In this blog, you will learn why return air ducts get dirtier than supply ducts. We’ll also cover what both types of air ducts are and how they handle ventilation, exhaust, and more.
Why Do Return Air Ducts Get Dirtier Than Supply Ducts?
The return grill picks up whatever dust and hair is circulating in the house, pulling that air back into the system, while supply air is coming out already conditioned and filtered through the coil.
Whatever dust is going into your house from the vents is usually the same dust that is getting sucked in by the return grill. Air is like water, water pours in, water’s got to have somewhere to go, supply and return.
Air Ducts Return vs Air Duct Supply
What Supply Air and Return Air Actually Are
The supply air is coming into the office, and the return air is leaving the office. Supply air comes from the air handler, going through a diffuser into the space, and it delivers either heated air or cooled air, most of the time cooled air at the desired temperature and air quality, delivered to that particular space through air ducts and vents into multiple spaces.
Return air is drawn from that space where conditioning is being done back into the HVAC unit. It returns the indoor air to the HVAC unit for reconditioning and recirculation, and it again travels through return spaces, generally, if there’s a false ceiling, it travels from the open space into the false ceiling, or return ducts are created, and there has to be some way that return is picked up either through the duct or through that open ceiling back to the unit.
Why the Return Side Collects More Dust
The dust inside the ductwork is usually caked on the inside of the walls. As air blows through the ductwork, the dust isn’t actually getting picked up and carried along. Whatever dust gets into your house from the vents is usually the same dust sucked in by the return grille.
If you have a lot of animals in the house, dogs or cats that shed hair, and there’s just debris and other garbage around the house that’s stirring up a lot of dust, your ductwork is going to get dirty a lot faster as well.
Why Every Room Needs a Return, Not Just a Supply
Every room in this house has a filter, and every room has a supply. It’s just basic stuff. Air’s like water, water pours in, water’s got to have somewhere to go, supply, return.
This is why houses don’t feel comfortable. You go in your bedroom, you shut the door, now you’ve got supply air blowing but no return air in there. So what happens is that the room gets stuffy, it gets, ya know, the air’s not moving, it gets stagnant.
There’s some packages out there, don’t be fooled, they call them jumper ducts. All it does is, here’s a room over here and here’s a room over here, and it’s two ducts attached to two rooms together, no return air, just attaches the two rooms. Jumper ducts are not what you want.
Ventilation, Exhaust, and Fresh Air
ASHRAE has requirements for how much ventilation air you need to bring into a space. Return air can be mixed with outside air, then sent back through the system as supply air.
Return air can also be taken straight to the outside; this is exhaust air, extracted and expelled from the building spaces, and sent back to the atmosphere. It is generally done to remove stale air, contamination, or excess air to maintain indoor air quality. Typically, it is extracted from kitchens, washrooms, hospital laundry spaces, ICUs or spaces like OTs where contamination is major, again extracted through ducts and with the help of fans.
Fresh air is the outdoor air brought into the building. It enters the building through the air conditioning units, it is generally filtered and conditioned in the HVAC system before it mixes with the indoor air. Outside air is nothing but fresh air, which actually helps to dilute the pollutants and replenish the oxygen levels.
Whether Duct Cleaning Is Actually Necessary
For 95% of people, it is completely unnecessary, and I’m pretty sure that most HVAC guys out there would agree with my opinion. Duct cleaning has never been shown to actually prevent health problems, nor do studies conclusively demonstrate that particle or dust levels in homes increase because of dirty air ducts.
Typically, if your ductwork is 30 to 35 years old, that’s no big deal, there is going to be some buildup inside of there, but that does not do any harm. If you open up your vents and you literally see just piles of dust and hair, then you probably do need your ducts cleaned.
