Mold and Undersized Ducting... options?

[SiriusDG]

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

[udarrell]

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!

[duckman06]

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.

[teddy bear]

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

[SiriusDG]

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.

[bob Juliano]

to small of a return will also cause excessive moisture and mold or organic growth

[udarrell]

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?

[teddy bear]

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

[udarrell]

In cases of mold problems; I agree with teddy bear...

[SiriusDG]

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?

[SiriusDG]

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.

[teddy bear]

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

[Shophound]

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.

[SiriusDG]

Thanx Teddy Bear.

The original system was 3 and the house was never less then 80 in the summer, we made the jump hoping to at least be comfortable. We got no warning of the dangers of doing so. The guys who came out the other day told us the ducting was sized for 2 or 2.5, so it appears someone else already upsized before we purchased, and we upsized their upsize, just compounding the problem.

[duckman06]

So you have a (3.5) ton system on a (2-2.5) duct system. So what's the plan by the company that discovered this?

If mold is present in the ductwork only one way to ensure it all gets removed and that's by removing it all and staring over with properly sized hvac system and a duct system that will deliver the right amount of cfm for both supply and return!

Load cal first to see what the home needs for hvac equipment and then manual d for the duct sizing. Once this things are done a estimate can be written up to correct the problem not try to fix something that is has caused the mold in the home.

I can't stress enough that I understand your problem but the only way to correct for 100% is to do the above listed. Oversized system on undersized ductwork needs to be corrected and move on. Bandaids want correct the problem. Mold is nothing to play with regardless if your are going to be saleing the home or not.

Untill you do you will still be exposed to it along with your family and real have to tell the buyers of the home when you sale it of the problems. If you correct right now will be better then waiting.

Sure is not ideal and sucks but it needs to be done regardless of the price to ensure it want happen again and that existing mold has been removed. You where dealed a bad hand but you have to know when to fold or keep playing the cards in hopes to win.

[SiriusDG]

So team two came out today, promptly steered the conversation off of a dehumidifier and right back onto the complete redo of all duct work. While I understand that this is the PREMIUM solution, there a lots of times in life when, for a variety of reasons, options B, C, and D may be preferable. Is this going to be my experience with everyone... "We do it RIGHT or not at all"? I simply am not going to put that kind of money into this house at this point... is there someone else, beside AC companies, I should call? Or some other way to properly say "I am not interested in new ducts, please quote me on a dehumidifier." that allows them to still be professional? A little frustrated, taking days off work to make no progress is adding to the irritation. Any opinions? Thanx guys.

David

[duckman06]

So team two came out today, promptly steered the conversation off of a dehumidifier and right back onto the complete redo of all duct work. While I understand that this is the PREMIUM solution, there a lots of times in life when, for a variety of reasons, options B, C, and D may be preferable. Is this going to be my experience with everyone... "We do it RIGHT or not at all"? I simply am not going to put that kind of money into this house at this point... is there someone else, beside AC companies, I should call? Or some other way to properly say "I am not interested in new ducts, please quote me on a dehumidifier." that allows them to still be professional? A little frustrated, taking days off work to make no progress is adding to the irritation. Any opinions? Thanx guys.

David

You should lesson to what all the pros are saying! If they all agree that the duct system needs to be removed and installing a new one is the best solution why would you want to try to it have a!!.

I wouldn't touch your home due to the following you have undersized duct work with oversized system which lead to your problem. Just adding a dehumidifier to the home will not correct the presents of mold in the ductwork. It might help but if not going to 100% fix the problem why bother?

You want the best if both worlds but don't want to pay for it. Which is your choose as its your home. I would say to you good luck and hopes it all works out but the truth is it want! You might find someone to put a bandaid on the system and tell you what you want to hear but want truly correct the probelm.

So it boils down to choose and you choose not to address the matter correctly in which I would again walk away as my name and my companies rep is on it.

Options B, C and D you talk about want correct the problem if the duct system has mold. You don't want to pay to have it done right! That might be why you are in the boat you are in with sizing of the equipment?

Sorry to be harsh but you want something done for a lower cost in hopes that it will fix your problem. In your case run the system as it stands and see what happens. You can't put a price on healthy air for you and your family. An when you go to sale remember this will come up and then what?

[precision hvac]

The problem is- anyone working on that system essentially marries it.
Mold? No friggin way am I shortcutting that job when I know what the right fix is.
So if I was bidding- it would be new ducts or nothing.
You called the pros out & don't like the answers they give.
You don't need a pro- you need a handyman who will tell you what you want to hear.

[udarrell]

Mold is a serious threat to the health of everyone in your home, & could cause your system to be condemned to where you could no longer use your central air for either heating or cooling; a proper fix would be required.

[duckman06]

Mold is a serious threat to the health of everyone in your home, & could cause your system to be condemned to where you could no longer use your central air for either heating or cooling; a proper fix would be required.

That's a simple as someone can put it!!! It's serious and needs to be addressesd before mattes get worse along with health problems.

Do it right now and you want have to worry about it. Sure it costs more but what's your health and homes value worth to you?