When it’s negative 8 Degrees in Canberra, how much heat is lost through windows?

Last weekend in Canberra was freezing!  The weekend minimums reached -8 degrees in some areas of the ACT and many residents would have noticed the cold spell.  But, if you’re heating your house, do you know how much heat is lost through your windows when it’s that cold outside?  It is going to vary greatly if you have single glazed, double glazed or triple glazed windows.


Let’s start with a simple formula for calculating heat loss through a wall, floor, window or door:

Q = A x Tdiff  x U


  • Q = Heat Loss (rate of heat flow) through the window assembly, given in Watts (or Joules per second)
  • A is the area of the element being investigated – in our case the window assembly, in square meters
  • Tdiff  is the temperature difference between outside and inside of the window assembly, in Kelvin
  • is the heat transfer coefficient of the window assembly (U-value), given in Watts per square meter Kelvin


This means that heat loss reduces if:

  • the area of an element is smaller,
  • the temperature difference between inside and outside becomes smaller
  • the conductivity of the material is reduced (ie the U-value becomes smaller)


In order to do the maths we need to make some assumptions.

Let’s assume that the occupants in Canberra like to keep their house at a cosy 20 degrees inside, and the area of all of their glass windows in their house is 50m2.

Therefore from the forumla above,

  • Area, A = 50 m2
  • Temperature Difference, Tdiff = 28 degrees  (20 degrees inside, minus minus 8 outside equals a difference of 28 degrees)


Lastly we need to know the U values for single, double and triple glazing.  Fortunately we can reference two of these from a reputable Australian source yourhome.gov.au, and the third from our German triple glazed window manufacturer.

Using Yourhome’s specifications we have the following U Values.

  • Single Glazed Aluminium windows: U-value = 7
  • Double Glazed UPVC windows: U-value = 3
  • Triple Glazed Timber Windows: U-value = 1


The formula we will use for each example is: Q = A x Tdiff  x U

Where A = 50, and T = 28, therefore Q = 50 x 28 x U Value


Heat lost through single glazed windows on a very cold day

For single Glazing,  U = 7

Q = 50 x 28 x 7 =  9,800W or 9.8kW

If the inside and outside temperature stayed stable for one hour,  it means that 9800 Watt-Hours will be lost through the windows, better known as 9.8kWh.  Thats almost $1.96 lost per hour with electricity prices at 20c/kWh.   Now imagine if it was this cold for 2 hours every day, for a whole month.  It would cost $117.60 for only two hours of heating each day!

Heat lost through double glazed windows on a very cold day

For Double Glazing, U = 3

Q = 50 x 28 x 3 = 4,200 W or 4.2kW

This is clearly a great improvement from single glazing, with less than half the heat loss.  With electricity prices of 20 cents per kWh this would cost about $0.84/hr to maintain temperatures of 20 degrees inside.  This is about equivalent to two large bar heaters running at high capacity.  if it was this cold for 2 hours every day, for a whole month.  It would cost $50.40 for only two hours of heating each day!

Now lets look at what the heat loss would be with high performance triple glazing

Heat lost through triple glazed windows on a very cold day

For Triple Glazing,  U = 1

Q = 50 x 28 x 1 = 1,400W or 1.4kW

With electricity prices of 20 cents per kWh, this would cost about 28 cents per hour, a huge improvement from single glazing, and a significant cost saving over double glazing.  If it was this cold for 2 hours every day, for a whole month.  It would cost only $16.80 for two hours of heating each day!

This formula shows just how much heat is lost through single glazing, and how much heat loss can be improved with double and triple glazing.



So now that you know how much heat you’ve lost through your windows on that cold day of July, why not look to do something about that, and install some German Triple Glazed windows.

You might not be able to afford not to.


DesignBUILD 2017

LAROS Technologies and RAICO Bautechnik GmbH are exhibiting at the 2017 DesignBUILD Expo, held at the ICC Sydney, Darling Harbour.

Dates: Wednesday 3rd – Friday 5th of May
Time: 9AM – 6PM

If you are around the area, feel free to swing by and see our booth at N15 and find out all about our high-performance timber facade systems.

Exhibit layout: http://designbuildexpo.com.au/wp-conte…/…/2017/04/070417.pdf

More info at: http://designbuildexpo.com.au

Curved Timber Roof Part II

Stage 2 – Complete!

Spectacular project in Melbourne is finally complete!

No one thought it could be done, but with the European smarts of HESS Timber & RAICO THERM+ H-I High Performance Curtain Walls and some clever design from the LAROS team, the doubled glazed curved roof for the Melbourne University College is now up! We can’t wait to see the building when it is complete!

Video footage of the construction will be available to view in the near future, to find out more about our high-performance thermally broken curtain wall technology head over to our RAICO page or simply contact us.

Keep an eye out for many more exciting projects that are coming up.


Curved Timber Roof Part I

Stage 1 – Complete!

Many thanks & congratulations to everyone from LAROS & Western Commercial Windows who was involved. It has been a successful outcome of the assembly on the ground.
Next stage… the LIFT, stay tuned for updates throughout the week!

HESS Timber + RAICO THERM+ H-I thermally broken double-glazed (12mm-8mm) curtain wall roof.

Early Christmas Present

Döpfner Timber Triple Glazed Main Door

Another wonderful ‘Spruce’ finish to the front door and another happy customer right before Christmas!

Share with:


Magnificent New Zealand Project

This outstanding building in Queenstown has a glorious “backyard” view of the mountains and scenery thanks to the recently fitted High-Performance Triple Glazed Döpfner Windows and Doors.  LAROS Technologies and the team at Eco Windows couldn’t be more pleased with the outcome. The photos and video below showcase the process of the installation and post-installation.

Feel free to contact us to find out more about our windows and doors or to arrange a quote for your new build or retrofit project.

Solutions used in this project:
High-Performance Triple Glazed Alu-Clad Döpfner Windows and Doors
Pro Clima Air-Sealing & Weatherproof Membranes and Tapes

Looks way easier than it actually was… ?
Posted by ECOWINDOWS LTD. on Wednesday, 31 August 2016


Share with:


KLH Cross Laminated Timber

LAROS Technologies is proudly representing KLH cross-laminated timber (CLT) construction timber solutions through-out Australia and New Zealand.

These solid cross-laminated timber elements are construction ready, suited for load-bearing, reinforced and non-load-bearing walls, ceilings and roof panels in a solid timber construction project.
Perfectly adaptable for the construction of a single-family home, multi-storey residential buildings, public buildings, administrative buildings, institutional buildings, commercial and extensions.

The panel thicknesses of the individual building components (wall, ceiling, roof) must be determined according to the static requirements. For normal room sizes in residential buildings we can assume walls from 94 to 128 mm (e.g. load-bearing interior wall on the ground floor of a 4-storey residential building) and ceilings from about 140 to 182 mm of panel thickness. A thorough static analysis is absolutely necessary.

Head over to our Timber Solutions page to find out more about these glorious CLT panels or come into our showroom to see and feel them in person.

Off Grid Passive Inspired House at Gundaroo

With thanks to Michael Mobbs at www.sustainablehouse.com.au and Sue & Danny O’Brian we would like to share an article written by the owners of a new PassiveHouse (Passivhaus) inspired house near Canberra.


This is a great read for those interested in building a new home in Australia, particularly though in colder climates such as Gundaroo & Canberra.


“In order to minimise our need for energy to heat the house during Canberra winters, when solar energy is in (relatively) short supply, we decided to build to PassivHaus standard. In other words, we’ve built a house in Canberra with NO heater….. and we’re not mad.”


“We’ve been in the house for 2 months now, and through warm sunny days, gloomy days and overnight temperatures of -6oC, the house has really shown that it is delivering on the promise. The temperature has not dropped below 19.2 degrees (even with the freezing nights) and has stabilised at a comfortable 21-23 oC during gloomy days and cool nights.”


Find the full article below: