i use a 2000w heatstick to heat my strike water ..... and boil my wort ... i've boiled almost 8 gallons of water with one stick .... make sure your running nothing else on the outlet and that your breaker is at least 20amps
i have yet to see how long a 5lber will last (ive only been kegging since early december) .. i bought a spare though ...only cost 8bucks to fill a 5lber at the local welding shop