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done_again_2

2nd floor AC running a lot

done_again_2
9 years ago

I'm hopeful someone can give me an idea if something's up with my AC. The 2nd floor AC runs a lot. When it kicks on, it's not uncommon to run for 90 minutes or more. I had an HVAC person do an inspection a couple weeks ago and told him about it. He said everything looks fine to him. The temperature at the vents was good. If I adjust the 1st floor AC it'll run and shut off as I would expect. The 2nd floor seems to maintain the set temperature but the unit runs so much. The house is shaded fairly well with large trees and no west facing windows.

2 story house with full basement
4200 sq. ft. (1600 on 1st, 1600 on 2nd, and 1000 finished basement)
2 separate AC's, one for basement/1st and another for 2nd
Keep 1st floor at 73 and 2nd floor at 75 during the day
Midwest location (averaging high 80's/low 90's with humidity recently)
Lennox units, approx. 10 years old

Should I have someone else check it our or this is common? It's our first time with a 2 story house.

Comments (10)

  • ionized_gw
    9 years ago

    To put it quite simply, when it is as close to "as hot as it gets", a well-designed system should be running all the time.

  • mike_home
    9 years ago

    Longer run times are better than short run times. If the AC is maintaining a 75 degree set point on the hottest days then there should be no problem.

    Have you checked on the amount of insulation in the attic? Do you draw the shades to block the sun? The second floor has a higher heat gain then the first. In addition the cool air from the first floor tends to fall to the first floor. This causes the first floor AC to operate much less.

  • done_again_2
    Original Author
    9 years ago

    I'll have to check the attic insulation. I'm not sure about that. The 2nd floor maintains the set temperature. I wanted to see if anything sounded off about how it runs. I appreciate the information.

  • ionized_gw
    9 years ago

    I know that I might sound like a broken record to some people on this site, but I think that you are a good candidate for getting an energy rater in to evaluate your house. It is usually a good investment if you think that you might want to make improvements in energy consumption. They can help you identify the best place to make savings.

    Local governments and utilities often have programs that help pay the fee, but sometimes not. Check around a little. In fact, the local energy raters should know of such programs.

    Here is a link that might be useful: Resnet

  • tigerdunes
    9 years ago

    What are outside conditions when condenser runs continuously?

    Take the average of several supply vent temperatures and post.

    What size is existing system?

    Any idea what delta T is?

    Age of system and last time it was serviced?

    Post back.

    IMO

  • done_again_2
    Original Author
    9 years ago

    It has been low 90s the past few days with heat index of close to 100. The system runs often during the hottest part of the day; noon to 6p. I had both ACs serviced/tuned up a few weeks ago. When the temperature was checked it was within half a degree of optimal, I believe. He added a small amount of r22 to the 2nd floor unit. The units are about 10 years old. I'm not sure of the size or delta t. We run ceiling fans as much as we can.

    Model #s (from HVAC receipt)
    13ACC-024-23001
    13ACC-030-23001

    Is there any benefit or harm to closing vents in unused rooms or should everything stay open throughout the house?

  • tigerdunes
    9 years ago

    I would not close room vents...

    IMO

  • udarrell
    9 years ago

    'Only if' the A/C is sized to a Manual J load-calc should the A/C be running a large percent of the time at design or above heatload conditions!

    The A/C can be oversized & running way too long to satisfy the room T-stat.

    Additionally, the duct system, if in attic, may lack insulation & also air tightness.

    Check the air temperature coming off the condenser compared to outdoor temp; at 78ðF & 50% indoor humidity with 10 to 12-SEER even new 13-SEER condenser's temp-split should be around 18ðF.

    Indoors at 50% relative humidity INDOORS the temp-drop should be 19 to 20ðF.

    Here is a link that might be useful: Free Whole House Load-Calc

  • done_again_2
    Original Author
    9 years ago

    The duct system for the 2nd floor is in the attic. I wonder if the attic insulation and ducts could be part of the issue. I did notice some ice buildup on the gutters this winter. It was unusually cold and snowy here. The house was built in 1987 with the outside units about 10 years old. The electric furnaces are original with a wood burning furnace also.

    I'll look into the energy rater and see if anything comes of that.

    Thanks again for your input.

  • ken_adrian Adrian MI cold Z5
    9 years ago

    i have a tri-level with basement ... that a quad level ... if there is such a term ...

    cold air falls ...

    if its sent upstairs ... it will fall... until it hits the lowest level ..

    in my case.. the basement ends up 65 ... and the top floor... whatever i set the temp to ...

    i spend a lot of time with the FAN ONLY running.. i do not have two zones ...

    in the alternative.. a door on the higher level.. will trap and maintain the conditioned air upstairs ... [now this will be a decorating conundrum]

    my point being... who says its not working ... perhaps its just that the cold air isnt staying up there... and the hot air from the lower level is constantly going up there.. thats why the lower unit doesnt run as much ...

    try temporarily hanging a bed sheet across the stairway .. or whatever.. to trap the cool air up there.. and see if that makes a difference ... [to keep the basement... from going total arctic... i use an adjustable twist shower curtain rod with a heavy floor length drape as a air dam ...]

    if it does.. and the system then runs to specs.. the the problem is not the A/C ... its gravity ... good luck with that.. lol ..

    ken

    ps: in winter.. its just as bad .. the upstairs is 90.. with all the rising heat ... and the basement.. again.. is 65 ... crikey ... more running of the fan to even temps thru the spaces ... because warm heated air.. wont stay DOWN in the basement

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