Preventing pipe freezing

My hydronic system has two locations in upstairs bedrooms where piping passes through unheated areas behind knee walls that are prone to freezing. It seems like the best approach to preventing this from occurring is to relocate those pipes into the heated area. However, perhaps insulating them or wrapping with heat tape is a better alternative.

Do you have a recommendation?

If at all possible relocating the pipes is the preferred alternative.

freeze

moving water takes more energy to freeze. You can devise a way to keep the water always flowing, move the pipes or add anti-freeze to your system. Always install a back-flow devise if adding anti-freeze.