Upgrade · Fabric · windows and doors · BER file 26 Sep 2026 · checked 8 Sep 2026
89.6% of homes sold or let still have older windows
New windows stop the draught and the cold pane at the sill. 89.6% of homes sold or let have windows that lose heat faster than today's double glazing (SEAI BER file, 26 Sep 2026). New windows move a rating only 10 points. But for homes just over the heat pump line, they bring 84% under it.
A fitter lifting a new window into its opening during a renovation.
Unrecognizable workman installing window in house during renovation process · Ksenia Chernaya · Pexels License
See your grants for windows and doors, and what you’d pay
About 10 seconds. See your numbers first, then get quotes if you want them.
89.6%
Of homes sold or let still have older windows
U > 2.0 · BER file 26 Sep 2026
BER assessment10.4
Points on the BER scale it adds, for the typical home it applies to
kWh/m²/yr · research lane, BER file 26 Sep 2026
Our model84%
Of homes just over the heat pump line, brought under by new windows
HLI 2.3–2.5 · research lane, BER file 26 Sep 2026
Our model42%
Of SEAI's typical semi-D price paid by the grant
€3,000 of €7,110 · SEAI H1 2026
Published figureUpdated · grants checked · BER file · prices SEAI H1 2026 · How we know · Corrections
Where this sits · the heat chain
Most heat leaves through the walls, roof, floor and windows. Fix these first and the heating has less to replace.
- Fabricwalls, roof, floor, windows
- Airdraughts and ventilation
- Heatheat pump or boiler, radiators, controls
- Usebills, comfort, the BER
- The idea behind itFollow the heat
- You are hereWindows and doors
- Next questionHow much does SEAI pay towards new windows and doors?
On its own, windows and doors moves a rating 10.4 points; a heat pump, 93
What one job on its own does to the typical home's rating, where the job applies. One letter on the new scale is 50 points. Our model
Windows and doors: 10.4 points on its own, where it applies
Where the job applies, the median gain is 93 kilowatt-hours per square metre a year for a heat pump, 60.7 for solar panels, 46.7 for wall insulation and 10.4 for new windows. One letter on the new scale is 50.
Each bar is the median improvement to a home's BER from that one job on its own, among homes sold or let where the job applies, worked out on each certificate's own figures. A heat pump moves the rating nearly two letters in the D to F range; attic insulation, draught-stripping and blocking chimneys barely move the rating on their own. The bracket shows one letter's width (50, for D, E and F). The bars are not additive.
EstimateOur model: the research lane's one-job recalculation on each certificate's own figures (BER file of 26 Sep 2026, not the site's 8 Sep file). It matches SEAI’s published heat loss to a median ratio of 1.00 and uses the electricity factor in force on each certificate’s date.
Sources: fixmyber research lane, research/ber/s4_thresholds.py, 26 Sep 2026
The numbers
| Job | Median gain, kWh per m² a year |
|---|---|
| Heat pump | 93 |
| Solar panels | 60.7 |
| Wall insulation | 46.7 |
| New windows | 10.4 |
| Attic insulation | 6.1 |
| Blocking chimneys | 2.4 |
| Draught-stripping | 0.4 |
A fifth of the heat a semi-detached house built 1971–80 loses goes through its windows
Where a typical semi-detached house built 1971–80 loses its heat. This job acts on the windows, pin 5. BER assessment
A fifth of the heat a semi-detached house built 1971–80 loses goes through its windows
Walls 32%, windows 18%, air 17%, floor 11%, roof 10%, junctions 10%, doors 2%.
A section through a semi-detached house built 1971–80, front to back. Each arrow's width is that element's share of the heat the house loses for every degree it is warmer inside than out, from the insulation values and areas on 4,498 BER certificates for homes sold or let, assessed 2022–26. The median wall lets through 1.10 watts per square metre per degree, the roof 0.40 and the windows 2.80; the median heat loss indicator is 3.15, over the heat pump line of 2.3. Air (draughts, vents and open chimneys) isn't measured on a BER: it is what's left once the six measured elements are subtracted, so it carries the most uncertainty. The numbered pins show where each of the jobs acts, in the order they're usually done.
EstimateAir is estimated as the remainder (heat loss indicator × floor area, less walls, roof, floor, windows, doors and thermal bridging). Shares are rounded to sum to 100.
Sources: SEAI BER Research Tool, 8 Sep 2026 · Certificates for a sale or private letting assessed 2022–26 with a heat loss indicator: semi-detached house built 1971–80, 4,498 certificates
The numbers
| Element | Share of heat loss | Median |
|---|---|---|
| Walls | 32.0% | 1.10 W per m² per degree, 89 m² |
| Windows | 17.6% | 2.80 W per m² per degree, 21 m² |
| Air (estimated) | 16.8% | the remainder |
| Floor | 10.7% | 0.64 W per m² per degree, 60 m² |
| Roof | 10.5% | 0.40 W per m² per degree, 61 m² |
| Junctions | 10.2% | cold bridges at joins |
| Doors | 2.2% | 2.95 W per m² per degree, 2 m² |
Older A- and B-rated houses are 7 times as likely to have high-performance windows
What older houses rated A or B have, against those rated C to E. BER assessment
26% of older A- and B-rated houses have high-performance windows; 3.8% of those rated C to E
The biggest gap is insulated walls: 63% against 25%.
- Insulated walls. Rated A or B: 63%. Rated C to E: 25%.
- Solar panels. Rated A or B: 47%. Rated C to E: 10%.
- An insulated floor. Rated A or B: 74%. Rated C to E: 40%.
- Attic at the grant standard. Rated A or B: 33%. Rated C to E: 19%.
- High-performance windows. Rated A or B: 26%. Rated C to E: 3.8%.
- A heat pump. Rated A or B: 21%. Rated C to E: 0.2%.
- Solar water heating. Rated A or B: 7.8%. Rated C to E: 2.2%.
- Mechanical ventilation. Rated A or B: 7.2%. Rated C to E: 0.9%.
Each pair of bars is the share of houses built before 2011 that have the upgrade, among those rated A or B (dark) and those rated C to E (grey), from every certificate issued 2019-2026. High-performance windows: 26.1% against 3.8%. It shows what the better-rated houses have, not proof of what got them there: newer houses are more often A or B and were built with some of these.
Sources: SEAI BER Research Tool, every existing-home certificate 2019–26 for houses built before 2011 (440,689 certificates), 26 Sep 2026 · Insulated walls: Walls U ≤ 0.37 · Solar panels: Solar PV · An insulated floor: Floor U ≤ 0.45 · Attic at the grant standard: Roof U ≤ 0.16 · High-performance windows: Windows U ≤ 1.6 · A heat pump: Heat pump · Solar water heating: Solar water · Mechanical ventilation: Mechanical ventilation
The numbers
| Upgrade | Rated A or B | Rated C to E |
|---|---|---|
| Insulated walls | 62.8% | 25.4% |
| Solar panels | 46.9% | 9.7% |
| An insulated floor | 73.6% | 39.9% |
| Attic at the grant standard | 33.3% | 19.3% |
| High-performance windows | 26.1% | 3.8% |
| A heat pump | 20.9% | 0.2% |
| Solar water heating | 7.8% | 2.2% |
| Mechanical ventilation | 7.2% | 0.9% |
What new windows and doors change, and what they don't
New windows stop the draught and the cold pane at the sill. They are also the upgrade people want first and the one SEAI fund last.
What it is
The old windows come out and new ones go in, one opening at a time, usually a room a day. Doors are the same job on a smaller scale. The measuring happens weeks before anything is fitted, because the units are made to the hole: SEAI put the wait between order and installation at six to ten weeks for windows and four to six for doors.
What you are buying is a number. Every window is rated for how fast heat gets through the whole unit — glass, frame and all — and SEAI won't grant one unless that number is 1.4 or better. Frames are a fifth to a third of the area of a window, so the frame matters nearly as much as the glazing.
The rest is detail that changes the number: two panes or three, how wide the gap between them is, a low-emissivity coating on the glass, argon in the gap instead of air.
Compared with what's in the openings now
| Old single glazing | Old double glazing | New, to the grant standard | |
|---|---|---|---|
| Panes | one | two, often a narrow gap | two or three, wide gaps, coated glass |
| The pane in winter | cold to stand beside, runs with water | cool | close to room temperature |
| Draughts | round the frame and the sash | seals hardening with age | new seals, and trickle vents if specified |
| Noise | little help | some | noticeably better |
| Grant | €3,000 for a semi, €800 a door | same | same |
SEAI's own share of the loss puts windows, doors and uninsulated floors together at up to 10% of a home's heat, against up to 30% for a poorly insulated roof and walls. That is the whole argument for the order of work, and it's why the windows grant has a condition the others don't: the attic and the walls have to be good already, or the house has to come in under the heat-loss limit after the job.
Grant €1,500 to €4,000 by house type for a whole-window upgrade, €3,000 semi-detached, plus €800 per external door to a maximum of two. Whole-window U ≤ 1.4 W/m²K required. Eligibility: HLI ≤ 2.3 W/(K·m²) after works, or attic and walls rated Good or Very Good in the BER advisory report. Restrictors required where the drop below an opening exceeds 1.4 m. Amounts verified 2026-10-03.
Where the saving comes from
Two different things are going on, and only one of them is glazing.
The first is conduction: heat crossing the glass and the frame. A modern unit slows that down a lot, and the number quoted on the quote is exactly that. The second is air — the old sash that never closed right, the gap under the door on a windy night. Air leakage is a real cost and a bigger part of what people feel than the glazing figure suggests, which is why a new window can transform a room that the numbers say should only have improved a little.
What new windows can't do is make a cold house warm. There is far more wall than there is window, and if the wall is losing heat the windows will not save you.
Modelled whole-window heat loss for that group of homes: U 2.80 → 2.01 W/m²K, an average over all the glazing in the cell rather than a single new unit. Cost €7,110 for a semi is SEAI's median for a complete set, January to June 2026. detached|1970-1989|D|oil: cost p50 €36,848, grant €22,300, you pay p25–p75 €7,300–€21,700, saving €1,797/yr, payback 4.7–12.4 yrs, n=23,707, confidence 0.9
Questions people ask
- Do I have to replace every window to get the grant?
- No. SEAI say you do not have to do them all, but the grant is paid once per property, so a job in two halves gets paid once. The house also has to come in under the heat-loss limit after the work, which is easier when the whole lot is done together.
- Double or triple glazing?
- Either, once it comes in at 1.4 or better — that is the number SEAI put in the grant conditions, and it is a whole-window figure covering the frame as well as the glass. Triple glazing performs better and costs more. It also lets in a little less sun, which is worth a thought on a north-facing room.
- Will new windows make the house stuffy?
- They can. Old windows leak air constantly, and when you replace them that leak stops. SEAI require a room with an open-flued appliance to keep a permanent vent, and they point to trickle vents in the frames to keep the air moving. Ask what ventilation is in the quote before you sign it.
How we know
- Ratings: From SEAI's BER Research Tool (files of 8 Sep 2026 and 26 Sep 2026): certificates for homes sold or let, and every certificate for houses built before 2011. A BER is a standard calculation, not a meter reading.
- One job at a time: Our model reworks each certificate with one job done, on the BER file of 26 Sep 2026. Its heat loss matches SEAI's own figure to a median ratio of 1.00. A group figure, not an assessment of your house.
- Grants and prices: SEAI's grant pages, read on the dates shown, and SEAI's median costs of individual upgrades for 2025. A median is a middle price, not a quote.
Sources
seai.ie · insulation · seai.ie · windows and doors · seai.ie · Median costs of individual energy upgrades
Found a mistake? Every fix is dated on Corrections. Method in full: How we know.
See your grants and what you’d pay
Four questions about your home, then your numbers. Get quotes from registered contractors if you want them.
Updated · grants checked · BER file · prices SEAI H1 2026 · How we know · Corrections