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  1. #1


    Is there one brand or another that is the "leader of the pack" in whole house dehumidifiers? It appears to me that Ultra-Aire and April-Aire are the two main competitors. I had occassion to speak with a tech at Ultra-Aire and was impressed with their product knowledge.

    This may be my next step to solving a major problem created when we replaced our SEER 12 heat pumps with two stage var spd air handler lennox 18 SEER units....Extreme duct sweating in attic and garage ceiling soffits...

    Will be closed cell foaming the roof to seal the attic, but in high heat and humidity coastal SC, I want to have plan C ready to go if I need it.

    I do have concerns about putting 280 cfm of dehumidified air into the supply plenum when the air handler is off.. causing backflow through the electronic air cleaner. Would be interested to hear alternate install options, including wiring interface. I had considered making the air handler come on when the dehumidifier was on... extra elec cost, but no problems with the air cleaner.

    This system also brings in 6" duct of outside air... which I thought was good to put positive pressure on the house.. Anyone know how to set that up? Don't own a Pascal meter, but can measure cfms..


  2. #2
    Join Date
    Nov 2000
    Eastern PA
    My question is; "why do you have a humidity issue when you have a cooling system?"

    There should be a way to make that system dehumidify better.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV

  3. #3
    RoBoTech: Yeah, the reasonable person might ask that question.... but once you live on the SC coast, you no longer ask that question. It is hot hot hot and humidity out the wazoo. The Lennox SEER 18 system blows 50 degree air on humidity control, which caused my ducts to sweat due to dew point in the attic.

    I was always taught you ventilate an attic, but I learned, not here. So I am about to remove my power vent and closed cell foam the roof down to the top plates to eliminate the moisture entry point and greatly control the heat (and consequently lower the dew point.)

    I hope you are right, that after we control the dew point that the first stage cooling with reduced cfms of the humidity contol function WILL be enough. Time will tell.

    Units were sized properly per manual J... as a matter of fact we went from two 3.5 ton SEER 12 Carrier units with 4 ton air handlers to one 3 ton and one 38,000 btu unit SEER 18 with 3 ton air handlers.

    I just want to be prepared for the next step. Even with the sweaty ducts, the lowest the Lennox system has been able to get the humidity is 60 percent. And to do that it has to go 2 degrees below the thermostat set point. Not good.

  4. #4
    Join Date
    Jan 2002
    East Grand Forks, MN
    I'm curious, is there any insulation on the duct?

    The duct must be air tight to keep it from sweating(condensation).

  5. #5
    Yes, the ducts were insulated when new with 2" of fiberglass. If you would like some (I think) very interesting reading, here are the background links to the whole story. I am still in the middle of this and have been left on my own to come up with a solution. I have gained tremendous info from this forum and in combination with other internet reading have decided on a course of action to extricate myself from a situation I believe could have been avoided, or at least minimized, if the HVAC contractor had been more forthcoming regarding the side effects of high efficiency units.

  6. #6
    Join Date
    Dec 2004
    Gulf Breeze, Florida

    I would suggest you wait until after you put the closed cell foam in your attic before you take your next step. Heat and humidity in N.W. Florida on the coast is certainly as bad as the S.C. coast. I was amazed with the humidity reduction in my home after removing the ridge vents and using icynene to seal the attic.

    I think you are on the right track to be prepared to use a supplemental dehumidification system should it be needed afterwards. It makes sense to dehumidify that "fresh outside humid air" before it enters your conditioned space.

    I had a local contractor advising me to spend about $2000 to seal the ducts he installed some years ago but since the attic is now semi-conditioned space I used that money towards the cost of the foam. Sealing the ducts wasn't needed as I had to add circulation vents in the ceiling to allow air movement between living space and attic area.

    I thought I would check before completing this post and the temp in my house is presently 73 degrees and the humidity level is 48%. Outside it is 83 degrees and the humidity is 92% at 3:00 a.m. My humidity would be lower but the attic area adjacent to the garage is open for a few more days during ongoing hurricane repairs so air entering from the garage into the attic is similar to an outside fresh air duct.

  7. #7
    Thanks, Iceman

    That is my plan, except we are going with the closed cell foam for extra moisture control. I was figuring the same thing relative to the supply duct leaks..... they would help condition the attic. I just cleaned our electronic air cleaners one month after installation. The downstairs unit was clean as a whistle. The attic unit was pretty dirty... leading me to believe we may be bringing in some attic air into the return side. (no kids or pets in the house)

    The anemometer I ordered will be here in a few days. I had planned to measure air in the returns and air out the supply to get a feel for supply duct leakage, but I don't know a way to check for return leaks without more equipment. Is there an easy way?


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