As most homeowners already know, HVAC units installed in homes are chiefly responsible for cooling and heating the house as the weather or outdoor temperature demands. However, the unit alone doesn’t determine how efficiently it will function all-year-round. There’s an array of important factors that play a role in determining functionality, and one of them is the size of the ductwork. You’re probably wondering how duct size can be so influential if the ducts simply expel air. In this article, our air conditioning service experts at Albert Air Inc. explain the reasons behind the importance of proper duct sizing, plus the different factors that come into play when sizing HVAC ducts.
A duct system, also called ductwork, is a network of ducts. Ducts are conduits or passages used in heating, ventilation and air conditioning to deliver fresh air and draw moist, stale air out of the living space. Ducts are generally made of galvanized steel, aluminum, polyurethane and phenolic insulation panels.
First, the HVAC unit fills the supply plenum with either heated or cooled air as needed, which is directed via the system’s ductwork. When fresh, clean air enters a room, it pushes out the existing air into yet another set of ducts. These ducts then deliver the old, stale air to the return plenum. This used air passes through a filter to ensure that it’s clean before it re-enters your furnace, air conditioner or heat pump.
If you find yourself needing an “air conditioning repair near me”, then you may want to let a technician inspect your ductwork as well while you’re at it.
Your ducts need to be appropriately sized and suitable for the system in order for your HVAC unit to perform efficiently and effectively, or else there’s a great chance that you’ll end up with an uncomfortable living space, worn-out heater or air conditioner and inflated energy bills.
Oversized ducts — Sure, ducts that are larger than normal are capable of handling more airflow, but the problem is that your HVAC system may not be equipped to produce or supply large amounts of air. In fact, your system requires a specific amount of air pressure in the ductwork to effectively distribute air throughout the house. Dealing with oversized ducts can cause your HVAC unit to limit the amount of conditioned air that reaches the threshold of your home, forcing your unit to work harder than before to reach the desired interior temperature. This often leads to equipment breakdowns, frequent tune-ups and repairs and increased energy usage.
Undersized ducts — Ducts that are too small to accommodate the air flowing through them will cause the pressure to increase and back up in the system, creating resistance in the blower fan and diminishing the efficiency, performance and lifespan of the HVAC unit. Over time, this can put significant stress on the unit components and eventually cause a system breakdown, forcing you to call a furnace or air conditioning service.
Manual D is the industry standard for sizing return and supply ducts and registers in residential spaces. It was developed by engineers at the Air Conditioning Contractors of America. This method involves evaluating individual rooms in homes to establish optimal airflow, regulate excessive noise, seal ductwork and provide adequate insulation. All of these work together to correct pressure imbalances as well as ensure the HVAC system operates as efficiently as possible, providing each room in your home with sufficient conditioned airflow.
Most of the time, HVAC technicians will determine the appropriate size of an air conditioning unit using a specific rule of thumb. In the simplest of terms, the accurate guide or principle states that for every 500 square feet of air-conditioned floor area, an air conditioner with a one-ton capacity should be installed for optimal performance.
Now that you’ve read about the general rule when it comes to sizing your HVAC system, it’s time to take a closer look at some important things to consider when calculating the best duct size for your home. An HVAC repair expert lists the important factors involved in the process below.
The area of your home in square feet.
The size of your air conditioning unit.
Friction loss.
Airflow velocity.
The static pressure of the HVAC unit.
Here are the steps to calculate the correct duct size:
Check how many BTUs (British Thermal Units) your furnace produces. This information is generally listed on the furnace plate. Proceed to divide that number by 10,000.
Multiply the answer by the CFM (Cubic Feet per Minute) airflow of your furnace unit. Oftentimes, 100 CFM is generated by a natural draft furnace, while 150 CFM is produced by a condensing furnace and 130 CFM by an induced furnace.
Next, divide the answer you get in the second step by 10. What you get is the measure of airflow allowed by the HVAC unit in your home.
To calculate the duct size, multiply the length by the width. So, if the vent size is four by eight inches, for example, the total CFM should be 32 per vent.
Now, divide the CFM per vent by the total CFM measurement for the furnace.
Proceed to calculate the square footage of each room. Do this by multiplying the room length by its width.
Lastly, divide the number of vents by the total square feet of each room.
If you don’t want to calculate these numbers manually, there are online calculators or programmed calculators available to help you figure out the correct duct size. Even professionals utilize these tools because they’re fairly easy to use and give reliable output. However, HVAC repair technicians have more advanced and sophisticated tools at their disposal, making their calculations more precise and reliable.
It’s great if you have an inclination for designing the ductwork system of your home. Still, we strictly advise that you consult a professional with pertinent knowledge and expertise to verify your calculations. A simple mistake on your part can prompt a lot of problems down the road, including premature system failure, high-cost repairs and wasted time and effort. Keep in mind that the size of your ducts can dramatically affect the comfort level inside your living quarters. To a great extent, it also determines the amount of cash that you’ll need to spend in order to keep your home sufficiently cooled or heated for many years to come. Since the largest percentage of your electric bill is comprised of your HVAC system, you need to make absolutely sure that your calculations are correct.
If you’re looking for top-rated heating, cooling and indoor air quality solutions such as ductwork maintenance or “air conditioning repair services near me”, turn to Albert Air Inc. Our certified technicians are committed to providing the comfort and efficiency you need through industry-leading products and outstanding customer service. Call us at (714) 248-0238 or fill out our contact form to request a free, no-obligation estimate. We work with residential and commercial building owners in Fullerton, CA, and surrounding communities.