OP
inie meanie
I have been using the Triac 10PCV2425 from Crydom. It has a built in snubber and comes as a complete package. I have been using it to run two immersion heaters. When the first is up to temperature I switch a contactor and bring in the second tank. I have just bolted it to the side of a metal case with a small copper shim and a small thin heat sink from a pc. At the very worst time I have only ever felt a very small rise in temperature so I can honestly say that heat is not a problem, and I have been working it hard from just a couple of watts right up to 3 kw continuously throughout the day. The discussed interference has not manifested it's self in any way and I don't think that it is a problem. I am sure that the Emma box uses the same off the shelf component and seem to not employ any extra supression.