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  1. #1
    Join Date
    Nov 2012
    Posts
    17

    Advice for Replacement System

    Hello, I have a 2700 SQ foot 2 story house and our upstairs AC unit is leaking and 12 years old so I've decided to replace it. Upstairs is about 1400 SQ Feet. We have a bonus room upstairs above the garage that has always been difficult to heat/cool.
    We use a woodstove so haven't used our furance (other than a yearly check-up) in 3 years so I'm leaning on only replacing the A/C side if possible, but realize that I'd need to replace the furnance in order to get the variable fan benefits. Last year we spend $0 heating the house and $600 in cooling during the summer. I've been told that I'd save around $100-$200 a year by upgrading to a 13 or 14 SEER.

    So I've gotten a couple of quotes and have gotten conflicting answers from both of them so I'm looking for advice!

    Current System:
    Condenser - Ruud 10 SEER 2 ton - UAKA-024JAZ
    Furnance - Ruud 50k btu - UGDJ-05EAUER

    Replacement System:

    Company A (did not do j-calc)
    Quote 1:
    Condenser - Lennox 14 SEER 2.5 ton - 14ACX-30
    Coil - CX34-36A

    Quote 2:
    Condenser - Lennox 13 SEER 2.5 ton - 13ACX-30
    Coil - CX34-36A

    Quote 1 is about $450 more than Quote 2.

    Company B (did j-calc and it came out to 2.25 tons upstairs)
    Quote 1:
    Condenser - Lennox 13 SEER 2.5 ton - 13ACX-24
    Coil - C33

    Quote 2:
    Condenser - Lennox 13 SEER 2.5 ton - 13ACX-30
    Coil - C33
    Furance - Lennox Variable Speed 80% 70k BTU - SL280V

    Here are the conflicts I've had:
    1. Company B states that I cannot support a 2.5 ton condenser with my current furnance and that if I wanted to go above 2 tons (which is what the J-calc recommends) I'd have to replace the entire system. If that's the case I'm not sure why Company A recommended 2.5. I'm concerned that if I go with a 2.5 ton with my existing furnance that the A/C side will suffer damage down the road. Any opinions?

    2. Company A said I would have to change out my copper line going from the coil to the condenser. They said it was 5/16" and should be 3/8". Company B said they could reuse it and that you don't need to go bigger unless you're 16 SEER or above. Thoughts?

    3. Company B said that if I increased from 2 tons to 2.5 that I'd have to increase my ducting to accomodate. So they priced in increasing the 2 return lines in our bonus room from 6" to 8" and increasing the intake in the same room from 8" to 10". It sounds good because maybe it would help with heating/cooling that room, but does that make sense?

    Any other suggestions/recommendations?

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,040
    That furnace has a 3 ton blower so it's fine. But normally we find that the ducts in a home can barely handle the size A/C you have let alone going 25% bigger. To really improve cooling, you likely will have to add 25% more ductwork to your supply and return. Sounds like company B is addressing that. Good for them! But he's trying to sell you a really expensive furnace you don't need so a big black mark for that. So tell him to enlarge your duct system, check static pressure and set the blower for around 1000 CFM for the 2.5 ton A/C. That's likely medium high or high on your Rheem.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    Doubt you'll save 100 to 200 bucks a year.
    Contractor locator map

    How-to-apply-for-Professional

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

  4. #4
    Join Date
    Nov 2012
    Posts
    17
    Quote Originally Posted by BaldLoonie View Post
    That furnace has a 3 ton blower so it's fine. But normally we find that the ducts in a home can barely handle the size A/C you have let alone going 25% bigger. To really improve cooling, you likely will have to add 25% more ductwork to your supply and return. Sounds like company B is addressing that. Good for them! But he's trying to sell you a really expensive furnace you don't need so a big black mark for that. So tell him to enlarge your duct system, check static pressure and set the blower for around 1000 CFM for the 2.5 ton A/C. That's likely medium high or high on your Rheem.
    Thanks for the info.

    We have a 14" main intake.
    We have 2 bedrooms with 1 6" return each.
    The master has an 8 inch intake with 2 6" returns.
    Master bath has a 6" return
    Spare bath has a 6" return
    The bonus room has an 8" intake with 2 6" returns

    Not sure if that's sufficient for a 2.5 ton or not though.

  5. #5
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,371
    Quote Originally Posted by tynman11 View Post
    Thanks for the info.

    We have a 14" main intake.
    We have 2 bedrooms with 1 6" return each.
    The master has an 8 inch intake with 2 6" returns.
    Master bath has a 6" return
    Spare bath has a 6" return
    The bonus room has an 8" intake with 2 6" returns

    Not sure if that's sufficient for a 2.5 ton or not though.
    I think you have your terms mixed up. I think by "intake" you mean return air back to the furnace, and "return" is your actual supply air to the room. By what you described, duct system is very marginal (supply side) for a 2 ton and definitely needs modification to support a 2.5 ton if that truly is what the heat load calls for.

  6. #6
    Join Date
    Nov 2012
    Posts
    17
    Quote Originally Posted by RyanHughes View Post
    I think you have your terms mixed up. I think by "intake" you mean return air back to the furnace, and "return" is your actual supply air to the room. By what you described, duct system is very marginal (supply side) for a 2 ton and definitely needs modification to support a 2.5 ton if that truly is what the heat load calls for.
    Thanks for the response and thanks for the correction. I'm such a new LOL! I was thinking about upgrading the 6" supplies in the bonus room to a 8" as was previous recommended in one of the quotes, but I'm not sure if that's enough or if I'd need to do anything with the returns. Need to do some more research

  7. #7
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,185
    Going from a 2 to a 2.5 ton won't save you money. if the 2 ton did the job go back with another 2 ton.
    Manual J is only as accurate as the person putting the numbers in.

  8. #8
    Join Date
    Nov 2012
    Posts
    17
    Quote Originally Posted by 54regcab View Post
    Going from a 2 to a 2.5 ton won't save you money. if the 2 ton did the job go back with another 2 ton.
    Manual J is only as accurate as the person putting the numbers in.
    That's one of my problems, I've had to put refrigerant in for the last few years so I don't know if the unit has been working like it should to know if it was doing it's job.

  9. #9
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,185
    Quote Originally Posted by tynman11 View Post
    That's one of my problems, I've had to put refrigerant in for the last few years so I don't know if the unit has been working like it should to know if it was doing it's job.
    I doubt you were getting2 tons out of it if it was low.

  10. #10
    Join Date
    Nov 2012
    Posts
    17
    Quote Originally Posted by 54regcab View Post
    I doubt you were getting2 tons out of it if it was low.
    Quote Originally Posted by 54regcab View Post
    I doubt you were getting2 tons out of it if it was low.
    And there lies my problem. I don't think I can go by how my 2 ton was performing. J calc from Company A shows I need 2.25, both companies are recommending 2.5.

    I'm in Atlanta, GA. This unit will service the upstairs of a 2 story house. The sq ft of the upstairs is 1400 sq ft. All walls are R19, ceiling is R60 with radiant barrier. 10 double-pane vinyl windows. We also have 7 double pane vinyl windows facing NE, 1 facing ES, 2 facing SE.
    The current ducting is as follows:
    Master Bedroom - 1 8" supply and 2 6" returns
    Master bath - 1 6" return
    Bedroom1 - 1 6" return
    Bedroom2 - 1 6" return
    Spare bath - 1 4" return
    Hall - 1 14" supply
    Bonus room - 1 8" supply and 2 6" returns

  11. #11
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    I think you have you "supply" and "returns" mixed up. A "supply" supplies air into the home, a "return" returns air to the equipment. The returns are a little unbalanced, but not too bad. If I designed it myself, I'd have all the return dimensions increased one size, decrease the hallway retrun and add and 8" return to each bedroom.

    The next question is what does the main trunk look like is terms of sizing? Are there dampers on the start of each branch for balancing (very improtant to get it all balanced). Many assumed capacity issues are actually balance problems.

    Do you know what desing temperatures they used for hte Manual J? Garbage in = Garbage out. Atlanta has cooler deisng tempratures that most would assume and I could see contractors using a higher temperature. However, it won't make a 10% difference to get you to 2 tons unless they used something foolish like a 100F design temp. Atlanta only has a 92F design temp, but is very humid. I think wet bulb desing is still 77F, like most of the south. Much of the SE isn;t really hot, it's just stays warm most of the year. Places like Texas are much hotter and jsut as humid and even many parts of the midwest are hotter and nearly as humid, but that only lasts for 2-3 months.

  12. #12
    Join Date
    Nov 2012
    Posts
    17
    Quote Originally Posted by motoguy128 View Post
    I think you have you "supply" and "returns" mixed up. A "supply" supplies air into the home, a "return" returns air to the equipment. The returns are a little unbalanced, but not too bad. If I designed it myself, I'd have all the return dimensions increased one size, decrease the hallway retrun and add and 8" return to each bedroom.

    The next question is what does the main trunk look like is terms of sizing? Are there dampers on the start of each branch for balancing (very improtant to get it all balanced). Many assumed capacity issues are actually balance problems.

    Do you know what desing temperatures they used for hte Manual J? Garbage in = Garbage out. Atlanta has cooler deisng tempratures that most would assume and I could see contractors using a higher temperature. However, it won't make a 10% difference to get you to 2 tons unless they used something foolish like a 100F design temp. Atlanta only has a 92F design temp, but is very humid. I think wet bulb desing is still 77F, like most of the south. Much of the SE isn;t really hot, it's just stays warm most of the year. Places like Texas are much hotter and jsut as humid and even many parts of the midwest are hotter and nearly as humid, but that only lasts for 2-3 months.
    The main 14" return doesn't have any dampers, but does have filters on each end of the run.

    Not sure what temp they used for the J calc. I'll ask.

  13. #13
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,185
    Most contractors want to get close to 500sqft per ton, reguardless of how well insulated the house is. My house is 1600sqft and R30 insulation. 2 ton keeps it 75 inside on a 100 degree day.

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