The "official" watt limit, according to Cecilia at ProVape, is 14.5 watts (& 3.5 amps). The real kicker is that there is a 3rd number that very few people seem to know about... For lack of a better term, I call it the "ProVari number"... It's the product of multiplying the watts times the amps... And it cannot exceed 50.
Both the amp limit and watt limit can, under certain conditions, be exceeded but the "Provari number" cannot... Under any circumstances.