How to choose the most energy efficient windows

Is your client after office or house windows with high thermal performance? As a builder or architect, it's up to you to recommend the very best products. Energy efficient windows will result in long-term cost savings for your client and keep their interiors protected against the elements - which can get pretty extreme during those New Zealand winters.

But what are the most energy efficient windows and how do you go about finding them? There are plenty of products out there that claim to offer high thermal performance, but the only way you can know for sure is to do your due diligence.

When your client expects not only a sophisticated aesthetic but the very highest thermal performance, you'll need to recommend products that can do the job.

1. Check the WEERS rating of the windows

The Window Energy Efficiency Rating System (WEERS) will give you some indication of the energy efficiency of the windows you're purchasing. Before they can be rated by WEERS, windows must comply with NZBC provisions on their structure, durability, performance and insulation. WEERS ratings are given to all WGANZ certified window manufacturers. Windows are given a star rating (six stars being the maximum) and rated on their thermal efficiency with an R value. 

To come up with the rating, WEERS measures the thermal performance of the window frame, the glass and glazing method, as well as the configuration and size of the window itself. If your windows are being supplied from overseas, you'll need to get their thermal efficiency examined by a BRANZ specialist to ensure they meet New Zealand requirements.

Before selecting your windows, check their WEERS rating to ensure they'll meet energy efficiency requirements. 

2. Check the Homestar rating of the windows

Some windows - including products manufactured by our suppliers - exceed the WEERS maximum rating of six stars. If your client is looking for top-of-the-line thermal performance, it pays to do some extra research before recommending suitable products.

Homestar rates whole homes on their performance and environmental impact based on seven categories:

• energy, health and comfort
• water
• waste
• materials
• site
• home management
• innovation (optional).

A Homestar rating can be done during either the design or the construction of a home, but it's best to do it as early as possible to provide assurance to your client. You'll need to register your project with the New Zealand Green Building Council before a Homestar Assessor will review the building specifications to come up with their rating.  

3. Choose windows with thermally broken aluminium frames

The best windows for energy efficiency need thermally broken frames.

Aluminium windows are low maintenance, durable, priced competitively and last for a long time. However, they are poor insulators, which is why the best windows for energy efficiency need thermally broken frames.

Thermally broken frames differ from standard aluminium joinery in that they have either a polyurethane insulating polymer or polyamide insulating thermal strips. The latter is what our windows use, and the insulated air spaces created by these strips prevent the transfer of energy.

Our Pacific Thermal Suite is the benchmark for excellence in thermal efficiency, adding up to 50 per cent more thermal efficiency to standard double glazing. Standard 4 mm glass has an R value of 0.15, but with a thermally broken frame this increases to 0.35. 

This Langs Beach property utilised awning windows and hinged doors from the Pacific Thermal Suite for maximum thermal efficiency. 

4. Select a window supplier known for high thermal performance

Fletcher is supported by a fantastic fabricator network that supplies the highest quality windows and doors for your residential and commercial builds. Not only do we boast an array of suites and products of the very highest thermal efficiency, but we have used these to create stunning, high-performing residential builds in Langs Beach, Woodside and Closeburn. 

To determine the energy efficiency of your windows, you'll need to make sure you do research, but it'll be worth it for the high thermal performance that will result. Get in touch with Altus Window Systems to find out how we can assist your next project.