BER vs ER: What Irish Homeowners Should Know

When planning energy upgrades, two ratings often appear side-by-side: BER for the whole home, and ER for windows and doors. They work toward the same goal—lower bills, better comfort, higher property value—but they measure different things. Knowing the difference helps you invest wisely and maximise results.

One goal, two ratings

Think of your BER as the report card for the entire house, and the ER as the technical spec sheet for each window or door. Together, they ensure you’re making upgrades that genuinely improve comfort and efficiency.

Quick definitions

Understanding BER (A–G)

Hover or tap bars for details

A

A rating — Most energy‑efficient homes with very low running costs; typical of modern new builds or deep retrofits. Lower bills, reduced waste, higher property value.

Best

B

B rating — Good efficiency and comfort with comparatively low heating costs; common after targeted upgrades like insulation and heat‑pump installs.

Strong

C

C rating — Average performance; scope to cut bills with attic/wall insulation, airtightness, and heating system upgrades.

Average

D

D rating — Below average; higher heat loss and running costs. Prioritise insulation and glazing to improve comfort.

Below avg

E

E rating — Poor efficiency; significant heat loss and bills. Consider fabric-first upgrades before system changes.

Poor

F

F rating — Very poor; extensive upgrades needed. Expect high bills and discomfort without works.

Very poor

G

G rating — Least efficient; major fabric and system upgrades required. Highest energy use and emissions.

Lowest

BER (Building Energy Rating)

Government-regulated rating from A1 (best) to G, based on calculated energy use per m² for heating, hot water, ventilation, and lighting. Required for selling or renting a home.

ER (Energy Rating for windows/doors)

Manufacturer rating for thermal performance, solar gain, and air leakage. Presented as a product label so you can compare glazing options easily.

Why people mix them up

Both use A–G scales and talk about energy efficiency, but scope is the difference:
BER = whole home
ER = individual window/door product

Who issues them?

BER: Registered BER Assessor after a site survey and DEAP modelling
ER: Window/door manufacturer or system supplier

Validity

BER: Up to 10 years (or until major upgrades)
ER: For the product’s certification period or model lifecycle

What they measure

BER: Standardised model of the home’s expected energy use—independent of occupant behaviour
ER: Tested performance of a specific window/door unit

U-values & airtightness: key drivers

U-value = heat loss rate (lower is better). Airtightness = how much warm air your home loses through gaps. Better glazing, tight seals, and quality installation all improve both BER and real-world comfort. Tip: A great window only performs well if installed properly—tapes, warm-edge spacers, and airtight detailing make a big difference.

How ER affects your BER

Assessors record window details (frame type, U-value, gas fill, coatings, spacers, etc.). Certified whole-window U-values replace default values and directly improve the BER calculation.

What your BER assessor will do

• Measuring floor, wall, roof, and glazing areas
• Checking heating systems & ventilation
• Recording window specifications
• Taking photos, verifying certificates, and logging model inputs

Documents to keep for BER accuracy

• ER certificate/data sheet (whole-window U-value + air permeability)
• Installation details (foam/tape system, warm-edge spacers)
• Invoices & dates
• Any blower-door test results
• Drawings or orientation notes if available

Without documentation, assessors must use default (worse) values.

Real-world upgrade examples

Home Type & Works	Typical Result	Benefit
1990s semi-D: Double glazing upgrade only	C3 → B3	~10–15% heating demand cut, warmer rooms
Mid-terrace: Insulation + windows	D2 → C1	Lower bills, stable indoor temps
2000s B-rated home: Triple glazing + airtightness + insulation + heat pump	B3 → A3 (maybe A2)	Major comfort jump, future-proofed

Typical timelines

• Windows/doors: 1–3 days install
• Insulation (attic/cavity): 1 day
• External insulation: 1–2 weeks
• BER survey + cert: A few days

Common mistakes

• Quoting glass U-value instead of whole-window U-value
• Skipping airtightness detailing around reveals
• Failing to keep product certificates
• Forgetting ventilation when improving airtightness

Grants (SEAI context)

Many upgrades qualify for grants if systems and installers meet SEAI requirements. Post-works BER is typically needed to claim support.

Choosing windows wisely

• Whole-window U-value
• Air permeability class
• Solar gain (g-value) — especially south-facing
• Warm-edge spacers
• Proven airtight installation system

After installation

• Get a post-works BER
• Track room temperatures & boiler/heat pump runtime
• Consider a blower-door test if airtightness was a goal
• Adjust vents, thermostats, and balancing valves

FAQs

Will ER windows automatically improve BER?

They help a lot, but insulation, airtightness, systems, and ventilation matter too.

Is triple glazing worth it?

Often yes—especially on exposed or noisy sides. Consider g-value balance on sunny elevations.

Do I need new windows before installing a heat pump?

Not always—but reducing heat loss often means a smaller, cheaper, quieter heat pump and a stronger BER lift.

Final advice for Irish homeowners

Start with your current BER, plan fabric upgrades first, choose certified ER-rated glazing, and insist on airtight installation. Documentation matters—keep everything for your assessor. Every upgrade should move your home toward a warmer, cheaper-to-run future.

Ready to upgrade with certified, energy‑efficient windows and doors?

Talk to Expert Windows for a free, no‑obligation consultation and a tailored quote.

Request your free consultation · info@expertwindows.ie · 01 233 6092 / 087 363 9977

Get A‑rated performance, professional installation, and documentation ready for your next BER—so your upgrade pays back in comfort, value, and lower bills.