HVAC Waters

descaling a boiler

Inhibited sulfamic acid (NH₂S0₃H) cleaning: 

• replace the boiler's brass or bronze plumbing parts with steel

• vent the boiler so evolved gases may escape

• isolate the boiler from the main steam header

• top off boiler and heat to maximum temp. permitted by inhibited acid

• circulate with acid-resistant pump from highest to lowest point of system

• add inhibited acid sufficient for a 3 - 6% solution

• add acid as necessary to maintain pH between 1 and 4

• when the pH of the water no longer rises, descaling is complete 

• drain the boiler and flush with tap water until pH of the drain water is 7 

• fill with trisodium phosphate (TSP) solution (1lb. to 100 gallons of water)

• fire boiler after TSP solution is circulated and water is lowering to normal level

• drain the boiler and flush with tap water

• if the boiler is to stand idle for more than a few days, protect it from corrosion

• wet lay-up with sodium sulfite residual of 50 ppm or greater is advised