Heat Pump Sizing and Home Suitability
Home suitability for a heat pump comes down to the Heat Loss Indicator, a measure of how fast a dwelling loses heat through its fabric and ventilation. TU Dublin research found roughly 3 in 4 Irish homes are already suitable, and most of the remaining quarter can qualify with insulation upgrades.
What the Heat Loss Indicator Measures
The Heat Loss Indicator is a dwelling’s total fabric and ventilation heat loss, divided by its floor area, calculated using SEAI’s DEAP software during a BER assessment.
Expressed in watts per Kelvin per square metre, W/(K·m²). Lower means the home retains heat better.
A concrete example: a 100 sqm home at HLI 2.3, with 20°C inside and 5°C outside, loses roughly 3,450 watts through its fabric and ventilation. The lower the HLI, the less a heat pump has to work to hold that temperature.
HLI Thresholds for the SEAI Grant
| Threshold | HLI value | Condition |
|---|---|---|
| Standard target | ≤2.0 W/(K·m²) | Qualifies without further conditions |
| Exception ceiling | ≤2.3 W/(K·m²) | Accepted where additional SEAI requirements are met |
| Rough BER equivalent | C1–C3 | Varies by house type and construction |
Most guidance simplifies this to “HLI 2.3 or below,” since that’s the outer edge of what can qualify. The clean target SEAI actually designs the grant around is 2.0, worth knowing if a home sits in that 2.0–2.3 band and extra conditions come up during assessment.
Is a Given Home Likely Suitable
Suitability tracks three things: how well insulated the home is, its age, and its current heating system.
A home’s current HLI is visible on its existing BER, if it has one under 10 years old. Look it up on SEAI’s BER database using the property’s MPRN before booking a survey.
How the Suitability Assessment Works
Check for an existing BER
Homes built before 2007 with a valid, current BER already showing an HLI at or below 2.3 can skip a full Technical Assessment and submit a Self-Declaration form instead.
Technical Assessment, where needed
An SEAI-registered Technical Advisor, a BER assessor with additional qualification specific to this role, evaluates insulation, windows and doors, thermal bridging, and air tightness.
HLI result and recommendations
The Technical Advisor reports the current HLI and, if it’s above target, the specific upgrades that would bring it down.
Insulation work, if required
Attic, cavity wall, or external wall insulation, itself grant-funded separately, reduces fabric heat loss and lowers the HLI.
Heat pump sizing
Once eligible, the installer calculates the property’s peak heat loss to size the unit correctly, not simply fitting a standard capacity.
Why Correct Sizing Matters
An undersized heat pump struggles to reach temperature on the coldest days and relies more on backup electric heating, raising running costs. An oversized one short-cycles, switching on and off more often than it should, which wears components faster and cuts efficiency.
Installer sizing decisions, not the equipment itself, cause most of the complaints homeowners report after a heat pump install. A proper survey calculates the home’s actual peak heat loss rather than estimating from floor area alone.
Getting a Home Heat Pump Ready
Sizing and Suitability Questions
How do I find my home’s current HLI?
Check SEAI’s BER database using the property’s MPRN, if a valid BER under 10 years old exists. Otherwise, a new BER assessment establishes it.
Does every home need a full Technical Assessment?
No. Homes built before 2007 with a current BER already showing HLI at or below 2.3 can use a Self-Declaration form instead of a full assessment.
What if my home’s HLI is above 2.3?
Insulation work, attic, cavity wall, or external wall, brings the HLI down. These measures carry their own SEAI grants, separate from the heat pump grant.
Is a bigger heat pump always better?
No. An oversized unit short-cycles and loses efficiency. Correct sizing comes from the home’s actual calculated heat loss, not the largest available unit.
Find Out If a Home Qualifies
An SEAI-registered installer checks the current HLI and confirms next steps during survey.
Get your free installation quote →