The condensate returns connect to the boiler via the Hartford Loop. This is an important piping safety arrangement to make sure that if a leak develops in any of the system’s wet returns, it could not drain the boiler and cause it to fire dry (which makes for a very big boom). How this connection is made is critical. It must be kept very short to avoid banging and water hammer. Most manuals call for a close nipple to be used to make the connection. At NES we always go one better and use a wye connection. It’s a bit more money and a bit harder to source, but it’s the right way to do it.