Gas and Oil Home Heating Furnaces - Electric Baseboard Heater

I am trying to install a Fahrenheat 4 foot electric baseboard heater, but the breaker keeps popping when I turn it on.

The heater is a 1000W, I ran 12/2 to a 20amp breaker.
The switch on the heater has 2 sets of red and black wires. One set on the top and one on the bottom of the knob.
I ran the white from the breaker to the red on top and black to black, and also tried running them to the bottom.

Nothing else is on this run.

Am I missing something simple?

Look at the schematic that is on the unit or the paper that came with it . You dont say if the unit is 110V or 220V could be;) ED

As Ed has pointed out, verify the operating voltage of the unit. The thermostat sounds like a double pole type. That means that line voltage should go to one red and one black and the other red should go to one end of the heater and the black should go to the other end of the heater. That way when the thermostat is open, there is no voltage present in the heater at all.

Ken

The unit is a 240V but says it can be used on a 208V supply at reduced wattage.

Does this meen I neet 10/3 and a 30 amp breaker?

You should have a double pole 20 amp breaker. You didn't say if you had a single or double pole breaker. You should have the black and white wires on the breaker and the ground wire on the ground bar in the panel box. Then the black from the breaker would go to the black on the thermostat. The white from the breaker would go to the red on the thermostat. The ground from the incoming line would get bonded to the ground screw on the heater. The other two wires from the heater go to the other 2 wires on the thermostat. It doesn't matter which goes to which.

Forgot to say: 12/2 is ok. You probably don't have 208 volts anyway but it wouldn't affect output too much.

I had a single but just went and bought a double pole.
When I was using the single, just the one breaker popped, now with the double the main pops.

Does it matter whether the white or black is connect to a certain spot on the double?

No it doesn't matter white or black on either terminal. Look at the thermostat and see if the wires are labeled line and load. Line is from the breaker and load is to the heater. I would be surprised if the wiring was different than I stated earlier but you obviously have a dead short and the thermostat could do that if it was not wired correctly.

Look at the schematic that came with the unit. Id also check out that the double breaker you put in got 220V from both legs. on some panels you can put a double breaker in and only get 110V.
like ken said you have a dead short. Sit down and draw it out on paper how to wire it if you cant Id get some one that knows electric ;) ED

You have two wires coming from the panel to the heater. Usually one is white and one is black. Both the white and the black connect to the 220V breaker you installed. Remark the white wire with a black marker. Make sure the breaker is not connected (not installed in the panel) yet.
At the heater the Tstat has 4 wires. Usually the red are the input, the black are the output. Make sure the Tstat is correctly connected to the heater. The two wires that came from the panel will connect to the 2 red wires. It doesn't matter which order. The ground wire (if you use NM) connects to the ground screw on the heater, and the ground bar in the panel. You will not have a neutral. There should be nothing connected to the neutral.
The instructions should tell you how to connect the Tstat to the heater.