Double Glazing a Home Costs Nearly Ten Years of Power Bills

Double glazing a home costs nearly ten years of power bills

The AER's default market offer is the price cap for households on standard electricity contracts. For 2026-27 it sets a typical Ausgrid customer in Sydney, using 3,900 kWh a year on a flat rate, at $1,899 including GST. A whole-home double glazing job ($18,000) equals about nine and a half years of that entire bill, which pays for the lights, fridge and hot water as well as heating and cooling. On Energex in south-east Queensland, where the default offer is $1,988, it equals about nine years. In Essential Energy's regional NSW network, at $2,604, it is about seven years.

Going Rate's whole-home price is for new double-glazed windows throughout a house, priced by the number and size of windows and the frame. Airtasker puts the median for double glazing at $720 per square metre, so the whole-home job buys about 25 square metres of double-glazed window at that rate. Double glazing costs about 20% more than replacing the same windows with standard glass ($15,000), so the second pane is a modest share of a full window replacement. Most of the bill goes on frames and labour.

Those bill figures cover electricity only. A home that heats with gas pays a separate gas bill that this comparison leaves out, so its heating spend, and the room for savings, can be larger.

The most a window could save

Energy Made Easy, the AER's consumer site, says heating and cooling make up about 40% of household energy use. Take 40% of the $1,899 Ausgrid default offer and you get about $760 a year. Set against a whole-home double glazing job ($18,000), that is a payback of about 24 years. On Energex the same sum gives about 23 years, and on Essential Energy about 17 years.

That is a generous ceiling, because it assumes the new windows cut heating and cooling to zero. The government's energy.gov.au advice says double-glazed windows can reduce heat loss by up to 30%. YourHome, the federal sustainable housing guide, says up to 40% of a home's heating energy can be lost through windows. Even on those upper figures, the windows account for part of the heating bill, and double glazing removes part of that part.

Gas-heated homes differ. A Melbourne house running a ducted gas heater through a long winter has more heating spend to cut than the Sydney electricity household the default offer describes, which is why published savings for Melbourne run higher than for Sydney or Brisbane.

Where the short paybacks come from

The most-cited figure is a 6.3-year payback from a 2023 study by Owolabi and colleagues in the Ain Shams Engineering Journal. It modelled one west-facing Sydney apartment upgraded to aluminium-framed double glazing. The job cost $6,570 and saved $1,046 a year, with heating energy down 41.2% and cooling down 21%. The study was a computer simulation of a single apartment, and nobody measured the savings in real houses.

A retrofit buyer pays the whole-home price. If a house saved the same $1,046 a year, a whole-home job ($18,000) would take about 17 years to pay back. That figure applies the study's modelled saving to a whole-home price. The modelled saving is also larger than the entire $760 heating and cooling ceiling on an Ausgrid default-offer bill, which suggests the modelled apartment ran its heating and cooling harder than a typical Sydney household.

The other short paybacks rest on a much smaller upfront cost. Viridian, which makes glass, modelled a typical single-storey home plan and reported savings of $838 a year in Melbourne with a 6.2-year payback, $598 in Sydney at 8.6 years, and $530 in Brisbane at 10 years. Viridian does not publish the upfront cost, but its savings and paybacks imply about $5,200, a fraction of a whole-home retrofit and in line with an extra cost paid at build time. Against a whole-home retrofit ($18,000), Viridian's Melbourne saving pays back in about 21 years and its Brisbane saving in about 34.

The frame does about half the work of a second pane

YourHome publishes whole-window U-values, which measure how much heat passes through the glass and frame together. Lower is better. A single-glazed aluminium window rates 6.9. Put a second pane in an aluminium frame and it rates 4.2. A single-glazed timber or uPVC window rates 5.5, and double glazing in a timber or uPVC frame drops to 3.0.

Aluminium conducts heat, so an aluminium double-glazed window, at 4.2, rates only somewhat better than a single-glazed timber one at 5.5. A buyer comparing quotes should ask for the whole-window U-value, which covers the frame as well as the glass, and should expect thermally broken aluminium, timber or uPVC frames to cost more.

YourHome's worked example shows what halving the U-value does. A home with 70 square metres of aluminium-framed clear glass, on a night 15 degrees colder outside than in, loses 6,510 watts through its windows, which YourHome likens to the full output of a 6.5 kW room air conditioner. Halve the U-value, for example with argon-filled double glazing in less conductive frames, and the loss falls to 3,255 watts.

Warm climates change the sums

In hot climates such as Darwin and from Brisbane north along the east coast, YourHome says the solar heat gain coefficient (SHGC), which measures how much sunlight passes through as heat, "is more influential than the glazing U value". A double-glazed window with clear glass can still let in most of the summer sun. Tinted or low-e glass, eaves and external shading do more there.

The Climate Council modelled bill savings from upgrading a new home's building fabric from 6 to 7 stars, which covers far more than the windows. The average saving was $457 a year nationally, $225 in Sydney and $119 in Brisbane, with Darwin highest at $945 because of its heavy cooling load. Even that whole-house upgrade saves a Brisbane household less than 1% of the cost of double glazing every window ($18,000) each year.

Secondary glazing and cheaper upgrades

Secondary glazing adds a second pane or panel inside the existing window. A whole-home secondary glazing job ($10,400) costs a little over half of a full double glazing job on Going Rate's prices, and Airtasker puts it at $400 per square metre. YourHome says it will not perform as well thermally as a factory-sealed double-glazed unit, but it can give good noise control.

It still cuts heat loss. A 2021 study by Bulut and colleagues measured secondary glazing in two ACT homes and found heat loss through the windows fell by 51.9% and 60.8%. The dollar savings were small. At the temperatures the occupants kept, the saving was $5.93 over 56 days in one home and $13.55 over 44 days in the other. Heated to 23.5 degrees, the figures rose to $19.88 and $28.75.

The ACT Government has said the same in policy. In an August 2021 written answer published in the Legislative Assembly's Hansard, energy minister Shane Rattenbury said no electricity retailer had delivered double glazing under the ACT's energy efficiency scheme, and that draught proofing, insulation, efficient heating and cooling and hot water heat pumps "generally have a better return on investment". The ACT's Sustainable Household Scheme loans covered solar, batteries, heating and cooling, hot water heat pumps, cooktops and electric vehicles, and left double glazing off. Climate Action Minister Andrew Barr said any product added later would need a loan that could be repaid through cost savings.

When double glazing is worth it

Noise is the strongest reason. YourHome says double glazing cuts medium and high-frequency noise such as voices well. For traffic and aircraft it recommends thicker or laminated glass with the largest air gap possible, so a buyer near a main road should ask for an acoustic specification. Double glazing also keeps the inner pane warmer, which reduces condensation on cold mornings and makes rooms near big windows more comfortable to sit in.

New builds and full window replacements are where the sums work best, because the buyer is paying for frames and labour anyway and the second pane is the only extra. Australia lags here. Researchers writing in The Conversation in 2023 found just over 10% of windows in new Australian housing are high-performance, compared with about 80% in the UK, US and New Zealand.

In Victoria, the Victorian Energy Upgrades program discounts some eligible glazing, which narrows the gap. For a retrofit bought mainly to cut power bills, a buyer should price secondary glazing ($10,400), draught proofing and insulation first, and treat double glazing as a comfort and noise upgrade that pays back slowly.

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