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Air ducts


July 10, 2009
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Are the duct sizing requirements the same for both heating and cooling?

Sometimes, but not often. Most of the time, the airflow requirements for cooling are greater than they are for heating.If cooling needs more air, it stands to reason that the ductwork that carries the air must be larger.If the designer wanted your duct system to handle just heating, chances are that it won't be large enough to meet the airflow requirements for cooling. If he designed the system for heating, but also thought about adding air conditioning to the system at some point, your duct work maybe adequate to meet your cooling needs.

How can I tell if the ductwork on my existing warm/hot air heating system is large enough to handle the cooling for my home?

The only way to know is to perform a heat-gain/loss calculation on the structure.

Will I have to change my duct system if I add air conditioning (cooling) to my warm/hot air heating system?

It depends. If your heating system was installed with no thought given to the future possibility of adding cooling, you will most likely have to alter the air-distribution system. These alterations will probably involve installing larger ducts.
If, when the heating system was designed, the designer sized the ducts for cooling,it is likely that the air-distribution system will not need much changing.

Most of the time, the airflow requirements for cooling are greater than the requirements for heating.The only way to know for sure is to have a heat gain/loss calculation done in the structure. There are situations where the airflow requirements for heating are greater than those for cooling. An example of this would bea basement area that is located below grade. The cooling requirements would be much less than the airflow requirements to heat the space.

Do I need to have my air ducts cleaned regularly?

Contraryto what others may say, the answer is no. You need to have your ductsystem cleaned only if there is excessive dirt accumulation. Dirt canget into your duct system if you operate the system without airfilters, or if there are leaks in the return side of the duct system.
Byusing a high-quality filter, you will prevent most dust and dirt fromentering the duct system. In addition, the filter must be properlysized so that there are no air leaks around the filter.
Ifthere are leaks in the return duct, unfiltered air from the structurecan enter the system. This dust and dirt can accumulate within the ductsystem.
If it turns out your ductwork doesneed cleaning,find out where the dirt is coming from and fix thatsituation. That will keep you from having to have your ducts cleanedregularly.

I have strange smells coming from the air ducts. What could be the problem?

Often,strange smells from the air ducts originate in the basement. If theductwork is not properly sealed, the blower will pull air into theappliance from the surrounding space. If there is a litter box near thefurnace, for instance, the odor from the box might enter the ductsalong with the air. The air will be heated (or cooled) and thendistributed to the entire structure.
The airdistribution system takes air from the occupied space, heats or coolsit, and then returns it to the space. As long as the duct system istight, and properly sealed, there should beno infiltration of odorsfrom the surrounding air (from either the basement or the attic).

Aheat exchanger separates the air flowing to and from the building fromthe gases produced during the combustion process. If the heat exchangeris in good shape, the byproducts of combustion should not interminglewith the air from the space. If there is damage to the heat exchanger,the fumes from the combustion process can seep into the air in thespace. If you suspect this, call a professional immediately to inspectthe system and the integrity of the heat exchanger.