Ductwork works around the clock to transport air through your home. Without correctly-sized ductwork, air won’t transport efficiently, and you’ll see higher energy bills and a shorter HVAC life span. If you’re dealing with an inefficient HVAC system, your ducts might be the cause. Improper duct sizing needs replacement to ensure your home is comfortable and your HVAC system works correctly. Understanding how to spot improper ductwork sizing, how to size ductwork and what to look for in a replacement can help save you lots of money.
Table of Contents
- Duct Sizing Basics
- Calculating HVAC Duct Sizes
- How To Tell If Your Ductwork Is Sized Correctly
- What Happens If Your Ductwork Is Undersized?
- Cost of Replacing Ductwork
Duct Sizing Basics
Sizing ductwork is a critical part of the HVAC process — it ensures everything will fit and lets your HVAC team know what ductwork you need. These factors influence budget and HVAC abilities. Duct sizing depends on airflow, air weight, home layout, HVAC size and home size. Ductwork needs to fit your HVAC’s size to ensure it can efficiently transport air through your home without strain. Calculating ductwork correctly involves several complex factors, and it’s easy for inexperienced installers to get it wrong.
Calculating HVAC Duct Sizes
While many companies will talk about using an HVAC duct sizing rule of thumb to quickly calculate needed duct sizes, there are better ways to do it. Some “rules of thumb” are not allowed under state regulations and often fail to account for your home’s unique needs and sizing. Getting your ductwork professionally sized is better to ensure it’s as accurate and well-fitting as possible.
Sizing HVAC systems involves considering cubic feet per minute (CFM), square footage and the friction loss rate. These three factors work together to give your HVAC professionals an idea of what duct size you’ll need:
- Cubic feet per minute: Calculating the CFM involves taking the HVAC unit’s size in tons and multiplying it by 400. Next, divide that total by your home’s square footage. That result gives you the CFM, which is used with the following factors to get the HVAC duct size you need.
- Square footage: HVAC technicians will look a floor plans or measure your home to get its square footage. Calculating square footage involves taking the length and width of every room and multiplying them together. Rooms are divided into smaller rectangles to get the most accurate measurement if they’re oddly shaped. Adding all those totals together gets you your home’s square footage.
- Friction loss rate: Measuring the friction loss rate is difficult if you aren’t a professional. The friction loss rate is the pressure loss in a channel — it’s affected by coil number, duct length, grilles, filters, turns, dampers and registers. The friction loss rate has a significant impact on your ductwork’s airflow. Without accurate measurements, your ducts won’t work as efficiently as needed.
How To Tell If Your Ductwork Is Sized Correctly
Finding the appropriate duct size is vital for your HVAC’s function. You want your duct system to work correctly so your HVAC can avoid working overtime to heat and cool your home. If you think your ductwork is sized incorrectly, you’ll want to get it looked at to restore your system to maximum function and efficiency. Here are some signs your ductwork is sized incorrectly:
- Odd noises: If you notice lots of whistling, rattling or other constant HVAC noises, your ductwork is probably undersized. The ductwork can’t handle the HVAC load being pushed through it.
- High energy bill: A higher-than-expected energy bill can be a sign of oversized ductwork. If your ducts are oversized, your HVAC system must work harder than it should. More HVAC work means higher energy bills as the system uses more power to get the air to you.
If you aren’t dealing with these issues, your ductwork is sized correctly, and you can wait to replace your ductwork until the recommended time.
What Happens If Your Ductwork Is Undersized?
Undersized ducts happen when the ductwork has been incorrectly measured. Your HVAC system needs the right ductwork size to ensure it efficiently and correctly pushes air throughout your home. If your ductwork is undersized, you’ll hear odd, intrusive sounds from your vents as the HVAC system struggles to move too much air through too-small ductwork.
Additionally, this added HVAC strain increases its energy use and decreases its life span. The harder your HVAC system has to work, the more energy it will use. Over time, this constant overworking will shorten your HVAC system’s life. You’ll need to pay for an HVAC replacement much earlier than expected. Getting the right-sized ductwork can help you avoid these issues and save money.
Cost of Replacing Ductwork
If you’re dealing with a duct system that doesn’t fit your house, you’ll need to invest in a replacement system. While this can be a significant investment upfront, you’ll save lots of money and stress going forward, and your home will be more comfortable. The average cost of replacing ductwork is around $8,000, but many jobs come in below this figure.
There are several factors influencing your ductwork replacement cost. While there’s no entirely accurate ductwork replacement cost calculator, you can get an estimate from your contractor depending on your ductwork.
Your total ductwork cost will depend on the following:
- Size: The larger your home, the more ducts it will have and the more expensive your ductwork replacement will be. Since you’ll need ductwork based on your home’s size, expect to pay more for a larger home. Additionally, if your ductwork is more complex, it will be more of an investment to replace.
- Location: If your ductwork is harder to access, it will cost more to replace. The job will also cost more if you have ductwork in cramped crawlspaces or if it’s in your ceilings and is challenging to get to. You’re paying for the increased difficulty — HVAC professionals want to get your ductwork as accurate as possible. Increased difficulty means more work to get it right, so you’ll pay more for the replacement services — especially if you want correctly-sized ductwork.
- Labor: Paying for professional ductwork replacement will add to your total cost. While DIY-ing is technically cheaper, it’s extremely difficult to get right without professional experience — you’re more likely to perform the replacement incorrectly. Then, you’ll need to pay a professional to correct any errors made during the DIY.
- Material: There are several options for ductwork material — fiberglass, aluminum and galvanized steel are popular. Picking a more expensive material will raise your ductwork costs.
See Our Commercial HVAC Ductwork Here
Hennemuth Metal Fabricators has delivered high-quality, lasting ducts and fittings for HVAC contractors in the Pittsburgh area for decades. With unmatched custom duct solutions, including custom sheet metal fabrication, you can rely on our family-owned company to provide you with the ductwork you need. Whether you’re looking for standard-sized or custom ductwork, we have the right product for the job. If you’re interested in ordering from us or want to learn more, contact us online today!