Both rowing machines and exercise bikes are good for exercise and working out as well as losing weight.
But a rowing machine gives you a much better workout with less work than an exercise bike does.
With an exercise bike you have to really pedal hard to work up a sweat before you start burning calories and you have to use the exercise bike more often to get the same results of weight loss from the exercise bike than you would with the rowing machine.
Still you can use both the exercise bike and the rowing machine to get the best results and you may notice faster weight loss and muscle toning as well with the use of both machines.
You can burn up to 400 to 600 calories with just 30 minutes of rowing exercise which is much more that you would on the exercise bike.