longer washing cycle or higher temperature?

[midnightexpress]

Apologies if this has been done before - haven't got time for a search this morning as I'm supposed to be working .

My washing machine has a button to reduce the temperature on any wash cycle, but it's broken. So, my question is, is it better to do a 30 degree wash that lasts 1h45 or a 40 degree wash that lasts 1h20? My head is telling me that the 40 degree wash must be more efficient (and cheaper...) but I wonder if I'm right?

from what I understand, the cooler the temp the longer the cycle, but the longer cycle doesn't use as much electricity as the heating of the water is what takes the vast majority of the power usage

that's right- Leo Hicks did this in the grauniad (ethical dilemmas) a while back.

Cooler temperature lower time is definitely more eco-friendly. Hence the 'wash at 30' campaigns lots of laundry product manufacturers and retailers have been running for the last couple of years.

sorry, that should have been 'LONGER time', doh

Thanks fo the replies. Zazette, that's what made me wonder - I'd always tried to turn it down to 30 from an existing 40 degree program though, where it would figure that the 30 degree wash would be better. Just wondered with a substantially longer cycle how it worked out. I will now proceed accordingly.