I want to install a 220 volt wall heater. The feed line has a red, black, white and copper ground. The heater only has a red, black and ground. What do I do with the white (common) line?

As long as there is 240 volts across the black and red, and 120 volts across each the black and red to the white, then this should prove the white is a neutral (common), and since the heater does not need a neutral, it can be capped with a wirenut.

Be sure the wire is of sufficient size to handle the heater load.

Thanks for the response. The 220 service was put in by a professional so it sounds like red t red black to black and cap the white. As always grounded.

Thanks again.