I just went through this with our 714 -- it takes a 20A dedicated circuit.
Was having issues with out smaller 609 (turned out to be a bad receptacle) and had an electrician in studio to inspect power on both our 120v test kilns. I was questioning the 20A circuit for the 709 since its amperage rating is too close and if we managed to fry a less amp kiln's wiring, what about the one drawing more juice. Both Skutt and the electrician confirmed 20A was the common setup on both models since a 25A circuit is only possible at the breaker side, there are no 25A receptacles and the kiln would have to be hard-wired to a shutoff for this to work. I need to be able to unplug the kiln for stuff like element and brick repairs after someone blows up their test tiles in these powerful little kilns - so I chose to just switch to dedicated 20A twist-loc receptacles and plugs for ease of service. The other way suggested by the electrician was to possibly setup the kiln with 30A and install a lower amperage inline fuse on the control box.