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Heat Pump question

Hi. Can anyone help me? There is so much condensation on my ductwork (throughout the house) that I have had to rip out the basement ceiling due to water damage and mold(ugh), and have recently come home to find the ductwork between the ceiling and floor of the upper two levels leaking through the drywall and paint of the main floor ceiling. It had been very humid for several days when this occurred and I have not experienced rain in my living room since--knock on wood. However, the problem was occurring in the basement for some time prior to my first noticing it in the upper levels, and may well have occurred in the upper levels previously, too, only to a lesser degree than recently.

I have a heat pump that is correctly sized for the house (don't know about for the ductwork), with a clean coil. In fact, the coil seems too clean given the condition of the ducts (dirty). The entire house has been poorly maintained for at least nine years prior to my purchasing it, and probably for its entire lifetime (~30 yrs). The heat pump is approaching the end of its life (both indoor and outdoor units). I believe the system is 10+ yrs old, which is another reason the cleanliness of the evaporator coil is so surprising (the previous owners were NOT the coil-cleaning type), but it still does its job.

Any suggestions as to why there is so much condensation and what I should do about it? Do I need to replace the entire HVAC system, including the ductwork? Any relevant insight/advice/suggestions would be MOST greatly appreciated. Thank you in advance!


  • thepogue
    thepogue Member Posts: 1
    AC question

    With properly running newer AC unit, is 20 degrees below the outdoor temp. acceptiable (normal)? I heard on a local radio show this "handy-guy" say that and I alway took it at face value. If that true is there somewhere I can find that in "print" so to speak. I seached through my sons HVAC book but I'm a Fire Captain by trade so once I got beyond boiling point and radiend heat...I was lost.

    My question comes from a co-worker that had a new AC installed in a shop approx 1000 sq. ft. he installed a 2 1/2 ton unit (I think it was a 2 ton unit before). It has been blazin' here for well over a month (w/ the heat index over 100 for most every day) and he's pissin cuz its only getting to 74 in the shop?...I told him I thoguth that ws pretty darn good...(course I didn't shell out any $$ that's easy fer me to say) but he want it to be 70...and he turns the unit off durning the there some where I can find the normal temp that an AC unit will drop the temp...thanks...and I'll split the beer (I"ll win from him) with anyone that can help!!
  • Marty
    Marty Member Posts: 109
    it depends

    It all depends on how it was sized. if it was sized to keep it at 70* inside when it was 100* outside it would be running all the time 24 hours a day(when its 100* outside). Unless it was grossly oversized shutting it off at night is the problem.
  • John Mills_5
    John Mills_5 Member Posts: 935
    20 is typical

    but depends upon airflow and humidity. If he's shutting the unit off all night letting the night very humid air to infiltrate, it may take most of the day to dry out the building and get a 20 degree drop. If he wants to keep the place comfy, he needs to set the temp back a few degrees at night, not shut it off.

    I have sensors watching mine. Most of the time it runs 16-18 difference unless we are very dry, which isn't too common.
  • Stephane Gautreau
    Stephane Gautreau Member Posts: 2
    20 is typical for TD across coil

    20 degrees is a rule of thumb for the temp. drop from the return air to the supply air. If you are talking outside temp and inside temp then the possibilities are endless. As long as the unit has been sized accordingly. An A/C unit should usually not cool below 68 degrees, but if you want to turn your house into a walk in freezer then size it accordingly.If his unit does not shut off all day then it is either undersized for his space or there is a problem with the unit.
  • Empire_2
    Empire_2 Member Posts: 2,343
    I agree

    Why is he even shuttin it down at night? All that humidity?,."Come on in, I'll worry about you in the day time hours". Then,...Complain about the run cycle of the unit. Gimme a 4 ton unit cause I'm the customer!
    Don't mean to sound sarcastic, but we all have to at least point our customers in the right direction as to how and why the system works the way it does. You seem to have a cust. that I call "Gimme a biger unit" hard to please type of man. Let us know how you make out.
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Heat Gain?

    The obvious question is whether or not the system was sized properly. The rate at which heat infiltrates the buiding through the walls, floors and ceilings as well as the amount of heat allowed to enter the building through open doors and windows can add a great deal to the heat gain of the structure. The insulation factor is also an important detail.

    For a properly sized air conditioning system, achieving a 70-degree indoor temperature will typically not be a problem.

    If the system is able to maintain the desired temperature when the outside ambient temperature is lower, the system may very well be undersized or, hopefully, was not properly charged on startup.

    If you want to be sure, gather the following information and repost it to my attention:

    Outside ambient temperature

    High side pressure

    Low side pressure

    Evaporator outlet temperature

    Condenser outlet temperature

    Return air temperature at the evaporator

    Supply air temperature at the evaporator

    Suction line temperature at the compressor
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380

    Let me take a step back for a minute. Have you ever Placed a cold drink on a table and, upon lifting the glass seen a water ring on the table? Of course you have. This occurs because the cold glass is below the dew point temperature of the air. This causes moisture in the air to condense on the surface of the glass. This is, in effect, what is happening to your ducts.

    Your ducts are not located in the conditioned space and I am 100% certain that your ducts are not insulated or lined. Since the air that flows in the duct is cool, the surface of the duct cools down as well. When the surface of the ductwork reaches a temperature that is below the dewpoint temperature of the air, moisture will condense on the ductwork and yes, water will begin to drip from it.

    The answer to your question may not be the answer you were hoping for. Since this has obviously been happening for quite some time, the best solutionis to replace your duct system. Not only are you providing a breeding ground for mold, but you are also losing system efficiency and cooling capaity as a result of heat being absorbed in to the duct due to the lack of insulation.
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