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Replacing 3 ton air handlers with 2-5 tons

Just bought a large 12,000 sq ft home that has 2-3 ton AC units servicing first floor. Units are relatively new but are grossly undersized based on my manual j heat loss calculations. I am replacing them with 2- 5 ton units with hydronic heat coils. I was wondering if there is anyway I can just get rid of the 3 ton air handlers and keep the 3 ton condensing unit a, line set and ac coil. I know this is unorthodox and not effecient but the current 3 ton condensers are relatively new and it kills me to throw them out. We rarely will use AC and use the units primarily for heating. I don't want to add extra units so they run in tandem as there is no room. Both existing units are on opposite ends of house.


  • unclejohn
    unclejohn Member Posts: 1,833
    First I would double check your load calc. 10 tons is a lot of cooling for one floor. Next you have to squeeze another 800 cfm into your existing duct work.
  • John Mills_5
    John Mills_5 Member Posts: 950
    Yea, most duct systems are undersized for what's there. You go throwing 66% more air through them and they gonna scream!
    EBEBRATT-Ed Member Posts: 14,483
    I would re-check the load.

    Even 10 tons doesn't sound right for 12,000 sq ft. Is that a typo????
    JUGHNE Member Posts: 10,898
    Above you mention your heat LOSS calculations.
    What is your heat GAIN calculation?
    Different animal all together.

    Where are you located, if you are in a climate where you seldom need AC then that 6 tons sounds pretty big.
  • aircooled81
    aircooled81 Member Posts: 205
    3 ton condenser and a-coil will do the same amount of work as they did before, so yes you could reuse. As you increase air volume across the coils, you will just see less of a temperature difference. This direction is not good for humidity control.
    Caution that the additional air will move through that coil at a higher velocity, so if they are horizontal consider where the condensate may fly off the face of the coil.
    HVACNUT Member Posts: 5,455
    @diesels12. Thinking about moving into a condo yet?
    What @JUGHNE said is correct. A different calculation is done for heat gain.
    I wouldn't recommend what your thinking. The existing ductwork is sized (or should be) for 3 tons of air.
    Installing a 5 ton drive motor to that is asking for trouble.

    You should be able to get a Manual J from your utility company.

    I'll get into it based on your answer to this, and your needed cooling capacity.
    Would it be possible to join the ductwork from both A/H's together, connecting from their largest openings, near the A/H's before any transitions?