possibly, I wouldn't really expect "size" but it depends on what you mean by size. A rowing machine is one of the best, total body cardio machines out there. If you perform the excercise in sets like intervals, you will burn fat but you will also tone up because interval training releases testosterone into your body which aids muscle growth. It raises your metabolisim and burns fat without forcing you to lose muscle the way traditional cardio can. You should perform 20 minutes worth of intervals and structure the workout with 30-60 second "bursts" of very fast, hard rowing followed by a 30-60 second recovery period of very light rowing. You want your heart rate to come all the way down during the recovery period, and you want your heart rate to be pumping between 175-190 bpm (depending on your capeability) during the "bursts" to mimic true intervals and get their amazing benefits. I always tell my clients: if you look at distance, marathon runners and compare them to sprinters, whats the difference? The difference is sprinters are always cut and marathoners are usually either emaciated or overweight- reason being: sprinters train using intervals which creats the post-exercise metabolic effect that releases testosterone and shreds your body up as opposed to long-distance cardio which tends to burn muscle as fuel. 

Check out my website for more info and other stuff like exercise videos and nutrition tips if you'd like!

http://www.nextlevelbodies.com