If my calculations are correct:

2 quarts of water = 4 lbs.
Temperature rise from 62F tap water to 212F = 150F rise.

1 BTU = 1 lb water 1F
so you would need 600 BTU's (but that's for 1 hour)

if you want it in 30 seconds (120th of an hour), you would need 600 BTU x 120 = 72000 BTU

1 Killowatt = 3400 BTU

72000 / 3400 = about 21 Kw

at 240 volts that = 87.5 amps

If you start with 140F water (72F rise), you could get by with half the energy needed:

240v 44 A

GOOD LUCK

Definitely use a single tube. I would use one with vanes on the inside to maximize surface area between the water and the metal.

Get a copy of Davies & Simpson's Induction Heating Handbook through interlibrary-loan.

See also:

Here is a link that might be useful: Induction Heating