Can a supply plenum be too big?

Single plenums should not exceed 24 ft in length. Double plenums should not exceed 48 ft in total length.

Can a return air 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 important is plenum size?


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 do I know what size plenum I need?

Quote from the video:
Quote from Youtube video: Rate that is in cubic feet per minute and V is the velocity. That is cubic that is the feet per minute and a is the area of the plenum box that is square feet.

Can you make a cold air return smaller?

Modify Cold Air Duct Sizes

Whenever possible, expand your existing ducts vertically by cutting out pieces of wallboard and installing a new cover and air filter to fit. If it’s not possible to expand vertically, expand horizontally as much as possible to fit the existing ductwork.

How big should HVAC return be?

Generally, if you are using a Duct Sizing Chart or calculator (such as the Trane Ductulator), size the re- turn ducts for 0.05 inches/100 ft (0.40 Pa/m) based on the expected airflow through that return air duct. The total sum of air from all the returns should be at least 250 CFM/nominal ton (33 l/s per-kW).

What size return do I need for a 3 ton AC unit?

Recommended airflow is typically 400 cfm per ton of AC. A 3 ton AC would therefore need 1200 cfm airflow. With only 423 sq in of return your air velocity through the grille would be just over 400 ft/min, a good number as far as noise is concerned.

Should supply and return ducts be the same size?

OK, I have heard from multiple HVAC contractors that a general rule of thumb in a single trunk return, single trunk supply duct system, the RETURN:SUPPLY ratio should be 1:1 or greater. In other words, the return should always be at least as large as the supply.

What happens if return duct 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.

What size plenum do I need for a 5 ton AC unit?

For 5-ton HVAC systems, an additional 6″ plenum on the bottom or the side of the furnace is super important.

How do I make a return air plenum?

Quote from the video:
Quote from Youtube video: Probably 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.

How do you attach plenum to air handler?

Quote from the video:
Quote from Youtube video: And 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.

Is it OK to put furniture in front of a return vent?

Home Inspection Insider explains that an air return vent needs 6-12 inches of space in front of it, and recommends that you do not put large, bulky furniture like couches and bookshelves in front of an air return vent.

Can you use round duct 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.

How do you size a return grille?

To calculate 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.

What size should the return air grill be for a 5 ton AC unit?

x 25-in. Return grilles are the best choice for a five-ton system in order to deliver 2,000 cfm back to the blower without causing the return to hemorrhage.

How do you measure a return air vent grille?

Quote from the video:
Quote from Youtube video: Always measure the width first followed by the height to make sure you buy the correct grill.

Should HVAC returns 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.

Why do I have two air returns?

Having two air return vents allows you to seasonally control which air is returning to the HVAC system. In older homes, this may not be an option. The theory is that in the Summer cooling season, you want to be circulating warmer air back through the HVAC system to be cooled.

How far away should a return vent be from a supply vent?

Return vent on wall adjacent to wall of supply vent. The return vent would be approximately five feet away from the supply vent.