Mold in air ducts

[jnw]

We are getting our entire air conditioning system repolaced -- condenser, evap coil & furnace. I just noticed yesterday all of the vents in the house have black mold spores all over them.  I am guessing there is mold throughout the duct work.

Rather than try and clean it.  Should I just pay a few grand and have all the ducts and vent grills replaced?   Rip it out and replace it?  I can't believe I didn't notice the black spores... never really looked up toward the ceiling much.  I thought perhaps it was a bit of dust but looking closely it has a spore pattern.

[jnw]

So interesting I just now notice this black mold on vents, about 26 days since I had home / duct sealed along upgrading of blown in attic insulation from R9 to R39.  They took every one of these vents off and sealed them 26 days ago. They are covered in black now -- black mold pattern (spots).  Why wouldn't of they said we have a black mold problem 26 days ago when they took them off.  I am surprised they even touched the vents since the mold spores are so dangerous.

OR... did all this black mold on vents build up in the past 26 days since they sealed the duct and home? Is it too humid in here now?   Is it possible it could of grown so fast?  I never noticed this before until a couple days ago when I was checking out the vents for air flow.  (Getting AC system replaced starting yesterday.. they are finishing today.. going to ask the AC installer when he comes later today about this black mold.)

[lthenderson]

First, there is a lot of difference between black colored mold and Stachybotrys chartarum, also known as black mold. Black colored mold is by far the most common mold is not toxic at all though it can be allergenic to some people. Strachybotrys chartarum black mold of the toxic to breath kind is very rare because it needs at least 72 hours of water immersion followed by plenty of consistent moisture there after to continue growing. So I wouldn't freak out about the mold on your vents because it is highly unlikely to be toxic to breath or touch.

Saying that, I'm guessing sealing your ducts was the trigger. I would guess that you are getting condensation where the cold dry air conditioned air is meeting the warm moist air of the interior of your house, i.e. at the vents. Previously, there was probably enough loss or infiltration of warm moist air through cracks in the ducts to not make it an issue. I would probably measure the humidity levels inside your house and make sure it is between 30 and 50 percent. If it is higher, you may need to get a dehumidifier going.

As for the vents, probably washing them in warm soapy water is the solution to removing the mold most cost effectively. But if you replace them, it shouldn't cost a few grand unless you are talking of a huge house full of very ornate vent coverings. I replaced all of mine in the house as part of a general remodel since the old ones were all paint splattered and it maybe cost a few hundred dollars to do so.

[jnw]

Thanks for that info.  I wasn't planning on replacing the duct work myself but paying for someone to do it.    I posted in this DIY forum because it's repair related and seemed the most appropriate place.  I figure it'd cost a pretty penny for all that labor replacing it all.

Here is a photo of the worst vent by far. I can't believe they'd take off this vent and seal the duct behind it and put it back on with all that mold on it.. and without saying anything to me about it.  (I'm thinking perhaps this mold grew in the past 26 days after they sealed it.)  [Or perhaps they did take them off with the black all over it because just above the vent faceplate on this wall there appears to be a smear.. perhaps from fingers?]  Btw, this is the vent I was looking at to feel air flow when I first noticed all the black.. it's so bad it caught my attention immediately... then I discovered there is some on all the other vents although only about 25% of this on the others.

[jnw]

The HVAC guy just got here today at 8AM and I talked to him about this issue.  He said that he think the new AC will take care of this issue.  He said he looked inside the plenum and down a little ways and said he saw no mold there.   He said the mold usually just condensates on the metal grates where the two tempeartures meet and says this is a common problem. He said he thinks I'll be okay if I take off the vents, spray/clean with a bleach/water mixture.  Let dry for 24 hours on boots.  Spray paint the vent faceplates with KILZ Spray Primer.. evidently there is something in this paint that mold hates.  EDIT: Actually I am just going to buy new vent registers throughout the house.. only $15 a piece.. rather than trying to clean them.  I'll spray the new vent registers with KILZ before installing.

I agree with you it's probably not hte dangerous mold.  So we'll do the cleaning ourselves and give this a go.

Might add dehumidifier/ionizer/uv light (or whatever) later on to help if there are humidity issues still.

Thanks again for your help.

[ChpBstrd]

As a diagnostic step, I suggest picking up a hygrometer. Humidity above 60% will result in mold breakouts, even if it's not the toxic variety.

https://www.amazon.com/GLOGLOW-Temperature-Clock-Shaped-Hygrometer-Thermometer/dp/B07DVMHLL2/ref=asc_df_B07DVMHLL2?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80814222102861&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4584413750461902&psc=1

Your new AC will probably help keep the humidity in check better than a malfunctioning AC with the coils frozen over could do. We just had ours replaced, and our thermostat is programmable to control humidity by allowing a wider band of temperature fluctuations and running the unit for longer stretches of time, which lets more of the water drain off the coils instead of just evaporating back into the air.

Anecdotally, when our AC went out last month, we put an old 5000 BTU unit in the dining room window until we could get the HVAC system replaced. Even though it was only big enough to cool one room, and the best it could do for our whole house was about 78F, that little window air conditioner running 24 hours a day dropped our relative humidity to levels we'd never seen. It felt quite good actually. The point is that even though it was not a big enough unit to cool the house effectively, it was still an effective dehumidifier because it was running 24/7 and just steadily draining water out of the air.

[lthenderson]

I think the HVAC guy gave you pretty good advice. Kilz is not a mold killer. It is a stain blocker that will prevent the mold from growing because the mold no longer has access to air and moisture. Any stain blocking primer will do the same thing. Honestly as long as your humidity is below 50%, I wouldn't even worry about it because it won't do anything that below 50% humidity wouldn't do already, i.e. kill any mold spores left. Once you have everything painted, it can still grow mold on top of the painted surface (Kilz primer or not) if the humidity gets above 50% in the future and you have more condensation on your vent grates. After cleaning them well, I would just get a good quality primer and paint color and call it good.

[ChpBstrd]

Honestly, that might be mold growing on top of dust. Maybe give it a good soap-and-water treatment?

[BudgetSlasher]

The house I grew up in has similar, but not as severe, mold/mildew on and near the grates; in some cases it even extended back the duct slightly. After I moved out my parents added a central dehumidifier (though a properly sized and designed A/C would probably accomplish the same thing) and once the humidity was lower the mold problem stopped.

It would appear what happened was the humidity would build up in the house between cycles of the A/C and when the warm wet air in the house was hit by the entering cold A/C air there was just enough condensation to result in mold/mildew development.

There are duct work cleaning services, I used one when we moved into our current house and made a pretty big difference. All of our duct work is rigid metal ducting, I do not know if they can deal with flexible ductwork.

[NaN]

Honestly, that might be mold growing on top of dust. Maybe give it a good soap-and-water treatment?

This. When was the last time you cleaned your vent covers before this?

[Dee18]

I replaced all mine.  It was well worth it.  Whatever is in your ducts will be blowing through your new system immediately.

[jnw]

Thanks for all the replies.  We decided to just replace all the register vents with new ones.  We are painting the new register vents with Kilz spray primer.   

I notice the mold is really just on the vents after removing one from the register.  We carefully removed and put in a kitchen bag and closed it up immediately -- then disposed of it.   For inside the boot we used a 75%/25% vinegar/water solution (respectively); I put it on a rag then carefully placed it over the surface before wiping to avoid and spores coming up.  After we wiped it down thoroughly I throw away each rag.  We then let the house fan run for about 30 mins to dry it out.   Then I put foil tape over the silicone sealer (or whatever they used), as a way to seal it even better and I guess to keep any existing mold spores from coming out of the crevices.  I then masked it off with painters tape and paper.  Spray painted inside the boot with Kilz.    Then put the new vent (freshly painted with Kilz as well) on the register.

Let me know if I should do anythign different than what I shared above.  I have only done one register.   Planning on doing the next 6 over the next couple days.

Here is a photo of the cleaned, aluminum taped and kilz sprayed register.. let me know what you think.



Here it is with the new vent installed:

[jnw]

We are also getting a dehumidifier to make sure humidity is around 45% or so.  It's at 51% right now.

Also we'll make sure to vacuum / clean the vents every few months.  Maybe every couple years take the vent cover off and clean all the loovers inside, and the backside of the vent.

[jnw]

I think the HVAC guy gave you pretty good advice. Kilz is not a mold killer. It is a stain blocker that will prevent the mold from growing because the mold no longer has access to air and moisture. Any stain blocking primer will do the same thing. Honestly as long as your humidity is below 50%, I wouldn't even worry about it because it won't do anything that below 50% humidity wouldn't do already, i.e. kill any mold spores left. Once you have everything painted, it can still grow mold on top of the painted surface (Kilz primer or not) if the humidity gets above 50% in the future and you have more condensation on your vent grates. After cleaning them well, I would just get a good quality primer and paint color and call it good.

So it doesn't make sense to spray the new register vents with kilz?  I read it prevents it from growing.. I didn't know they meant from underneath only.. bleh

[NaN]

I think the HVAC guy gave you pretty good advice. Kilz is not a mold killer. It is a stain blocker that will prevent the mold from growing because the mold no longer has access to air and moisture. Any stain blocking primer will do the same thing. Honestly as long as your humidity is below 50%, I wouldn't even worry about it because it won't do anything that below 50% humidity wouldn't do already, i.e. kill any mold spores left. Once you have everything painted, it can still grow mold on top of the painted surface (Kilz primer or not) if the humidity gets above 50% in the future and you have more condensation on your vent grates. After cleaning them well, I would just get a good quality primer and paint color and call it good.

So it doesn't make sense to spray the new register vents with kilz?  I read it prevents it from growing.. I didn't know they meant from underneath only.. bleh

Yah, I think if dust accumulates and moisture builds over the new ducts then you can easily have mold. The mold may not grow on the surface of the duct as well, but it will still grow on dirt.

[jnw]

Yah, I think if dust accumulates and moisture builds over the new ducts then you can easily have mold. The mold may not grow on the surface of the duct as well, but it will still grow on dirt.

Thank you. I think our health has been suffering the past couple years due to mold on the vents perhaps.   The one in the photo above .. was pretty bad because it was in a room we never go into and the vent is above a bookshelf.. so easy to miss for cleaning. 

But now that we know how bad things can get, we'll make sure to vacuum the vents perhaps every other month; also once per year we'll take them all off and vacuum in the register and get every piece dust off the vent mechanism including the internal louvers.

Today, with the new AC install, humidity inside has ranged from 52 to 56% at 71F.  Outdoor temp currently 85F with 71% humidity; it's supposed to get up to 95F today -- will be a great test for our new AC system; I'd so love to see the AC actually turn off while it's 95F outside.

I suppose I should invest in a dehumidifer and perhaps set it for 44% or so. I imagine I wouldn't have to run the AC at 70-73F then since water will evaporate so well off the skin.   Maybe a comfortable temp would be 75F or so with the dehumidifier.   I am thinking I should probably get an oversized dehumidifier?  Even though I have 1000 square feet maybe I should get the 4500 sf so it never has problems keeping up and so I don't have to empty it as often?   2000 square feet dehumidifiers are around $150.. the 4500 square foot is around $249, so not much more.

[lthenderson]

Today, with the new AC install, humidity inside has ranged from 52 to 56% at 71F. 

You really do need to do something about your humidity. 56% inside is flirting with more mold being able to grow anywhere there is moisture condensing such as windows, vent covers as you have seen previously, bathrooms and kitchens, etc.

I don't have a humidity problem so I can't recommend any dehumidifiers. We actually run a whole hose humidifier to add moisture to our air all winter long. But the more humidity you have, the warmer it feels which is a good problem to have in the winter but not so much now in summertime. You will be surprised at how comfortable hot air can feel that has be dehumidified compared to the same temperature of air with more humidity. So running a dehumidifier in theory can offset your electrical bill for running your A/C by allowing you to keep it set a couple degrees warmer than you might have otherwise.