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  1. #14
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,095
    What's the complete model # of the furnace?

  2. #15
    Originally posted by ahdofu
    Hello,
    My existing furnace has 5-ton blower in it. I'm trying to have a central AC installed. Most of the contractors who looked at my house indicated that I should be installing a 5-ton AC unit. One contractor, however, performed a manualJ? analysis and concluded that a 3-ton unit would be the right size. From what I've learned, it would not be a good idea to install a 3-ton coil on top of my furnace as this restricts the airflow too much. What the contractor suggests is that I should opt for a 4-ton AC unit and have a 5-ton coil mounted on the furnace. Supposedly this is a compromise between a 5-ton and 3-ton AC units. Anyway the question that I have is that does this make sense? Would there be any problems with a mismatched AC components e.g. 4-ton AC with a 5-ton indoor coil?
    Thanks in advance,
    Matt






    What the contractor suggested does make sense and will work when properly designed for any changes a multi speed blower can provide.
    I would double check the capacity ratings for matched OR mismatched coils.


    That starter collar Dash referred to was/is famous in Ruud airhandlers to help get heat away from the indoor coil better in heat mode. Ruud has had a devil of a time with head pressure problems related to their fan coils inability to keep air moving there.
    I still see it frequently and have found several Ruud high press cutout switches bypassed Big Ruud following here

  3. #16
    Join Date
    May 2005
    Posts
    14
    what sq ft is your house and what the location? something seems strage

  4. #17
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    What your contractor suggests,oversizing is just wrong and can have results you won't want to live with.

    Baldie asked for the complete model number so we can help up out .It not your fault that they are giving you bad infromation,but you are the one that needs to find a better contractor,it your home.


    I have no idea why Chillbilly is talking about Rheem/Rudd collars,that's not what was reffered to in this thread,and doesn't apply here.

  5. #18
    Join Date
    May 2005
    Posts
    8
    My earlier reply contains the model no. Please refer to my post at the end of page 1.
    Thanks

  6. #19
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Originally posted by ahdofu
    BaldLoonie,
    The so called "horsehockey" quote comes from the contractor. Basically he will not put in anything smaller than a 4-ton AC on my system. I've talked to other contractors and even though they all had initially suggested a 5-ton AC, none of them is willing to go below 4-tons again (I have tried dealers representing Carrier, Trane, Bryant & Lennox). As for my furnace, it's made by Payne & the model number is 383KAV.


    That's not a complete model number ,can't tell size and cfms from that.

  7. #20
    Join Date
    May 2005
    Posts
    8
    I apologize for the incomplete data!
    Looking inside the surnace, I see:
    Product: 383KAV060111ADJA
    Model: 383KAV06011

  8. #21
    Join Date
    May 2005
    Posts
    8
    Regardining my house - it's about 4000 sq feet and it has three floors. My home is built on a sloping hill such that the first floor is under the ground in one end and at the other end it's at ground level. The first & second floors cover roughly 1500 sq feet each. Finally I live in Seattle area.

  9. #22
    If you have incomplete data, how do you determine that the sizing procedure will not work?
    It's safe to post statements like, "it may not work".
    I would be more inclined to believe the contractor who has seen the job and verified equipment and loads as opposed to one who is supposing what "may" be an appropriate match.
    Refer to ARI and/or manufacturer for definite conclusions.

  10. #23
    Join Date
    May 2005
    Posts
    8
    "If you have incomplete data, how do you determine that the sizing procedure will not work?
    It's safe to post statements like, "it may not work".
    I would be more inclined to believe the contractor who has seen the job and verified equipment and loads as opposed to one who is supposing what "may" be an appropriate match.
    Refer to ARI and/or manufacturer for definite conclusions."

    Chillbilly,

    I'm not following what you're trying to say if the above was intended for me. According to my earlier posts, I've had contractors (six total) examine the house and determine the cooling requirements. However the suggested solutions vary from a 3-ton unit up to a 5-ton unit. And my problem is that I don't know who to believe! I also contacted one manufacturer and in that case I was asked to contact their local dealer!
    Repeating from my earlier posts, one contrators performed a Manual-J anaylsis and determined that I needed a 3-ton AC unit. He has no issues with installing a 3-ton unit on my furnace that supposedly has a 5-ton blower in it. The other five contractors did not perform the Manual-J anlysis but looked at my furnace, took data such as square footage, number of rooms, register counts and they all came back with a 5-ton AC!. Anyway having received inconsistent data, I contacted three of the contractors and told them about the 3-ton AC recommendation. All three indicated that they would not install a 3-ton AC system but as a compromise, they could do a 4-ton outdoor unit with a 5-ton indoor coil. So at the end of the day I had three options:
    1. 3-ton AC unit with a 3-ton indoor coil
    2. 5-ton AC unit with a 5-ton indoor coil
    3. 4-ton AC unit with a 5-ton indoor coil.

    And my quetion to the forum was/is whether the last option made any sense or whether it posed any problems that I was not aware of.

  11. #24
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Baldie will post the "fan data" on that furnace before too long,and give you a good idea if a 3 ton coil will work.However for your guy to know for sure the External Static Pressure needs to be taken,I believe baldie posted ,that's what he does and there is likely no problem with the 3 ton coil.

  12. #25
    Join Date
    Nov 2001
    Location
    Seattle, WA
    Posts
    7,760
    Most of the advice you are going to get here are from guys working in hot and humid climates where cooling is critical. Seattle has more of a heating climate than a cooling climate so the logic usually gets reversed. It's quite normal for a "large" furnace to operate a "small" air conditioner around here. Lowering the cooling blower speed to match as closely as possible the air requirements of the "small" A/C works and is typical.

    We have more of a sensible cooling load here in place of trying to wring out humidity as the worst cooling load tends to be for a short while in the afternoon and early evening then the temperature drops to where some heating may be necessary. And this happens frequently in the middle of summer. This week we had two days of the 80's in the afternoon and now we are back into the 60's and will stay that way for a while.

    Dash and Baldie are correct in their advice. Taking the static measurements and comparing them against the proposed system will give you a much closer answer to what you need then guessing.
    "The American Republic will endure until the day Congress discovers it can bribe the public with the public's own money.
    - Alexis de Toqueville, 1835

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