Condensation on plenum

Discussion in 'Maintenance and Troubleshooting' started by WestMichigan, Jun 5, 2013.

  1. WestMichigan

    WestMichigan New Member

    This is my first summer with a properly working geo and I am noticing lots of condensation on the ductwork for about the first 3 - 5 feet after the geo unit. It is installed in a basement which has a higher relative humidity to begin with. The condensation is so bad I am getting pools of water on the floor around my unit and on top of it from where it runs down the ductwork. Can I insulate the ducts to prevent this or is there some other way to prevent all this water collecting on the unit?
  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Check air flow and airside delta-T. If system is overcooling its ducts, they can sweat.

    Alternatively, basement may be too humid, and steps to address that may be needed. Protracted high RH invites mold and other problems
  3. mtrentw

    mtrentw Active Member Industry Professional Forum Leader

    Same problem during initial install last year. It was solved as soon as I put in the geospring Heat Pump water heater in the same closet which knocked a good bit of moisture out of the basement air. I also wrapped my ductwork in the aluminized bubble foil insulation for the first 4 feet or so.
  4. /// My 2 cents worth: I run into similar issues with commercial ductwork in large commercial buildings from time to time. Residential / light commercial is tricky. With air to air systems, you need good overall ac air flow in the summer time; too little and your coils might freeze, too much and you can actually "blow" condensate off the evaporator coil into the duct plenum. Good quality commercial grade metal ductwork typically is often insulated with metal clip fasteners retaining insulation on the INSIDE of metal ductwork. (They shed a few fibers) There are aerosol products that can be sprayed on bare metal, but the metal must be clean and completely dry. Unless you foam the ductwork, they would have to be to be properly rewrapped. On some ac systems, especially ECM, you can adjust air flow + or minus 15% by small amounts. The SLOWER the air flow, the more condensate that can be removed at the coil, (which is also why we like to run AC on smaller capacities for LONG periods of time) One advantage of fiberboard duct plenum (which should be used in some places and not others) is that it will insulate and not sweat. (It is not made of metal). Ductboard however, should never be used under a house and shouldn't be used if an ac system is "throwing water or condensate at the outlet" into a fiberboard plenum.
  5. mtrentw

    mtrentw Active Member Industry Professional Forum Leader

    HVAC Tech brings up a good point which I hadn't thought about. While it may not be enough of a change, it could have some effect. If you were to increase your airflow (assuming your newer unit has variable flow ECM) it would reduce the Delta T in airflow or increase discharge air temp. Basically you'd be blowing more air at not as cold a temperature. The slight change in temp could reduce duct condensation
  6. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    You may insulate all the duct work or dehumidify the basement which is what most do around MI.

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