You didnt need to do that, though. It peobably wouldve been easier to use manual j (or some software) to estimate the heat loads in the house, with given set points, using weather station data.
Then, because the answer is almost always going to be "yeah, it's going to be really close...", I felt well-advised to prove it via experimentation rather than commit to changing the heating plant to a system that could not provide 150°F flow temperature.
If your heater can go low (mine bottoms out at 50 unfortunately), by far the easiest is to just test.
Alternately, to get a realistic measure, you'll need to set your boundary conditions about what the heat flow out of the room will be, which is a bit simpler to setup with U-values, area, delta-T, and heat capacity of materials. You'll also need to do this to every other room in the building simultaneously. This is a Manual J, or heat balance method or the radiant time series method load calculation that will balance out with the amount of heat leaving your radiator without knowing its specific shape.