Mold on HVAC vents?

[Chef]

What would be causing mold to grow on my HVAC Vents? WE change filter religiously with the expensive ones. Keep the house about 74 in summer and 67 in winter. House is about 8 years old. No other mold that we have found.

[warrington]

I had the same problem

You have to seal around the vent it self

The hot air from the attic is getting pull out.

I sealed around each vent and out more insulation around the duct and a wiling junction and it stopped the mold

[Todd-ty729]

This is going to sound strange but your ac system is not running enough.

Not removing enough humidity from the house.

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[txoutdoorsman24]

This is going to sound strange but your ac system is not running enough.

Not removing enough humidity from the house.

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Yes, that could be the issue. More than likely there is an underlying issue. Air flow is the issue. Could have a hole in a air handler, duct or plenum. Fan speed could be too slow. I.E. fan motor going bad, bad control board of you have variable speed fan. Have someone come out a take a look or you can yourself for the obvious. Inspect the ductwork and feel for air leaks.

[Todd-ty729]

I am going to refer to the expert above!

We foamed our house and then the moldy registers started.

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[Uncle Saggy]

This is going to sound strange but your ac system is not running enough.

Not removing enough humidity from the house.

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Yup


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[Johnny Dangerr]

Invasion of the body snatchers. We are all going to die.....

Yea time for me to get a rag and clean our registers.......

[txoutdoorsman24]

I am going to refer to the expert above!

We foamed our house and then the moldy registers started.

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I've heard of that quite often. Gets too air tight lol

[muzzlebrake]

Sounds like the system is oversized. An oversized system will short cycle and not remove enough moisture since it doesn't run long enough at one time.
The system needs to run longer to pull out more latent heat. Your thermostat only sees sensible heat. The fix could get expensive. If you have mold on the registers there is more than likely mold inside the ductwork and maybe in the condensate drain pan at the evaporator coil.

[Mountaineer]

If you mean on the supply vent registers it could be what is stated above due to oversized tonnage/short cycling or possibly a because the register and supply plenum box is not sealed to drywall ceiling, this can allow warm/moist attic air to leak through and condense on metal supply register.

[enewman]

What would be causing mold to grow on my HVAC Vents? WE change filter religiously with the expensive ones. Keep the house about 74 in summer and 67 in winter. House is about 8 years old. No other mold that we have found.

Unless your system was designed for these expensive filters your doing more harm then good on your system.

[LFD2037]

Unless your system was designed for these expensive filters your doing more harm then good on your system.

I'd like to know why as I use the expensive ones from HD/Lowe's myself.

[JayB]

Another thought to process....with airflow past an object, it creates a small vacuum (think airplane flight) and will allow the accumulation of dust/dirt. Mold usually appears and grows on this type of surface. It may just mean you need to dust the supply registers a little more frequently.

[enewman]

I'd like to know why as I use the expensive ones from HD/Lowe's myself.

This is a touchy subject.

All units require a certain amount of air flo to operate correctly. I'm just going to use numbers. A 5 ton on average is 1800 cfm of air needed to flow through the coil. So when looking at this all units show how much static it can have to have this air flow. Most units around .7 is max. There are some that can go up to 1 but average is .7.

Lots of coils have a static drop of .25 to .35. So this is deducted from the .7. Let's split the differences and say .3. So we have .4 left for the duct system. So when designing a system you want 2/3 of that drop on the supply and a 1/3 on the return side. So we have .133 to play with on the return side.

Now we look at filters. They have a drop across them. So let's say your filter is in the unit and it's in a closet. This means you have one filter. So you need to find a filter with less then .133 drop and that includes grills.


When figureimg filters you should do them at 300 fpm. But if it's a single filter it's done at 500 fpm.

So let's look at the filters your buying. Merv 8 is a common filter. So let's look at this 5 ton unit average filter is 20x25. So according to the spec sheet I use this filter at 500 fpm is good for 1750 cfm. Little shy but close enough you won't know. But the static drop is .27 on a 2 inch filter. It's .42 on a 1 inch filter. So as you can see we have used up all our static drop just on the good filters.

So what happens. We don't move enough air across coil. So coil runs cold. This means the Freon will not turn to a gas before leaving coil. So liquid gets back to compressor. This causes oil to migrate from compressor. So it premature failure.

All from a filter. Lol. Crazy isn't it. I hope that makes since. Oh and that's brand new filter. Wait ti it starts to get dirty

Sorry long explanation I didn't know any other way to explain

[enewman]

Let me add. How do you know with out doing a ton of research if you have an air flow problem. And this is just a couple. Have you ever had a compressor replaced with less then 5 years in service. have you ever had the compressor replaced more then once in 10 years. If you have a high effeniency unit that has the ecm motor. Have you had to replace the control mod on the back of motor with in a few years. And have you replaced more then one while under warrenty at all. That motor and mod unless it gets hit by a voltage spike is a 15 year motor.