Sorry to come in so late on this topic.
I used to install a lot of locally-made "Avon-Air" heaters, ranging from 2kW up to 45kW.
Yes you will need a contactor or two in there.
One thing that no-one else has mentioned is a control circuit to cut the power to the elements, if the fan motor fails.
Mind you, you'd think that would already be in the "box", I did get caught once with this.
That wasn't an Avon brand heater though, it was something the Boss bought cheap.
Food for thought though.