Mold on registers

[seilervision]

I have a problem with mold on three registers of a 16 register system. the indoor coil and ducting near the unit is clean as a whistle. The three affected registers are on three different floors, not near each other. One room has two registers but only one of these has any significant mold growth. the rooms include two bedrooms and a spare, little used, kitchen. They say this started after their electronic air cleaner was replaced with a mechanical filter (4" paper type filter). Do you see any correlation between the two? The blower runs continually. I did find some slight mold build up on the trough of the humidifier. I cleaned all areas noted with diluted clorox but would appreciate anyone's insight on this matter. Nothing wlse was noticed that I can include at this time.

[drk]

could be all kinds of things that can cause this

[dash]

The new filter has higher Pressure Drop (more restrictive),this likely reduced the air flow,which makes the air colder in cooling.The colder air caused the grilles to reach the dew point ,and they began to sweat.

I'd be concerned about the reduced air flow and damage to the equipment.Call around until you find someone you can test"External Static Pressure" and compare to the fan chart for cfms(air flow).If it's a gas furnace have the temperature rise checked to insure proper air flow.

As for the grilles,remove the grille and be sure they are sealed off from the unconditioned space behind them,then look in that space to be sure there is insulation around the "box" the grille is in.

[Carnak]

They sound like they are floor registers so I would guess they are near an external wall, maybe under windows.

Maybe next time you are there take a good look at the windows to see if they are leaky. Take a look outside and see if there are hose bibs, receptacles, wall mounted ligths etc, on the rimjoist of the joist space the registers are in. Maybe there is some humid air infiltrating in near these few registers.

Are the registers on the same wall, perhaps the one the prevailing wind blows against in the summer?

[seilervision]

Two of the three registers are in the ceiling on inside walls. The other is on an inside wall on the floor. The mold is on the register edge and the ceiling adjoining the register. The boot and inside fitting (90 degre el) is clean.

[Senior Tech]

Make sure the boots are insulated above the ceiling in the attic, if not they will reach dew point and you will see moisture on them, one of the ingredients needed for mold.

[seilervision]

The ceiling registers have a room above so boot temperature shouldn't be an issue. the house has been around for years and this problem has just arisen.

[Carnak]

May still be humid air in the joist spaces.

It can come down the walls from attic through holes for wiring through the top plate or through the walls through unsealed openings in rimjoist.

Is there some kind of exhaust from the unused kitchen, a rangehood maybe? Does the exhaust have a back draft damper, is the penetration sealed? Good be a place where humid air is coming in.

The new filter could be a little more restrictive and the system runs a little colder like some have suggested, but you would think that the majority of the registers would be sweating not just three.


[Edited by Carnak on 11-07-2005 at 08:25 AM]

[Gunslinger]

I noticed that you said that the blower runs continuously. This is not a good idea. Try leaving the blower on the "auto" mode.

[thecomp]

Doug, I am new to IAQ.

Why is running the blower a bad idea? I have seen this at times on A/C equipment which doesn't shut down on EMS.

[Gunslinger]

In the cooling mode, the fan can pick up moisture from the drain pan and distribute it onto the coil and ductwork which can lead to mold formation problems. when I went thru a mold remediation class, they advised against using the fan on the continuous mode when cooling is desired.

[ocean a/c]

Originally posted by doug kahane
In the cooling mode, the fan can pick up moisture from the drain pan and distribute it onto the coil and ductwork which can lead to mold formation problems. when I went thru a mold remediation class, they advised against using the fan on the continuous mode when cooling is desired.

That's Right^ You probably don't have enough return air
or too much filter.

[teddy bear]

Filter restriction slows air flow, lowering coil temperature, removing more moisture, and increasing the a/c runtime. "On"mode-continuous fan evaporates water off the coiling coil/pan during the a/c off cycle. This makes the air space of the home more moist during most of the low/medium a/c load time. If you can maintain <50%RH in the home during this time, the continuous fan operation keeps the evap/ducts/grills as dry as possible. A good dryout everyday dramatically reduces mold growth in these wet areas.
Unfortunately most homes are 60-70%RH during the cool/warm wet time of the year. This wet air very slowly will dry things out, but the grill is the last piece in the air stream to dry. Overcooling causes more condensation on the duct exterior and on grills. Monitor the air in the home. Maintain <50%Rh, avoid overcooling, provide dry time of a couple hours everyday to assure all of the air handling equipment including the grills. Mold has the ability to grow for a couple days, go dormant for a week, a month, a year, and then reactivate growth in less than a day near wetness. Therefore mold growth is cummulative over a period of years.
In most climates, maintaining <50%RH requires supplemental dehumidification during the low/no a/c load periods.

[syntropicsystems]

The latest research shows that continuous air flow helps to maintain a good temperature and air quality mix. Visit http://www.hoffmancontrols.com for some results that independent testing showed in using their particular brand. The additional benefit is that you have less peak load start-up requirements on fan motors. You also obtain full heating and cooling energy exchange, resulting in better energy efficiency. Something you might want to check into is the use of RCI Cell systems per recent Kansas State University research results. ASHRAE recently recognized two photocatalytic oxidation (PCO) systems for innovative products (of course, they were submitted by exhibitors for consideration and don't reflect everything out in the field.) Historic treatment is try to "kill" the spores, then reduce humidity and food sources. I'm looking into a product that is EPA approved for hard and porous surfaces which is claimed to highly effective in eliminating mold spores and other pathogens, but don't have enough information to confirm or deny its effectiveness.

[ocean a/c]

Thanks for the link. What make of UV lamp do you use,recommend? >Rob

[Edited by ocean a/c on 12-22-2005 at 10:38 PM]

[syntropicsystems]

I normally don't use standard UV applications - preferring the results from radiant catalytic ionization for continuous pathogen and VOC reduction throughout the duct and facility. Modifying the indoor air using the photocatalytic oxidation technology a la NASA use for closed environments is much more effective and safe. That particular system uses a 25000 hour effective life proprietary UV bulb with a PPC external coating to prevent release of mercury should any internal breakage occur. A side benefit is that the PPC coating is virtually unbreakable even with a hammer. The system design is to replace the UV/catalyst probe every 3 years, sending them back to the manufacturer for complete recycling. Effective life of 25000 hours is achieved by internal coating of the bulb to prevent deposition build-up resulting from the mercury burn. Standard UV bulbs have deposition build-up inside that reduces output, resulting in a 4000-6000 life. Even if the bulb is still burning, useful energy output is nil after 6000 hours.