Page 1 of 2 12 LastLast
Results 1 to 13 of 23
  1. #1
    Join Date
    Jun 2013
    Posts
    6

    Mold and Undersized Ducting... options?

    9 years ago, we had our 2.5 ton system replaced with a 3.5. Now, we have visible mold on the vents. Yesterday, we were told that our duct work was sized for a 2 ton, and that was the root cause. Their suggestion was a full duct redesign and replacement and HEPA filter with RGF/REME system. The price tag was staggering. This is a average middle class ranch home in central florida built in the 70's, and we plan on being out of it in 5 years anyway, so no way am I doing massive renovations. Reading here, I already see that the RGF/Reme/Hepa thing is likely just expensive hyped crap. And general research says taking care of my humidity problem, which means taking care of my airflow problem, will cause the mold to die off on it's own. So here is my big question... since the bottom line is I have too little airflow in and out of the air handler, wouldn't adding a few appropriately sized vents and returns fix that problem? I realize it will not be balanced, and it will not make my warmer rooms cooler or my cooler rooms more comfy...all things the proposed complete redesign would do... but I also don't think it will cost me 15k either. Simply looking for the most realistic answer here... would like the mold to be gone, and my system to run efficiently, which will hopefully lower my electic bill; beyond that, I am not looking for massive redesign, perfection, rocket science or magic. Thanx for any input.

    David

  2. #2
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,460
    We always have to check the duct system & air handler sizing before replacing a condenser.

    Usually, the duct system & Return Air filter areas are undersized; going up in tonnage is nearly always the worst thing, & most costly, that one can do!

  3. #3
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,441
    I understand what you are trying to do but the fact that the entire ductwork system might have mold in it. You need to have it all removed and replaced. Other wise when you try to sale the home this issue will come up and you might not be able to sale it without doing the work or at all. The word mold scares people as it should I woundnt want to purchase or live in a home with it.

    I would get a load preformed to determine the hvac size that is needed then a manual D to determine the new ductwork size. Period end of story. Trying to avoid this will not end well for you. Whiles is a bad situation for you and I am sorry. The truth of matter is that it needs to be corrected and the only true way to ensure if this is to have all the ductwork removed. Load cal to size the hvac equipment propely along with ductwork. So this want happen again.

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,062
    Quote Originally Posted by SiriusDG View Post
    Simply looking for the most realistic answer here... would like the mold to be gone, and my system to run efficiently, which will hopefully lower my electic bill; beyond that, I am not looking for massive redesign, perfection, rocket science or magic. Thanx for any input.

    David
    There is mold or dirt on many grills in green grass climates. How does small ducts cause mold? Many high velocity systems have small ducts. Wet spots for extended hours grows mold. Have pulled the grills and cleaned them in 9 years? Also looked inside the ducts? What is the temp/%RH in your home when the a/c is running? Crawlspace or slab on grade? Location of the air handler?

    Can you maintain <50%RH inside your home during any of the cooling conditions?
    Generally small ducts on a large a/c deliver low dew point air to the home. Cold grills sweat when exposed to high dew point air. This happens in a damp home with short cold cooling cycles.
    also so as wet a/c coils dry during the off cycle, the moisture moves into the home through those cold grills. Results wet grills. Wet grills for extended hours-Grows mold.
    Give us more info. Monitor the indoor temp/%RH.
    Keep us posted with more info.
    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
    Jun 2013
    Posts
    6
    Home is on a slab. Temp and RH as I type this is 77 and 48%. Normally it is fairly comfortable in the house. The vents do sweat, a lot, and we cleaned them once or twice but not lately. When I pull the vent and look up into the duct, I do not see mold, but when they looked inside the air handler yesterday there was visible mold in there. The air handler is in the attic.

    Based on what I see, I tend to agree with the "wet grill" theory.

    I also tend to keep the fan On, rather than Auto, as I get very uncomfortable in stagnant air. About two seconds after the fan clicks off I will be moving towards the thermostat. I have heard both sides of the argument on that setting, but am open to any input there was well.

    Thanx.

  6. #6
    Join Date
    May 2013
    Location
    Florida
    Posts
    104
    to small of a return will also cause excessive moisture and mold or organic growth

  7. #7
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,460
    I would use other fans to circulate room air; not the air handler fan; set tstat on auto & let the furnace blower cycle off with the A/C.

    I use floor type fans that are vertically adjustable.

    Do you have ceiling fans that will move enough air?

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,062
    Quote Originally Posted by SiriusDG View Post
    Home is on a slab. Temp and RH as I type this is 77 and 48%. Normally it is fairly comfortable in the house. The vents do sweat, a lot, and we cleaned them once or twice but not lately. When I pull the vent and look up into the duct, I do not see mold, but when they looked inside the air handler yesterday there was visible mold in there. The air handler is in the attic.

    Based on what I see, I tend to agree with the "wet grill" theory.

    I also tend to keep the fan On, rather than Auto, as I get very uncomfortable in stagnant air. About two seconds after the fan clicks off I will be moving towards the thermostat. I have heard both sides of the argument on that setting, but am open to any input there was well.

    Thanx.
    The a/c coil is loaded with several lbs. of moisture whenever cooling the home. The supply ducts are +85% RH from the cooling coil to the exterior of the supply grills when cooling. When the cooling cycle ends in the "auto" fan mode, the entire duct system is near 100%RH until the moisture on the coil evaporates back to the home. This takes 1-2 hours with the fan off. Therefore there is a probability that mold can grow in the a/c ducts through a typical cooling season. Mold will not grow in a space that is thoroughly dried for several hours every day. Surfaces that are wet for more than 24 hours must be cleaned periodically to avoid a visible build up of mold.
    Fan "on" mold rapidly dries the cooling coil and ducts when the compressor is off. Usually <45 mins. is required for the air in the ducts to be the same %RH as the air in the home. The difficulty is that rapid re-evaporation of the 2-5 lbs. of moisture in the coil/pan makes the high indoor %RH especially during moderate cooling loads.
    Maintaining <50%RH in the home, operating the fan for several hours every day without cooling to thoroughly cool/ducts should assure minimal mold growth. In green grass climates, you need supplemental dehumidification to maintain <50%RH when the outdoor dew points are +60^F and the home is occupied. Usually about 3-4 lbs. per hour of dehumidification is required from the a/c or a dehumidifier with +2-4 lbs. per hour with high outdoor dew points and several occupants.
    More focus can be put on the ducts by using a whole house dehumidifier like an Ultra-Aire connected to the supply side of the a/c ducts. This unit is controlled by a dehumidistat located in the open part of the home. When the a/c is maintaining <50%RH, no dehumidification is needed. As the cooling load declines and the outdoor dew point is high, the indoor %RH rises +55%RH, activating the dehu which blows dry into the supply a/c duct which dries the ducts quickly and circulates the dry throughout the Home.
    I have fixed many problem mold homes with strategy. The a/c can be oversized or off, the home will be ,50%RH throughout and the ducts except when the compressor is cooling the home.
    Keep us posted.
    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 2005
    Location
    SW Wisconsin
    Posts
    4,460
    In cases of mold problems; I agree with teddy bear...

  10. #10
    Join Date
    Jun 2013
    Posts
    6
    That is brilliant, than you. I would never have thought of simple dehumidification. I will definitely make that a point of conversation as we get second and third opinions... I do not plan on doing this as a DIY project.

    Excuse my dullness this morning, but to ask very simply... if I follow this strategy, then should I go with Fan On or Fan Auto?

  11. #11
    Join Date
    Jun 2013
    Posts
    6
    As my wife and I discuss this, we realize we kinda tried this last summer... we got a standalone in home dehumidifier. Problem was, it heated the room up so much we immediately took it back. So... how do we not end up fighting ourselves with heating/cooling the same space just to dehumidify? Different kind of dehumidifier? Specific recommendations? Thanx.

  12. #12
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,062
    Quote Originally Posted by SiriusDG View Post
    That is brilliant, than you. I would never have thought of simple dehumidification. I will definitely make that a point of conversation as we get second and third opinions... I do not plan on doing this as a DIY project.

    Excuse my dullness this morning, but to ask very simply... if I follow this strategy, then should I go with Fan On or Fan Auto?
    The aggressive move is to keep a small amount of air moving through the ducts to encourage drying. The fan of the dehumidifier when connected to the a/c supply duct will be adequate.
    http://ultra-aire.com/products/dehum...ra-aire-xt105h

    Do a return from the open part of the home and route the dehu supply to the a/c supply. Locate the dehumidistat in the open space. Dehumidifiers will not operate as long as the a/c maintains less than 50%RH. The warm dry air is routed to the a/c supply ducts and will distribute the warm dry air throughout the home. The warming effect is minute when mixed to the home. Stand alone dehu tend to warm the space around the dehu.
    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"

  13. #13
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    May I ask why the tonnage went from two tons to 3.5? That's quite a jump. It may also be the largest contributing factor to the problems you now have with mold and humidity control.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event