Acid cleaning iron deposits from heat exchanger

Discussion in 'Open Loop' started by KENTON COLLING, Apr 3, 2021.



    I have a WaterFurnace Model ATV034D110NLT unit in service for 22 years. The heat exchanger likely needs acid cleaning.
    My question is what strength Muriatic acid (HCl ) do I need to use to do the cleaning.
    I have heard it should be around 10 %. Do I need any additives to remove the iron deposits.
    Should I recycle the acid after it comes out of the heat exchanger or should I use several new batches of acid.
    I plan on pumping it from 5 gal. pail with a transfer pump and collecting it in another pail.

    Well has following test results: Iron 0.1 mg/L , Ca CO3 230 mg/L , Fluoride 0.7 mg/L
    Looking at other piping shows a black deposit that sometimes flakes off. I believe it to be iron.

    Unit is 34,000 BTU or 2.833 ton. It is running at 6 to 6.5 GPM on well water 40 to 60 psi. @ 50 deg.F inlet and 40 deg.F outlet. Heat exchanger is Cupronickel coaxial.
    The Kilowatt-hrs use for a season have gone from 10,000 KWhr. to about 12,000 KWhr. in the last 2 to 3 yr.
  2. Valveman

    Valveman New Member

    Acid will work. I am not sure of the strength that needs to be mixed up. Vinegar might work as well for something less caustic. I have never had to clean mine. Mine is set up differently and the water flows through the heat pump all the time, even when the heat pump is not running. This seems to wash out the hard water deposits as I have never had any build up.

    It is not good for your well pump to cycle on/off between 40 and 60 while running 6 GPM to the heat pump. If your well pump has lasted 22 years working that way you are incredibly lucky. If your well pump isn't lasting 20-30 years a Cycle Stop Valve will stop the cycling and make your pump last longer.
  3. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    If your unit does not have a cupra nickel coil, I would avoid acid all together. I once ran muriatic acid through a fhp unit that was before cupra nickel to remove scaling and we ended up buying them a new compressor section.
    Valveman likes this.


    Thanks for the info. My well system has a 120 gal. pressure tank so pump does not cycle on very often. After 21 years I had to pull pump out of well because of hole in the galvanized 1" pipe (120') supporting it. Pump was OK, stainless steel.
    Replaced pump because I don't want to pull it up in a few years. Replaced galvanized pipe with plastic.
  5. Valveman

    Valveman New Member

    A 120 gallon pressure tank only holds about 30 gallons of water. I hear people say, "My pump doesn't cycle very much. I only hear hear it maybe every 5-10 minutes or so". Well there are 1440 minutes in a day and a heat pump runs most of those. A cycle every 5 minutes can still be 288 cycles per day, which is not good for pumps, tank bladders, check valves, starting capacitors, pressure switches, and many other things. Even it you are lucky enough for your well pump to last a long time cycling like that, it would still last several times longer if it didn't cycle.




    Need some advice.
    I have backflushed my Waterfurnace now that the heating season is done. I used three gallons of 5% white vinegar pH = 4. Ran 1/4 Hp, 16 GPM pump for one hour, then shut down for 1 hr. Only small amount of discoloration of vinegar. Restarted and pumped for 3 hrs. Purged heat exchanger with water. Back flush effluent showed some darkening compared to clean water. A few particles of black scale in bottom of pail. Looked like iron.
    Question: Do I need to use a stronger acid like Muriatic or pump longer with vinegar. I had expected more black deposits from the iron in my well 0.1 mg/L.
    Any advice is appreciated.
  8. Valveman

    Valveman New Member

    Is there anything there to clean out? Why are you cleaning in the first place? Has the differential pressure or temperature changed?


    Sorry for the delay in answering but I was away from the grid.
    I had noticed a black deposit on inside of some outlet piping I had replaced while revising the discharge to my ponds so I wondered if the heat exchanger was coated also. I had also replaced solenoid valve at outlet because it had black deposits inside and was sticking open occasionally.
    PS I agree Valveman there may not be anything to clean out.
    Last edited: Jun 18, 2021
  10. SShaw

    SShaw Active Member Forum Leader

    Thanks for the update. I don't have enough experience with open loop to offer any other thoughts.

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