How big should my return air duct be?
How big should my return air duct be? As for any duct, size is dependent on duct length, air flow, and allowable static pressure drop. For most systems, the minimum duct size (see Table 1) is sufficient for up to 25 feet (8 m) with no more than three 90° bends.
Can you use flexible duct for your return air?
You can use flex ducts for your return ducts. However, you have to make sure it fulfills all the necessary criteria. These include pressure checks, proper wrapping, and marking, airflow control, etc. In this article, we’re going to discuss everything you need to know about flex ducts.
Are return air ducts equal in size to supply ducts?
Yes, return ducts are usually larger than supply ducts to ensure that air within the home is balanced. There are generally more supply vents in the system creating the need for return vents to be larger. Ensuring that there is sufficient air supplied and returned is critical to maintaining an ambient environment.
How to calculate air return?
Calculate the return duct size based on the air conditioner's size and the type of duct you are using. Use the following formulas: For rectangular duct: Size of air conditioner (example: 4 tons) x 144 square inches = return air duct in square inches. For round duct: Diameter of duct x 3.14 = return air duct in square inches.
What happens if return air vent is too small?
If the return duct is too small, there are an inadequate number of return grilles or they are undersized, it can't return enough air to recirculate back into the system. The average duct system has 25% less return air than required according to National Comfort Institute.
How do you size a return air duct for a room?
To calculate the required equipment size, divide the HVAC load for the entire building by 12,000. One ton equals 12,000 BTUs, so if a house or office needs 24,000 BTUs, it will take a 2-ton HVAC unit. If you get an uneven number, such as 2.33 for a 28,000 BTU load capacity, round up to a 2.5-ton unit.
Should return duct be larger than supply?
In other words, the return should always be at least as large as the supply. And preferably the return should be larger than the supply.
How big does a return air plenum need to be?
Single plenums should not exceed 24 ft in length. Double plenums should not exceed 48 ft in total length.
What size duct do I need for a 12x12 room?
A 12×12 foot room will need a 4×8 inch supply duct to get an adequate CFM rate, which is about 144 CFM.
Can flex duct be used for return air?
Yes, you can use flex ducts for your return air. However, to maximize its usefulness, it needs to conform to technical specifications such as its insulation rating, pressure checks, dust filters, duct sizing and placement, and lastly, the installation requirements.
Can a return duct be too big?
No such thing as too much return. It will not take in any more air than it pushes out, thus no such thing as too big. Its hard to imagine a return that is too big ,but you want the return to have some draw to evacuate an area.
How many return vents should a house have?
Ideally, every room except the kitchen and bath should have its own return air grille. At the very least, each level of the house should have one. Even so, many homes were built with just one or even no return ducts in an attempt to cut costs.
Should every room have a return vent?
Does Every Room Need Air Return Grilles? While it is a myth that air return grilles are required in each and every room in the house, it is definitely necessary to have more than one of these grilles installed at strategic places in the house. The most important place to have these would be the bedroom.
How long can a return air duct be?
Duct Size - Single Return For most systems, the minimum duct size (see Table 1) is sufficient for up to 25 feet (8 m) with no more than three 90° bends.
How big do cold air return vents need to be?
16 inches by 20 inchesA typical return vent is 16 inches by 20 inches, according to Hunker. It includes the cold return air duct grille. If you consult the duct CFM sizing chart, you can quickly figure out that a 16×20 inch can handle about 1,500 CFM airflow.
How do you design a return air duct?
0:185:27Basic Return Duct Sizing Made Simple - YouTubeYouTubeStart of suggested clipEnd of suggested clipThere's a couple basics that you want to know and the basics. Are design your duct system at a pointMoreThere's a couple basics that you want to know and the basics. Are design your duct system at a point 0.5 static. Pressure you want 200 square inches per ton on the return grill. So it don't whistle.
How do you calculate return air vents?
To calculate the return air grille size, take the CFM of the HVAC unit and divide it by 350 to get the grille area in square feet. Next, multiply the grille area by 144 to convert it into square inches. Finally, choose your preferred grille size that matches the required grille area.
How do you design a return air duct?
0:185:27Basic Return Duct Sizing Made Simple - YouTubeYouTubeStart of suggested clipEnd of suggested clipThere's a couple basics that you want to know and the basics. Are design your duct system at a pointMoreThere's a couple basics that you want to know and the basics. Are design your duct system at a point 0.5 static. Pressure you want 200 square inches per ton on the return grill. So it don't whistle.
What is the good rule of thumb in sizing Ductworks?
When you hire a professional to install your ductwork, they'll often size your HVAC ducts using a rule of thumb that states an air conditioner with one-ton capacity should be installed for every 500 square feet of air-conditioned floor area. They'll also take into consideration the size of each room of your home.
What size should a bedroom return be?
The Size Of Your Return Ducts In most cases, if you are installing ducts in each room where there is a supply, you will want to go with the same size as your supply vents. If you are installing just one or two return vents, you will want to go with a 12-inch return for 2-ton units and lower. 14- inches for 3 and up.
How to calculate return air duct?
For round duct: Diameter of duct x 3.14 = return air duct in square inches
Why is it important to properly install an air conditioner?
Properly sizing and installing your air conditioning system are important in making sure your air conditioner operates efficiently, according to the U.S. Department of Energy. One thing to remember is that you must have enough supply vents (vents blowing air out) and return vents (vent sucking warm air back in the air conditioner). Also, improper duct installation will impact your air conditioner's efficiency and your electric bill.
Why is it important to have a duct size?
Having the correct duct size installed in your home is essential for it to do it’s job correctly. If your ducts are too small, or too large, you will allow the air to escape, and it will end up costing more in your heating or cooling bill. This is because the heat or air is escaping, and not making it to the rooms of your home, so you keep it running.
What is the next important unit to know when determining duct sizing?
The next important unit to know when determining duct sizing is the friction loss rate. This will ultimately help your contractor establish the static pressure of your unit, another measurement that affects air flow.
Why Is Duct Size So Important?
There are many different options available for duct sizing and these are meant to correspond with the different size heating or cooling systems so that the correct amount of air is circulated around your home.
Why is my ductwork so noisy?
Ductwork that is too small for your heating or cooling system will cause a surge in static pressure. This means that your ducts will be noisier than normal and have to work harder to service your home. To adequately heat or cool your home, your system will need to run longer, costing you more money on your bills.
What is the most important thing to consider when it comes to heating and cooling?
Duct sizing is by far the most important aspect to consider when it comes to your heating and cooling systems. Improperly sized ducts can result in unnecessary wear and tear, place too much pressure on your units and end up costing you more money on your energy bills.
Why do you need to match duct size?
Your duct sizing must match perfectly with the sizing of your heating or cooling unit in order to ensure that the correct amount of air is distributed around the home. Choosing ducts that are oversized will cause your air handler to have more area to cover.
How to calculate CFM?
This calculation gives you the multiplier to determine the CFM for all your rooms. For example, if your living room is 300 square foot, multiply 300 by (unit size x 400) / overall square footage. Repeat this for every room in your house. Here are the formulas for further clarification: 1 Cubic Feet Per Minute = (Unit Size in Tons x 400) / total square foot of your home 2 CFM for each individual room = Room’s Square Footage x (Unit Size x 400) / total square foot of your home
Why Does Duct Size Matter?
Ducts that are small in size make your HVAC system work harder to keep your home at the desired temperature. If your duct size is big, the velocity of air gets compromised. It means you will not be able to feel the air flowing through the air vents.
What is AC duct?
AC Ducts. Ducts are channels or passages that are used in heating, ventilation, and air conditioning (HVAC) to distribute fresh and get rid of stale air. The HVAC unit fills the supply plenum with either cooled or heated air, as desired. It is directed via the ductwork of the system.
What is the HVAC unit?
The HVAC unit installed in your home is responsible for its heating and cooling as the weather demands. The unit alone does not determine how efficiently it will work. There are many other factors that play a role in deciding so. One such decisive factor is the duct size.
How to find BTUs in a furnace?
1. Look on your furnace to see how many BTUs (British Thermal Unit) it produces. This information is usually given on the furnace plate. Divide that number by 10,000.
How to calculate square feet of a room?
6. Calculate the square feet of each room by multiplying the room length with its width.
Is it good to design HVAC ducts?
It is good that you want to design the HVAC duct system of your home. Still, we strictly advise that you consult a professional with expertise in this context to validate your calcula tions. It is because a mistake on your part can prove to be costly, both in terms of money and effort. The size of your ducts can alter the comfort level inside your home drastically. It also determines the amount that you spend to keep your home appropriately cooled or heated. Since the biggest contributor in your electricity bill is your HVAC unit, you want to get your calculations correct in the first instance itself.
Why is it important to have return air ducts?
It’s important that roughly the same amount of air moves through supply ducts as return ducts, in order to maintain neutral air pressure in rooms.
What happens if you don't have a return duct?
If supply air doesn’t have a way to return to return ducts, it will leak out of the house through cracks and openings in the home’s outer envelope. In the winter, this means you’re losing heat energy to the outside, and rooms won’t stay warm for long.
How does forced air work?
After the air is conditioned, a blower or air handler blows the air through supply ductwork, which delivers it to rooms throughout your house, where it emerges from registers and vents. The air has to have some way to return to the HVAC equipment, and that’s where return air ducts and vents enter the picture. The same fan operation that delivers air to your home’s rooms draws that air back to the equipment via return ducts.
Can you be forgiven for not knowing about your air duct system?
A person can be forgiven for not knowing much about their home’s air duct system. It plays a vital role in the home’s forced-air heating and cooling system, performing its job quietly and without much attention.
Do you need a return vent in every room?
For this reason, it’s important that house construction doesn’t scrimp on return vents and ducts. Ideally, there should be a return register or vent in every room where a supply register is located. If that’s not possible, there should be easy airflow between rooms, via such strategies as air pass-through grilles in doors or jumper ducts in ...
What Exactly Is A Return Ducts Function?
A return duct is the part of the system that carries the air back to the furnace or air handler where it will then be circulated back out through the supply vents. That’s right, your heating and air system is nothing more than a big circulation unit. Without the return duct, the air in the home would not be able to properly circulate. This would not only cause your energy bills to rise, but it will cause your entire system to not function at full efficiency. Since the return duct is basically applying negative pressure to the system it is the one that houses the filter.
Where do you put your ducts?
If you make a careful not you will probably notice right away that most of your supply ducts are either installed by the windows or doors. This is because this is where most heat enters the home. The ducts are installed strategically in these locations to help battle this heat loss or heat gain. And, this is just one of the reasons that the return ducts need to be installed directly across from the supply vents.
Why is it important to clean air ducts?
You also learned that return ducts aren’t supposed to be installed in bathrooms and kitchens because they will just circulate the odors and moisture from the rooms throughout the duct system. This is just another reason why cleaning the air duct is important. A dirty return duct will just cause the system to circulate dust and debris throughout the home over and over again.
What does it mean to choke down ducts?
Choking down the ducts that are located on the first floor or close to the return duct will allow you to allocate more air to the ducts that don’t have as much suction power.
What is a supply vent?
The supply vents would be the vents that blow air into the home. Even though your filter is located in-line with the return duct it is one that is oftentimes forgotten about. Of course, it could be forgotten about during the installation because without the return duct the system just wouldn’t heat and cool the home properly.
Do return air ducts work?
Yes, some systems are designed to work this way, but most modern duct systems will just usually have one or two returns accounting for the entire system. And, these systems are more than effective. But, before you think about installing a new return air duct you should think about cleaning air duct service to make sure your ducts are clean ...
Do you need a return duct in every room?
Now, this does not necessarily mean that you need a return in every room.
Where should HVAC return air ducts be?
"An HVAC return air duct should be in every room except a bathroom and kitchen. They should be on interior walls across the room from the supply ducts that should be washing exterior walls with conditioned air."
What is the air duct in your house?
The air ducts in your house should be designed exactly like the blood vessels in your body. Think about it. The veins and arteries supplying blood to the different parts of your body, even out to your fingers and toes, are the same size as the veins and arteries returning that blood back to your heart.
Why does my furnace need return air?
The reason for return air is simple. Your furnace is simply a recirculating pump. Instead of pumping water, it is pumping air. We need to get the air back to the pump. Furthermore, without a return air duct in each major room, the supply duct air has to "push" all of the air in the room out of the way as it makes its way towards you.
What is the purpose of a return air grill?
The intent is to wash the exterior walls with heated or cooled air. You are trying to combat the heat or cold at its source. The single giant return air grill in the floor balances the load at the furnace motor but does nothing to promote cross-ventilation in each room.
How to get the most bang for your return air buck?
If you want to really have a way to get the most bang for your return air buck, think of installing grill covers on the wall that have operating louvers. This will allow you to choke down rooms possibly on the first floor that are drawing too much air.
How to size an air conditioner?
To properly size an air conditioner, one has to perform a heat gain calculation. In other words, you must determine how fast heat is getting into your house and what things inside the house are contributing to heat gain .
Where should the air conditioner be located?
Supply air from furnaces and air conditioners should be on outside walls. The return air vent openings need to be on the opposite side of the room so the conditioned air is pulled across the room.
