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conflicted on steam boiler draining

Hi all,

I am a bit confused on all the information out there regarding draining a steam boiler. I have a 99 Mclain residential boiler. I fully drain and flush in the fall and spring just to get the rusty water out of it. Unfortunately I am confused as to whether or not to regularly drain the boiler. Obviously flushing the boiler will keep the water in the boiler clean, but I am also reading that fresh water contains oxygen which will result in increasing the corrosion of the boiler and pipes.

Does anyone have a recommendation of which is worse: flushing all the time and bringing in new water, or letting the existing "rusty" water remain in the boiler. Or is there a happy medium that I should try to find?

As a note, I keep my boiler fairly well so there isn't any sludge in it. I skim it once a year, but the 70 year old pipes keep the water from being anything close to clear!

Thanks in advance for your help!


  • Adding Fresh Water to Your Boiler

    It is highly recommended that after adding fresh water, you heat the boiler water to the point where it is making steam . This drives off the excess oxygen which can cause a corrosion problem.

    I follow a similar pattern to yours. I drain and flush my boiler in the spring and do the same in the fall. I also use Rhomar 9150 & 903 especially to store the boiler over the summer.   I've been very happy with the result.

    - Rod 

  • Big-Al_2
    Big-Al_2 Member Posts: 263
    edited November 2009
    Me too

    I do wonder what is the best as well.  I drain and flush my Burnham IN-6 annually . . . open up a 2" NPT drain cap on the mud leg and hose it out well inside . . . and then refill it and fire it up to a boil right away.  I also blow down the float-type LWCO  during the heating season, and drain a little water out of a drain valve low on the boiler and refill it right away.  I do it first thing every Saturday morning, when I know the boiler will be starting up from the overnight setback.  For the first couple of  seconds, the drain water is always really rusty.  As soon as it starts to look clear, I quit draining.  After the blow-down, the water in the sight glass goes from clear to "weak tea" for a little while.

    I might drain a gallon out each week.  My boiler has a manual water valve, and the level in the sight glass might only drop 1/2" or less per week, so there isn't any other make-up water. 

    I do wonder if this is not enough blowdown, too much, or about right.  It also bothers me that the water gets rusty again so soon.  Maybe I think about this too hard.

    Any opinions, experiences, or guidance would be appreciated.
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