Both heating and cooling come down to one fundamental problem; how to put heat where you want it and keep it there. That means outside in summer and inside in winter.
The rate that heat enters or leaves a building is governed by the materials that make up your “building envelope”: the surface which surrounds your living spaces. You have to stop heat crossing the boundary of your walls, ceiling, floor, windows and doors without your permission.
We say “without your permission” because in winter your first priority must be getting sunlight into the house and stopping it leaving again.
Direct sunlight is almost entirely ultraviolet (UV) radiation, which passes easily through glass and into your living room. Once it strikes an object it heats up and the sunlight becomes infrared (IR) radiation, which is best thought of as radiant heat. IR radiation doesn’t pass through glass as readily as UV radiation, so the room heats up. Ever left your car in the sun for a day where it is a lovely 25 degrees outside but 60 degrees inside your car? It is exactly this mechanism at work.
Insulation will stop heat crossing boundaries. If you own your house, the path is well trodden and fairly simple. Start with the ceiling, adding the thickest insulation you can find.
Next consider how the wall insulation can be improved. There are some new materials and processes available for this task now and you can pay someone to come and pump insulation into your wall cavity for $2000 and upwards. Doing this can make your house about 2 degrees warmer.
Window treatments are just about on-par with walls for making a difference; even more so if you include doors.
If you’re on a budget, or renting, there’s a lot you can do with windows and doors. First, seal all the gaps around doors in the house, even the internal ones, to control the size of your heated space; there are rubber seals that can do the job for doors and windows.
Then seal all the ancillaries that let heat escape, like bathroom vents and the rangehood, which vents outside. This is where renters can get creative and reap rewards; rolled towels under doors are a good start, but why not go further? Tape a garbage bag over the window that opens onto the neighbour’s bathroom. Block the old chimney with anything you can find. Do anything you can to stop heat going where you want it to go.
Curtains and pelmets are virtually mandatory in cold climates. Curtains must be as heavy as possible, touch the ground and the walls next to the window. Windows are the last great frontier in home insulation; and honestly, there’s no cost-effective way to retrofit them. Energy payback on double-glazing your windows could be close to 70 years. But as with all energy efficiency upgrades there is more to it than the energy savings. What is niceness worth to you? How much nicer is it being in a house which is 14 degrees instead of 10? What is that worth to you?
Once your windows are done think about what you can do to the floor. Slabs are hard to change, but there are products for suspended boards which will make a big difference.