What should my heart rate be for steady state?

I've recently been trying to do a lot of volume rowing (around an hour a day) in order to get faster for the spring season. My friend told be the best way to steady state is to keep your heartrate between 130-140 so I bought a monitor and have been doing so. However, this feels way too easy even though I know steady state should hurt your ego (rowing at ~2:40 split when I have a 6:59 2k). After trying to find out if what I've been doing is optimal, I discovered using the Karvonen formula to calculate my zone 2 area, which it says should be between 160-170 bpm (this might not be as accurate as possible, as I had to estimate my max HR). If I'm doing large volume rowing, should I row with the HR my friend said or the Karvonen formula?

Any advice helps, thanks.