Before you begin
What decides where an Irish home sits on the BER scale
Describe the home as it is today, not planned work.
If the property already has a BER, the certificate on the national register is the real rating and this estimate adds nothing to it.
Floor area is the one figure worth looking up rather than guessing, because hot water and any solar generation are spread over it.
Reading the answer
Understanding this indicative rating
The A-G thresholds used here are the current residential scale introduced on 24 May 2026, which replaced the fifteen sub-bands from A1 to G.
The starting value is an official CSO average for homes of the same period and type. That average already contains the heating and fabric those homes typically have, so the estimator strips that out before applying your answers — otherwise a heat pump would be counted twice in a period where most homes already have one.
Because the anchor is an average of a wide spread of real homes, the result publishes the neighbouring bands alongside the point estimate. Treat a result sitting near a band boundary as unresolved rather than decided.
The estimate counts modelled primary energy, which is what a BER measures. It is not a bill, and a rating can improve while a household's actual spend does not.
Boundaries
Assumptions and limitations
Working assumptions
- The CSO stock-average primary energy for the construction period and dwelling type is the calibration anchor.
- That anchor is decomposed into space heating, hot water and fixed services, so a fabric answer moves only the space-heating part and a heating answer moves everything the boiler or heat pump serves.
- The share of each period already running a heat pump is taken from the CSO and removed from the anchor before your own heating answer is applied.
- Insulation and glazing are measured against the fabric a home of that period typically already has, rather than against one fixed reference for the whole stock.
- Solar PV is credited as generation rather than as a percentage, so its worth depends on array size and floor area instead of on how poor the home already is.
- A0 is never assigned, because it requires zero-emission criteria these inputs cannot verify.
Where to be careful
- This is not a DEAP 4.3 calculation. SEAI's method uses far more survey and system data than this form collects.
- The CSO calibration anchors come from the last directly comparable stock-average table published before the May 2026 DEAP factor and methodology update.
- Airtightness, thermal bridging, ventilation, orientation, exact U-values, controls, hot-water storage and installed product performance are not captured.
- Solar generation is modelled from capacity and floor area only, with no orientation, pitch or shading, and no account of how DEAP treats exported units.
- Only a registered BER assessor can publish a BER certificate or advisory report.
Worked example
The same question, answered end to end
A 110 m² semi-detached home built in the 1990s with a condensing boiler, attic insulation but uninsulated walls, double glazing and no solar.
What was entered
- 1978-1999 construction period, semi-detached, 110 m².
- Condensing boiler, attic insulated with uninsulated walls, double glazed, no solar.
How it is worked out
The CSO stock-average anchor for a 1978-1999 semi-detached home is 212 kWh/m²/year.
Lighting, pumps and fans account for 6 kWh/m²/year of electricity, or 10.5 of primary energy, leaving 201.5.
4% of that period runs a heat pump, so its typical generator spends 0.04 × 0.58 + 0.96 × 1.22 = 1.197 kWh of primary energy per kWh of heat. 201.5 ÷ 1.197 = 168.4 kWh/m²/year of heat.
Hot water is 2,600 kWh a year over 110 m², or 23.6 kWh/m²/year, so the average home of this period is left needing 144.7 kWh/m²/year of space heat.
Attic-only insulation and double glazing are exactly what this period typically has, so the fabric multipliers are 1.00 and the space demand is unchanged.
A condensing boiler spends 1.1 ÷ 0.9 = 1.22 kWh of primary energy per kWh of heat: (144.7 + 23.6) × 1.22 + 10.5 = 216 kWh/m²/year.
That is 216 against the C threshold of 225, so the band is C — and 66 kWh/m²/year above the B threshold of 150.
At ±20% the figure spans 173 to 259, which crosses the C/D boundary at 225, so the honest answer is C to D rather than C alone.
Changing only the heating answer to a heat pump takes the same home to 109 kWh/m²/year and into B, which is why it leads the list of remaining measures ahead of the 4.2 kWp array's 60.
What the tool returns
- Indicative BER band
- C
- Modelled primary energy
- 216 kWh/m²/year
- Plausible band range
- C to D
- Distance to band B
- 66 kWh/m²/year
- Biggest single move left
- Switch to a heat pump
Common questions
Questions about this tool
Is this a valid BER certificate?
No. It uses the current scale and official Irish stock data as anchors, but it is a deliberately short screening model rather than DEAP 4.3, and only a registered assessor can issue a certificate.
The home already has a BER. Is this any use?
Not for the current rating — the certificate on the national register is the real answer. It is still useful for the other direction: changing one answer shows roughly what a measure would be worth before you pay for it.
Why does the estimator not give A0?
A0 is not just an energy cutoff. It also requires the Zero Emission Building conditions, including no fossil fuel use, which this short form cannot verify. Where the modelled figure is inside the 42 kWh/m²/year threshold the result says so instead.
Why does a heat pump help less in a new home than an old one?
Because the starting value already contains one. 84% of homes built since 2020 are heat-pumped, so that period's CSO average is a heat-pumped average; crediting the same heat pump again would count it twice. In a 1990s home, where only about 4% have one, the same answer is worth far more.
Why can two similar homes get different real BERs?
DEAP uses measured dimensions and detailed fabric, ventilation, heating, hot-water, controls and renewable-system data. This estimator compresses all of that into nine answers, which is why it publishes a range of bands rather than one.