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An old timer trick to remove air from monoflo® with convector systems where the vents were behind painted covers and not easily accessible, was to operate the circulator pump at a higher pressure and lower temperature to have the air be absorbed in solution (Boyles Law) then heat up the boiler and drop the pressure and let the air vent near the boiler. Then let the water temperature drop and increase the pressure again to absorb more air from the loops. (…rinse and repeat)

I know you don't have convectors or moniflo tees but the principal will work. The idea is that cold high pressure water absorbs air. It actually makes the air dissolve into the water. Hotter lower pressure water releases air, the air actually bubbles out of the water. This trick kept the mechanic and his dirty boots and fingerprints off of the white panted covers and light colored rugs upstairs.

If you are repiping, and you want to make Boyles Law work to your advantage. Add the air purger right after a valve on the supply port of the boiler. Then pump away from the expansion tank that is connected to the bottom of the air separator.

This piping arrangement actually puts the lowest pressure and the highest temperature of the entire system in the same place, along with the device that can remove the air when it gets there. You will be amazed at how the air just goes away after operating the system for a few hours. all of a sudden radiators that never were hot before will warm up and start heating the rooms.

you don't know that if you haven't done a heat loss calculation. the loss is only on the outside. is the 180,000 btu/hr input or output? Even the best windows are a bit worse than the worst solid wall so windows are more about how much area they are and how good the weatherstripping is. a modern house with a wall of glass of the best windows is going to be far more lossy than an old house with 100 year old windows without storms if they are in decent shape.