mold on registers

[southernmechanical]

I am a contractor in Texas and have never gotten into mold or mold removal as part of my business. I have come across a client who has had several specialist out to his house for mold around the air registers. Not one of them have been able to give him an answer or fix the problem. I told him I would research the problem and have been able to find nothing on what causes this. My first thought is that the humidity level is to high in the house. But it was about 50%, perfect. One contractor split one of his evap coils with a second stage. Now this is a large house with 7, 5 ton units. There is no mold in evaps or in ducts just unsitely mold on registers sparsely thru the house. Any one have any ideas on what causes this or what to do about it.
Thanks,
Bo

[James 3528]

Have they tried cleaning them?

[southernmechanical]

he says he cleaned all registers about 4 months ago.

[Steve Wiggins]

I was sent to clean electronic air cleaners once in a huge house where all the cells were installed backward. The power packs didn't come in contact with the power so no air filtering was done. Dust everywhere.

I would suspect the grilles are reaching dewpoint from poor air flow. Are the blowers on high?

Also gross oversizing can cause these symtoms. 35 tons is a lot even for Texas. Must be a huge house!

[airman1]

poor air flow ...oversized cooling coil..no expansion valve...low temp drop across the cooling coil...inctrease it to 25 degrees to 28 degrees and the mold will not come back unless there is duct leakage and envelope problems

[Frank_G]

1) Probably the registers have been painted with latex paint. Replace them and leave the factory finish or paint with oil based paint.
2) If the sheetrock around the registers are involved remove the registers, clean up the mold on the sheetrock, seal it with oil based paint, gasket the registers so that no air flow exits laterally between the register and the ceiling. (Before someone gripes, I know what the CIHs say, but if it's only at the register, why remove the sheetrock.)
3) The furnace should cycle "OFF" during the cooling cycle. No blowers should be run in the constant "ON" position.
4) If the contaminated registers are closest to the evaporator, while the ones more distant are clean, moisture from the evaporator is probably the cause. Measure the RH at the mouth of those registers. If it is above 55% you probably have too short a distance between the evap and the register. The moisture content of the air from the supply plenum has not had time to dissapate. Cleaning the evaporator coil may help, but I haven't found a satisfactory cure for this problem.
5) Check the temperature of the air leaving the evaporator. if it is less than 55 degrees you're probably OK, but if it is 52 or even 51 degrees that's probably better. A warm evaporator doesn't generate sufficient condensation to resist blow off and won't flow properly.
5a) A warm coil causes air flowing across the evap to be too high in moisture content and it will find a place to condense downstream.
6) Is the duct system designed correctly? Too much velocity across the coil will cause condensation to blow off the fins.
6a) Is the duct system tight of is it leaky? A tight system is more resistent to mold problems.
6b) What is the set temperature of the thermostat? Low temperatures are more prone to mold. I have a customer who is on oxygen and he runs four systems as low as he can get them. Colder temperature makes it easier to achieve Dew Point (especially in Houston) and easier to grow mold.
7) Check the temperature at the registers. If it is below dew point you may have to warm the registers or just accept the problem.

There is no such thing as a "Mold" problem, it is always a "Water" problem and it doesn't matter whether the water is liquid or high moisture content of the air.

Control the water and you control the mold.

Hope one or more of these hit. Good luck.

Frank

[Frank_G]

P.S. I think 50% RH is a little high. Get your Psyc chart and figure your Dew Point temps. Far better to have the RH around 40%.

Frank

[James 3528]

Hey Frank, your wrong unless you want static discharge on ever thing in the house.

[southernmechanical]

Thanks for all the tips guys, I appreciate it and will try them. I hope I can help one of yall with a problem someday.
Thanks,
Bo

[Frank_G]

Hi James,

Southernmechanical asked about stopping mold, nothing was said about static charge. If one wants to get rid of mold, one has to control the water. If I had a choice between static and mold I assure you I'd take static charge.

My home in the Dallas area is consistently maintained in the low 40% range during the summer without static, although two years ago after encapsulating my ducts with polyurethane foam and air sealing the structure, the RH did get low enough to cause static discharge sufficient to be unpleasant, but after I cleaned the evaporator that problem stopped.

I cool my 2450 SF ranch style home with 3 1/2 tons of air. The set temp on the t-stat in the day is 80 and it often feels too cold, because of the low humidity. In this time when mold is common, we have none in the A/C system (None anywher else either that I know of.)

Frank

[a\c don]

Living in Florida it's not uncommon to see indoor humidity levels at 65-70% with no mold problems. We usually find this type of problem when grille cans are not properly sealed to drywall ceiling penetrations allowing hot humid attic air to contact cool grille surface. We seal the ceiling penetrations with membrane and mastic to eliminate this problem. Remove several grilles and look for moisture stains around penetrations. Just a thought. :)

[sneezer]

I have this problem on ONE small register in the one added upstairs room. (It is woefully undersized for AC, but O.K. for heat. There is also a window unit in that room.) I recently bought this house and I puzzled over it for a while and decided that I need a bigger duct.

Frank_G's suggestion for checking for infiltration between the register and wall, I will take. As I was thinking through the responses it occurred to me that if anyone is going to replace latex-painted registers with new ones, you might consider plastic rather than metal. They will have less heat capacity and condense less water when the flow is off.

[teddy bear]

A comment on monitoring %RH in the home. The actual %RH is determined by many factors. Measuring %RH one time is risky unless its during is the worst condition the home is subjected to. The worst condition is with 70-75^F outside temperature, raining for 3-4 days, 10-20 mph wind making the home breathe, and a full load of people. The a/c only operates enough to make the grills cold and maintain the setpoint, but not enough to remove the 10 gals. of water per day required to control the %RH in the home (<50%RH). If the home is <50%RH during the above condition, you will not grow mold on the grills. If if live a region that the above condition is routine through the summer, a/c will not keep the %RH below 50% during low cooling loads without the help of reheat or a dehumidifier. Use Hobo data loggers to monitor a home during a wet time before you decide if the home is dry. +60%-70%RH is typical during extended wet low cooling load conditions. Relative humidity meters are available from Wal-mart for $15.

[cem-bsee]

be CAREFUL in using plastic registers -- I replace mine which were 1 yr old, because the free area was ~40%, unlike the steel registers having 66%.

[ek]

It sounds like you are pulling in warm moist air from the attic. I would smoke puff the return system. Cover 80% of the return grille to compound the air leaks. This will make it easier to find the problem.

Or you have some major supply leaks and the house is going BIG TIME negative.

[qac1]

Just my 3 cents, but how about a plugged condensate drain, or dirty coil holding the moisture?

[fastfred]

Originally posted by Frank_G
Hi James,

Southernmechanical asked about stopping mold, nothing was said about static charge. If one wants to get rid of mold, one has to control the water. If I had a choice between static and mold I assure you I'd take static charge.

My home in the Dallas area is consistently maintained in the low 40% range during the summer without static, although two years ago after encapsulating my ducts with polyurethane foam and air sealing the structure, the RH did get low enough to cause static discharge sufficient to be unpleasant, but after I cleaned the evaporator that problem stopped.

I cool my 2450 SF ranch style home with 3 1/2 tons of air. The set temp on the t-stat in the day is 80 and it often feels too cold, because of the low humidity. In this time when mold is common, we have none in the A/C system (None anywher else either that I know of.)

Frank

what kind a/c equiment do you operate to maintain 40% RH? The SHR? Variable speed blower? SEER?Thanks for any info.

[bradjmx4]

No ERV's? ERV's and UV seem to be the great mold solution. Controled humidity and air filter. It needs to be removed and stopped from spreading. Constant fan with UV and erv will solve 90% of mold problems and static and alergies and dust and pressure If installed correctly by sombody who understands mold and pressure.

[Frank_G]

University of Central Fla., at their Florida Solar Energy Center, did extensive testing on using the fan in a constant "ON" position, in a hot and humid climate, during the cooling season. It is a mistake!

I wish it were my original saying but I'm stealing it from the people who manufacture the Sahara Aire Dehumidifier. Engineers who designed the variable speed fans for constant "ON" and during the cooling season "flunked psycometrics."

Frank

[tab-tech]

....... constant "fan on" is preferred to keep CO2 levels and the latient heat associated with it in check during mechanical cooling loads. Minimum outside air concerns are important especially in the flu season.
Otherwise, for residential applications "fan on demand" is works good.

[midhvac]

Originally posted by Frank_G
University of Central Fla., at their Florida Solar Energy Center, did extensive testing on using the fan in a constant "ON" position, in a hot and humid climate, during the cooling season. It is a mistake!

I wish it were my original saying but I'm stealing it from the people who manufacture the Sahara Aire Dehumidifier. Engineers who designed the variable speed fans for constant "ON" and during the cooling season "flunked psycometrics."

Frank

That's an eye opener. I'm going to have to check that out. What about setback stats in humid climates? Has anyone seen any studies on those?

[california]

Originally posted by James 3528
Have they tried cleaning them?
http://www.click-smilies.de/sammlung0903/spezial/Sarge/MetalHeadGrin.gif

[SNOOKER]

First thing is to make sure your satic pressure in your ducts are right both supply and especially return. Ofcorse this is assumeing that the systems are the right size for the load.7 5 ton units ? Thats a lot of conditioning.Assumeing all these conditions are right the next thing is to check the seal auond your registers.That is if it has spread to the drywall, If it's only on the grill then you have a capacity problem either with units or ducts.if you have mold om grill you are reaching dewpoint at some point in the cycle. mold need moister and food to grow the food wuold be the dust in the space and the moister is the hummidity at the grill not in the space.
Take a humidity reading at the resister you will proboly find it to be high.

[joeslemus]

Get 1/2 in armaflex sheet insulation,line all register boxes inside!! Same problem in Florida!!

[joeslemus]

Line all register boxes with 1/2 in armaflex insulation!! Also check for ROOF leaks!!!

[Bob Bielser]

Lots of suggestions in this thread. It might be nice to find out what the actual problem was and what was done to correct it???? BB

[energy_rater_La]

New to this forum, but I read this post and think
the problem is this. I see this all the time in this
hot humid climate, where heating systems and
ducts are located in attic.
When a/c boxes are installed, one side is attached to
joist. When register is attached from interior of
home the side of the register that is attached to the
joist snugs tightly, whereas the other side which is
not attached to joist or blocking will often not snug
tightly. I often see one side of the a/c box lifted
off the attic flooring anywhere from 1/4" to 1" by the
screws that attach the register.
What happens is that hot and cold (or attic and interior)
temperatures meet on these metal surfaces and condensation
begins. In some cases it is mold.
This is called the Ventura effect, just learned that,
nice to know it has a name!
By sealing a/c boxes to attic flooring by caulking
it will help to reduce the air infiltration and eliminate
the problem.
An easier (read cooler) way to achieve the same air sealing
quality is to remove a/c register from interior of home
and use a hardcast mastic tape to seal boxes to sheetrock.
Care has to be taken to keep tape within area covered
by register when reinstalled.
Great forum, I am reading and learning and laughing!

[airman1]

so how do you address sweating in the attic of ductwork?

[energy_rater_La]

No blanket answer for this one, it depends
on what is going on in attic and ducts.

I mostly see this (sweating ducts) on hardpipe
ducts, and usually it is in areas where the
insulation is not continous on ductwork or is
loosley installed. Wherever hot and cold air
can meet is where condensation will occur.
Of course we all know this from seeing it over
and over again. On flex duct the condensation is
often at the plenum where insulation is not well
attached to the take off collars at the plenum.

I realize that this is very general information,
more specific information would be based on more
details of areas of condensation.

I have also seen condensation on mechanicals located
in attics. (hot/humid climates are my experience)
Power vents are often installed to cool off attics
and will draw conditioned air into attic from openings
between attic envelope and building envelope. This will
add to condensation in attics also.

I am not by any means as experienced as many of you
on this forum, as I have only been doing this type of
work for the past 6 years. My first experience with the
diagnostic testing was as a building inspector for HUD
on low income weatherization. While I did eventually get
out of that line of work in to the current work I do, I
realized early on that there were more areas of concern
that were not being addressed and contributing to unhealthy
homes.
What I am hoping is that by opening lines of communication
that we can exchange information or at least bring up
questions that will help us to find workable solutions to
the problems that occur on standard installs. By exchanging
information we can improve our services and learn a bit
more as we go along.

[pjs_dallas]

Hi all, particularly fellow Dallasites Frank_G and southernmechanical. I stumbled across this forum while researching the mold smell emanating from my registers in my 2900SF ranch.

As a "civilian", I'd like to enlist some help from y'all. This moldy smell has been coming from the registers for about 4 months. I'd like someone to help me fix it.

I had one contractor come by and tell me he suspected that there was "water pooling in the plenum", but since I'm pretty clueless about HVAC, I thought that sounded like a medical condition...

He also didn't provide me with any information or ideas on how to combat it.

So, Frank_G or southermechnical, would you be willing to come by (I'm in Richardson) and figure out where the smell is coming from?

My email is pjs.spam1@attbi.com.

Thanks,

Paul

[belcon12]

To jsp 1205
It has now been a month since the Pureatech installation was complete. I have been on the lookout for humidity, but so far we have only run the fans and there has been nothing. I called Steven Bush and told him about all the negative stuff that I have been reading about and asked if I should buy a dehumidifier and put in the attic. He said no. He also said that all those people who have humidity problems had the problem before the system was installed, but the fan is now making them more aware of it. I say that the big test will be on a hot and rainy day. I asked him about the temperature on the thermostat, and he said that it should be around 76. We normally keep it between 78-80 in order to cut down on the bill. I plan to stay on top of this. By the way, our installer was Justin, and he is suppose to be one of the best. I hope that the system is everything that I anticipate. I live in Plano. Let's keep each other informed.

[stanthman]

I have run into this a few times,may be mold then again may be soot from candles. Sounds crazy but, there have been a few instances where stopping candle soot has eliminated the problem.

[drumcat]

In NC when the fan is left in constant "on" position with thermostat, mold can develop around vents very easily. When system cycles on and off the fan picks up residual moisture left in the coil drain pan. When we tell customers to leave fan in "auto" position this helps considerably.
This is of course a "non-technical" position since I am only a salesman. :)

[nvr2old]

Southernmechanical, are the register boots the type lined with ductliner or the plain 601 style unlined metal boot?

[jrbenny]

Something tells me that southern might not get your message...

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Last Activity: 04-04-2004 09:05 PM