I only ever washed in cold water, unless doing a strip wash. I did a strip wash when the nappies weren't as absorbent as usual, or got a bit stinky. Maybe every 4-6months.
I used either 1/2 amount of normal washing liquid/powder each wash, or soap nuts were really good, and bicarb did a great job too. Can't recommend enough sun, sun and a bit more sun I had a little squirt, well the DP home made Bunnings version ($45) loved it, couldn't have done with out it!

Once the initial outlay is done, not forking out every week or fortnight for disposables will save you heaps. And those fluffy bum are soooo cute