A dishwasher includes a first washing chamber and a second washing chamber capable of performing a washing operation separately and/or concurrently. Each washing chamber includes a wash pump, a drain pump and a heating unit that are operatively connected to a controller. When initiating a washing fluid in one washing chamber, the controller determines if the other washing chamber is active. If the other washing chamber is active, the heating unit for the one washing chamber is operated at a low power level. However, if the other washing chamber is inactive, the one washing chamber is operated at a high power level to rapidly heat the washing fluid and thus shorten the duration of the washing operation.