With the goal being to burn fat? A lot of volume at low and moderate intensities would allow you to burn the most total calories. Probably mix in some other kinds of conditioning, so it's not all on the rower. Something as simple as gradually increasing the total weekly volume at a particular intensity, before dropping the volume back down and increasing the intensity. The concept 2 rower will give you watts, as will many other devices, so it's a good measure of intensity.
That said, and you're probably already aware of this, but diet is by far the most important part of fat loss. If it's not on point, it doesn't matter how much activity you do. Activity only makes the diet aspect easier.