There are a bewildering array of eco-friendly products. Here are some things that the retailers may or may not have told you.
For instance did you know that:
a) Solar hot water systems can reduce the water heating bill by at least half if placed in a sunny location. They can be one of the most effective ways of reducing electricity bills However, their performance markedly drops off if they are allowed to be partially shaded. On the other hand, a heat pump will reduce electricity consumption by a third and will work regardless of time of day or available sunshine
b) Hydronic in-floor heaters are a comfortable way of heating but they are no cheaper to run than gas ducted or reverse-cycled AC heating. Hydronics cost at least 50% more to install. If you use a 4000K solar pre-heater to help heat the water in winter, you will save about $150 on your yearly heating bill (about 20 years to pay itself off)
c) Some reflective window tints can reduce the heat by direct sunshine up to 70% but reflective awnings can reduce it over 90%. Curtains are the worst way of stopping the house from overheating.
d) In a dry climate a 5kL rain water tank will be inadequate to water your garden. A grey water diverter provides a constant source of recycled water for your plants and can reduce your water consumption by up to half (but watch out which detergents you use inside the house)
e) Drawing your curtains over bare windows (even double glazed ones) on winter nights greatly reduces your energy loss. Every square metre of exposed window can add $1.50 to $5/m2 to your yearly energy bill.
f) Charcoal heat reflective paint can reflect away 20% of the sun's energy compared to a normal dark roof. However, a white roof will reflect 50% and foil sisalation under the roof will reflect > 95%. White heat reflective paint doesn't add much more to just normal white paint.
g) By ducting a roof ventilator (whirlybird) through your ceiling you can help draw heat out of the house during summer (but they can only work if there is a way for fresh air to get into the house). But just removing hot air form the roof space with a whirly has almost no effect on cooling the inside of the house
h) A 4 person solar hot water system saves as much energy as a 1.5 kW (10 panel) solar PV system generates in a year. Solar hot water systems are four times as efficient as a solar panels in converting sunlight into useful energy.
i) Using double glazing instead of single glazing reduces heat loss twice as much as adding insulation. For the technically minded they each represent an improvement in U value by about 2 to 4 W/m2/K over an uninsulated, singled glazed house. This means that every square metre of insulation or double glazing installed will reduce the energy bill by about $5-30 per year. But double glazing is at least five to six times more expensive than insulation per square metre.
j) An evacuated solar hot water system is up to twice as efficient in winter as a flat plate collector. However, both will provide 100% of a household's hot water needs during summer. Averaged over a year, the evacuated tube system amounts to only an improvement of 8% in savings. (Evacuated tube heaters are not more efficient because of their shape but because of the glass sleeve that insulates the heating element).
k) Compared to incandescent globes, compact fluorescent globes use 1/4 the energy and last up to 15x as long. They cost five times about more. However, if CFLs are switched on and off constantly (such as using them on a motion sensor) their lifespan can be as short-lived as normal globes.
l) A 150 W solar panel can save household energy up to $50 per year at current energy prices. However, PV panels take at least 20 years to pay off from the savings they provide. If they are installed under partial shade, the yearly savings can be reduced considerably and the payback period will increase accordingly. Most panels are expected to lose 20% of their efficiency by the time they are 25 years old.
m) An induction cooktop uses half the energy of a gas cooktop. However, gas is half the price of electricity so the cost savings cancel each other out. With induction you have to toss out your copper cookware because they won't work.
n) Apart from weather sealing, the next most cost-effective way of reducing heat loss is to add insulation. However, it won't perform as well if is installed improperly with gaps or is compressed.
l) Ceiling fans help cool people by encouraging evaporation of perspiration and can be effectively combined with air-conditioning to reduce cooling costs. However, they do nothing to reduce air temperature so there is no point in leaving them on if the room is unoccupied.
m) An efficient wood heater is one of the cheapest ways to heat a house. However, the amount of energy they use and their greenhouse emissions are not much different from using a reverse-cycled air-conditioner. Each wood heater emits as much particulate matter as at least 10 cars.
o) Excess energy generated by domestic solar panels can be fed into the grid and in many states, the utilities will pay you three times the market electricity rate. A dedicated solar 'farm' situated in a perfectly sunny location can pay of the system in less than a decade this way. However, an average household will consume most of the energy it generates during they year and will generate little excess.
p) Using thermal mass in a house can help stabilise extremes in temperature to make the house more comfortable. However where you put the mass is important. In a brick-veneer house the mass is on the outside and has minimal effect on the comfort of the building. If you expose a double brick construction continuously to direct sunlight during a heat wave it will overheat and make the house even more uncomfortable. How you use mass greatly depends on your local climate. There are important principles about how much you use, where you put it and how thick it needs to be.