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  1. #1

    AC Upgrade Question

    We are closing on a used home and are planning on replacing the HVAC system. My question is I have three quotes I'm looking at as follows.

    First quote is not to replace the furnance; only the units and coil. The people who quoted said furnace looks newer, but is "builder grade." I don't remember the name, but could get it if needed. Question is it a good idea to replace the AC without replacing the furnace? Would I be ok with this option? Cost is about 28% less than option 2. However, I want it done right and am willing to pay that cost if it would make a difference.

    I don't think I'm going with the 2-stage system due to costs, but I'm wondering if I should upgrade the single stage to the G60V Furnace to get the variable speed motor if I got with option 2? Any advice is appreciated.

    Current Units:
    10 Seer
    4 tons down
    2.5 tons up

    Approx Square Footage: 2600
    2 stories
    1st - 1878
    2nd - 722

    Location: Dallas, TX

    Lennox Equipment
    Quote 1: XC14 with existing Furnance with CH33 Coil - (1) 2ton, (1) 5ton
    Quote 2: XC14 with G50UH with CH33 Coil- (1) 2ton, (1) 5ton
    Quote 3: XC16 with G60UHV with CH33 Coil- (1)2ton, (1) 5ton

  2. #2
    Join Date
    Jul 2006
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    Virginia
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    did the contractor do a load calc because it appears they are going from a 4 ton to a 5ton and a 2.5 ton to a 2 ton also that seems like a lot of ac for the down stairs a larger unit is not a up grade unless it is needed and if the furnace is a 4 ton furnace it most likely will not work with a 5 ton

  3. #3
    Yes he do a manual J calculation. So you would not put a new AC unit on the existing furnace?

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,875
    Quote Originally Posted by deliverer33 View Post
    Yes he do a manual J calculation. So you would not put a new AC unit on the existing furnace?
    How old is the furnace.

    How much of the duct work do that have to change to be able to move enough air for that 5 ton unit.
    The old duct wasn't sized for 5 tons.
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  5. #5
    Join Date
    Apr 2008
    Location
    Texas
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    63
    How old is the home?

    Why change to a 5 ton instead of a 4 ton? A 5 ton is normally way too big for 1878 square feet. Can you describe the construction of the house? Windows, wall, insulation, etc…

    Unless you say that you have 12 foot ceilings and all single pane glass facing South & West then you probably don’t need a 5 ton system. If you want to send me the Manual J report I will be glad to take a look at it for you.

    Why are you replacing the units in the first place?

    It is best to replace the furnace also but in Texas a furnace will usually out last an air conditioner 2 to 1. However, in most cases to get a higher efficiency unit you will be better off with a variable speed furnace. Changing to variable speed furnace is a really good investment. A 2-stage furnace is good but don’t spend any money on any furnace higher than a 80 percent efficiency.

    To answer your question, it should be not a problem to change out just the coil and condenser without changing the air conditioner. Do you plan on staying the house for more than 5 years?

    You might want to consider getting the XC14 with the G60UHV furnace. For example, in the 2 ton version, the XC14-024, G60UHV, CH33-25B and expansion valve gets an ARI rating of 16.0 SEER. The variable speed is definitely the way to go. It will be higher also with the 4 ton system but probably not get a 16 SEER.

    Ask the contractors if they are going to reuse the refrigerant lines. Quiz them on reusing them with the 410a refrigerant. Ask them if they are going to install driers. (The lines do not necessarily need to be replaced, you just need make sure they are going to install driers.)

    Based on what you are telling us here, this is a quote I would ask for from the contractors:

    XC14-048, G60, CH coil, TXV, Lennox Comfortsense 7000 thermostat
    XC14-024, (keep old furnace), CH, TXV, Lennox Comfortsense 5000 thermostat

  6. #6
    Here you go.

    Why change to a 5 ton instead of a 4 ton? A 5 ton is normally way too big for 1878 square feet. Can you describe the construction of the house? Windows, wall, insulation, etc…

    ++ House built 1999. Doesn't appear to have low E windows. Mostly brick on the outside. Walls are drywall. Insulation not sure.

    Unless you say that you have 12 foot ceilings and all single pane glass facing South & West then you probably don’t need a 5 ton system. If you want to send me the Manual J report I will be glad to take a look at it for you.

    ***He did a Manual J and said the downstairs was undersized. His calculation was 46,926 on the Sensible Heat Gain, 9845 on the Total Latent Gain came out to 4.7 Ton. We have 18' vaulted ceilings downstairs.


    Why are you replacing the units in the first place?

    ++ Replacing as home was inspected and inspector found leak in unit in the attic and the previous owners dog chewed away parts of both AC units outside. I have had AC issues in the past and want a good comfortable system that will last us for years to come.

    It is best to replace the furnace also but in Texas a furnace will usually out last an air conditioner 2 to 1. However, in most cases to get a higher efficiency unit you will be better off with a variable speed furnace. Changing to variable speed furnace is a really good investment. A 2-stage furnace is good but don’t spend any money on any furnace higher than a 80 percent efficiency.

    ++ Confused on this part. I was quoted one system with a G50 and one with a G60V funance. Is the G50 still a variable speed? I thought it was manual versus the automatic variable on the G60?

    To answer your question, it should be not a problem to change out just the coil and condenser without changing the air conditioner. Do you plan on staying the house for more than 5 years?

    ++ Did you mean without chainging Furnace? Yes we will be in this house more than 5 years.

    You might want to consider getting the XC14 with the G60UHV furnace. For example, in the 2 ton version, the XC14-024, G60UHV, CH33-25B and expansion valve gets an ARI rating of 16.0 SEER. The variable speed is definitely the way to go. It will be higher also with the 4 ton system but probably not get a 16 SEER.

    Ask the contractors if they are going to reuse the refrigerant lines. Quiz them on reusing them with the 410a refrigerant. Ask them if they are going to install driers. (The lines do not necessarily need to be replaced, you just need make sure they are going to install driers.)

    ++ I have a call into him and will reply with the results once I hear back.

    Based on what you are telling us here, this is a quote I would ask for from the contractors:

    XC14-048, G60, CH coil, TXV, Lennox Comfortsense 7000 thermostat
    XC14-024, (keep old furnace), CH, TXV, Lennox Comfortsense 5000 thermostat[/QUOTE]

  7. #7
    Quote Originally Posted by beenthere View Post
    How old is the furnace.



    How much of the duct work do that have to change to be able to move enough air for that 5 ton unit.
    The old duct wasn't sized for 5 tons.
    House is 9 years old. One tech said the furnace looked newer. I don't know what that means. I could get the model number if that would help out?

    I've had two AC companies out and they both have said the ductwork is currently undersized for both the current units. Both my quotes include adding a return to both the upstairs and downstairs.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    Its the serial number that tells the age.

    Its not just your return that is undersized.

    You'll need more then just more return. Unless you don't mind loud air noises coming from your supplies.
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  9. #9
    Quote Originally Posted by catmanacman View Post
    did the contractor do a load calc because it appears they are going from a 4 ton to a 5ton and a 2.5 ton to a 2 ton also that seems like a lot of ac for the down stairs a larger unit is not a up grade unless it is needed and if the furnace is a 4 ton furnace it most likely will not work with a 5 ton
    Just an update we got the appraisal back and it shows the downstairs as 1828 and the upstairs as 792.

    I also attached the manual j report.
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  10. #10
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    So you set your stat to 70°F, that load calc is done for 30° differential.
    What mechanical ventilation do you have. That load calc shows you have a fan running 24/7.
    Is your second floor built that it doesn't cover any of the first floor. The calc is done that the first floor is under, and unconditioned attic.
    Your house by that load cacl isn't built very well. Because it also shows 175 CFM natural ventilation beside the mechanical.
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  11. #11
    Quote Originally Posted by beenthere View Post
    So you set your stat to 70°F, that load calc is done for 30° differential.
    What mechanical ventilation do you have. That load calc shows you have a fan running 24/7.
    Is your second floor built that it doesn't cover any of the first floor. The calc is done that the first floor is under, and unconditioned attic.
    Your house by that load cacl isn't built very well. Because it also shows 175 CFM natural ventilation beside the mechanical.
    I would say 3/4 the second floor is over the 1st story and the other 1/4 is over the garage.

    As far as ventiliation each room has a duct and there is a total of 2 returns, one downstairs and one upstairs.

    Wouldn't the HVAC person need to do a blower test in order to determine how well my house is built or not built? He did not do that.

    I have other HVAC companies coming out next week.

    Are we saying then this calc was done wrong then?

  12. #12
    Join Date
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    Quote Originally Posted by deliverer33 View Post
    I would say 3/4 the second floor is over the 1st story and the other 1/4 is over the garage.

    Look at that load calc, it doesn't allow for that.


    As far as ventiliation each room has a duct and there is a total of 2 returns, one downstairs and one upstairs.

    The ventilation I am refering to is fresh air ventilation, do you have a fan that brings in fresh air, or exhaust it, 24/7. If you do a lot of cooking, then hte kitchen exhaust fan must be allowed for. If you don't, then 200 CFM for mechanical ventilation, is high.

    Wouldn't the HVAC person need to do a blower test in order to determine how well my house is built or not built? He did not do that.

    That would be the only way to know for sure. Many don't do it. (I don't) So my infiltrations are a guess also. But I never guess that high, unless its old construction with single pane windows.

    I have other HVAC companies coming out next week.

    Good.

    Are we saying then this calc was done wrong then?
    I'm inclined to say that it looks like it was done to meet the salesman's first impression of what he thinks the house needs.

    What temp are you planning on setting your stat to?

    Also, where is your duct work for the first floor, in a basement, or attic.
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  13. #13
    Quote Originally Posted by beenthere View Post
    I'm inclined to say that it looks like it was done to meet the salesman's first impression of what he thinks the house needs.

    What temp are you planning on setting your stat to?

    Also, where is your duct work for the first floor, in a basement, or attic.
    I would like to be able to keep the house at 75 during a 100 degree day. The duct work for the first floor runs through the attic.

    We do some cooking and have a vented fan to the outside, but I don't think we would turn this fan on everytime we cooked a meal.

    I've called HVAC contractors, Nate certified, one recommended from the vendors website for each of Carrier, Trane, and Lennox. Hopefully I'll have more data next week. I just hope I can find someone to do the job right.

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