Full Answer
What is a return plenum?
The return Plenum is concerned with getting rid of used air in a room. To be clearer, whenever any newly heated/cooled air is pumped into a room, the air from the previous cycle of heating/cooling is already lingering in the area. This air is pulled back into the internal system, and it is refreshed and reused to heat or cool the room.
Do I need plenum rated cable for my plenum air return?
A plenum air return would unknowingly circulate toxic air throughout an office. Since both you and the Fire Department don‘t want you to die from breathing in toxic fumes from your cabling, code requires Plenum Rated cable installed through any plenum air return space.
What is the return air plenum for the Ahu?
The entire room act as a return air plenum for the AHU. Using AHU rooms as the return air plenum not only saves the cost of ducts, it also resulted in significantly more saving from the reduction of the room size. AHUs no longer need to have a separate return air plenum and thus, their physical size is smaller as well as the room size.
When should I replace my HVAC plenums?
When changing the air filter in your HVAC unit, you’ll probably find it between the two plenums. Or, if you’re having difficulty with air flow coming from your air conditioner or furnace, the HVAC technician may say something about replacing the plenums.
Why do you need a return plenum?
1:313:35Titus Timeout Podcast - What is Plenum Return? - YouTubeYouTubeStart of suggested clipEnd of suggested clipThere are a couple benefits to using plenum return plenum return has less ductwork. So it costs youMoreThere are a couple benefits to using plenum return plenum return has less ductwork. So it costs you less to install. And there's less material.
Is a plenum necessary in HVAC?
A plenum in heating, ventilation, and air conditioning (HVAC) systems is a box that connects to the HVAC system. It has a critical function and that is to bring in, distribute, and remove air. Each HVAC system typically uses two plenum boxes: a supply plenum and a return plenum.
Is a plenum necessary?
Q: Is a plenum necessary? A: In modern forced-air HVAC systems, you must have a plenum installed.
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.
How do I make a return air plenum?
0:0516:43Furnace Return Air Plenum Fabrication - YouTubeYouTubeStart of suggested clipEnd of suggested clipProbably gonna be a 3-piece box. You can make them a five-piece you can make them you know three-MoreProbably gonna be a 3-piece box. You can make them a five-piece you can make them you know three-piece there's numerous ways that they can be made. And ain't none of them wrong necessarily.
Do you need a plenum box?
Plenum boxes are used to distribute heated or cooled air throughout your home's interior. After producing heated or cooled air, the HVAC system must move that air through the ductwork. Plenum boxes take in this air so that it can be pumped into the ductwork and, therefore, distributed throughout your home's interior.
How important is plenum size?
SIZE IS CRITICAL The only thing you really need to know is the plenum boxes must be correctly sized or your HVAC systems won't heat and cool efficiently. It's another reason why it's important to hire only qualified technicians to do HVAC work in your Steger, IL or Crown Point, IN house.
How much does it cost to install a return air vent?
A return air drop replacement will run around $300-$400, including installation. In rare cases where a second drop needs to be added, the cost can be up to twice that amount.
What is a plenum used for?
The supply plenum is an air distribution box. It's attached directly to the supply outlet of the HVAC equipment–that is, the outlet that releases chilled or heated air into your home. The air ducts that distribute the air into the individual rooms of your living space all connect to this plenum.
What happens if there is not enough return air?
If there is not enough return air available, your HVAC system will not heat or cool properly. They must be properly sized — Return air ducts must be large enough to carry a sufficient amount of expended air back to your furnace, air conditioner, or heat pump.
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.
Should return air vents be high or low?
For optimal efficiency, it's ideal to have return registers installed. To ensure efficiency during the cooling season, your home should have high registers. High return registers draw hot air that rises to the ceiling back into the system to repeat the cooling cycle.
What is the difference between plenum and duct?
A plenum is an air-distribution box attached directly to the supply outlet of the HVAC equipment that heats or cools the air to make the house comfortable. The ductwork that distributes the heated or cooled air to individual rooms of the house connects to the plenum.
How do you attach plenum to air handler?
5:457:29Assembling & Installing a Plenum - YouTubeYouTubeStart of suggested clipEnd of suggested clipAnd basically mate up to the top of the air handler. And then we're going to connect our fabric ductMoreAnd basically mate up to the top of the air handler. And then we're going to connect our fabric duct after and it's going to run the length of the room.
How does plenum ventilation work?
Plenum ventilation facilitates air circulation in a building. It may be used to heat or cool air. The spaces between the dropped and raised ceiling or sometimes a raised floor area where you will find plenum ventilation. They allow easy airflow and keep your house fresh and comfortable.
What is inside a plenum?
The supply plenum is an air distribution box. It's attached directly to the supply outlet of the HVAC equipment–that is, the outlet that releases chilled or heated air into your home. The air ducts that distribute the air into the individual rooms of your living space all connect to this plenum.
What Is a Plenum?
The plenums, or plenum boxes are responsible for moving heated and cooled air through the house and back through the unit. Nearly all HVAC units have two boxes, the supply and return.
What to do if plenum box fails?
If your plenum box has failed, you may want to save some money by repairing or replacing it yourself. While the component doesn’t look complicated, if it’s not installed properly to allow proper air flow, your unit’s coils can freeze, the furnace can trip, and over time the compressor itself may malfunction. Relying on a certified, experienced HVAC technician for plenum box repair and other heating and air conditioning repair will ensure the job is done correctly and your system can keep your home warm or cool as you need it.
Why is my plenum box frozen?
If the plenum box is the wrong size or isn’t connected efficiently, you may experience frozen coils or a malfunctioning heat exchange. Try changing the air filter first because if it’s clogged, air can’t move into the return plenum box. If it’s clean, the ducts may need to be professionally cleaned or the box itself may need repaired.
1. Supply Air Plenum
The plenum box on a supply air diffuser helps to distribute cold air equally across the diffuser. Besides, the plenum box act as an adaptor to connect the diffuser and flexible duct. Furthermore, a plenum box can have a damper to regulate the airflow of the diffuser.
2. Return Air Plenum
The plenum box on a fan coil unit or ducted air conditioner helps to mix the return air and thus, averaging the return air temperature so that the air conditioner can regulate its cooling power appropriately.
3. Ceiling Return Plenum
Many buildings use the space above the ceiling as a plenum for their air conditioning system. Typically, return air grilles are installed on the ceiling without connecting to any ducts.
4. Room Return Plenum
Air handling units (AHUs) often use their own room as the return air plenum. These AHUs connect duct only at their supply air outlet. The room itself also has a fresh air opening with a damper to introduce outside air. The entire room act as a return air plenum for the AHU.
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How do I determine if my building uses Plenum Air Return?
If you have a large wall or ceiling return air grate; remove and see if there the air is channeled through sheet metal ducting. If there is no sheet metal duct; just the open ceiling or wall space, then you are required by law to use Plenum Rated cable.
Why is plenum cable required?
A lot of times when conduit is not installed, plenum cable is required because the cable is “freely installed”.
What is the problem with PVC cable?
Standard cable is jacketed in PVC (Polyvinyl Chloride), with the Chloride element causing the trouble. When PVC burns or smolders it releases toxic fumes into the air (Hydrocloric Acid and Dioxin). A plenum air return would unknowingly circulate toxic air throughout an office.
How to tell if you need a plenum rated cable?
Obviously your air conditioner should be running at the time! The lack of wall or ceiling return air grates is usually a sure sign that you require Plenum Rated Cable.
What is a plenum rated cable?
A “plenum space” is the part of a building that enables air circulation by providing pathways for heated/conditioned and return airflows at a higher pressure than normal.
Is a drop ceiling considered a plenum?
Typically, spaces between the structural floor or a dropped ceiling are considered plenum. Some drop ceilings are actually designed tight enough to where air circulation is restricted and may be considered a non-plenum area. A lot of times when conduit is not installed, plenum cable is required because the cable is “freely installed”.
Do you need a plenum cable for fire?
Since both you and the Fire Department don‘t want you to die from breathing in toxic fumes from your cabling, code requires Plenum Rated cable installed through any plenum air return space. Our Installation Team is required run Plenum Rated cable if they determine the air space in not ducted.
When Should Plenum Cable be Used?
Article 800 of the National Electrical Code (NEC) states that plenum cable should ALWAYS be used in plenum airspaces and air ducts to slow down the spread of flames and reduce smoke and toxic fumes from circulating throughout the building. Due to their higher safety standards, they can be freely installed inside plenum areas – no need to use a conduit. In addition, they can also be installed in non-plenum spaces.
What is Plenum?
Plenum is an HVAC term used to identify open airspaces – usually above drop-down ceilings or below raised floors – which facilitate airflow circulation for heating and cooling. In most plenum airspaces, air ducts are used to connect the HVAC unit and the supply vents to distribute the air supply throughout a building. The return vents don’t use ducting to feed the HVAC unit, creating an open airspace.
Do I Need Plenum Rated Cable in My Home?
While it's definitely acceptable to use plenum-rated cable in your home to install a signal booster, a WiFi network, or something else, more often than not, it’s not necessary. Most residential buildings don’t have plenum airspaces. Plenum areas are more common in commercial buildings. However, if your house does happen to have a plenum airspace or you need to run cables through an air duct, then plenum-rated cable is required.
How do I Know if a Cable is Plenum Rated?
The numbers and letters printed on the cable’s jacket will usually tell you everything you need to know about the cable, such as the jacket rating, who manufactured it, who verified it, temperature rating, reference number, and more. Here is a great and easy read on how to read a cable’s jacket legend.
Who Sets Plenum and Non-Plenum Cable Standards?
In the United States, the National Fire Protection Association (NFPA) is in charge of setting fire and building safety standards regarding which cable jacket ratings can be installed in plenum or non-plenum areas and under what circumstances. Those standards are outlined in the NFPA’S National Electrical Code (NEC).
Why is it Important to Follow the NEC’s Cable Requirements?
The NEC’S goal is to safeguard persons and property from electrical shocks, fires, toxic smoke, and other hazardous situations.
What is a plenum cable?
The term “Plenum” and “Non-Plenum” simply refers to the outer jacket/cover that protects the cable.
Why is a plenum return system cheaper?
The obvious advantage to a plenum return system is that it is cheaper to install mechanically because of less ductwork that is need. However all the electrical devices will have to be plenum rated. The problem is if you are going with a plenum return system you must be able to guarantee that the build is constructed air tight and that there are no leaks above the ceiling space. So you will have less control over where the air travels. I never design an existing building with a plenum return unless it was already a plenum return.
Will Eng tips check this out?
The Eng-Tips staff will check this out and take appropriate action.
Can you balance a plenum with a RA load?
If you don't really know the RA load, it's hard to size the unit with a plenum. Plenum systems are also almost impossible to balance because what was the lowest RA pressure path to the fan today will not be the same tomorrow after ceiling tiles are removed/altered.
Do RA plenums have a roof load?
With RA plenum, the space does not see the roof load (well most of it), the coil does. With a ducted return, you will need more air flow, thus larger ducts, larger fans, etc..and you will need much more ceiling space since now you will have supply and return ducts crossing at the ceiling.
Is ceiling return a disaster?
I found that ceiling returns are usually a disaster especially if they are a few years old. A large floor ceiling return takes a long time to balance and a very short time to unbalance. I found that most maintenance men who service these types of buildings don't understand the consequences of removing ceiling tiles and not replacing them. The farthest returns from the fan barely move any air so that the area gets very warm.
Is a plenum an automatic?
RA plenums are not an automatic, but any time you can use them. They are great for mold prevention. Designing hard ducted RA systems because you think so and so is really irresponsible. If you did it for me, you would be out the door.
When should you use plenum cable?
Most building codes mandate that only plenum-rated (CMP) cable be used in “plenum spaces” and air ducts.
How do you know if a cable is plenum rated?
In the US, Underwriter’s Laboratories (UL) is the de facto body entrusted with the certification of cables. If the plenum rated cable carries a UL trademark marking and an approval number that can be verified on UL’s website, you’re good to go.
Why is using the right cable important?
If you use non-plenum cable in the plenum ceiling, inspectors won’t give you an occupancy or building permit, and you may be subject to fines.
When can you use non-plenum rated (CMR or CM) cable?
Non-plenum cables can be used anywhere except plenum space and air ducts.
Do you need plenum cable if it’s in conduit?
If you’re using plenum-rated conduit, you don’t need to use plenum-rated cable. This is true even if the conduit is in a plenum space. The most common types of plenum conduit are innerduct (often used for fiber runs) and metal. PVC pipes are generally not plenum-rated.
