On Tue, 22 Jul 2003 13:42:09 +0100, Christian McArdle wrote:

snip

Another alternative is to stick a 3kW immersion heater in some suitable
chamber and pump the water through. An immersion is dirt cheap and I'm sure
you can find some suitable "cylinder" to immerse it in, provided suitable
safety precautions are taken. (I might consider a vent pipe straight up to a
metre or two above the pool level from the top of the chamber, for example).

Hmm, pool heaters are essentially un-vented flow boilers (albeit with an
excess pressure safety valve). It's the passage of water through the boiler
that keeps it operating safely. They *must* be wired so that they only work
when the filter pump is on. I think you'd need to get some sort of cylinder
that was little bigger than the bore of the (usual) inch and half diameter
pipework.