Does a 900 to 950 watt require a separate electrical circuit?

Depends more on the application and what else you might have on a current circuit you would use if you didn't install a separate circuit.

At 120 volts you are only talking about drawing 8 amps. On a 15 Amp circuit this is fine. However, if there is a motor involved there may be excess start-up currents.

There are certain appliances like stoves, refrigerators, dryers, dishwashers and so forth that require separate circuits. If you have a small heater you move from room to room then you can use an existing circuit that would not trip when you added the appliance. Use the cord that comes with the device directly into an outlet rather than using an extension cord.

If the appliance needs to be hardwired into a box then use a dedicated circuit.