New problem....smelly vents

[CathyAnn]

I posted earlier about humidity issues.

Well, now we have been noticing smelly vents the past month or so.

Tech came out yesterday, checked the system completely and could find no problem(s). Changed the t-stat to "humid" and no change.

From what I have read, we now have dirty sock syndrome??

Had the manager come out and check this morning. Recommending we change the coil and/or the whole AC system, as it is 15 years old. If we just change the coil, we are gambling on the outside unit to last......

This is what we currently have:

It is a York Affinity PVC9CONUP11 92.02 two-stage (left old condenser coil)

White Rogers IF85-275 programmable thermostat.

The AC is a 15 year old Concept (still looking for info)-don't think I have the manual anymore.....

Two story- 2900 square foot house. Fan set on "high" for cooling cycle.

HELP!!!!!!!!!!!!!!!!

[beenthere]

Fan on high, may not be the right setting for the A/C.

May be better off with new A/C, instead of just coil.
Would be more expensive changing the coil now. And then again in another 5 or 6 years down the road when the condenser needs changed.

[CathyAnn]

Yes, we are contemplating which avenue to take with the coil.....

I just want to make sure that the humidity and odor are controlled spending this kinda $$.

[CathyAnn]

bump

[beenthere]

Don't bump, its a good way to get your thread closed.

[CathyAnn]

:oops:

Apologies.......

[ControlBIZ]

CathyAnn, I am not sure I fully understand your problem. You say your vents smell. Do they smell like mold and mildew or some other odor. I see in your thread your system is about 15 years old. Is the duct work run in a crawl space? I have tackled several smelly units over the years and I am interested in your installation. Could you please provide some more detail as to the type of odor, how the ductwork is run, the size of your unit and geographic location? I am assuming you have heat using the same ductwork. What type of heat is it, gas, heat pump, electric, etc. Do your vents smell in the winter as well?

More information will be helpful in diagnosing and correcting the problem.

[CathyAnn]

A musty smell, not sure how else to describe it? I did not detect it until we switched over to AC and it was weeks before it began?

Gas furnace is located in a basement. The AC is 4 ton, according to my tech guy.

[ControlBIZ]

An A/C unit is designed to remove moisture from the air and reduce humidity levels. Moisture will condense on the coil and then flow to the condensate pan. If everything is working properly the moisture will drain out of the pan. If the pan is not level or the drain is not working right, moisture (water) will collect in the pan and biological growth will occur.....which will smell.

I would suggest looking inside your air handling (fan) unit and see what the coil and condensate pan look like. An old dusty coil has all of the biological food source it needs to start growing mold if it get wet.......and you know the coil is designed to remove moisture from the air. If the coil is clean but the pan is holding water, check your condensate drain to make sure it is draining.

Good luck investigating your unit.

[CathyAnn]

The drain pan and coil appear clean.....The coil is damp even after cycling...is this normal?

Also, why would it take years for the odor to show up?? Could it just be the musty smell from the basement? Though, it has also been that way for years? We do run dehimidifier....

[ControlBIZ]

If your basement smells musty and it is the same odor you smell coming from you vents, then you have multiple design problems with your duct work and possibly even the construction of your basement. This is not an uncommon problem, but one that is difficult to fix after the fact. Below are some of the issues that will impact the moisture level (odor) in a home.
1) Most basements were never built properly. Concrete is pourous and moisture will permeate through the concrete into the basement. This causes high humidity in your basement. A dehumidifier will help, but will not make the problem go away completely. If you have any outside vents that are open in your crawlspace/basement this will only compound the problem. I have seen no shortage of return ductwork installed in homes that is nothing more than a piece of sheet metal nailed across the floor joists and the floor joist space is being used as the duct work. The interior of your return ductwork is now exposed wood and subflooring. This is all cellulose based.....a good food source for mold. Anytime you have temperatures over 50 degrees F and 50% relative humidity you have the perfect growing environment for mold and mildew. To make matters worse, the other trades have most likely drilled holes in the sides of the these same floor joists which will allow the moisture and odors from the basement into the Return air duct. Remember the Return Air Duct is under negative pressure so any hole in the return air duct is going to pull air into the ductwork. The other question to ask is if the A/C unit is properly sized. Bigger is not better. If the unit is oversized it will cool your home but will not have enough run time to remove the moisture from your home.

As you can see this can be a very complex problem. I'm not trying to confuse the issues, but there may be no one issue causing your problems. It might be a combination of many with some of them not easily fixable.

As for your coil being damp, this is normal. It means it is removing moisture from the air. Obviously it is not removing enough moisture from the necessary areas as you are smelling a musty odor. Do you have any supply vents in your basement that you can open up?

You said you recently had your condenser (compressor) changed out. How did the service company size this unit? Did they match the unit to what was previously installed? Did they run any Heat Load calculations to determine what was necessary, etc?

I know more things to consider, but they are all playing a part in your problem. Let me know what you find.

[CathyAnn]

Thanks, CB.

Haven't installed new AC and coil yet cause I'm not sure that's the problem?

No vents to the outside in basement, closed windows.

Calculations being done for me by tech.

I just don't know which way to turn!! Frustrated!

[ControlBIZ]

CathyAnn:

I apologize for my misunderstanding. I thought you already installed the new unit.

Remember that musty, mildew, moldy smell can only exist with moisture. If this is a problem that just started, then something has most likely changed or accumulated to the point where you now notice. Water by istelf has no odor. Water and moisture (can be in vapor form, i.e. humidity) in excess of 50% RH will allow these spores to grow. They are everywhere but need a food source. That food source can be dust, anything cellulose based (wood, paper, etc.) This is why I mentioned panning floor joists and using stud cavities in drywall walls as return air duct and sometimes supply air duct (which is regularly done) is a very bad idea. There could be exposed insulation inside your coil box which has collected dust and now has moisture accumulated and mold growth. The possibilities are endless.

I would start by cleaning the coil. If the unit is 15 years old, it might have collected enough dust with moisture to begin to smell. If you can access the coil, this is something you can do yourself. Anything that kills mold and mildew will work as a solution. Make sure whatever you use you are not senisitive to as it will be distributed through the ductwork when the unit runs again. If you use any type of a chlorine solution, be sure to thoroughly rinse the coil with water when you are done and flush everything out of the pan through the condensate drain. Also make sure you know where the condensate ultimately drains to. I have seen condensate drains go to basement sump pits. A chlorine solution dumped into a sump pit may not be what your sump pump wants to see. Years ago, I had a mini split A/C in a small office that had to have the coil cleaned about twice a year because it just started to smell. If you don't want to clean the coil or cannot access, you can try turning the furnace on and drying out everything in your duct work. If this makes the smell go away, you know it was moisture somewhere in the duct work. If this fixes the problem, I would still consider cleaning your coil.

Good Luck

If this does not correct the problem, then you have a moisture problem sufficient enough to promote mildew and mold growth somewhere else. Check any insulation that might be exposed inside the duct work.

[CathyAnn]

Not sure what "panning floor joists" refers to?

I can only access the front side of the coil due to way it is positioned in the duct.

[rubberduck]

Where are you getting your return air from?

[CathyAnn]

Had another tech out...the stench is definitely in the coil......

No outdoor air being pulled in, just using air from ductwork.

[ControlBIZ]

CathyAnn, glad you found the smell. A good coil cleaning should get rid of the problem.

Make sure you are using a good quality air filter as moisture on the coil is normal. It has to have a food source to grow mold, mildew, etc. Dust, pet dander, etc is a good food source. It is important the coil stay clean.

Good Luck

[CathyAnn]

Thanks, CB.

We are probably going to replace the AC system along with the coil. It's almost 15 years old, but choking on $$ a bit as it is still working.

My original HVAC guy will probably be upset as we are plan to switch as we have been with him for many years. The new tech was much more knowledeable about indoor air quality and explained the situation. The return air handler above the evap coil was placed to high and configurerd incorrectly. The sheet metal should have been run straight up rather than flared out as it was in the old system (they didn't change it when they installed the furnace) This caused poor air flow over the coil, as well as throughout the house.

My only concern is his MJ calc shows 4 ton rather that 3.5 ton -3250 sp foot, 2 story, tight home.


May I ask where you are located? So that I might refer friends to you, if needed?

[ControlBIZ]

Hi CathyAnn,
If you want to check your Load Calc's yourself, I think you can still purchase a single use license of HVAC Calc. I believe it used to be less than $50 for a single job license. It was for the purpose of allowing you to do your own load calcs. It is fairly easy to use and might give you the comfort level you are looking for about unit sizing. Square footage is not a good indicator of unit sizing.

A friend of mine has a home that I helped him design that is 5,000 square feet with less than a 3 ton A/C load because of the quality and type of construction. Ordinarily this would have been a 5 ton+ load.

It's good to know the tech actually ran Load Calc's because many just automatically install the exact same size as originally installed. Numerous units are never sized properly upon initial installation. I do not know where you are located, but if you have high humidity, it is better to err on the side of a little too small, then to go too big. The more run time on the unit, the more humidity you will remove.

While improper ductwork installation does not surprise me as most new construction residential mechanical contractors are the lowest bid and cut every corner in the book to get the job done. Without seeing your installation it is difficult to know why the coil was smelling. Again, moisture alone will not cause odor. There has to be a food source for bacteria, mold, mildew, etc to grow and cause smell. I suspect the coil is dirty with dust, lint, dander, etc. If you ran 14 years with no smell and now it smells this year, something has changed. Maybe you just accumulated enough dust and debris on the coil?

While 15 years is definitely an older unit, without knowing the number of months of A/C load, this does not mean the unit is ready to be changed out. If the unit is cooling, i.e. the temperatures and pressures on the unit are good and the utility bills are not killing you, I would not necessarily change it out because of a smelly coil.

When I mentioned "panning floor joists", this is very common in new construction. Instead of building metal ductwork, they will nail or screw a piece of sheet metal to the bottom side of the floor joists in your basement and use this area as the return air duct. They will also use the open cavity between the studs in your walls as the plenum with the studs and drywall making up the "make shift ductwork. Again, new construction residential mechanical, especially a spec house, is all about lowest bid. These are widely accepted practices in parts of the country. Many times it's these installation practices that lead to the ongoing dust in your system and ultimately the food source necessary to grow "muck" on your coil.

Hopefully with some creativity you will find a way to access the coil and clean it. Even a spray bottle with a bleach solution can work. You can most likely do this yourself if you are mechanically inclined.

As for where I am located, I spend most of my time in the Midwest but maintain an office in the West. I am not a Mechanical Contractor. I am a Controls Engineer in the commercial and industrial world. We control the mechanical systems so we have to fully understand all aspects of mechanical system operation. Your post caught me eye as I am passionate about indoor air quality. I only "help" out in the residential world whenever I can be of assistance. Most residential HVAC installations I encounter are just messed up from the start. I personally have had to deal with several of my own. I once bought a house 30 years old as a remodel project. How bad could a 30 year old house be? There was no filter bank ever installed. We cut a hole in the ductwork to see what the inside looked like. We gutted the entire system. We ripped out the entire mechanical system, ductwork and all. The microbiological growth inside the duct system was unbelievable. We found empty bottles of antibiotics, from the previous owners all over the house during the remodel.

Anyway, keep me posted and let me know if I can be of any assistance.

[Cory Fowler]

dirty sock syndrome is a bacteria that is growing on the evaporator somestimes in the pan. Clean the pan and drain before removing and cleaning the evaporator. Also check for dead animals (rats.etc.)