What size breaker do i need for a 4000 watt heater?

If you have a heater that uses a total of 4000 watts in a 240 volt connection, you'll need a minimum of 20 Amps. If it's only a 120 volt connection, you'll need a minimum of 35 Amps in the circuit. However, if you need to plug anything else into the same circuit, you'll want an even higher amperage to avoid blowing the breaker.