Mold at supply registers

Originally Posted By: mpettitt
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Did a home that had (what appeared to be a little mold, not dirt) on the outside surface of all of the ceiling mounted supply registers. Can anyone tell me some of the reasons that this happens. thanks


Originally Posted By: five.five
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were the registers the old metal type ?


Chances are, due to the condensation and dirt over the years, mold formed on the registers.


You will see it a lot in bathrroms with no window, and a dirty exhaust fan.


Originally Posted By: mpettitt
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No, just normal ceiling type (metal) with flexible insulated ducts on a 89 home. Every register thoughout the home had some on it with a little reaching onto the ceiling. I thought I’d read somewhere that it could be caused by leaks, leaks from what, I don’t know. I’m 99% sure its mold, not dirt.


Originally Posted By: mpettitt
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Still searching for an explanation for the mold, any thoughts.


Originally Posted By: rzimmerman1
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mpettitt wrote:
Still searching for an explanation for the mold, any thoughts.

Mike,
Mold needs food, water and temp to live. Food and temp are everywhere in a home. It is water being introduced that usualy results in Mold growth.

My guess is the AC unit is circulating miosture. Not enough to affect other areas of the home, just enough to feed the Mold arlund the vents.

When was the last time the AC was services? Could be low on its charge causing some freeze-up resulting in moisture. The drain line could be not properly working. The coils could be dirty. Just guseeing here.

I would also suspect there is mold build-up in the AC ducts that you could not see.

Recommend the AC unit be checked and services as necessary by a licensed contractor.

Recommend the buyer/owner consider having the ducts checked for Mold and possibly have a Mold/Air quality check done.


--
Rob Z.
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Originally Posted By: lewens
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I think, and this is only a guess, you will find the ducting isn’t insulated causing condensation which leaks into the ducting and drips down to the regester, etc.etc.



Just my usual 12.5 cents


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Originally Posted By: phinsperger
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mpettitt wrote:
I thought I'd read somewhere that it could be caused by leaks, leaks from what, I don't know.


I beleive that was in referance to a leak in the heat exchanger. Often I see a black soot around the registers from a leaking heat exchanger with an oil burning furnace.


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Originally Posted By: whandley
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I agree with Larry. If there’s any exposed, un-insulated metal ducting within the system and especially at the register boots the formation of condensation would be anticipated. Keep in mind, mold does NOT need water to form, exist and or grow. It only needs relative humidity of 50% or greater for growth to begin within 24 hours. icon_idea.gif


Originally Posted By: mpettitt
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Thanks everyone for replys. BTW the ducts were insulated and I could shine the light up into each duct for about 12 to 18 inches (no signs of mold that far). This was a heat pump split system and the temperature differential was high at 31 degrees (which I neglected to mention earlier), the evaporator coil was a little dirty but not bad, filter was clean, drain line draining, duct size okay. I wrote it up okay by recommending further evalation. Just trying to understand it better.


Originally Posted By: mboyett
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Mike,


You mentioned that the temperature differential was 31?. That seems excessively high and could indicate a system low on freon but you probably already wrote that up. Anyway, one issue that can cause the ‘mold’ problem is an oversized system. If the a/c unit is oversized it will not run long enough to pull the moisture out of the air and the result is mold, especially at the registers like you saw. Do a quick, down and dirty, sizing analysis of the system to get a feel if that might be the problem. Some of the more HVAC savvy folks here on the board might chime in but I think the standard is about 750 sf per ton of a/c here in the hot, humid south. Also, 12,000 btu/ton so if you have the a/c data you should be able to calculate the needed numbers.



Mike Boyett


Capital City Inspections


Austin, Tx


www.capcityinspections.com

Originally Posted By: mpettitt
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Hi Mike, The home had 2139 sq. ft. of conditioned space (living area) the condenser was a 4 ton. By your calculations of 750 per ton the unit would be oversized. However correct me if I’m wrong but I was always taught that it was 600 or in some cases 550 per ton. So I caluated 4 x 550 which gave me 2200 which is close. I should of, and usually do record all the information from the data plate but failed to this time. Now I’m thinking you’re right. Thanks for your reply, keep’em coming. Mike P.


Originally Posted By: mhaley
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I often find that the installers fail to adequately insulate (and seal) the supply boot all the way to the ceiling drywall. This exposed metal will also lead to increased condensation at the grills- here in NC you can see them dripping in the summer.


Originally Posted By: mpettitt
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Thanks, Mike Haley. Here we go again, everyones name is Mike, must be a good name. thanks again everyone for replys.