I am installing a wall heater in a room. The heater has a ground wire and a black and red wire. How do you hook it up to 240 volts? Do I need to run four wires, three wires? I have a double breaker at 20 amps already in the circuit breaker panel but what do I need to hook up power. Does one of the wires on the heater need two power wires to make the 240?

Hire someone who knows what they are doing.

The 240 VT ( normally referred to as 220 vt) will have three wires, two hot wires of 120 each and one ground wire.

Your black and white wires are for the "hot" wires, the other the ground.

You will have one hot wire coming from each breaker or ( two wires from the double breaker) and then a ground wire that comes from the grounding plate in your box.

HI,
I strongly suggest following the first answer you received, and hiring someone to do this. You are going to need a 220-240 Volt wall receptable, as well as a 220 Volt male plug-in, wired to your heater wiring, which to plug into the receptable.
This has to be done according to the Codes in your local area. I do wish you the best.

Part of your confusion may be the black and red wires in your heater, and the black and white of the 2 wire cable you have. Code allows a 2 wire cable with black and white to be used for a 240 volt circuit, therefore the voltage across both the black and white can be 240 volts. The code does require you to re-mark the white wire with colored tape to indicate that this white wire is not a neutral of a 120 volt circuit, but is a hot wire.

The black and white of your 2 wire cable will connect to the black and red at the heater, can be black to black and white(with black tape) to the red on the heater.

Be absolutely sure that the ground wire is connected both at the source and at the heater, this is the most important wire in an electrical system.

And to clarify, 220 volt is no longer used in North America, was popular many decades ago. The nominal residential voltage now is 120/240 volts. There are other voltages used for commercial and industrial applications, such as 208, 277, and 480. I have had electricians use "220" volts while explaining something to me, they were reprimanded and told to go on their own time to test and read the exact voltage of what they were working on, as knowing the exact voltage is important with ratings of equipment, etc.