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Revised:
December 28th, 2022
There are two times when you pay close attention to your HVAC: when it fails, or when you’re buying a new unit. But let’s be honest: How many times do you worry about the ventilation system?
If a room is too cold in the summer, you might close the damper on the register, hoping that might balance things a bit. For the record, that doesn’t work, but more on that later.
So all of those vents do their job unnoticed for the most part. But let’s consider what happens when you drive on a set of automobile tires that are underinflated. Your car has to work harder, putting more strain on the engine, which causes it to fail earlier. To say nothing of the fact that your gas mileage will suffer, which costs you more.
Your ductwork is similar. You can invest thousands of dollars in a top-notch air conditioner and/or furnace, but if the airflow is compromised, the best system won’t be able to compensate for the deficiencies in your ducts.
This can cause needless repairs and a shortened life cycle for your furnace. You’ll be pouring money into your energy bill that could have been avoided. Also, your air quality will degrade, potentially worsening conditions for allergy sufferers.
The solution? A duct system that custom sized and fitted especially for your home. That’s where your HVAC technician should shine. Ductwork is vital to your comfort. We’ve seen thousands of duct configurations, and can help you with problems small (one room is always uncomfortable) and big (upstairs is ten degrees warmer than downstairs).
We’ll start by walking through our process to help you navigate this essential subject.
How Do We Determine the Size of Your Home?
Square footage is only part of the equation when we measure your home. First, we determine the load of the house. We look at the design, the layout, the room sizes, and the ceiling height. There’s volume, square footage, number, size and type of windows. It also matters which way the house is oriented, the number of occupants, and the presence of an attic or basement.
All of this is standard when we do a Manual J Load Calculation, which is required by national building codes and most state and local jurisdictions. That gives us an excellent idea of how much air the system needs to condition and move.
Then we figure out how many air changes we need per room. The return air ducts draw the air out of the room and the supply puts the conditioned air back in. How many times that happens per hour is an air change. (It's also referred to as the “air exchange rate” or “air change rate.”
Manual D is the industry standard for sizing home HVAC return and supply ducts & registers. Manual D duct design ensures the correct amount of heating and cooling is going to each room.
And based on those measurements and the data we collect there, we come up with duct sizing.
How Much Air Do the Ducts Need to Move?
We use duct sizing charts to calculate the airflow. And we’re looking at the amount of air - CFM (cubic feet per minute) – the velocity, which is the feet per minute of air we need to move.
We have to make sure that the duct size falls within certain parameters. We also need to calculate how big the supply side needs to be, including how many return vents. We’re measuring the airflow closest to the furnace and farthest away from the furnace. It should be close.
Our goal is to create a system that can maintain a 70-degree temperature year-round.
Sizing the ductwork is pretty easy because the chart gives you the answer. Now we have a space we have to try to fit this in. In that space, we have to get X amount of certain-sized ductwork, vents that will run to the actual registers where the air comes out, and return air grills where the air comes back into the system.
One more set of standards we have to follow. SMACNA dictates what sized ductwork we must use; it has to be at a certain gauge of metal. We can have only so many turns in the ducts. Every turn adds about five linear feet. If I have a room that’s 80 feet away but I have to bend the air five times, that’s an additional 25 feet.
All of those calculations on the front end help us get that design parameter. The second challenge is: “Can I get this design parameter in the confines of the building?” We might have to go around a staircase to get to this room or put a run in the attic so the ductwork is not on the ceiling. The farther we have to push that warm air, the more heat loss will occur.
Is it a 4500-square-foot house, which might require two systems? Is it a 1200-square-foot ranch? Planning ductwork gets more difficult when we’re looking at a two-story foyer; big, open great rooms; not a lot of interior walls. We consider the thickness of the outside walls, insulation, windows, and the availability of either floor space or wall space to accommodate the proper size registers.
Moving Air in Ducts Is Like a Freeway
I explain it like being on a freeway. How many cars per hour have to go down this lane? Do we size it for the average traffic or peak time? You will get stuck in traffic because there’s not enough roadway for the number of vehicles.
In ducts, we need a big enough roadway to move the air where we need it.
You want to have the volume of air in that pipe moving at a certain speed. If you walk across a register and it blows your skirt up, it’s too much air. It’s moving too fast. That probably means other places are being robbed of airflow.
Read More: HVAC Ductwork: Best Practices for Cleaning, Modifying and Care
Proper Ductwork Can Benefit the Entire System
If that ductwork is not sized properly, it causes issues inside the system, which is designed to last 15-20 years if you take care of it. Bad ductwork shaves years of life off of that system. It’s making it work under conditions it wasn’t designed to work under. It’s not getting enough return air, or it’s having to push too much air, or both.
Dampers Can Make Adjustments to the Airflow
Balancing dampers sit inside the ducts and can be opened or closed. If one line on the supply side is getting too much air, a damper can reduce it or eliminate it. You want dampers to be as close to the trunkline as possible. That way the vent has a chance to move the air somewhere where it’s needed.
There’s also a finishing damper; that’s the damper on the register. A lot of people get confused: they think if they shut that, they can balance the airflow. But all it’s doing is stopping the air from coming out. All of that pressure has made it all the way down to this point and you’re going to be missing other areas. That pressure should stay inside the main trunk line.
What Are Air Ducts Made Of?
We use galvanized sheet metal ductwork. Galvanized ductwork has a zinc coating on the inside so it doesn’t rust. If it’s in an attic or unconditioned space it needs to be insulated or wrapped. There’s a duct wrap with a vapor barrier on it that 100% has to be there.
A different product is called duct board, which is made from Fiberglass. You can cut it, fold it, and make any sized piece you like. There are even some older ducts we see that are made out of wood.
You have a different friction rate in metal vs duct board. If you have duct board, it harbors mold, mildew, and fungus. All of that will be transported throughout the home. Fiberglass breaks down, and the fiberglass can enter the air stream.
The galvanized metal is less likely to accumulate mold. It’s easier to treat, it lasts longer and it doesn’t break down.
Can We Replace a Single Part of an Air Duct, or Do We Need to Replace the Entire Line?
We can replace a section of ductwork, or install an entire line. We want to maximize the benefit and minimize the cost.
A couple of days ago, there was a job where we had to disassemble the return air side, but only three sections of the supply.
Duct design is probably the most important, and least appreciated, of HVAC. Everybody thinks ductwork is the least expensive part. It typically isn’t if it’s done right.
How Important Is Ductwork?
Anyone can sell furnaces and air conditioners, but poor airflow causes probably 70% of the issues in a home. A lot of techs get trained on how to fix a furnace, but they don’t understand any part of the duct system.
Improper ductwork can contribute to the breakdown of a piece of equipment: burned-out compressors, burned-out blower motors, faulty coils, coils that leak, improper humidification or dehumidification. Hot and cold spots. All of these are caused by faulty airflow.
We move air. And we treat the air. We heat it, we cool it, we humidify it, we dehumidify it, and use air purifiers to clean it, we filter it, and we disinfect it. But if the air isn’t moving properly, you’re not going to be comfortable.
Back in the day, the Building Industry Association (BIA) had a standard that most homes were built on. They said a 10-degree difference between the first and second floors was acceptable. So, your thermostat is typically on the first floor. If it was set at 72, that means it was acceptable that your upstairs temperature was 82 degrees.
Today, the best of the best can maintain a 2- or 3-degree temperature difference from any room compared to any other room.
Taking Care of Your Ducts
Replacing your furnace’s filter is a great idea. That will help keep dust and other debris from entering the ducts.
One other thing you can do for your system is to give it a thorough duct cleaning. If you just moved into a new home, or haven’t had them cleaned in a number of years, it’s time.
You can try to clean ducts by yourself, but even a good vacuum won’t be able to dislodge years worth of stubborn dust. Mold flourishes in damp, dark places. It’s an unhealthy situation, but it can be remedied.
The best way to clean them is to hire a professional duct cleaning service. Here at Fire & Ice, we clean ducts and firmly believe that our process is tops in Columbus, Ohio.
Watch the informative video below to get an idea of our methods:
Read more: Home Duct Cleaning in Columbus Ohio
Are You Having Ductwork Problems in Columbus, Ohio?
By now, I hope you’ve learned that duct problems can be major headaches or the cause of a nagging comfort issue. We’re here to help. If you’d like us to come out and give a free estimate, we’d be happy to do so. Just fill in your zip code on the map below to get started. We look forward to talking with you.
