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  1. #14

    Arrow Question...

    If the 4 ton system never kept up and cooled all these years why the sudden urge to upgrade ?

    The difference ebwteen a 4 ton and 5 ton isn't goign to make alot of diference to you if the probelm is in inflitration of that hot Oklahoma temperture...

    Invest in some good insulationa nd look into better windows and sealing that house up...

    As a contractor I sure wouldn't stick my neck out on a 5 ton if the 4 ton was less than marginal... Yopu've got some other issues goign onthere that need to be corrected first and foremost...

    I think the options of a VS air hadnler or FAU is great it will help over come any static pressures issues. But until you have the issues corected, isntallign a 2 speed system such as the Infinity System you'll find your self with some dissatisfaction guaranteed....

    Have your house carefully evalulated for it's heat loss and gains, you be glad. Especially if you figure out where all this coolness is going...

    [Edited by AllTemp on 03-14-2005 at 02:34 AM]
    AllTemp Heating & Cooling

  2. #15
    Join Date
    Feb 2005
    Posts
    19
    House has R30 attic insulation, HVAC units are spotless, freon levels correct (I have unit serviced every year to get best performance out of them), attic power vented.

    Contractor ran heat load calculations/test and says that this 2,750 sq. ft house should have a 5 ton AC and a 125,000 furnace. Contractor says that he calculated that the current duct work will handle 1600 cfm which is correct cfm for a 4 ton AC system. He said that the new 5 ton AC system calls for 1,800 cfm (talked to him this morning). He said that the 5 ton will work fine on the 1,600 cfm ductwork system with just a little increase static pressure.

    Plus would get a little bit more force of air (because have to turn up the speed of the blower to handle 5 ton AC instead of 4 ton speed) in the duct work so would get more air pressure to the far, 60-70 ft. run to the master bedroom.

    Is what my contractor telling me correct?

    Going to replace whole HVAC as the units are around 25 years old. I am hedging my bet that they will break for good soon. I would rather deal with replacement of all HVAC when it is an emergency to replace. I would rather replace everything at once and get a matched complete system that is more energy efficient.

  3. #16
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Could be the 4 ton didn't cool well ,due to undersized ducts.

    Sounds like your guy has checked the duct system,and knows it will be okay.We can tell fromm here,without a lot more info.,and we still wouldn't know for sure.

    Did they check the External Static of the current system?If so what was it?

    Return ducts can be increased ,this will decrease the ESP,and allow more air flow.
    350cfm per ton of cooling(1750) is the max. you want in a humid climate.

    Supply grilles can often be changed to increase air flow.

    Go with a variable speed indoor fan,for sure,check out an Infinity Control System,by Carrier.

  4. #17
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513

    Talking

    to start off sorry for the spelling. i can spell just cant type new to the pc and typing sucks hehe. now that you have the info you need from your contractorwe have something to go on. i deal with lenox mostly for 14 years now so i will use lenox for example onlt doesnt mean it is better. i was talking to my lenox tech rep about nate and other thing so i ran by him this problem and here is some facts for you. with a variable speed blower in your system you can set it to ramp up to full speed +10% it will give you a total of 2250 cfm in the duct work. this motor will overcome the static presure of under sized duct work. even if your ducts were sized at 1600cfm this blower will still ramp up enough to give a true cfm it is told to give. since you are concerned about the size of your ducts and air flo a variable speed blower will solve your conserns. carier, trane, york, goodman, all carry it.
    the variable speed blower solve a lot of problems air flo is only one. another is himiditi is is another. with lenos you can use a two stage condenser where the compressor has two speeds high speed 5 ton and low 3.2 tons system reaches set point say 74 degrees the blower will ramp down and condenser will go to high stage pulling humiditi out with out cooling. when reachs humiditi set point will go to low stage on condenser and ramp up blower to maintain cooling. will need a humidistat also. now trane and carrier have the same setup also and works well only lenox two stage will not give you a seer rateing higher then 11 seer. only draw back to it.

  5. #18
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    There are limits to what a VS fan can do,especially when you get in the 5 ton range.

    Most can't deliver 2000 cfm above .4 ESP ,now 1750 cfm can be delivered up to .7 or .8 ESP.

  6. #19
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,074
    What Dash said.

    Plus, you might not like the noise from that supposed 1600 cfm duct, if you put 2200 through it.

    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  7. #20

    Post 5 ton ... Requires 2000 CFM

    Am I the only one picking up tht this morning his contractor told him he neded 1800 CFM for 5 tons....

    YOU NEED 2000 ...
    AllTemp Heating & Cooling

  8. #21
    Join Date
    Mar 2002
    Location
    Eufaula OK
    Posts
    4,175
    I agree with your contractor on one point, 4 tons is not enough for your 2700 sf home in Oklahoma. I live in Oklahoma.

    But increasing to a 5 ton?,, the answer is NO, It will not work. The answer is in simple physics. You can not pump more air through the same sized ducts without increasing static pressure. If it is properly sized for a 4 ton, the static pressure is maxed. If you are not getting equal air flow in all rooms, the ducts are improperly sized, which will translate into static that is too high already.
    Have your contractor run a static pressure test and you will see what your are up against.
    There is no easy solution to your problem. Pumping air 70 feet is a log way.
    I would opt for a 4 ton with the VS blower.
    Jax

  9. #22
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    variable speed blower will for the most part overcome the static presure and yes your air noise will go up to. every action has an equal reation. 1600cfms to 1800cfms is not enough diferance to realy matter and sorry to say wont change anything as far as cooling the. my opinion only
    5 ton is 2000 cfms 1600 is 4 tons why split the differance
    get other prices and opinions from other contractors first.

  10. #23
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Humid climate,set it up for 350 cfm per ton,for better dehumidification.

  11. #24
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    Duct noise

    You *might* get a real increase in duct noise when blowing more air thru your system. I am a S.Texas homeowner who has experienced upon upgrading an air handler. ACCA Manual D (I know a little not a lot here) urges you to keep air speed below 700 fpm. Your contractor has given some meaty info so far, it could well be he has checked this out.

    In my opinion, I would lean toward getting a variable speed air handler. That could help maintain air flow "no matter what" with a marginal supply system -- within limits of course, as Dash has pointed out. The choice of 350 cfm/ton sounds like a good choice to me, so you will be asking the ducts to carry just 1750 cfm or so, vs. the 2000 cfm at the classic 400 cfm/ton.

    You should get radiant barrier in your attic if you don't already have it, that could be relied on for about a 10% load reduction. And probable comfort improvement. If you can get your house leakage tested, and find some ways to decrease air infiltration, that will be a material help also. For both comfort and A/C adequacy. Are you sure your duct leakage is as low as it can go?

    Best of luck -- P.Student

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