>Well I was asked from some firm here in YU to build this for them
>because they have 2000 heaters and want to build regulators by
>themselves. That's only reason!

Use a CA3059 SCR/Triac controller.

http://www.onsemi.com/pub/SocketSearch/1,1319,,00.html?qt=ca3059

These devices are just so simple to use there is no argument.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.