Upgrading your windows is one of the most impactful things you can do for a cold, draughty New Zealand home. But for many homeowners, the conversation tends to stop at one question - what's it going to cost, and how do I pay for it?
Here's something most Kiwis don't realise - that New Zealand's major banks now offer dedicated green home loans with heavily discounted interest rates, sometimes as low as 0%, specifically for energy efficiency upgrades including double glazing. If the upfront cost has been putting you off, this could change the numbers significantly.
What Is a Green Home Loan and Who Offers Them?
A green home loan is a mortgage top-up offered at a discounted interest rate in exchange for spending the funds on verified energy efficiency improvements. Banks offer them because they need to reduce the carbon footprint of their lending, which means that helping you upgrade your home works in their favour too. All of New Zealand's major banks offer some form of green home loan product, with rates currently ranging from 1% p.a. down to 0% depending on the bank and loan term.
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ANZ Good Energy Home Loan - up to $80,000 at 1% p.a. for 3 years, with double glazing explicitly listed as an eligible upgrade alongside insulation, heat pumps, ventilation, and solar.
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BNZ Better Future Home Loan Top-Up - mirrors ANZ's product with the same 1% rate, 3-year term, and $80,000 maximum.
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ASB Better Homes Top-Up - same 1% rate for 3 years, up to $80,000, with double glazing explicitly listed as eligible. A $99 top-up fee may apply.
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Westpac Greater Choices Home Loan - the standout offer at 0% interest for 5 years on up to $50,000. Requires your regular income to be credited to a Westpac account and a minimum existing Choices home loan balance of $150,000.
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Kiwibank Sustainable Energy Loan - takes a different approach, contributing up to $2,000 over 4 years rather than offering a discounted rate. Primarily focused on sustainable energy systems, so confirm with Kiwibank directly whether double glazing qualifies in your situation.
These products are structured as mortgage top-ups, meaning you'll generally need at least 20% equity in your home and an existing home loan with that bank. Rates, terms, and eligibility criteria vary between lenders and change regularly, so it's always worth confirming the current details directly with your bank before applying.
Do Duco Windows Qualify for Green Home Loans?
Yes, double glazing is explicitly listed as an eligible upgrade under ANZ's Good Energy Home Loan, and you can borrow up to $80,000 at 1% p.a. over 3 years to pay for it. Westpac's Greater Choices loan covers double glazing, insulation, heat pumps, ventilation, and more, with a loan of up to $50,000 interest-free for 5 years.
This applies to both retrofit and full replacement windows. If you're unsure which option suits your home, our guide Full Window Replacement vs Retro-Fit Windows in New Zealand walks through the key differences, and if your home has timber frames, it’s worth exploring whether timber retrofitting and double glazing is a worthwhile investment first.
Your bank will require an itemised quote or invoice from a professional installer. DuCo's installation process includes full documentation to support your application.
What Does a Green Home Loan Actually Save You on Double Glazing?
Let's take a realistic example. A full retrofit installation across 12 windows in a 3-bedroom NZ home might cost $18,000 - $28,000 depending on window sizes and glass specification. Costs will vary depending on your home, and our guide to double glazing prices in New Zealand breaks down what to expect before you get a quote.
On a $20,000 project, the difference between borrowing at a standard floating rate (approximately 7%) versus Westpac's 0% green loan is roughly $7,000 in interest saved over 5 years. That's before you factor in the energy savings.
According to BRANZ, double glazing can reduce heat loss through windows by up to 50%. For a home that already has floor and ceiling insulation, EECA's guidance on window insulation confirms that windows are often the single biggest remaining source of heat loss, meaning the upgrade pays dividends in lower power bills year after year.
Is a Green Home Loan Right for You?
A green loan makes the most sense if you plan to stay in the home for 5 or more years, your home already has ceiling and floor insulation, and you'd prefer to keep savings liquid rather than spending a lump sum upfront. At Westpac's 0% rate, borrowing to upgrade now is essentially the same cost as saving up, but you get the warmth and comfort benefit immediately.
Still working out whether to retrofit or replace? Our 5-point checklist covers the key decision points.
Ready to Get Started?
Green home loans make upgrading your windows significantly more accessible, and with several NZ banks now offering rates as low as 0%, the timing is good. The best first step is getting a real cost figure in hand so you can approach your bank with confidence.
Get a free measure and quote from DuCo today.
