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  1. #1
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    Sep 2019
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    Seeking Advice/Second Opinion - Temperature Issues

    I recently purchased a 4-year old home and when we moved in it was in the high 70's / low 80's outside. We kept the thermostat set to 73 in the day and 71 at night without issue. The past few days the outside temperature has been in the low 90's. With the setpoint set to 73 all day, the A/C unit turns on at around noon and runs non-stop the rest of the day and the temperature continues to rise up to 78 degrees with the A/C unit still going.

    I thought there may be an issue with the unit needing more refrigerant so I called a local HVAC company to come evaluate. They came and looked at it and told me that the unit itself is fine and the problem is with how the duct work is routed through the house. They said they measured a 19 degree differential between the inlet and outlet of the unit which they said was great. They said that the design of the duct work is all wrong and the vents should be on the exterior walls but mine are mostly on interior walls. They also said that the reason no air blows out of the vents in the ceiling of the upstairs master bedroom and the upstairs hallway is because the run of duct work (~60') is too long. They said in order to fix the issue they would have to cut up the floor and move the vents to exterior walls, etc.

    I'm not an expert on HVAC units but I'm shocked that a 4-year old unit that is properly operating can't maintain the temperature lower than 78 degrees (on the 1st floor) when it is running continuously and the outside temperature is 90-93 degrees. The house was built by a home builder that has been around 40+ years so I have a hard time believing they continuously build from sets of home plans that has the duct work so poorly drawn out and still remain in business. I could be entirely wrong and I want to get a second opinion but service calls are not cheap, especially if they are going to tell me the same thing. Any information, advice, or suggestions is greatly appreciated as I'm not entirely sure what to do at this point.

  2. #2
    Join Date
    Jan 2004
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    PA
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    Like many things in new construction. The actual HVAC job was subbed out to an HVAC sub contractor. Probably the lowest bidding one. So yes the duct work could be that bad. And often is.

    Depending on the type of register boot that was used. A register can be used that will throw the air to the outside walls from your current register locations.

    Lack of return air could be causing some of your upstairs issues, and even you downstairs temp issues.

    I believe a second opinion is in order though, as some techs are sales techs.
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  3. #3
    Join Date
    Aug 2002
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    Very common in new construction, whether custom built or standard plans.

    They pick the cheapest contractor and switch whenever someone is cheaper. They also sell on the useable square foot, so they don’t want to give up floor space for better locations or larger duct sizes for proper operation.

    It is sad, but they sell off of the counter tops and the view not the comfort.

    It is very common to have poor layout of ductwork and very undersized ductwork in most homes.

  4. #4
    Join Date
    Aug 2002
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    Southold, NY
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    I agree with the Two comments above.
    Find a contractor you can trust. Please keep in mind most are salesman!

  5. #5
    Join Date
    Sep 2019
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    Thread Starter
    I appreciate the advice and information. I have another contractor coming to give a second opinion on Monday. The part that is puzzling me though is it was 76 degrees in the house when I woke up this morning and only ~67 degrees outside. I turned it off last night to give it a break since it had ran all day. When I woke up I dropped the setpoint to 74 degrees thinking it should have no problem to cool a few degrees while the sun is not quite out and it is cooler outside. The unit has continuously ran for the past 4 hours and has actually went up to 77 degrees. I'm still puzzled as to why this has just now became an issue. We have been able to keep our thermostat at 71-73 for the first 3 weeks that we have lived here and have it maintain that temperature without issue when the outside temp is between 70-85.

    If the other contractor comes to the same conclusion, what are my options? Replace the duct work and move the vents? Get larger than a 3.5 ton unit?

    How invasive is moving/replacing the duct work?

  6. #6
    Join Date
    Jan 2004
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    PA
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    How evasive varies with the house.

    If a tech evaluates a system just by checking refrigerant pressures, he really isn't checking properly. Needs to go by SC and SH. He should also check actual air flow. And how clean or dirty the coils are.
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  7. #7
    Join Date
    Dec 2007
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    Quote Originally Posted by Swack View Post
    I appreciate the advice and information. I have another contractor coming to give a second opinion on Monday. The part that is puzzling me though is it was 76 degrees in the house when I woke up this morning and only ~67 degrees outside. I turned it off last night to give it a break since it had ran all day. When I woke up I dropped the setpoint to 74 degrees thinking it should have no problem to cool a few degrees while the sun is not quite out and it is cooler outside. The unit has continuously ran for the past 4 hours and has actually went up to 77 degrees. I'm still puzzled as to why this has just now became an issue. We have been able to keep our thermostat at 71-73 for the first 3 weeks that we have lived here and have it maintain that temperature without issue when the outside temp is between 70-85.

    If the other contractor comes to the same conclusion, what are my options? Replace the duct work and move the vents? Get larger than a 3.5 ton unit?

    How invasive is moving/replacing the duct work?
    You can't just get a larger system and solve the issue!!!!!! You duct work must be sized for the amount of air the system delivers. Similar to water, you can only flow so much through a pipe/duct. You need to increase the pipe/duct is you want to increase flow.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
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  8. #8
    Join Date
    Jan 2010
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    Have you had the insulation checked in the house particularly in the attic?

    Have you had a blower test done to check for air infiltration?



    Sent from my SM-G965W using Tapatalk

  9. #9
    Join Date
    Nov 2004
    Location
    SW FL
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    INITIAL EVALUATION

    60' LONG DUCT LENGTH ALONG WITH SEVERAL BENDS
    will likely create a significant air flow rate issue upstairs.

    Measurement of the ESP provides some indication on the extent
    of the air flow rate problem.

    ESP - External Static Pressure
    ---- basically, ESP = Air Pressure across the air handler
    ___ generally, ESP must be < 0.6" to achieve proper air flow rate

    .... to be performed by HVAC TECHNICIAN
    _ _ _ _ https://www.contractingbusiness.com/...x-simple-steps

    3.5 Ton system should have air flow rate > 1260 CFM
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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