPs upfront, but save £150-£200/year in running costs.
  • Grants cover 50-60% of EAHP costs, making them competitive with ASHPs post-subsidy.
  • Gas boilers are cheaper to install but 3x more expensive to run in 2026.

Efficiency in Airtight vs. Leaky Homes

EAHPs shine in airtight properties (e.g., Passivhaus, new builds) but struggle in older, draughty homes. Here’s why:

  • Airtight homes: Heat loss is minimal, so EAHPs run at optimal efficiency (COP 3.5-4.5).
  • Leaky homes: Heat escapes faster than the EAHP can recover it, dropping COP to 2.0-2.5-worse than an ASHP.

Check your home’s airtightness:

  • Blower door test: Measures air changes per hour (ACH). <3 ACH = good for EAHPs.
  • MVHR requirement: EAHPs need ducted ventilation (not just extractor fans). If your flat lacks this, ground source heat pumps or ASHPs may be better.

Grants and Incentives for UK Homeowners in 2026

Boiler Upgrade Scheme (BUS): £7,500 Grant

The UK government’s Boiler Upgrade Scheme (BUS) covers EAHPs under the same rules as ASHPs:

  • £7,500 grant for air-to-water EAHPs (most common type).
  • Eligibility:
    • Your property must have an EPC rating of D or above (check GOV.UK EPC register).
    • The EAHP must replace a fossil fuel system (gas/oil boiler).
    • Installation must be MCS-certified (find an installer here).
  • How to apply: Your installer applies on your behalf. No upfront cost-the grant is deducted from your bill.

Pro tip: The BUS is first-come, first-served and runs until 2028. Apply early to avoid missing out.

Other Incentives

  1. 0% VAT: EAHPs qualify for 0% VAT until 2027 (vs. 20% for gas boilers).
  2. Smart Export Guarantee (SEG): If you pair your EAHP with solar panels, you can sell excess electricity back to the grid (rates vary by supplier).
  3. Local council grants: Some areas (e.g., London, Manchester) offer top-up grants of £500-£2,000. Check your council’s website.

Is Your Flat Suitable for an Exhaust Air Heat Pump?

Not all flats are EAHP-ready. Use this checklist to assess your home:

✅ Ideal Conditions for EAHPs

  • Airtightness: <3 ACH (air changes per hour) on a blower door test.
  • Ventilation system: Existing MVHR or ducted extractor fans (e.g., in bathrooms/kitchens).
  • Heating system: Low-temperature radiators or underfloor heating (EAHPs work best at 35-45°C).
  • Space: Internal cupboard or balcony for the indoor unit (no outdoor space needed).
  • EPC rating: D or above (required for BUS grant).

❌ Dealbreakers

  • No ductwork: If your flat lacks mechanical ventilation, retrofitting ducts is expensive (£3,000-£6,000).
  • Leaky windows/doors: Heat loss >3 ACH makes EAHPs inefficient.
  • High-temperature radiators: EAHPs struggle to heat water above 50°C, so old radiators may need upgrading.
  • Shared heating systems: If your flat is part of a district heating scheme, EAHPs won’t be compatible.

Next steps:

  1. Book a home assessment with an MCS-certified installer.
  2. Check your EPC for airtightness and insulation levels.
  3. Compare quotes using our savings calculator.

Installation Process: What to Expect

Step 1: Survey and Design (1-2 weeks)

  • An MCS installer visits to:
    • Test your home’s airtightness (blower door test).
    • Assess your ventilation system (ductwork compatibility).
    • Size the EAHP (typically 3-8 kW for flats).
  • Cost: £200-£500 (often refunded if you proceed).

Step 2: Ductwork and Unit Installation (3-5 days)

  • Ductwork: If you lack MVHR, new ducts are installed (adds £3,000-£6,000).
  • Indoor unit: Mounted in a cupboard or balcony (size of a fridge).
  • Hot water cylinder: Replaces your old boiler (if applicable).
  • Controls: Smart thermostat (e.g., Nest or Hive) for optimal efficiency.

Step 3: Commissioning and Handover (1 day)

  • The installer tests the system, sets up controls, and explains maintenance.
  • MCS certificate: Required for the BUS grant.

Timeline: 2-4 weeks total (longer if ductwork is needed).

Running Costs and Savings: EAHP vs. Gas in 2026

Annual Cost Comparison (2-bed flat)

SystemElectricity/Gas Use (kWh)Unit Cost (2026)Annual CostSavings vs. Gas
Exhaust Air Heat Pump2,500 kWh£0.24/kWh£600£600
Air Source Heat Pump3,000 kWh£0.24/kWh£720£480
Gas Boiler12,000 kWh£0.10/kWh£1,200N/A

Assumptions: 65m² flat, 12,000 kWh heat demand, OFGEM price cap 2026 (£0.24/kWh electricity, £0.10/kWh gas).

Payback Period

  • EAHP: £8,000-£12,000 (after grant) / £600 annual savings = 7-12 years.
  • ASHP: £2,500-£6,500 (after grant) / £480 annual savings = 5-10 years.
  • Gas boiler: No upfront savings, but higher running costs forever.

Long-term benefits:

  • Carbon savings: EAHPs cut CO₂ emissions by 70-80% vs. gas.
  • Future-proofing: Gas boilers may be banned in new builds by 2025 (Scotland) or 2035 (England).

Common Problems and How to Avoid Them

1. Poor Airtightness

  • Symptom: EAHP struggles to maintain temperature; high electricity bills.
  • Fix: Seal gaps around windows/doors with draught-proofing strips (£50-£200). Retest airtightness.

2. Undersized Ductwork

  • Symptom: Weak airflow; system short-cycles (turns on/off frequently).
  • Fix: Upgrade ducts to 100-150mm diameter (£1,000-£3,000).

3. High Flow Temperatures

  • Symptom: Radiators feel lukewarm; system runs constantly.
  • Fix: Replace radiators with low-temperature models (£200-£500 each) or install underfloor heating (£50-£80/m²).

4. Noise Issues

  • Symptom: Indoor unit hums loudly (40-50 dB).
  • Fix: Install acoustic insulation (£100-£300) or relocate the unit to a cupboard.

Pro tip: Choose an MCS-certified installer to avoid these issues. Check reviews on MCS’s website.

FAQ

1. Can I install an exhaust air heat pump in a listed building?

Yes, but with caveats. Listed buildings often have strict ventilation requirements, and EAHPs may need planning permission if they alter the building’s exterior (e.g., new ducts). Check with your local council and use an installer experienced in heritage properties. The BUS grant still applies if the system meets MCS standards.

2. Do exhaust air heat pumps work with radiators?

Yes, but not all radiators. EAHPs work best with low-temperature radiators (designed for 35-45°C flow temperatures). Older radiators may need upgrading to double-panel or triple-panel models (£200-£500 each). Alternatively, pair the EAHP with underfloor heating for optimal efficiency.

3. How much maintenance do exhaust air heat pumps need?

EAHPs require less maintenance than gas boilers but more than ASHPs:

  • Annual checks: £100-£200 for a service (includes refrigerant top-up, filter cleaning, and efficiency test).
  • Filter cleaning: Every 3-6 months (DIY or included in service).
  • Ductwork cleaning: Every 2-3 years (£150-£300).
  • Lifespan: 15-20 years (vs. 10-15 for gas boilers).

4. Can I use an exhaust air heat pump for cooling?

No. EAHPs are heating-only systems. If you need cooling, consider a reversible air source heat pump or pair your EAHP with passive cooling (e.g., night ventilation). Some EAHPs can integrate with separate cooling units, but this adds complexity and cost.

5. What’s the difference between an exhaust air heat pump and MVHR?

  • MVHR (Mechanical Ventilation with Heat Recovery): Recovers 30-90% of heat from outgoing air but doesn’t generate heat. It’s a ventilation system, not a heater.
  • EAHP: Uses the same principle but upgrades the recovered heat via a refrigerant loop to actively heat your home. Think of it as MVHR + a heat pump in one.

Sources