How can I determine what is causing a bad odor from a residential HVAC unit?

Question

Apparently the odor has been there for at least three years in various degrees, but now getting very bad. The smell seems strongest in the air flow above the filter and does not appear to originate in the duct work. It is somewhat musty, but much stronger and not really a burning smell.

Answer 1

It sounds like a build-up of fungi(mold) on your evaporator coil. That is the radiator-like device that cools the air and extracts moisture. Because it is generally wet, and because bits of debris find their way into the fins of the coil, the fungi will grow if nothing is done to prevent it.

Beyond the evaporator coil, it is not unusual for the fungal growth to appear on the blower wheel, the supply plenum (ductwork just above the air handler) and the inside of the air handler cabinet.

Depending on the age of your air handler, you will have to decide between a clean-up or replacement. Generally, an air handler older than 6-7 years would not be a good candidate for a clean-up. You need to get an honest assesment from a qualified a/c technician that understands indoor air quality.

After you address the contamination of your air handler, be sure to install a germicidal lamp in the cabinet to control future fungal growth. Air filtration is also a key. Make sure there is plenty of air flow, the filter is changed on a regular basis, and at a minimum use pleated media.

For information on the health effects of air-born fungi, I suggest reading "The Fungus Link" by Dr. Douglas Kaufmann.

Answer 2

Connected to your furnace, usually on top, is a evaporator coil that is used with your a/c. This coil has a water pan that condensation water drains into as it draws humidity out of the house. If the pan does not have proper drainage stagnant water with mold and mildew will sit in it and create an odor. Also if the a/c was ran without a filter in the past, dirt, lint and such stick to the evaporator coil and when wet will give off an odor. Your evaporator and drain pan need to be cleaned and the drainage checked for proper drainage, good vent and no clogged lines. Check to see if your ductwork has a black insulation on the inside, if it does you may never get the smell out as this will absorb odor.

Answer 3

Simple answer to a simple problem.

If it smells it has the potential to make you sick. You need to have it professionally cleaned. After which you need to take actions to help stop further problems.

If you have your system cleaned by someone who knows what they are doing, you are probably going to spend between $750 - $2000. It is well worth the money spent.

Whoever cleans your system will be able to advise you on what steps you need to take to ensure you keep a healthy system.

Change that filter at least every 30 days. And please , please, have your system regularly serviced. Shop around for a service contract that is done twice a year.

If your system is 7 or more years old, you should probably consider having the system replaced, including the duct work, with the latest and greatest products on the market.

Remember, this is the most important comfort product you will ever be in contact with. Shouldn't you take better care of it? If it isn't making you feel good, what is the use to have it ?