By Kerry L Thomas, Contributing writer

Are you properly maintaining your home's air duct system? Most people tend to forget about the duct work when it comes to maintaining their HVAC system.

Of course, not every home will have duct work -- this depends on the type of heating and cooling system that you have.

If you do have air ducts, then you need to be aware that they sometimes need maintenance too. Over time your air ducts can become littered with dust, dust mites, animal hair, rodent and insect feces and even mold. Most of these pollutants are known allergens and can contribute to poor indoor air quality.

Surprisingly, these pollutants can be in most any home's system regardless of the cleanliness of the home. The main reason here, of course, is the inability of the homeowner to access and clean the entire duct work system.Vacuuming out the registers can clean that immediate area, however, cleaning the rest of the system requires special equipment that is designed to loosen and remove the debris within the ducts.

Changing the air filters in your system frequently can help as well. You should be aware that most air filters are actually not efficient enough to capture all the debris that can be sucked in through your system's return air duct. Eventually your system will accumulate enough debris to cause a concern.

Here's some tips to help you make informed decisions when it comes to maintaining your HVAC system and duct work:

1. The first consideration is determining if you actually need the duct work cleaned.

A visual inspection of the inside of the ducts is the only feasible way to determine if you have problems.You can make an attempt at this yourself if you are physically able to access all areas of your system. The drawback to doing this yourself is that you will find it very difficult to inspect all the areas.

This is where you may want to consult a air duct cleaning professional.Most professional duct cleaning services will have video inspection equipment that can be inserted into the air ducts to allow for a closer inspection. The homeowner can actually observe for themselves and visually see any excessive debris in the system.

2. Next you need to determine the amount and type of debris in the ducts.

We know that all ducts that have been used will have debris within them.

Most of the debris will consist of dust, lint, pollen, animal dander, carpet fuzz, insulation, and even rodent and insect feces. It is not uncommon to find signs of rodents and insects in the system. Mice will tend to gather nesting materials and can restrict the air flow with these materials.

It is possible that mold can be growing inside your system. Certain types of mold can lead to serious indoor air quality issues as these molds tend to produce allergens. If mold is found, the ducts need to be thoroughly evaluated for moisture problems. Identifying the particular type of mold in your system usually requires laboratory analysis. Dealing with mold is not something the homeowner should tackle themselves.

3. To clean or not to clean?

All systems that have been in use will have debris -- it is not recommended to clean ducts that have relatively small amounts of dust, etc. You should clean your air ducts if you observe debris that has accumulated to the point of clumping up and collecting on dampers, protruding screws, and joints. This type of buildup can restrict the free flow of air through the system and affect the system's efficiency as well as lead to premature failure of the system in extreme cases.

It is recommended that you clean the duct work system anytime you find evidence of rodent or insect activity. Cleaning ducts will remove the rodent/insect feces but it will not eliminate the problem with the rodents/insects themselves. Before you clean you will want to get rid of the pests first -- a pest control professional can help with this process.

If you identify a problem with mold, it is definitely recommended that you clean the ducts. It is very important to look for moisture problems that contribute to the growth of mold. Use the same approach here as outlined above for rodents/insects. Get rid of the factors that contribute to the growth of mold and then clean your system.

Remember, this is not a do-it-yourself type of project. A professional air duct cleaning service will have access to mold remediation equipment and special training in dealing with mold.

If you suffer from allergies, then you may be looking at cleaning your ducts to improve the indoor air quality. This is a controversial subject as there is a lack of scientific studies to offer guidelines. There is really no concrete data to suggest that cleaning your ducts will help allergy sufferers.

Do not have your ducts cleaned based solely on claims that doing so will help with your allergies. Cleaning your system may or may not help your allergies. At this time no one can predict if this will help you. Be weary of any claims to the contrary. Allergy sufferers may want to have their ducts inspected to see if problems can be identified. You may want to discuss the inspection results with your physician/allergist to see if this is something you want to try-just remember there are no guarantees this will help.

It is not recommended to clean your ducts yearly as part of the normal pre-season servicing. Debris buildup takes time and if your duct work is relatively new or has been cleaned recently then you will only need to clean them according to the guidelines above. Remember it is normal to have small amounts of dust in the system.

A reputable air duct cleaning service can look at your individual circumstances and recommend an inspection schedule.