by Leeny Hoffmann 
I often walk into the gym to get the rowers set up for my class, only to find
that many of the dampers are set all the way up to 10. This always amazes me
because I know what a slog rowing at a 10 can be. I understand that people
don't always know better and often treat a damper setting like resistance. They
think, "If I set this thing at a 10, it will make me work harder and I'll get a
tougher workout, and that will make me a badass." You will have a tough
workout, and quite possibly a miserable experience and a backache to boot.
Understanding what the damper actually does for you will allow you to row more
efficiently and create a more "enjoyable" experience on the erg.
Damper 101
First of all, damper setting is NOT resistance. The damper setting creates a
drag (allows more or less air into the flywheel). It gives you the feel of a
heavier boat or a lighter boat. To move both types of boats quickly, you have
to put more energy into the system. If you want to move a lighter boat quickly,
you must row faster or harder. However, if you just paddle along, even a light boat will
go slower. It all depends on how much energy you put into the oars. Imagine a
sleek, one person racing boat. The faster you move the oars through the water,
the faster you will go. The same principle applies to the erg. At a lower
damper setting (1-3), you will move quickly on the slide, and it is easier to
row at higher stroke ratings. Rowing at a low damper means that the flywheel is
more closed and less air is able to come in and slow it down. This also means
that the flywheel doesn't decelerate as quickly so at the catch, you can
continue to move quickly into the next drive without taxing the leg muscles too
much. Once again, your pace will be determined by how much pressure you put
into your footplate and handle. At a lower damper, you can move faster and
rowing at faster stroke rates tends to be more cardiovascularly taxing. 
On the flip side, rowing a heavier boat requires more pressure into the oar to 
move the boat through the water. As with a lighter boat, to move a big boat faster, 
you have to row harder.  On the erg, rowing at damper settings between 8-10 can feel like 
a big, heavy boat.  The damper opens up the flywheel allowing more air to circulate, 
thereby requiring more energy to keep it moving. The flywheel also decelerates
quicker, requiring more muscular energy at the catch to get it moving again. This typically 
means a slower stroke rate.  Rowing at a high damper setting can be more muscularly taxing.  

Which one do I do?
Damper setting is a very personal preference. You need to row at different
dampers to find out where YOU are most efficient.
Some questions to ask yourself... Do you like to move faster like a sprinter?
Do you like to move slower but pull a heavier load? What type of build do you have? What 
type of piece are you rowing?  Smaller people with petite builds seem to have good 
luck at the lower damper settings. Bigger, taller, more muscular people can often
handle a higher damper. I find that rowing somewhere between 4-5 works well for me for
all purpose rowing. 
For very short pieces or when looking for max power or calories, you may consider bumping
up the damper a notch.  It's always good to practice and see where you feel the most
powerful.  Try a watt test...row at damper 2 for 30 seconds at heavy pressure and see what 
watt output is.  (Bodyweight plus is a good thing to shoot for).  Rest 30 seconds and try
again at damper 4.  Feel any different?  Continue up the flyhweel until you get to an 8 or 9.
As you go to a higher damper number, when do your returns begin to diminish?  Play around
with it and you will find a damper that seems to give you what you want.
For a great article and more info on damper setting and drag, visit the Concept2 website here:
This article is fantastic and I borrowed heavily from it.