With the UK pushing for air-source and ground-source heat pumps as a key part of its net-zero strategy, many homeowners are surprised to find that installing a heat pump doesn’t guarantee a stellar Energy Performance Certificate (EPC) rating.

At EPCrate, we regularly encounter properties where heat pump installations deliver real-world efficiency, but the EPC assessment software undervalues their performance due to outdated or simplified calculation methods.

Why Heat Pumps Should Theoretically Boost EPC Ratings

Heat pumps are considered high-efficiency renewable heating systems, with Coefficient of Performance (COP) values typically between 3.0–4.5. This means for every unit of electricity consumed, the system provides 3 to 4.5 units of heat.
In theory, this should elevate a property’s EPC rating significantly, especially when replacing older gas or oil boilers.

So Why Does the EPC Rating Sometimes Barely Budge?

1. RdSAP Software Uses Conservative Default COP Values

Unless detailed installation and performance data is provided, EPC assessors must rely on default Seasonal Performance Factors (SPFs), which are often lower than the system’s actual efficiency.

2. Flow Temperatures Aren’t Properly Accounted For

Many heat pumps operate optimally at low flow temperatures (35-45°C). However, if the property still has traditional radiators, the EPC algorithm may assume higher flow temperatures, reducing the system’s calculated efficiency.

3. Lack of Heat Emitter Upgrade Recognition

If underfloor heating or low-temperature radiators are installed but not properly documented, the EPC will default to generic radiator efficiency assumptions, penalizing the heat pump’s rating impact.

4. Electrical Energy Factor in EPC Calculations

EPC algorithms factor in the carbon intensity of electricity. Although grid electricity is rapidly decarbonizing, the EPC software may still use outdated emissions factors, reducing the heat pump’s perceived benefit.

5. Air Tightness & Insulation Assumptions Can Offset Gains

If the building fabric remains inefficient (poor insulation, high air leakage), the heat pump’s efficiency gains may be overshadowed by excessive heat loss calculations.

How to Ensure Your Heat Pump Installation Positively Impacts Your EPC

  1. Provide Full MCS Certification & Technical Specifications
    Ensure assessors receive installation reports specifying:

    • Model numbers

    • Seasonal Coefficient of Performance (SCOP)

    • Flow temperatures

    • Control systems details (e.g., weather compensation)

  2. Upgrade Heat Emitters and Document It
    Low-temperature radiators or underfloor heating must be properly documented to adjust EPC software inputs.

  3. Conduct an Air Tightness Test
    Demonstrating low air permeability through a blower door test can improve overall heating demand calculations.

  4. Consider a Full SAP Assessment for New Builds or Complex Retrofits
    RdSAP may oversimplify inputs for existing buildings. For high-investment projects, a bespoke SAP calculation provides a more accurate reflection of energy performance.

Real-World vs Algorithmic Efficiency: The EPC Gap

Even if your heat pump delivers lower energy bills and reduced carbon footprint, EPC assessments may lag in acknowledging its full impact due to the above limitations.

However, EPCs are evolving, with future updates expected to better account for dynamic renewable systems and real-time grid decarbonisation.

At EPCrate, we ensure every piece of documentation is utilised to prevent default penalties that diminish your property’s true efficiency score.

Book a Heat Pump-Aware EPC Assessment with EPCrate

Installing a heat pump? Ensure your EPC reflects its efficiency gains.
Book your assessment with EPCrate and avoid default penalties through our expert documentation process.
Check our pricing plans or contact us for bespoke heat pump EPC assessments.