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  1. #1
    Join Date
    Jun 2013
    Posts
    7

    Whole house dehumidifier questions

    Hi, I am having a new AC & furnace installed soon. I have an 1800 sq ft ranch located in Nebraska. The unfinished basement is an additional 1700 sq ft, we plan to finish about 1300 sq ft of that this year.

    I've decided I want a whole house dehumidifier, especially after reading many of teddy bear's posts. My house has humidity problem, the basement smells musty sometimes and I find mold grows easily in our house. I'm getting a basic AC unit (single stage, 13 or 14 SEER) and a 95%+ furnace with variable speed fan.

    All of the 4 hvac companies I've talked to do not know much about dehumidifiers. They say they can do it but it sounds like they have never done it. What do I need to do to make sure they install it correctly? Should it simply pull from the return somewhere before the blower? And then output into the main duct after the coil? They want to use a Honeywell DR90. Is this an appropriate size unit for my house?

    The installed cost is very high, almost double what I can purchase the unit for online. So I'm thinking about installing it myself. Is this possible for someone who is handy? If I went this route I think I would want the Ultra-Aire XT105H but I don't see where I can purchase online. It is much more efficient than the Honeywell. I'm pretty confident I could handle the mechanical install, but I'm unsure how to hook it into the fancy new thermostat that comes with my new system (either a Honeywell IAQ or Trane comfortlink II).

    Thanks a lot for your feedback.

  2. #2
    Join Date
    Jun 2013
    Posts
    7
    I should add that I want to pull in some fresh air with this dehumidifier also.

    After reading some more of teddy bear's posts it sounds like he recommends a separate return for the dehumidifier. I think I can pull that off pretty easily. Would a single return in the basement be sufficient to dehumidify the whole house? I plan to have my variable speed furnace fan running on low all the time. So that should distribute dry air to the whole house?

    With the fan running all the time is there really any reason to use a separate return dedicated to the DH? Would that help dry out the basement more than tapping into into the main return? My basement isn't finished yet so the installers may be reluctant to just have the DH return sitting there next to the furnace. But once I finish the basement I can connect that to a register in the wall that pulls from the finished area.

    Another idea I had is to have a separate return for the dehumidifier and then feed into the hvac before the filter. This way my outside air would go through my 4" filter. My wife has bad allergies and I am concerned about bringing in allergens from outside.
    Last edited by zirconx; 06-30-2013 at 12:19 AM. Reason: added more info

  3. #3
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,702
    Because of the expenses, whole house DH were a hard sell. But the more I saw the high humidity levels after new "hi-eff." A/C installations, the more I believe in WHDH. Your set-up idea has merit if the fan runs all the time as you stated it would.

    HOWEVER, it probably is not advised. You would be sucking air (too much) through the DH (at times) and reducing it's de-humidification qualities. The DH come with a Merv 11 filter and the outdoor air inlet is an option or can be metered.

    You'll want to add returns off your HVAC system to the basement as well as the new supplies.

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,470
    Quote Originally Posted by zirconx View Post
    I should add that I want to pull in some fresh air with this dehumidifier also.

    After reading some more of teddy bear's posts it sounds like he recommends a separate return for the dehumidifier. I think I can pull that off pretty easily. Would a single return in the basement be sufficient to dehumidify the whole house? I plan to have my variable speed furnace fan running on low all the time. So that should distribute dry air to the whole house?

    With the fan running all the time is there really any reason to use a separate return dedicated to the DH? Would that help dry out the basement more than tapping into into the main return? My basement isn't finished yet so the installers may be reluctant to just have the DH return sitting there next to the furnace. But once I finish the basement I can connect that to a register in the wall that pulls from the finished area.

    Another idea I had is to have a separate return for the dehumidifier and then feed into the hvac before the filter. This way my outside air would go through my 4" filter. My wife has bad allergies and I am concerned about bringing in allergens from outside.
    Fresh air is important for year around indoor air quality right nest to maintain <50%RH inside the home including the ducts. During cold windy weather, the wind and stack effect usually provides adequate the fresh air. But during calm moderate weather, mechanical filtered fresh air change is needed to purge indoor pollutants and renew oxygen. The whole house ventilating dehumidifier is an ideal method of providing fresh filtered air when the home is occupied. Units like the Ultra-Aire are able to provide fresh air when needed, mix it with house air, filter both, and circulate it through out the home via the a/c ducts. With an idependent return from the home, a fresh air inlet, and the dehu supply connected to the a/c, circulation and dehumidification can be done without operating the a/c blower. This is a big energy advantage over having to operate the a/c blower.
    If concerned about cost, the Ultra-Aire 70H is 20% less cost and would handle you home. The UA 105H is the most efficient dehu made but cost more and has more capacity.
    The air filters are Merv !! which catch all mold spores and pollen.
    Keep us posted. Encourage your contractor to do the Ultra-Aire, He or his supplier can purchase the unit from Madison, WI factory. We encourage you to deal with your local a/c contractor. It is well worth the addition cost to assure compatibility with the equipment.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  5. #5
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,051
    Could you briefly describe how the supply air is distributed without running ac blower? Cant quite grasp that part.

  6. #6
    Join Date
    Dec 2010
    Location
    Down by the river
    Posts
    1,664
    It conect to your supply duct...and has its own blower.

  7. #7
    Join Date
    Jun 2013
    Posts
    7
    Thanks for the replies. Is the Honeywell DR90 the a rebadged Ultra-Aire 90H?

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,470
    Quote Originally Posted by zirconx View Post
    Thanks for the replies. Is the Honeywell DR90 the a rebadged Ultra-Aire 90H?
    Yes. The Ultra-Aire DEH 3000 controller provides fresh air on a routine occupancy. If the home is occupied evenings, fresh air is matched to the schedule. There are features that the DEH has. The UA 105 is unique to the UAs.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  9. #9
    Join Date
    Jun 2013
    Posts
    7
    The Honeywell rep was here this morning. He strongly recommended not bringing in outside air into the dehumidifier. He said you'd just be pumping humid outdoor air into it. He also said there could be problems in winter with it freezing and breaking the coil, and he wouldn't warranty that. Instead he suggests to duct a fresh air intake into the air handler return.

    Any thoughts?

  10. #10
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,470
    Quote Originally Posted by zirconx View Post
    The Honeywell rep was here this morning. He strongly recommended not bringing in outside air into the dehumidifier. He said you'd just be pumping humid outdoor air into it. He also said there could be problems in winter with it freezing and breaking the coil, and he wouldn't warranty that. Instead he suggests to duct a fresh air intake into the air handler return.

    Any thoughts?
    Yes, I do have some thoughts, but they are not nice.
    I should be more patient, I also thought like that 20 years ago.
    If you follow our suggested ducting of mixing fresh air with house air, the air entering the dehu is +32^F. If the air is <32^F no damage will occur. Ultra-Aire will warranty our unit with fresh air direct. Fresh air into the furnace fan meas operating the fan whenever fresh air is needed. This means most of the time. Also geting 70-90 cfm through a 6" duct with a furnace fan on low is difficult.
    All in all, do what ever you want, not the end of world. You can always change the ducting. I also prefer fresh air when occupied as compared to 24/7 on/off dependent on outside weather. I believe that fresh may not be needed after cold windy weather arrives. You can tell if the home gets too dry with a couple occupants.
    There are experts everywere, they have a honest difference of opinion. Have a happy 4TH. Keep us posted, many are watching.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  11. #11
    Join Date
    Jun 2013
    Posts
    7
    He also said that an ERV would help my negative pressure problem. I question this because an ERV pushes are out, too. So say 100cfm in and 100cfm out. How would that help my negative pressure problem? He said it is smart and has dampers that will adjust. Is this true?

  12. #12
    Join Date
    Jun 2013
    Location
    NORTHERN
    Posts
    991
    perhaps drop the teddy and be like bear, for mostly what he wrote...

    in variable compressor (VFD, Iq, VarC) or dual compressor (3-staging sm+lg, then both) in lowest staged a/c there is little need in southern to northern homes (90%) for additional DeHumidification. The air speeds of the blower can drop (as adj prog. allows) some to some 320 cfm per compressor-inside-labeled-ton (300 per most ratings-tons outside label) and wring moisture out of the air. At those systems designs the heatexchangers are 3 to 4x's oversized at that staging. Other sensing at "compressor-off" at frosty conditions, really makes a difference.

    Commercially it is said dry air and humid air meet faster than the speed of sound, so less overall- placed distribution- is usually fine. AIR MOVEMENT in lower cooler sections keeps a lot of moldies from adhearing, alone, at higher than recommended rHum #'s.

    A little ducted 4.1/2" to 6" 25w-40w fan serves ~ 500 sq ft hanging 6" off ceiling, in basements IF NOT RECEIVING RADON GASSES at the low level flooring.
    BUT: THE fan gets dirty in 3-5 years, and although reported over 15% cooling savings and over 20% heating savings in poorly distributed spaces, you do not see many- other than very narrow-aisle paper and item storage facilities that have no use for paddle fly-pushers or changing ducting and tubes with holes, etc.

    Vertical air rotation in for destabilizing humid/tempered-cool air movement is helpful, when applicable.

  13. #13
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,470
    Quote Originally Posted by zirconx View Post
    He also said that an ERV would help my negative pressure problem. I question this because an ERV pushes are out, too. So say 100cfm in and 100cfm out. How would that help my negative pressure problem? He said it is smart and has dampers that will adjust. Is this true?
    Yes, installing and erv and not exhausting any air will help the negative pressure in a house. Of what good is the erv? Its an expensive make-up device. All things considered, clothes driers, bath fans, and kitchen hoods all need make-up air. Also in middle of winter, I expect your home needs very little supplemental fresh air to purge indoor pollutants.
    70-80 cfm of make-up fresh filtered air blended with house air when occupied through the spring/summer/fan and on into winter until the home gets too dry would be the best. Maintaining <50%RH is important to avoid mold mildew and dust mites. As I said before, I can remember when I agreed with Honeywell Rep.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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