We assumed a North American Standard of 7amps x 110v = 770 watts. Take a look at another 100w amp and see what the current draw is at full output, because in Class A, your amp is at full output at idle...that is why it gets so hot because it need to dissipate all that power when not driving a load.
My old (100w Class A) ML 20.6 amps drew 500w each at idle for a total of almost 10 amp (1000w). Since the Krell KSA 100 is also 100w Class A, 700-800watts at idle does not seem that far off.