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  1. #1
    Join Date
    Mar 2020
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    Dehumidifiers ( wholehouse/lower level )

    LOCATION: South Carolina midlands region.

    WEATHER: Hot & very humid

    TERRAIN: limited Shade with northern exposure lake front.

    HOUSE: 1999 yr Ranch with walkout lower level. MAIN level 3100 sq ft w/9 ft ceilings & extended height tray ceilings. LOWER level 1100 sq ft, w/9 ft ceilings with 3 sides being 3/4 below grade.

    R19 walls, R38 ceiling joists & numerous windows facing lake. Main house windows Simonton insulated, Florida room single pane non insulated.

    Current HVAC: (1999) Zoned Amana 5 ton single stage a/c & Amana 90 plus gas furnace.

    AC: 2 supply zones, 1 main level & 1 lower level. 3 return air grates main level off a large return main & 2 return air grates lower level (1) 10 inch main branching into (2) 8 inch pipes. NOTE: Returns NOT zoned, all work whenever AC unit is running.

    Main level humidity tolerable but unit cycles often. Lower level humidity extremely high & being 3/4 surrounded by earth temps are pretty steady so AC zone rarely comes on.

    PLANNED UP GRADES: New 2 stage or variable stage AC unit & new 90 plus heater with variable speed fan.

    ULTRA AIRE 98H or 120 mounted in craw space using 10 inch flex duct to ONLY accessible wall in lower level. Currently one of the lower level return air grates is in the middle of this wall. Can’t relocate it. Was going to put a dehumidifier grate on each side of the return grate. These grates would be 12 feet apart from each other & each would be 6 feet from the centered main system return.

    QUESTIONS:

    1. Will that centered return air grate cause any problems with the Dehumidifier grates being 6 feet away with some dryer dehumidified air being sucked into the return and across the AC coil.

    2. With lower level returns not being zoned and always working even when lower level supply is off, its creating a negative pressure situation in the lower lever. I can fix this easily with a large grate above the lower level door or zone the lower level return to only come on when lower lever supply is on. My concern with that approach is that if the lower level return is part of the overall return air calculation and having it closed off when main level zone is on, could it starve the system of return air? Seems the large grate above the lower level door is a safer/easier bet to equalize the pressure and it does keep air circulating throughout the house.

    3. Should I pipe some dehumidified air into main level supply ...OR...if I put a large grate above the lower level door.....with the returns in the lower level always going when ever AC is on.....create enough circulation to bring some dehumidified air from lower level up to main level. *** I will also be eventually be putting in an outside duct to the dehumidifier for fresh air replacement-***

    I know this is a lot of info but I am trying to put forward as much info as possible.

    Thanks so much for any advice !

    Tom

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    9,768
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    Quote Originally Posted by Tom34 View Post
    LOCATION: South Carolina midlands region.

    WEATHER: Hot & very humid

    TERRAIN: limited Shade with northern exposure lake front.

    HOUSE: 1999 yr Ranch with walkout lower level. MAIN level 3100 sq ft w/9 ft ceilings & extended height tray ceilings. LOWER level 1100 sq ft, w/9 ft ceilings with 3 sides being 3/4 below grade.

    R19 walls, R38 ceiling joists & numerous windows facing lake. Main house windows Simonton insulated, Florida room single pane non insulated.

    Current HVAC: (1999) Zoned Amana 5 ton single stage a/c & Amana 90 plus gas furnace.

    AC: 2 supply zones, 1 main level & 1 lower level. 3 return air grates main level off a large return main & 2 return air grates lower level (1) 10 inch main branching into (2) 8 inch pipes. NOTE: Returns NOT zoned, all work whenever AC unit is running.

    Main level humidity tolerable but unit cycles often. Lower level humidity extremely high & being 3/4 surrounded by earth temps are pretty steady so AC zone rarely comes on.

    PLANNED UP GRADES: New 2 stage or variable stage AC unit & new 90 plus heater with variable speed fan.

    ULTRA AIRE 98H or 120 mounted in craw space using 10 inch flex duct to ONLY accessible wall in lower level. Currently one of the lower level return air grates is in the middle of this wall. Can’t relocate it. Was going to put a dehumidifier grate on each side of the return grate. These grates would be 12 feet apart from each other & each would be 6 feet from the centered main system return.

    QUESTIONS:

    1. Will that centered return air grate cause any problems with the Dehumidifier grates being 6 feet away with some dryer dehumidified air being sucked into the return and across the AC coil.

    2. With lower level returns not being zoned and always working even when lower level supply is off, its creating a negative pressure situation in the lower lever. I can fix this easily with a large grate above the lower level door or zone the lower level return to only come on when lower lever supply is on. My concern with that approach is that if the lower level return is part of the overall return air calculation and having it closed off when main level zone is on, could it starve the system of return air? Seems the large grate above the lower level door is a safer/easier bet to equalize the pressure and it does keep air circulating throughout the house.

    3. Should I pipe some dehumidified air into main level supply ...OR...if I put a large grate above the lower level door.....with the returns in the lower level always going when ever AC is on.....create enough circulation to bring some dehumidified air from lower level up to main level. *** I will also be eventually be putting in an outside duct to the dehumidifier for fresh air replacement-***

    I know this is a lot of info but I am trying to put forward as much info as possible.

    Thanks so much for any advice !

    Tom
    A little confusing. I like the idea of sucking air from the upper level of the home to the dehumidifier with a significant portion of the dry air going to the lower levels with the balance going to the upper part of the home via the cold air supply of the a/c. This will aid circulation plus provide warm dry air to the lower lever which needs warm dry air more than the upper levels of the home. Keep us posted on the results. I realize I did not answer the question but it was confusing. A balancing damper to be able to adjust the distribution of dry air between the lower level and the mainfloor will help. Sucking from the mainfloor though the dehu to the lower level will max the drying effect on the lower level and cause circulation. Could work.
    Keep us posted and raise any issues that come up. Dry air from the dehu should not be routed into the a/c before the cooling coil but after.
    Thanks for picking the Ultra-Air, is it removing moisture with warm dry air coming out of the supply. Should remove +3 lbs. of moisture per hour.
    Regards Teddy Bear
    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"

  3. #3
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    27,233
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    In theory

    Warm Moist air (2nd floor) will naturally migrate to a cool dry environment (1st Floor)

  4. #4
    Join Date
    Mar 2015
    Location
    Medford, N.Y.
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    What is the Load Estimate? W/O one its a crap shoot. What temp are you maintaining? Have you tried putting the fan in the "on" position? W/O proper returns it is a lot difficult to zone correctly. ACCA has a Manual Z which is all about zoning.

    5t seem's a little small, and the AC cycling off means no cooling which means no dehumidification. Is there an air (indoor/outdoor) exchange unit for a "tight" house which I think there has to be w/ 4200 sq.ft. And how many cu.ft.?

    Where is the t'stat located in relation to the Supply registers/Return grill?

    Get the Load Estimate before replacing the equipment.

    This is all an "I think" situation.

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    9,768
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    Quote Originally Posted by Tom34 View Post
    LOCATION: South Carolina midlands region.



    PLANNED UP GRADES: New 2 stage or variable stage AC unit & new 90 plus heater with variable speed fan.

    ULTRA AIRE 98H or 120 mounted in craw space using 10 inch flex duct to ONLY accessible wall in lower level. Currently one of the lower level return air grates is in the middle of this wall. Can’t relocate it. Was going to put a dehumidifier grate on each side of the return grate. These grates would be 12 feet apart from each other & each would be 6 feet from the centered main system return.

    Missed the planned part.

    QUESTIONS:

    1. Will that centered return air grate cause any problems with the Dehumidifier grates being 6 feet away with some dryer dehumidified air being sucked into the return and across the AC coil.

    Good for dehu return location. The dehu supply should be split the basement area and the a/c supply to the rest of the home. A couple balancing dampers to adjust the amount of dry air to the two areas.

    2. With lower level returns not being zoned and always working even when lower level supply is off, its creating a negative pressure situation in the lower lever. I can fix this easily with a large grate above the lower level door or zone the lower level return to only come on when lower lever supply is on. My concern with that approach is that if the lower level return is part of the overall return air calculation and having it closed off when main level zone is on, could it starve the system of return air? Seems the large grate above the lower level door is a safer/easier bet to equalize the pressure and it does keep air circulating throughout the house.

    Agree, avoid negative pressure on the lowest level, it sucks in soil gases/moisture.

    3. Should I pipe some dehumidified air into main level supply ...OR...if I put a large grate above the lower level door.....with the returns in the lower level always going when ever AC is on.....create enough circulation to bring some dehumidified air from lower level up to main level. *** I will also be eventually be putting in an outside duct to the dehumidifier for fresh air replacement-***

    Split dry between lowest level and the rest of the home with a dehu return favoring the main floor. Also fresh air return from outdoors to the dehu. If home is not occupied 24/7, use an electric damper in the fresh air duct controlled by DEH3000 controller to ON/OFF fresh air when occupied.

    I know this is a lot of info but I am trying to put forward as much info as possible.

    Thanks so much for any advice !

    Tom
    Sorry for the confusion on my part.
    Keep us posted.
    Regards Teddy Bear
    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"

  6. #6
    Join Date
    Mar 2020
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    Thread Starter
    Thanks guys, really appreciate the info. House was a fixer upper both inside and outside and we have only lived in it for about 1.5 years so still at the bottom of the learning curve.

    Main living area (3100 sq ft) (Zone 1) with (3) 10”x 30” return air grates seems ok but generally not very long AC cycles.

    Lower level (1100 sq ft) ( Zone 2 ) is where the issue is because of the low heat load / steady temps caused by the lower level being largely below grade. AC just doesn’t run that often to maintain say 74 degrees so the humidity doesn’t get removed. Go to low with the temp setting and condensation starts forming.

    Because the lower level returns are not zoned with the lower level supply, air is drawn out of the lower level returns any time the blower is operating which is causing negative pressure in the lower level. This in itself caused damp air to be drawn out of the craw space into the lower level through a common leaky wall. Leaky wall fixed ( 2 inches of 2 lb closed cell spray insulation) & I will put a 10”x30” air pass through grate above the door heading down to the lower level to allow air to flow down there when returns are sucking air out.

    Thinking Ultra Air 98 dehumidifier in the craw with a 10 inch duct drawing air out of lower level and a 10 inch duct supplying dehumidified air back in to the lower level is the least complicated way to go. When the main level AC zone is on, the lower level return is drawing air so with the added 10x30 air pass through grate above lower level door I should get some of the dehumidified air upstairs and will call it a day with that.

    Will have to have a Manual J performed because I think they sized a 5 ton AC based on 4200 total sq foot when in fact the 1100 sq foot lower level has a very low heat load being mostly underground and the real heat load is only in the 3100 sq feet on the main level which is causing the old 5 ton single stage to short cycle.

    When I replace the AC thinking of going 2 stage. Cost for variable stage pretty high & not sure about the skill level where I am at to install / diagnose & repair a real complicated communicating system. I know this is outside the initial topic and you guys have probably pounded the subject in the past but is a 2 stage significantly better with humidity (vs) a single stage.

    Thanks, Tom

  7. #7
    Join Date
    Mar 2020
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    Thread Starter
    Not sure on load, just bought the house. Will definitely be getting that done. Ton of glass w/a big Florida room that has marginal quality windows w/single pane glass. Also a lot of recessed can lights and worn seals on exterior doors so not overly tight at the moment. Thermostat is a standard programmable Honeywell in a hall, about 5 feet high & about 3 feet under a 10x30 return air vent near the ceiling. Lower level thermostat is the same and about 2 feet to the side of the big 10x30 return. That thermostat can easily be moved at this time before Sheetrock goes back up.

  8. #8
    Join Date
    Mar 2020
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    Thread Starter
    Sorry if I repeated my self on some issues or was confusing. I am horrible with this new world of spending an hour typing something that used to take a 5 minute phone call to explain. My inches abbreviation came up as capital As 🤪

  9. #9
    Join Date
    Mar 2015
    Location
    Medford, N.Y.
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    Get the load estimate. Get Manual Z.

  10. #10
    Join Date
    Aug 2006
    Posts
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    I went with Square Footage, did my research. I was a Sante Fe guy, until I read the reviews, also found out you need to buy the warranty. I ordered a whole house AprilAire, warranty included. The extended warranty was cheap, and both were basically over the counter.
    Retired, after 43 Years

  11. #11
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    How much does an extended warranty cost for a Santa Fe?
    Regards Teddy Bear
    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"

  12. #12
    Join Date
    Aug 2006
    Posts
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    Sylvane is who I purchased the humidifier from, they have Santa Fe, AprilAire, and Honeywell for Whole House. The times I need one is Spring and Fall, when Im not Cooling or Heating.
    Retired, after 43 Years

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