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  1. #1
    Join Date
    Feb 2005
    Posts
    19
    5 ton unit on 4 ton ductwork? Duct work is sized for a 4 ton but Icontractor wants to put in a 5 ton condensor & evaporate coil unit to cool the house better. House is 2750 sq ft. The contractor thinks I really need a 5 ton unit instead of a 4 ton. The problem is that all the duct work is in the concrete slab and can't be expanded. I realize that the cfm for a 5 ton should be 2000. The cfm on the old duct work is 1600.

    Will the 5 ton perform well in a 1600 cfm duct work system? Or will it NOT perform well in a 1600 cfm ductwork?

    The return suppy is currently sized at 1950 cfm. It can be increased because it is in the attic.


  2. #2
    If the contractor feels that a 5 ton is what you need, and he feels that your ducting is adequate, then get a second or third opinion. If you are going to spend $ on your residence, and this is not chump change you owe it to yourself to get other opinions. just remember that the people giving you bids are salesmen not techs. call around untill you find the right person that makes you feel confident in them doing the work. Should be no less than 18 inch opening on return side ductwork. I do believe that your return air runs in the concrete. thats how it is in az. . where is the air handler located?

  3. #3
    Join Date
    Jul 2004
    Location
    West TN
    Posts
    983
    Did the contractor perform a load calculation?
    Or did you comment to him that "my old unit ran all the time" and he said "Oh... we can fix that by putting in a bigger unit"?

    If he's going by your comment... then he'll make more money from you by selling you a bigger unit and you will be happier under the 'false' impression that "BIGGER IS BETTER"

    Did you add on to the house and add more heat load since it was built?

    Setting aside the units run time.... did the old unit keep you comfortable? (you may have to think back to when it was first put in... neglect and poor maintenance will have a serious impact on how you feel during the later years of the units life) If it was comfortable back then... then a new 4 ton should be comfortable now.

    Not sure where you live, but check with your local power distributor to see if the have a program like this one in Tennessee... http://www.energyright.com/heatpump/index.htm
    Very nice program in my opinion.
    They've set excellent standards on installation, have a list of qualified contractors you can get estimates from, they come out and inspect the work to verify correct air volume and heating/cooling capacity. They even require you get a 10 year parts and labor warranty. So your good to go for years to come.


  4. #4
    Join Date
    Jul 2004
    Location
    West TN
    Posts
    983
    oh yeah... consider a variable speed blower also.

  5. #5
    Join Date
    Feb 2005
    Posts
    19
    The old 4 ton did not really keep the house cool. That is one reason why the contract is saying go with the 5 ton unit.

    The house is 45 years old, 2750 sq ft in hot, humid Oklahoma. Contractor said I should really have a 5 ton to cool this house good. But all the supply ducts are in concrete floor. The cold air return is in the attic.

    The contractor said that the supply ducts is 1600 cfm and that a 5 ton unit should have 2000 cfm. He said that it should work fine to put in the 5 ton since we cannot add any more supply ducts since they are in the concrete. The cold air return in the attic is already 1950 cfm.

    Will a 5ton unit work good on this set up? and cool the house better then a 4 ton set up?

  6. #6
    Join Date
    Feb 2005
    Posts
    19
    Contractor is going to put a TXV valve installed to help regulate wide outdoor temperature swings anyways. If coil freezing might be an issue then the TXV valve should help keep the coil from freezing if that is an issues about a 5 ton on a 1600 cfm duct work.

  7. #7
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,639
    Just because the duct work is sized forr 1600 cfm does not mean that it will not supply 2000 cfm. What it means is higher velocity and a little more noise. The static pressure will rise in the ducts. I personally do not believe you will have a problem.

    Was your old system running constantly all day on warm days and not reaching setpoint?

    If you were comming home and turning it down that is not the way cooling is sized. You are better off from an energy standpoint to keep the 4 ton and have it have very long run cycles that a 5 ton cycling. My cooling unit cycles on and off until 12pm then does not shut down until 8 pm when 90 degrees or more which was its design temp.

    I would increase the seer rating to at least 14 seer and stay with a 4 ton, most likely the currect 4 ton unit has dirty coils and blower which is contributing to your lack of capacity. How did the 4 ton unit work when new and how old is it?
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  8. #8
    Join Date
    Jan 2005
    Location
    Perth - Western Australia
    Posts
    775
    what brand / seer is he selling you ?

  9. #9
    Join Date
    Feb 2005
    Posts
    19
    Old coil is spotless as I have the unit serviced every year to keep it running the best it can since not cooling house like house should be cooled.

    Old 4 ton would run all the time and not be really cool enough in the house. Would think 5 ton would cool the house to be confortable.

    Rooms are large and could use more force coming out the register to stir the air in the rooms. I would not mind that.

  10. #10
    Join Date
    Sep 2004
    Posts
    116
    Maybe you could go with a 5 ton ,2-speed unit and var. speed a/h, will run at 1/2 capacity lots of days for better moisture removal. Costs more, but worth it!

  11. #11
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    i am not sure i read right first 5 tom condenser ok now if it is a 5 ton coil only and not furnace and the furnace is rated at 4 ton air flo 1600 cfm you will not gaina thing with out changeing the furnace to with a 5 ton drive
    if it is a 5 ton fan coil airhandler then you are fine
    since your duct work cant be changed than you should concider haveing a varitabale speed blower installed it comes with furnaces and airhandlers most manufactors have them. some will not agree but they were made for this problem and they also increase the the seer rateing to
    this blower will ramp up to 2000 plus cfms depending on how the control board is set up. this blower will over cum the stadic pressure in the duct work and give you a true 2000 cfm see your dealer and ask about if or go on line i am sure you can fined out more check under davelenox,com or trane. or carrier they will show you just how it works and you wont have to worrie about you ducts or cfms

  12. #12
    Join Date
    Feb 2005
    Posts
    19
    Furnance will be new 125k. New condensor & coil will be 5 ton. Everything new except duct work. Existing duct work is in concrete floor and is sized 1600 cfm for a 4 ton unit.

    Current condensor & coil is 4 ton. House has always had problem cooling enough. House is 2,750 sq ft in hot Oklahoma with all brick and large large windows. Also furnace is on one side of house and master on the opposite side with around 60 -70 feet of duct to get to it. With faster blower setting for 5 ton he said would get more air flow in that long run to master.

    Contractor says the house really needs a 5 ton unit to cool the house better for this size house. 4 ton has not really cut it in the past 15 years.

    My question is will the new complete 5 ton unit work OK in the old, 1600 cfm duct work system? Or should I have the contractor install a 4ton complete air unit?

  13. #13
    Join Date
    Mar 2005
    Location
    Ca
    Posts
    2
    How do you know you have 1600 cfm of air in your ducting? Unless you run a test you wont know if your ducting will handle 2000cfm of air flow. Do you need a 6 ton system? Who knows ,no one could with out a load calc. Good luck

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