I presume you are looking at C02 heaters? They stop the regulator freezing up with high flow rates. Only necessary if you are using a lot of gas very quickly.
Esab have a plug for heater on some of the older mig sets
Think I have a heater some where for CO2, it was a unit that fitted into the gas line about the size of a small baked bean tin in brass with a wire to the plug in to front of base unit Think welder model was 150, 3 phase unit if I remember plug was 110 volts, but it was a long time ago.
Bomb proof unit with removable head
There are a lot out there http://nichegas.com/heaters.html