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Should the water supply flowing into a steam boiler be cold water or hot water?
Should the water supply flowing into a steam boiler be cold water or hot water (from the hot water heater) or does it matter?
When I made the oil-to-gas switch, the plumber also installed an A.O. Smith natural gas hot water heater (the upright storage tank variety with anode rods inside). He had hot water going into the boiler. After 15 years, that hotwater heater began to leak, and I had to shut off its cold water input. This deprived the boiler of hot water so I had to (a) either shut off the boiler and live without heat or (b) allow cold water to flow through the leaking hot water heater so the boiler had water input and mop up the leak on the floor.
To get around this problem, the plumber who replaced the hot water heater (with another AO Smith) redid the piping so that the boiler is fed by cold water. I wanted him to give me the option of feeding hot water or cold water into the boiler. He said there's no good reason to feed hot water into the boiler, because the amounts of water added to the boiler is small and would make little difference from a heating efficiency standpoint. In We Got Steam Heat, Dan writes that tap water contains oxygen and minerals that are corrosive, so it is better to fix leaks and limit the amount of fresh tap water flowing into the steam heating system. By heating tap water, doesn't the hot water heater remove some of the oxygen from tap water and doesn't its anode rods absorb some of the corrosive elements in the tap water. In this sense, does it make sense to feed hot water from the hot water heater into the boiler over cold water from the tap?