In simple terms, a Heat Loss Indicator (HLI) tells you how quickly heat escapes from a building. Lower is better. Here’s what you need to know about it.
Heat Loss Indicator Interpretation + Grant Rules
| HLI | Technical Suitability for a Heat Pump | Heat Pump Grant Eligibility |
| Less than 2 | House retains heat well and is “heat-pump ready” | Yes |
| Between 2 and 2.3 | It would be preferable to upgrade insulation before going for a heat pump. But a well-designed heat pump system can still work efficiently under these conditions | Yes, if not economically viable to achieve a HLI under 2 |
| Between 2.3 and 3 | The home is generally not considered “heat pump ready”. It’s still possible to make a heat pump work well. But it’s more tricky, and most installers will struggle to make the system run efficiently. | Only under a pilot scheme through One Stop Shops |
| Above 3 | It will be very difficult to heat the home using a heat pump, unless a high-temperature heat pump is used. In this case, the system can be made to work, but savings on bills are likely to be minimal or none compared to oil or gas heating | No |
What Determines Your Heat Loss Indicator?
Insulation: The better the insulation, the lower the heat loss
Air tightness: Airtight homes retain heat better than draughty ones
Heat recovery ventilation: This recovers waste heat from stale air as it leaves your home, resulting in a better HLI
Shape of the home: A compact, cube-shaped, home retains heat better than complicated layouts with more wall area
Sheltered sides: Mid-terrace houses and apartments retain heat better because several of their sides are pressed against other heated spaces, rather than exposed to the outside
How to Find Your Heat Loss Indicator
Provided your home has an up-to-date BER Assessment, here are the steps to find your HLI:
- Go to the SEAI BER Database
- Enter your electricity meter number and click search
- Download the Advisory Report
- Check the first row of the recommended upgrades table on page 3
- This will show you both your current HLI, and the HLI you could achieve with the recommended insulation upgrades
If your home doesn’t have an up-to-date BER (last 10 years), then you won’t be able to find your Advisory Report on the SEAI database. In this case, you’ll need to get a BER Assessment done. Alternatively, if you have lots of spare time, you can do an unofficial BER Assessment yourself for free, using DEAP software.
If you’re serious about getting a heat pump, then it may be worth getting a Technical Assessment, which will determine your HLI, and more.
Estimating HLI Based on Building Age
The table below shows the average HLI for buildings of various years of construction. It also shows the proportion of dwellings in each of four HLI categories.
Heat Loss Indicator Formula
The heat loss indicator is the estimated heat loss per metre square of living space in your home, per °C of temperature difference between outside and inside (W / m2 °C)
For example, if it’s 20 °C inside, 5 °C outside, and your 100 m2 house is calculated to lose 2,800 Watts of heat then your HLI would be:
HLI Accuracy
Heat Loss Indicators are calculated as part of the Building Energy Rating (BER) process. The BER process is useful, but far from perfect. Here are some sources of error:
- Human error on the part of the BER Assessor
- Use of estimates, rather than actual measured data, for U-values
- Thermal bridges are generally estimated, not calculated
- The assumption of proper construction methods is not always accurate
- Evidence of construction details is often not available
HLI and Heating Demand
You can get a quick estimate of the annual heat requirement (in kWh) using the formula below
For example, a house in Ireland might have
- A HLI of 2.3
- A floor area of 112 m2
- 2196 heating degree days in an average year (source)
In this case, the annual heat requirement would be:
