How big should my return air duct be?

Asked By: Maximiliana Nicolucci | Last Updated: 30th June, 2020
Category: home and garden indoor environmental quality
4.5/5 (730 Views . 36 Votes)
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.

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Regarding this, should return duct be larger than supply?

Return ducts are always larger than supply trunks. 3. Supply air and return air is always equal because its a closed loop system to the equipment.

Likewise, how do you run a return air duct? How to Install a Return Air Duct

  1. Locate where you want your return air ducts.
  2. Go into the basement and locate the holes.
  3. Install the square return air duct perpendicular to the joists.
  4. Cut a hole in the bottom of the return duct next to where the furnace is.
  5. Install your HVAC filter into your filter rack.

In this manner, how do you calculate duct size?

How to Determine Duct Size Per Room

  1. Look at the plate on your furnace to figure out how many BTUs it produces.
  2. Multiply that number by the amount of cubic feet of airflow per minute (CFM) your type of furnace produces.
  3. Divide your number by 10.
  4. Calculate the size of your ducts vents by multiplying the length by the width.

How do you increase return air flow?

3 Simple Ways to Improve Your Furnace's Airflow for More Comfort

  1. Unblock and clean your vents. Here's a super easy way to increase air flow.
  2. Change your filters and clean your return grill. A dirty air filter impedes air movement and makes it hard for your furnace to work efficiently.
  3. Seal leaky ductwork. Snap on some goggles and a dust mask, it's time to check out your air ducts.

34 Related Question Answers Found

Can you have too much return air?

While there is no such thing as too much return air for the equipment (actually, there is, and it causes fan cavitation, but very rare), this CAN be an issue for the house. It has the potential to throw off pressures in different areas of the house.

How many CFM is a 3 ton?

The airflow is measured in cubic feet per minute (CFM). 350 to 400 CFM per ton of cooling is required for proper air conditioning system operation. For example, if you are checking a 3 ton system, the air flow required is between 1050 and 1200 CFM.

Do you need a cold air return in every room?

DEAR TIM: Ideally you want to have cold air return registers in every room. If you can't easily install a true cold air duct back to the furnace from each room, you can sometimes fake it. You can install a cold air return register above the door from each room that connects to the hallway.

How do you calculate return air cfm?

Example: You determine a return grille pressure zone required 340 CFM of return. It's a 1600 CFM system with 200 CFM of outside air (200/1600 = 12.5% of outside air). Take 100%-12.5% to find a multiplier of 87.5%. 340 CFM of return air x 87.5% = 298 CFM.

How many CFM is a ton of return?

Air quantities (cfm):
400 cfm per ton of cooling is needed for normal comfort applications, 500 cfm per ton of cooling for heat pump and high sensible heat applications, and 350 cfm per ton of cooling for high latent heat applications.

How do I increase the airflow in a room?

How to Increase Airflow to One Room
  1. Change your air filter – A dirty air filter restricts the flow of air throughout the system by forcing it along an alternate path.
  2. Clear your vents – Supply and return vents should remain open and unencumbered by furniture, drapery, or other large objects.

Do return vents need filters?

Do not put filters in your supply vents. Your AC system should have a proper fitting filter on the return side. By placing a good fitting, high quality filter on the return vent, you will remove particles from the air before they can enter the AC system.

Do return ducts need to be sealed?

Joints, seams and openings on the air handler, furnace or ductwork near the air handler or furnace should be sealed with both fiberglass mesh and mastic due to greater local vibration and flexure. Return systems should be “hard” ducted and sealed with mastic in order to be airtight.

Where should the return vent be located?

Place your cold air return vents on the inside walls of buildings at the lowest point. The return vent pulls cold air from the bottom of the room and returns it to the furnace to be reheated and returned as warm air. Unlike supply vents, return vents do not need to be cased in metal.

Is it OK to cover a return air vent?

Avoid covering your cold air return vents with curtains, drapes or rugs. Always check your air filters and replace them when needed. Clogged air filters can also cause cold air return blockages.

What are vents in walls for?

Ventilation is the deliberate replacement of air in a house with fresh air from outside through, for example, open windows, trickle vents or extractor fans. It is the ease with which air is exchanged between the inside and the outside of the house through the fabric of the building, and it can't be easily altered.

What is return air duct?

The ductwork in your residential forced-air HVAC system is the network of pipes through which heated or cooled air travels. Return air ducts balance airflow in your HVAC system — The primary role of return ducts is to bring air that has been warmed or cooled back to your furnace or air conditioner.

What is the difference between supply and return air?

The biggest difference between supply and return vents is the direction in which the air flows. In a supply vent, the air flows out of the ductwork. In a return vent, the air flows into the ductwork. A second difference is the size of the vents.

How do you know if your air ducts are leaking?

Signs that your Air Ducts May be Leaking
  1. High Utility Bills.
  2. A Dusty Home.
  3. Uneven Heating and Cooling.
  4. Look for Obvious Tears.
  5. Turn your HVAC System on Full Blast.
  6. Check the Duct Joints.
  7. Look for Duct Tape.
  8. Light a Smoke Pencil or Incense.

How do you measure duct size?

How to Measure Ductwork
  1. Measure the top width of the ductwork.
  2. Measure the side height of the ductwork.
  3. Ascertain the size of the ductwork.
  4. Wrap a string or other flexible object completely around the circumference of the ductwork.
  5. Unwrap the string and stretch it out on a flat surface.

Is flex duct any good?

Flexibility. Flex ducts are better for existing trunk-and-branch heating and cooling systems. This is because they're more versatile and flexible. Metal ducts are more rigid due to the nature of steel, making them ideal to build an entire HVAC system.