Energy efficient blinds and shutters
How window furnishings cut the heat load on a Queensland house, and what we can honestly promise about your power bill.
The short answer
Windows are the weakest part of a Queensland house. An energy-efficient window furnishing does one of two things: it stops sunlight before it reaches the glass, or it puts a layer of trapped air between the glass and the room. The best ones do both.
Where the heat actually gets in
Walls and ceilings in a modern Queensland home are insulated. Glass is not. On a summer afternoon a west-facing window behaves like a radiator: sunlight passes straight through, hits the floor and the furniture, and turns into heat that is now inside the room and has to be removed by the air conditioner.
That is the job an energy-efficient blind or shutter is doing. It is not making the house colder. It is reducing how much heat gets in, so the cooling you are already paying for has less work to do.
What “energy efficient” actually means here
Two different mechanisms get sold under the same phrase, and they are worth separating.
Blocking is stopping the sunlight before it becomes heat. Anything mounted outside the glass does this, which is why an external screen or shutter outperforms an internal blind of the same fabric. The heat never enters the room in the first place.
Insulating is slowing the transfer of heat through the window once the sun is off it. This is trapped air doing the work, which is why a honeycomb cell insulates better than a flat blind, and why a dense shutter panel does better again. Insulation matters in both directions: the same layer that keeps heat out in February keeps it in on a July night.
A product that only blocks will help on a summer afternoon and do very little in winter. A product that only insulates will help in both seasons but never matches external shading on a bad afternoon.
The options, most effective first
- External shutters and screens. Aluminium shutters and ZipScreen outdoor blinds intercept the sun before it touches the glass. Nothing fitted inside can match this on a west-facing window or an exposed patio.
- Plantation shutters. A solid panel with an air gap behind it, covering the whole opening. Third-party testing shows our Thermalite™ panels block as much as 16°C of temperature coming through the window, and they carry over two to three times the insulation of timber and vinyl shutters.
- Honeycomb blinds. The air-cell structure is the most insulating fabric option, and the only one built specifically for the job. Good in bedrooms and anywhere you want insulation without the bulk of a shutter.
- Blockout roller blinds. Genuinely useful on glare and light, and they do reduce heat load. But they are a single flat layer, so the insulating effect is modest compared to the three above.
- Sheer and light-filtering fabrics. These are chosen for how a room looks and feels. Treat any thermal benefit as a bonus rather than the reason.
The gap around the edge decides most of it
An insulating blind with a 30 mm gap down each side is a chimney. Warm air rises behind it, spills out the top, and pulls more air in at the bottom. The fabric may be excellent and the result still disappointing.
This is the single most common reason an energy-efficient product underperforms, and it is entirely a measuring and fitting question. It is also why we measure every opening ourselves rather than working from numbers over the phone.
What this does to a power bill
We are not going to quote you a percentage. Anyone who does is guessing, because the answer depends on which way your windows face, how much glass you have, how well the roof is insulated, what temperature you set, and how long the air conditioner runs. Two identical houses on opposite sides of the same street will not get the same result.
What we can tell you is the mechanism, and it is not complicated. Less heat entering the room means the air conditioner reaches the temperature you set sooner and cycles less often to hold it. The effect is largest on the windows taking direct afternoon sun, which is usually a much smaller number of windows than people expect.
If cooling cost is your main reason for doing this, say so at the consult. It changes what we recommend, and it usually means spending the budget on two or three windows properly rather than spreading it across the whole house.
Getting it right in a Queensland house
West and north-west windows are where the money is. They take the afternoon sun at the hottest part of the day, in the season you are running the air conditioner most. If you only do a few windows, do those.
Humidity matters as much as heat. Timber moves in a subtropical climate, so in a bathroom, a kitchen or a laundry a material that does not swell or warp will hold its seal, and a seal that holds is a seal that keeps working. That is the practical reason we manufacture Thermalite rather than timber.
Read on: what blinds keep heat out, ranked by what works; how honeycomb blinds insulate; and blinds and shutters through a Queensland year.
Free consult and quote
Brisbane and the Gold Coast. No obligation, and we do the measuring.