I live alone in a house. I want to know which is more energy efficient

(1) Switch on hot water in the evening and do all laundry, bathing, cleaning, then switch heater off

(2) Leave hot water on all the time.

I asked this question at work and it almost started WWIII.

Option #1 is the most energy-efficient. But it sure ain't convenient.

While water is heating up, run your sprinklers, cold-water wash-cycle and wash your car first to maximize efficiency to your schedule, before doing your hot-water stuff.

Tell your co-workers that it is a waste of energy to keep water hot for 8-16 hours a day. It's no different than using a freezer for making ice cubes. Does it make sense to keep a freezer running for 24 hours a day when you only need it to run for five hours- enough to make some good, solid ice cubes?

Mr(to protect and conserve)Sensitive

Thanks, mr.S.

That is what I thought, too.

Some people were saying that you have to heat a whole tank from cold to hot and that takes more energy than just keeping it hot, but I thought that since the water is cooling off all day, it takes a lot to keep it hot also.

Not necessarily so. It really depends on how efficient your system is, how much water you use and mostly on how well insulated your hot water tank and hot water pipes are. Forget about having to heat new water that enters the tank when you use some hot water, since this is the same requirement for both scenarios (i.e. when you use hot water the tank is filled again by cold water, which you then would have to heat up whichever method you use).

Assume for the sake of argument, that your hot water tank is insulated completely and you suffer no heat loss during the day. Once you have heated your tank once then you do not need to expend any energy to keep it at that temperature (since you lose no heat because it is well insulated). In this scenario it makes much more sense to keep your heater on.

Now assume that you tank is poorly insulated. It loses heat very quickly therefore you must spend a large amount of energy maintaining it's temperature. In this scenario it makes much more sense to only heat the water you need to use straight away, for example once per day in the evening. And you better use it quickly because it's losing heat also when you're only heating the water once per day....as you're heating it!

The real answer lies somewhere in between...i.e. it depends mostly on how well your hot water tank (and the hot water pipes) are insulated. Somewhere there is a crossover-point. On one side it is more efficient to keep your system on the whole day and on the other side to only heat when required.

Moral of the story. Whichever method you use, make sure that your hot water tank and hot water pipes are very well insulated. This always saves money.

Hmm. Thanks, Chancy, that makes sense.

I guess there's no choice. I'll have to run a test.

(1) Day one. Switch off tank and drain it completely of hot water, doing a bunch of laundry and a long hot bath.

Switch off all appliances, even clock radio, all lights, and so forth. Check my meter is showing no activity. Read meter. (READING #1)

(2) Evening, day one. Switch on only hot water tank. Monitor meter. When it no longer shows activity, switch off hot water tank and record meter reading. (READING #2) Switch on lights, clock radio, etc., and resume my life.

Drain hot water tank till water runs cold. (Now I'm washing my curtains. Everything else is clean.)

(3) Bedtime, day one. (READING #3) Switch on hot water tank only. Next morning, dress in the dark and breakfast at McDonald's.

Evening, day two. Check meter reading. (READING #4) Then switch on electrical systems normally used.

Compare (reading #2 - reading #1) with (reading #4 - reading #3)

I think this should work.