Harold Kestenholz
When the water in the boiler turns to steam, it actually becomes distilled; it carries no dirt or rust up to the radiation. The water that comes back contains rust particles from the pipe. Filters present a high resistance to the flow of water, so you would have to pump the return water through the filter to send it to the boiler. This takes a great deal of investment to replace the chore of draining the boiler until the water runs clear and adding water again. IMO it is a lot of investment to install a filter that has not been necessary for steam boilers during the past 100 years.
