@WacoJohn,
As long as an extension is rated for the maximum current the device is using, there should be no problem. To calculate the current, use....
.....Device Wattage divided by Voltage (110) = current in amps.
(Note that 1kw=1000watts).
If in doubt use the thickest, shortest extension cord available (3 core if you need an earth wire). Loops in cables should be avoided because they can cause extra resistance to current.