Some comments on an earlier post suggest this would be useful to set out.
The energy required to keep your house warm in heating season is exactly the energy lost through the exterior walls, windows, doors, roof, and up the chimney if you have one. Period. First lesson: cut that loss. Weatherstrip, get storm windows, close windows, close the shades at night, insulate, close the damper (or the whole fireplace; a fire in an open fireplace actually cools your house by inhaling warm air and blowing it up the flue), etc. These losses are about proportional to the temperature difference between inside and out, so if you turn down your thermostat at night, when you’re not at home, and even when you are (put on a sweater), you are absolutely ahead. You already know to do those things, but most people underinvest in them. You can save a lot of money and do the planet a big favor by just keeping heat in your house better. Second lesson: live in a smaller house, or an apartment building with living units on the other side of some of the walls and the ceiling.
This lost energy is replaced in several ways. The first way is stuff you do for other reasons, like people and pets in the house metabolizing food, lighting , and operating your various appliances. You can pick up a fair amount of free energy from the sun through your windows if you attend to the shades and drapes. All the electricity used by all your devices turns into heat; they are 100% efficient space heaters from the plug onwards. The light from a light bulb too; it turns into heat when it’s absorbed by whatever it hits. All this is usually not enough, so you have the second way: a furnace or boiler to make up the difference, and a thermostat to make this happen automatically (recall first lesson: turn it down). Every time you turn off a light bulb, you are turning on your heating system.The electricity these gadgets use delivers from 30 to 50% of the energy consumed to make it if your power is thermal (coal or gas), counting generation and transmission losses. Your home heating system is either electric or burns fuel; if the latter, it’s between 70 and 85% efficient. If it’s electric, you have nothing to gain by turning off the lights or the TV; you can just skip to the next section. If you buy gas or oil to heat with, and your electricity is from gas or coal, your net energy saving is only about 30% of whatever electricity you save by managing lights and appliances. Not nothing, but nowhere near as important as managing heat loss through the envelope of the building. Perversely, if your local power is nuclear or hydro, and you don’t have electric space heating, you are accelerating climate change (though you are probably saving money) by turning out the lights or substituting CFLs for incandescent lamps, because you are burning more fossil fuel instead of using near-zero-carbon energy. Lesson three: energy, money, and climate savings from being careful about home electricity use in the north, and in the winter, are much smaller than you would think just by looking at the wattage of your various devices. It’s neither comfortable nor safe to use your gas range as a space heater, but it’s 100% efficient, so there’s no reason to be stingy with it: go ahead and fry up those
burgers soy patties.
During the short periods when you are neither heating nor cooling your house, what you see, wattage-wise, from conserving electricity is what you get. It’s worth taking care.
When you are air conditioning, everything changes. It takes about half a joule to pump a joule of energy out of your house into a hot day. So lesson one again: weatherstrip, insulate and all that, and also keep the sun from shining in your windows. Awnings are much better than interior shades for this. Make sure you have a really efficient air conditioning system. Do the math; it may be worth upgrading sooner than you think. Turn the thermostat up; put on shorts and pad around barefoot.
Cheat the air conditioner as much as possible by taking advantage of cool outside air at night. Most people don’t know how to do this. What you need is a whole-house fan, installed in your roof or in the top half of a window, on an upper floor if you have one, in a room you don’t occupy at night. Look for at least 3000 cfm, more for a large house; this is not a drugstore box fan, though a couple of these will work in a smaller house. Don’t worry about the electricity it uses; it will be in the low hundreds of watts, and your air conditioner draws thousands.
The fan needs to blow air out, not in. Out. Open a window in each of the rooms you want to cool and open the doors between those rooms and the fan. With the fan running, this will generate a nice jet of cool air perpendicular to each window, right across your bed if you can arrange it. There are very few places in the US where you need air conditioning at night if you can get outdoor air to blow in at you. Overnight, your house will fill up with nice cool air. In the morning, shut off the fan and close everything to keep that air inside as long as possible, and keep the sun from shining in. With good insulation and shading, you will need minimal air conditioning when you come home from work until you can use the fan again.
All the energy you use in lights, cooking, and appliances costs you and the planet almost half again as much as their wattage, so using less energy for the same light and other services (CFLs, efficient refrigerator, etc.) starts to really pay off, especially as the air conditioner and the appliances are all on the same electric grid. Lesson four: during the summer and in the south, get down with fluorescent lighting, and turn things off when you don’t need them. Kitchen range…well, how about a nice salad for dinner? As the summer is getting longer and hotter, and the south is moving north, these skills will be increasingly valuable.