Cold Air Return Vents: What Are They, How Many Do You Need? (+furnace)

What is a cold air return vent?

Simply put, a cold air vent returns cool air back into the furnace. No furnace can operate adequately without an adequate return air supply.

If we imagine that a furnace is like a lung. This ‘To breathe’ hot and it ‘To breathe’ cold breeze. Air return vents are necessary for the ‘inhale’ process. they are located on the walls or floor; They low installed On the wall because the density of cold air is high and it gets deposited near the floor.

Installed and open cold air return vents deliver cold air to the furnace; The furnace returns the hot air through the ductwork.

Here’s the deal:

Many questions can arise regarding these cold vents. We’ll tackle several of the most important ones with regards to cold air return vents, including:

  • How many return vents should a house have? Do you need 1 for each room? It depends on the cold air return requirements of the furnace.
  • Can you use a cold air return in the basement? The basement is usually the coldest part of the house. How many vents will you need in the basement?
  • How to install cold air vents in walls? We include installing a cold air return in a 2×4 wall example.
  • What will happen if the cold air return vents are blocked? Blocking the return vents of cold air in the summer is standard practice for some homeowners.

Let’s start with the most popular question:

How many cold return air vents do I need?

a house can be anywhere 1 to 10 gusts of cold air. Here are two ways you can calculate how many return air vents you need:

  1. HVAC Engineer Calculations. HVAC engineers calculate the number of cold air vents needed based on the furnace’s CFM output and square footage. we’ll see how they do it
  2. Rule of thumb calculation. this is a Very simple Anyone can use the method.

Let’s first look at how an engineer would calculate the number of vents. This will give you an idea of ​​what specifications you need to be aware of when doing these calculations. It will also explain how we calculate the simple rule of thumb (Method 2) we will show you next.

Method 1: HVAC Engineer Calculating How Many Return Vents a Home Should Have

The exact number of cold air return vents depends on the CFM output of your furnace.

That’s because we have at least Matches the volume of hot air furnace. The furnace cold air return vent has to supply enough air to the furnace to keep ‘breathing’. If we calculate incorrectly how many return vents to install, the furnace will receive insufficient air flow and will start ‘suffocation’; Operating at less than 100% capacity.

Now, first, we have to find out how much air flow (measured in CFM) Whether your furnace needs to operate at 100% capacity. These are furnace cold air return requirements. You can check the air flow on your furnace’s specification sheet.

If you’ve misplaced it, or can’t get furnace airflow to the furnace itself, you can use this simple rule:

“For 10,000 BTUs of 200 CFM Heating Output”

This means that a 60,000 BTU furnace produces 1,200 cfm of air flow. Similarly, an 80,000 BTU furnace produces 1600 CFM airflow and a 100,000 BTU furnace produces 2,000 CFM airflow. You get the gist.

Here’s what the cold air return vent looks like:

When we find out how many CFMs our furnace outputs, we need to combine that output with the CFM input. Here’s where the cool breeze blows in:

have a specific return vent 16 inches by 20 inches, according to Hunker. This includes the cold return air duct grille. If you consult the duct CFM sizing chart, you can quickly find that a 16×20 inch can handle approximately 1,500 CFM airflow.

most people here make a Mistake. Common sense would dictate that if you have a 1,500 CFM vent and a 1,500 CFM furnace (that’s a 75,000 BTU furnace), you’ll only need 1 cold return air vent. it’s not like that at all.

A typical air return vent size (16×20) can provide airflow with a maximum of 1,500 cfm. To get to that 1,500 cfm, we need a great deal of pressure pushing air through the ducts and through the cold air return grille.

Even with the floor cold return air vent (the place where the pressure is highest due to the cold air going down), we don’t get that kind of pressure. At most, you’ll get anywhere 10% to 30% His; This is 150 CFM to 450 CFM per standard vent. The estimated average is around 300 cfm. There is a large range of CFMs, although a standard size of cold air can go through the return.

if we take 300 CFM Perception, we can quickly figure out how many cold air vents in a 100,000 BTU furnace, for example, are needed. Approximately 2,000 cfm of airflow is required for a 100,000 BTU unit.

7 standard sized vents each with 300 cfm will allow 2,100 cfm of airflow. This means that a 100,000 BTU furnace requires 7 standard sized cold air return vents (with cold air return grills, of course).

Note: Exact calculation is done with the help of manual Air Conditioning Contractors Association. They have charts for specific vent sizes, pressures, and allowed airflow.

You can use these assumptions to calculate the number of air holes needed for your furnace. That’s how an engineer does. However, most people prefer the easy-to-use Rule of Thumb method. Let’s see if you can calculate that number yourself very easily:

Method 2: Simple Rule of Thumb Calculations

As we have seen, figuring out how many air return vents we need to install in a house is not that easy. However, we can simplify that whole thing with this simple rule of thumb:

“install 1 cold air return vent in each room Which is bigger than 100 square feet (10×10)”

It is quite easy to understand. If you have a 7-room house, you need 7 cold air return vents. If you have a 12-room house, you need 12 return vents.

Now, we don’t count small rooms under 100 square feet. On top of that, we need to install 2 cold air return vents for the larger rooms. they are usually rooms 500 sq. ft. Above this square footage.

This method won’t give you the most accurate results but it will give you a fairly good estimate of how much cold air you need to return.

Let’s look at how these vents should be used in a basement:

cold air return to the basement

The basement is usually the coldest air in our house. Basement air has two distinctive characteristics:

  1. the basement air cold.
  2. the basement air Moist.

What we usually don’t want is what we have in the basement – cold and humid air. A perfect solution is to suck that air through the cold air and back into the furnace. This will reduce the humidity of the air in the basement and increase the temperature.

on top of it, basement air is heavy. It is a good thing; The standard size cold air return vent is likely to be able to draw over 300 cfm of airflow towards the furnace.

How many of these basement cold air return vents do we need?

Well, as always, it mainly depends on how big a furnace we have. Still, in many cases, we can estimate the number of cold air return vents needed in a basement by square footage.

you should Install 1 return vent per 200-300 square feet of basement. This is not an exact figure; This is a ballpark guess. For accurate figures, you will need to consult an HVAC specialist.

Example: If you have a 500 square foot basement, you’ll probably need 2 cold air return vents.

Installing Cold Air Return in a 2×4 Wall (Example)

When you figure out how many cold air return vents you need, you’ll need to install them. The most common practice is to install a cold air return in a 2×4 wall; We will use this example to explain how air return vents are installed.

This is an example of how you can install a cold air return between two studs. Here’s how you do it step by step:

  1. Measure the center line. Take a look at your ductwork and measure the center line from the part of the 2×4 wall that is closest to the parallel wall.
  2. Mark the duct. Measure the duct. Knowing how wide the duct is, measure 1/2 of that distance from the center line. Add 1 inch to make it perfect. Example: If you have a 16-inch duct, measure and mark 9-inches from the center line.
  3. Compare the marks with the wall studs. This is to check if the wall studs are sufficiently spaced (you may need to cut them).
  4. Cut the studs.
  5. Install ducts.
  6. Fill in the blank between the two studs.

This is the general principle. You can find more detailed installation instructions here Duct Kings.

Blocking cold air return vents in summer: should you do it?

Should you adjust your cold air return vents with the seasons? Should return vents be open or closed in summer?

Some homeowners already know that you should adjust return vents with the season. The air return grill should adjust to varying room temperatures.

what do you do here cold:

  • block upper vents (You don’t want to draw hot air).
  • open lower vent (You want to draw cold air).

what do you do here Heat:

  • block the lower vent (You don’t want to draw cold air).
  • open upper vent (You don’t want to draw hot air).

This is very important to prevent the return of cold air in summer. If you only use cold air vents for the furnace (not air conditioning), you should close all cold air vents. They don’t do any work in summer.

So why should you do this? What will happen blocking the return of cold air?

Well, it will at least clog the vents accumulated dusthandjob filth, or even potential mold. With open vents and humid and hot summer air, the chances of mold infestation in your vents increase.

Closing the vents (you simply block the return vents of cold air with the grill) can protect your air vents.

Hopefully, this all helps someone who is trying to figure out what cold air return vents are and how to handle them.


Leave a Comment