Standard boiler antifreeze (not the same as automotive) can be used, but I would carefully consider if it is necessary. Not only does it try to leak out of every valve stem and imperfect joint, it is pretty expensive. Have you priced out the quantity required to treat your system?
They make "conditioner" that can be added to boiler water, but not all of the products are compatible with antifreeze. Your local plumbing supply house should have something that will work either way.