I have a 1980 Repco Boiler and took the output (138,000 btu) devided by input (175,000 btu) and get  .  is this the efficiency?   Wouldn't a new standard cast iron boiler of  efficiency be the same?   Also, how would i flush sediment / scale out of it?  Any feedback is much appreciated.    Also, are older American Standard  boilers any good?  I was given a smaller 130,000 btu unit and am thinkng of cleaning it up and replacing the repco.  I think it's around the same age maybe older???
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