I posted this on the Alternative Technology Association forum ( http://www.ata.org.au/forums/topic/5744#post-34881 ):
“We are renovating a house. According to our ‘first rate’ energy report we can use single clear glazing. Doing so means that we will use 41000 mega joules per year for heating and cooling.
We will use natural ventilation to cool the house and hydronic heating (radiators) to heat the house. The energy rating gives our heating component of energy use at 30540 mj/annum. At 1.8c per megajoule we are looking at $550 per year to heat the house (no cost to cool)
If we use double glazing throughout then our heating consumption changes to 24170mj/annum. This translates to $435.
This is an annual heating saving of $115
The single glazing option is $15941 + gst
The double glazing option is $20311 + gst
A difference of $4370 + gst or 38years of $115 to pay off?!
Have I miscalculated?”
I received many replies generally agreeing with my calculation but recommending double glazing never-the-less. The arguments put forward were reducing CO2 emmissions, better sound insulation, increased resale value and reduced temperature fluctuations internally. These were all valid to some extent but not what drove us to choose double glazing. The reason we went for it is best articulated by ‘Phil A’ who wrote:
“If you go with the double glazing you will have a really good set up.
Imagine the place in ten years time and power has doubled again. You will be glad you did. The place will even “feel” better with double glazing, being warmer and quieter.
Hydronic under floor heating over insulation and double glazing are three things I will never be without again. Magic.”
A nebulous sense that we will have ‘a really good set up’ in ten years time rather than a ‘we could have afforded double glazing, I wonder if we should have’ in ten years time.