In our house, a debate has raged for eons over the power-surge theory.

This is the claim that it is better to leave an appliance like a computer on while you pop out for milk because there is a power surge when you switch it on that cancels out any energy-saving benefit you would get from turning it off and then back on again 20 minutes later.

I've always taken the position that this is nonsense, without actually knowing whether it is or not, so with Big Energy Saving Week coming up, it seemed like a good moment to get my facts straight. It's not the only point of confusion about domestic energy use. For instance, if you are using only one room, is it more efficient to use a portable heater than put on the central heating? And can electrical appliances that are plugged in but switched off still use power?

Brian Horne is knowledge manager at the Energy Saving Advice Service, which makes him the perfect person to answer these questions. (I'm tempted to use the word "guru", but will resist.)

First the power-surge theory. Is it better to leave your computer on while you pop out? No, is the short answer. Horne explains that while it's true many appliances use more power when switched on than when running, the amount is truly tiny, the equivalent to a few seconds of running the device. So it's always worth switching it off when not in use, even for a short space of time.

Most of us are aware by now that habitually leaving TVs and other appliances on standby wastes power: the Energy Saving Trust (EST) estimates Britons could save £1.7 billion annually by not doing this. But that's not all. Even if a device is plugged in but not on standby, it might still be using power, depending on the appliance.

If you leave your phone or laptop plugged in beyond the point it is fully charged, it will still draw power but just waste it; even if your charger has no appliance attached, it will do the same. So the EST advises switching appliances off at the wall or unplugging them altogether when not in use. Easier done of course if the plug is not wedged into an extension cable behind your desk.

As for portable heaters in one room versus the whole central heating system, it really depends how you are using them. Central heating costs about a third what it would cost to heat your home with freestanding convector heaters and the likes, but if you are only in one room, what then?

Well, if you can be bothered turning off radiators in all the rooms you're not using, says Horne, that might be the cheapest option. Your boiler will heat water to fill the radiators to a high temperature. If that water is only going to one radiator and back, it will lose very little heat on its journey and take comparatively little energy to reheat, but if it is going round every radiator, it could lose as much as 20 degrees, costing more to heat back up again.

If you get an efficient portable heater, you could save money by using that over the central heating, assuming it is not an inefficient fire that guzzles vast amounts of electricity.

So there we have it, a few questions cleared up, thanks to Brian Horne. I do like to win an argument.