I’ve posted on Double Glazing but that not the only way to save heat loss through windows so I thought I would do a numerical comparison of the various options for glazing treatment of windows.

In a bedroom of our current house the South facing windows were approximately 4m square (We are in Australia so these windows don’t get any sun).The basis of my calculations is a difference of 15^{o}C between internal and external temperature.

The equation used to calculate heat loss is:

Heat Loss = Area x Temperature Difference x ‘U’

for

‘U’ single glazing = 7*

‘U’ double glazing = 3*

‘U’ brick veneer = 0.51

** ‘U’ value includes effect of frame.*

## Option 1 Do Nothing

Heat loss through glass = 4 x 15 x 7 = 420watts = **0.42kw/hour**

Remember this heat loss is for one room only.

## Option 2 Reduce window by 40% to 2.4 m

Heat loss through glass = 2.4 x 15 x 7 = 252watts = **.25kw/hour**

Heat loss through brick = 1.6 x 15 x .51 = 12 watts = **0.012kw/hour**

Total heat loss = 0.25kw/hr + 0.012kw/hr **= 0.262kw/hour**

**With our builder this was a no cost option that has reduced the heat loss by 38%.**

## Option 3 Double Glazing

Heat loss through glass = 4 x 15 x 3 = 180watts =** 0.18kW/hour**

**This is a heat loss reduction of 57% but at a significant cost.**

## Option 4 Reduce Window by 40% and Double Glazing

Heat loss through glass = 2.4 x 15 x 3 = 108watts =** 0.108kW/hour**

Heat loss through replacement brick wall = 1.6 x 15 x .51 = 12 watts = **0.012 kW/hour**

Total = ** **0.108kW/hour + 0.012kW/hour** **= 0.12kW/hour

**This final option has reduced the heat loss by over 70% and will be around 30% cheaper than double glazing the original large windows.**

I hope this has given you some food for thought!