Can anyone recommend a cheap but reliable heater to warm up a small (15L) bucket of water on water change day?

On a water change related subject, given the commonly seen pH change in water if left overnight, should water be left out overnight prior to a change?

Tom

If you are only changing that amount of water it would probably be as easy to add some water from the kettle to the bucket before dechlorinating? People who use heaters are usually doing much bigger water changes.
At the moment I usually do a 30 litre change on one tank and a 60 litre change on the other, but not on the same day. I run off the buckets the night before and I know from experience that I need to add about 1/3 of a kettle of boiling water per room temperature 10L bucket for my temperate tank and a whole kettle per bucket for my shelldwellers to get the right temperature, so it is not much of a fiddle.
Having said that I've had all sorts of heaters, so far all have eventually failed except a Jager one, which was more expensive than the others, and the heating element in my Eheim thermofilter.
When I had more tanks I used to use Mr C's 5 gallon bruheat which was very quick and had a useful tap as well but they are about £100 new
Whether to draw the water the day before depends on how much your tap water changes in that time.