Buying · quotes
Comparing double glazing quotes: what to ask and what to check
Two quotes for the same windows can be thousands of dollars apart and describe different products in different words. Put them on one page, in the same units, before you decide.
What we found
Our calculations, data as of 23 October 2026
- Quotes for the same house vary widely. One owner on a New Zealand forum was quoted $20,000 to $35,000 for full replacement in 2019; another, in 2021, $35,000 for a large retrofit, $56,000 for new aluminium joinery and about $72,000 for thermally broken.
- Compare price per m² of window, not per window. Our model’s mid-points are $600 per m² for a low-E retrofit in aluminium, $750 in timber, and $1,250 for new uPVC.
- Ask every glazier for the glass Ug and the whole-window R-value. A low-E unit in a plain aluminium frame rates R0.30; the same glass in timber R0.56. Glass-only figures look much better than either.
- Check what is excluded: scaffolding can add $1,000–5,000 on a two-storey house, and repairs to rotten sashes or flashings are often quoted separately.
Put quotes in the same units
Quotes come per window, per opening, per room or as one total. Convert each to dollars per m² of window and check it against published 2026 ranges: roughly $450–800 per m² for a retrofit and $800–1,600 for new joinery, more for timber. A price well outside that range is not necessarily wrong, but it should have an explanation: large sliders, heritage sashes, scaffolding, or a premium glass.
What the quote should specify
- Glass. Thicknesses (for example 4-12-4), low-E type, argon or air, and the Ug value.
- Whole-window R-value. Including the frame. The Building Code’s table gives typical figures; see glass and frames.
- Spacer. Aluminium or warm-edge.
- Frame work. For retrofits, how sashes are adapted and what beads or seals are used; for replacements, the frame system and whether it is thermally broken.
- Safety glass. Where the Code requires it, such as doors and low windows.
- Draught seals. Whether they are included.
- Making good. Reveals, linings, flashings and painting after new joinery.
- Access. Scaffolding or an elevated work platform.
- Removal. Disposal of old glass and frames.
- Timing. Measure, manufacture and install dates; owners report lead times of weeks to months.
- Guarantees. On the sealed units and on the workmanship.
Questions worth asking
- What is the whole-window R-value of what you are quoting, and where does that figure come from?
- Will the frames run with condensation after the upgrade?
- Which windows can and cannot take a unit, and why?
- Is anything in the house likely to change the price once the work starts, such as rot or out-of-square frames?
- Does any of the work need a building consent? Window work on a house of up to two storeys is usually exempt, unless a window under 15 years old has failed; see building consent.
Weigh the answer against the saving
A cheaper quote with plain aluminium frames and clear glass may save almost as much power as a dearer one, because the first step from single glazing does most of the work. A dearer quote may buy dry frames and quieter rooms. Use the calculator to see what each option saves in your city, and decide what the comfort is worth to you.
This week: Palmerston North
Single glazing in an aluminium frame runs below the dew point about 2,430 hours a year in Palmerston North (H1 zone 3); clear double glazing cuts that to 350. A low-E retrofit of 25 m² saves $190 a year heated mornings and evenings with a heat pump, or $569 heated all day. Fastest payback here: DIY magnetic secondary glazing, 17 years.
Cheap fix. EECA estimates that closing curtains before dark saves $80–90 a year. Lined, full-length curtains with a pelmet work best. Read more