FAQ

No, grants cannot be backdated. All information must be submitted during the application process & must be approved before any work is carried out.

A Heat Loss Indicator (HLI) is a numerical measure that quantifies how much heat a building loses through its structure — including walls, roofs, floors, windows, and doors — relative to its size. It gives homeowners, builders, and energy assessors a simple, standardised way to evaluate the thermal efficiency of a home.

The lower the HLI score, the less heat the building loses, and the more energy-efficient it is. Conversely, a higher HLI score indicates significant heat loss, leading to higher heating bills and a less comfortable living environment.

If you hold an existing BER Certificate, your HLI is shown on the advisory report that accompanied your certificate. It is typically located on page 3 of the report. Please note: Advisory reports issued prior to 2020 do not display the HLI.

The HLI is typically derived from a combination of factors assessed during an energy survey or audit of the property:

  • Fabric Heat Loss — Heat escaping through walls, roofs, floors, windows, and doors (measured by U-values)
  • Thermal Bridging — Heat that bypasses insulation through junctions, frames, and structural elements
  • Air Permeability — Uncontrolled air infiltration through gaps and cracks in the building envelope
  • Building Geometry — The surface area of the home relative to its volume (the more compact a building, the lower the heat loss)

The result is expressed in watts per degree Kelvin (W/K) or sometimes as watts per square metre per degree Kelvin (W/m²K), giving a measurable indication of energy performance.

Understanding your home’s HLI is a critical first step in making meaningful energy improvements. Here’s why it matters:

💰 Bills – A high HLI means your heating system must work harder to maintain a comfortable temperature, leading to significantly higher energy bills.

🌡️ Comfort – Poor heat retention leads to cold spots, draughts, and temperature inconsistency throughout the home.

🌍 Carbon – Heat loss is a major contributor to a household’s carbon footprint. Reducing your HLI helps lower your environmental impact. 

🏠 Value – Homes with better energy ratings (linked to lower HLI) command higher resale values and are increasingly attractive to buyers.

Most homes — especially older properties — suffer from one or more of the following heat loss sources:

Improving your HLI doesn’t have to mean a complete home renovation. There are measures at every budget level:

Quick Wins (Low Cost)

  • Draught-proof doors, letterboxes, and keyholes
  • Add draught excluders to windows and skirting boards
  • Install thick curtains or thermal blinds
  • Lag hot water pipes and insulate your hot water cylinder
  • Use radiator reflector panels on external walls

Medium-Term Improvements

  • Install or top up loft insulation to at least 270mm depth
  • Insulate your cavity walls (if applicable)
  • Upgrade to A-rated double or triple-glazed windows
  • Fit a smart thermostat to optimise your heating schedule
  • Seal gaps around floorboards and skirting

Major Upgrades (Higher Investment, Biggest Impact)

  • Install solid wall insulation (internal or external) for older pre-1920s homes
  • Upgrade to a high-efficiency heat pump or condensing boiler
  • Install underfloor heating with insulation below
  • Consider a whole-house mechanical ventilation with heat recovery (MVHR) system
  • Explore solar panels or other renewable energy systems to offset remaining demand

A professional energy assessor can calculate your home’s HLI as part of a home energy audit or SAP (Standard Assessment Procedure) calculation. This is commonly done when:

  • Applying for an Energy Performance Certificate (EPC)
  • Seeking grants or funding for home improvements (e.g., ECO4, Insulation Scheme)
  • Planning a renovation or extension
  • Assessing compliance with Part L building regulations (new builds)

You can also use online tools and calculators to get a rough estimate of your home’s heat loss before commissioning a full survey.

The Heat Loss Indicator is one of the most powerful tools available to homeowners and professionals for understanding and improving the energy efficiency of a home. By identifying where and how much heat is being lost, targeted improvements can be made that deliver real, measurable reductions in energy bills, carbon emissions, and improve overall comfort — making your home warmer, greener, and more cost-effective to run.