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  1. #1
    Join Date
    Sep 2009
    Location
    Kennesaw, GA
    Posts
    619

    2.5 air handler with 3 ton condenser?

    Hey guys

    I have a question on matching units. In my dads house his electric heater recently got busted. I opened the air handler to just check it out and also saw it was very dirty. I was kinda disgusted lol and I was like if its going to cost a couple of hundred to fix it , what if we just replace it and also replace his plenum and ductwork. He has a 3 ton rheem r22 system and its about 10 yrs old. I;ll post its model # later for you guys. The unit is kinda of oversized also because his house is 1187 sq ft. I haven't done a hvac calculation yet. But the 3 ton has been working good for a while.

    But anyways that's just background info for you guys. So in my quest of looking for a new air handler I found a brand new 2.5 ton Goodman AWUF300816BA air handler for a nice price at surplus equipment outlet shop.

    This the PDF manual for the unit.

    This unit has a flowrater and no txv. I don't know if that will have a problem with the outside unit by not having a txv. I know this has 2 speeds with high at 1255 cfm and low at 1115 cfm. His current rheem air handler is set also I think at 1200 cfm. The unit takes both R22 and R410. I was thinking of getting this unit for the time being and later change the outside condenser to also 2.5 ton with R410 freon. Also I will add some more insulation in his attic as there isn't much there except for very old compressed cellulose insulation.

    Do you guys think the it will be ok to use the 2.5 ton air handler with the 3 ton condenser? The unit is going to be installed by my uncle who is a licensed mechanical contractor in florida...lol although I havent ask him yet. If you guys think its a bad idea or this unit is a bad unit then I will look for another air handler then.
    Last edited by BaldLoonie; 12-30-2010 at 03:01 PM. Reason: removed link to DIY site

  2. #2
    Join Date
    Dec 2010
    Location
    Palm Beach,Fl.
    Posts
    990
    Its a commom mismatch in south florida. Great for dehumidification as the coil runs a little colder. Mismatching the reverse of that ( smaller cond/bigger airhandler) is a big nono.

    Should be fine, although a load calc needs to be done before replacing the condenser.

  3. #3
    Join Date
    Jun 2008
    Location
    Cincinnati, Ohio
    Posts
    2,176
    Quote Originally Posted by SoFlaDave View Post
    Mismatching the reverse of that ( smaller cond/bigger airhandler) is a big nono.
    Why? I thought the greater the surface area of the coil, the greater the cooling efficiency. My evap coil is sized a full ton larger than the condenser for this purpose.

  4. #4
    Join Date
    Dec 2010
    Location
    Palm Beach,Fl.
    Posts
    990
    Its not the evap coil,its the air flow,talking strictly of non variable speed equipment. Excessive air flow causes a drop in heat transfer and moisture removal. For example 4 tons worth of airflow across 3 tons of cooling capacity would lose a lot of latent capacity.

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,601
    Harder on efficiency since the system usually has to be a tad overcharged to keep the suction pressure up. So you lose SEER and a little total capacity but gain latent capacity which sucks your Florida humidity out a bit better.

    A TXV would be nice, also helps with mismatched stuff.

  6. #6
    Join Date
    Sep 2009
    Location
    Kennesaw, GA
    Posts
    619
    So the system will work but when we replace the condenser is better to do a load calculation. I can actually do the load calculation tomorrow at his home (with hvac cal 4.0) and see what result comes out. I read somewhere on the hvac talk forum is always better to have a TXV over the Flowrater? This one has a flowrater...well at least based on the model it says that. I did not physically inspect the unit or ask the store clerk.

  7. #7
    Join Date
    Sep 2009
    Location
    Kennesaw, GA
    Posts
    619
    Quote Originally Posted by BaldLoonie View Post
    Harder on efficiency since the system usually has to be a tad overcharged to keep the suction pressure up. So you lose SEER and a little total capacity but gain latent capacity which sucks your Florida humidity out a bit better.

    A TXV would be nice, also helps with mismatched stuff.
    Oh I did not see your reply, I had the reply page opened for a while before I actually replied. Can a TXV be added? Ah then its better I look for an air handler that has the TXV already there. Well the system can run a bit harder for now and later we will replace the condenser and then we can also use the R410 freon. My real driver on this was that the cost of that air handler was costing a bit more then fixing the unknown electric heater problem on the current air handler. I mean what if I get the electric heater fixed and then the sensors later go bad and have to pay for service repair again. Rather just pay one shot and also get nice new duct work for my dad which I can actually do after my uncle makes me a new plenum box for the unit.

  8. #8
    Join Date
    Jul 2009
    Location
    South Carolina
    Posts
    3,365
    If you're relying on all electric heat & you don't have a heat pump that unit only comes with 7.5kw heat strips. That's not much if you're all electric. If you're sure that's enough then O.K. but if you're not sure I would rethink things.
    Gary
    -----------
    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

  9. #9
    Join Date
    Jul 2009
    Location
    Plant City, Florida
    Posts
    2,198
    Quote Originally Posted by garyed View Post
    If you're relying on all electric heat & you don't have a heat pump that unit only comes with 7.5kw heat strips. That's not much if you're all electric. If you're sure that's enough then O.K. but if you're not sure I would rethink things.
    He is in Miami, there are a lot of people down there with no heat at all, they rearely need it, 7.5 kw is plenty for the size of his house and his unit is probably oversized.

    Since he has a 2.5 ton airhandler and a 3 ton condenser, he only has a 2.5 ton system.

  10. #10
    Join Date
    Dec 2010
    Location
    texas
    Posts
    333
    yes you can install a txv which is the way to go. to me a system is not running at its full performance with out it as for a flowrator you can always change the piston thats what determines the tons for a fixed oriface coil but i would check with goodman to make sure. i myself dont bother with them i always install a txv.

  11. #11
    Join Date
    Dec 2010
    Location
    texas
    Posts
    333
    remember i would only do this for a temparary fix until you can get a outside unit that is matched for the inside and then install a txv.

  12. #12
    Join Date
    Sep 2009
    Location
    Kennesaw, GA
    Posts
    619
    Quote Originally Posted by martin&sonsa/c View Post

    yes you can install a txv which is the way to go. to me a system is not running at its full performance with out it as for a flowrator you can always change the piston thats what determines the tons for a fixed oriface coil but i would check with goodman to make sure. i myself dont bother with them i always install a txv.

    remember i would only do this for a temparary fix until you can get a outside unit that is matched for the inside and then install a txv.
    I just remembered my dads current Rheem air handler unit does have a TXV installed....I wonder if we can reuse that on the new air handler. I will check that with my uncle. Thats a good idea to get a new TXV when I get the new outside unit installed later. I am going to do the Heat load Cal tomorrow and see what result I get before making a move. Thanks for your guys replies.

  13. #13
    Join Date
    Dec 2010
    Location
    texas
    Posts
    333
    i think you miss understood use the flowrator and put a 3 ton piston in so its atleast matched to the condencing unit than when you decide to change the outside unit install the correct txv for that system.

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