These heaters require 240V. But think twice about buying this heater - I bought two and both were faulty. Checked online and others have had the same problem. I think there's a serious manufacturing flaw.

Yes, you need to purchase a thermostat - you can wither get a wall-mounted model, or I believe you can get a thermostat that mounts in the unit. Rule of thumb is 10W per square foot, so this should be good for about 250 square feet assuming a reasonably insulated space and 8-foot ceilings. But think twice about these heaters - I bought two and they were both faulty. Had to return them and buy others.

Good Morning,
Please contact Dimplex technicians at 1 888 346 7539 M-F 8-4:30pm EST for assistance .
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Good Morning,
Home Depot has 240/208 volts.
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Good morning,

In regards to the wire and breaker size you need to contact the local building and electrical code in your area..

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A typical figure for calculations is 10 watts per square foot.
2500 watts would be good for about 250 square feet.