Heating & Cooling

How Far Should the Thermostat Be From the Air Return

Return Vent Lg

When designing your HVAC system, there are certain things you cannot afford to get wrong. Among them includes the location of the thermostat. So, where exactly should you place it, especially concerning the return air vent’s position? 

Thermostat placement does not affect its ability to function, though some HVAC specialists prefer to install it near an air return. The air in the return duct is at room temperature, so there’s no concern with your thermostat making a false detection and altering its performance.

A thermostat controls temperature changes to manage the operation of the air conditioner. However, for the best results, you must position it strategically. But which zones are ideal and not ideal? Read on for this and more insights.  

What Are the Ideal Thermostat Locations?

The fundamental intention of temperature regulation is to make the house comfortable. Hence, place the thermostat where heat control is necessary. Otherwise, placing it in the wrong areas will be a waste of electricity and money, of course. 

Ideally, you should install your home’s thermostat on one of the interior walls of the house. The best position is at the center of the house. Here, it will detect the actual temperature changes without external influence. Also, it should be where you and your loved ones are fond of staying. 

Furthermore, avoid situating it close to plumbing ducts or air vents. The direct supply of air will alter its functioning. 

Should the Thermostat Be Close to the Air Return?

There is no harm in mounting the thermostat near the air return duct. Typically, the air in the air return duct is at room temperature. It has already been regulated to meet the desired temperature standards as per the air conditioner’s settings. 

Hence, air from the air return duct has no significant impact on the thermostat. Nonetheless, you must be keen on where you place the return duct. Ensure that it is situated close to the ceiling or the floor. The space should be sufficient to separate the vent from the moving air. 

Also, ideally, purpose not to have the thermostat close to any moving air. Hence, if you can avoid placing it near the return, the better. There’s no actual harm, though, in having the two components close. 

Where To Avoid Placing the Thermostat?

Adjusting Nest Thermostat Lg

It’s essential to avoid placing the thermostat in areas that are likely to interrupt its functioning. Here are the zones to avoid:

1. In Direct Sunlight

Placing the thermostat near sunlight will give false readings. The device detects the temperature of the surroundings to determine how the air conditioner or heater should respond. When the thermostat is facing direct sunlight, it will interpret that the room is warm. 

Consequently, it will unnecessarily prompt the air conditioner to regulate the temperatures. 

Also, it may cause the heater to remain off when it is supposed to be on. Thus, placing the thermostat near direct sunlight will bring confusion in temperature regulation.

2. Near Air Vents

Avoid placing the thermostat near air vents. The temperature of the air coming in via the vents is different from that of the room. Thus, the thermostat will make a ghost reading. Consequently, your temperature regulation will be costly for no value. 

3. Close to the Kitchen

The kitchen will get warm faster than any other part of the house. Thus, it should be the last place to position a thermostat. When placed close to the kitchen, it will always read that the house is warmer than reality. 

Also, when someone is cooking, the thermostat will prompt the air conditioner to unnecessarily cool other parts of the room. 

4. In the Hallway

You spend relatively less time in the hallway than in other parts of your house. Also, neither of your loved ones occupy the hallway for an extensive duration. Thus, avoid placing the thermostat in such places where there is limited traffic. 

The thermostat will give false readings if situated in such an area. The airflow in the hallway is also not ideal due to air restriction in a narrow space. Instead, consider placing it in rooms where you and your loved ones are most fond of staying often. 

5. Near the Windows and Doors 

Avoid areas where there is a waft, such as windows and doors. The thermostat will read that the spaces are cooler than the actual temperature. 

6. On Exterior Walls

Do not place the thermostat on the exterior walls. Such walls are likely to be influenced by radiant heat, especially during the summer. Also, exterior walls tend to be colder in the winter than the actual temperature in the house. 

Thus, under such conditions, the HVAC will keep going on and off unnecessarily. 

7. Close to Electronic Appliances 

According to the U.S. Department of Energy, it’s advisable to avoid mounting the thermostat close to electronic devices. They emit heat and thus can immensely balloon your air conditioning budget, especially in summer. 

What Are Air Vents?

Vents are typically the channels via which air enters and leaves your HVAC system. If you have already installed your HVAC, you will have two types of vents. They include: 

Supply Vents

They supply air from the air conditioner or heater to the rooms. You can easily identify the supply ducts as they are the only vents that blow out air to the rooms. Air flowing from the supply vent is air-conditioned. 

Return Vents

The return vent draws air from the rooms and carries it to the heater or air conditioner systems. Since they need to draw relatively more air, return vents are larger than supply vents. You can thus easily identify them. Also, no air comes from them, unlike the supply vents characterized by a gush of air. 

Their main role is to remove the excess air pressure after the HVAC delivers air to a room. 

How Many Return Vents Do I Need?

In conventional homes, you will find single air return vents. The vent in such homes is centrally placed. Nonetheless, such air return vents are not as effective as where there are many of them. Retrofitting in such a house is imperative in boosting the HVAC’s performance. 

In most contemporarily constructed homes, you will find an air return vent in almost every room. Ideally, a home should have at least two to three large air return vents. 

So what do you do if your house has a single air return duct? It’s pretty simple. Ensure that your rooms are well aerated. Open the doors or windows in the rooms regularly for aeration. Also, it’s imperative to clear the vents from any barriers, such as upholstery or furniture. 

In addition, when doing duct repairs, this is the ideal time to install more return vents. More air return ducts will, without a doubt, improve the performance of the A.C. 

What Should the Temperature Difference Be Between Supply and Return?

There is no ideal temperature for an HVAC system. Nonetheless, for the difference between supply and return air, a range of 16 to 22 degrees Fahrenheit is the best. This difference is called the evaporator coil’s Delta T.

Thus, when the difference between supply and return is in this range, the system functions efficiently. If it is away from the range, the HVAC is not in top condition. 

Delta T also gives the state of the air conditioner’s evaporator coil. The component controls the functioning of the cooling property of the HVAC. So how do you determine the Delta T of the system? 

Here are the steps:

  1. Find a temperature probe – The probe will be handy in determining the temperature of the supply and return air vents. 
  1. Take the temperature of the return vent – Using the temperature probe, measure the return vent’s temperature and record. 
  1. Take the temperature of the supply vent – Next, measure the temperature of the supply vent using the temperature probe and record. Remember to take the temperatures of three supply vents. 
  1. Find the supply vent’s average temperatures – Calculate the average temperature of the supply air vent. Add the three temperatures and divide by three to obtain the average. 
  1. Calculate Delta T – Find Delta T by subtracting the return air duct temperature from the supply duct’s average temperature. 

What If the Delta T Is Higher Than Intended? 

Your Delta T may be higher than the preferred value. If this is so, there is a problem with the HVAC. When you find a higher difference, the airflow across the coil is too low. 

It could be due to several factors such as:  

  • Your evaporator or air filter could be dirty. Cleaning it can be handy in rectifying the issue. 
  • The air duct could not be big enough to support the air conditioner. 
  • Also, it could be that the fan is not moving at the appropriate speed.

You can fix this challenge via these solutions: 

  • You can opt to replace the air filters. If you note that they often clog with dirt, consider replacing them regularly. 
  • Also, you can engage a professional to fix the speed of the blower motor. The technician will also repair the coil and diagnose other challenges that could be affecting the HVAC. 

What If the Delta T is Lower Than Intended?

You may find out that your Delta T is below 16 degrees Fahrenheit. It means that the temperature difference between the supply and return vent is not sufficient. 

There are several probable causes of a low Delta T:

  • The refrigerant levels could be lower than normal
  • The reverse valves could be faulty and leaking
  • The air return ducts could be leaking
  • Lastly, the compressor valves could be loosely attached. 

The remedy to fixing a lower Delta T than the recommended range is to involve a technician. Do not attempt to fix the components. Most likely, you’ll struggle to diagnose the faults in the valves and ducts. 

Should You Put a Filter In a Return Vent?

Air Filter Lg

Like any other system, the HVAC will function optimally under clean conditions. Therefore, it is imperative to keep the return vent free from dust or debris. The A.C.’s evaporator coils are prone to get clogged by dust and debris. Similarly, the return vent is also likely to face the same issue. 

Conducting routine maintenance is good. Nonetheless, it is better to prevent the issue than fixing it when it has already happened. Thus, the installation of a filter on the air return vent is essential. 

All air conditioners will have a filter to clean the air. However, adding a filter on the return vent is important in further reinforcing the air filtration process. That way, the performance and operation life of the HVAC will improve more. 

What Happens If There Is Not Enough Return Air?

If there is insufficient return air, the HVAC will not cool efficiently. Such a scenario is likely when there is only one return air duct. Thus, you need to rectify this challenge by installing enough air return ducts. 

Here are the ideal properties of well-working air return ducts: 

  • They must bring back sufficient air to the HVAC system – The fundamental function of air return ducts is to return air to the HVAC system. It helps create a balanced airflow by ensuring sufficient air is cleaned and returned to the room. 
  • They need to be optimally sized – The size of the HVAC matters a lot. They must be big enough to carry sufficient air back to the HVAC system. When the available air returns are not big enough, supplementing via the addition of additional ducts is essential. 
  • They must be well situated – When the air returns are obstructed, they will not function efficiently. Therefore, the ideal location is in hallways or under stairwells where there is no obstruction. When placing them, the aim should be to enable the maximum return of air to the HVAC system. 
  • They must be in good condition – It is important to keep the return ducts in top condition. Also, you must fix them tightly and make sure they are well sealed to prevent contaminants from getting into the HVAC. 

Note that pollutants that enter via the return duct will be recycled to the home indoor air system. Even when you have installed filters in the air return, they can still be clogged by contaminants. Thus, it’s best to ensure that the pollutants do not, in any way, enter the system. 

What Causes Low Air Return? 

Several factors can inhibit air return. They include:

1. Poor Design of the Air Return Duct

When the air return duct is poorly designed, it will deliver low air return. For example, the air return duct could be made in a way that inhibits efficient airflow. For instance, the air return duct should not be elongated a lot or twisted. Such a duct will be poor in air return. 

2. Presence of Duct Leakage

Most of the duct systems in U.S. homes have leakages. According to the U.S. Department of Energy, a duct system is likely to have up to 50% leakage. Such a challenge is enough to cause low air return. 

3. Lack of Sufficient Air Return Ducts

An air conditioning system is supposed to operate in a closed-loop. The air that the HVAC supplies via the supply duct should be circulated and returned to the system. When there are insufficient air return ducts, there will be low air return. 

4. Poorly Sized Air Return Duct

The air return duct should neither be too big nor extremely small. If it is big, it will create low air pressure, thus limiting the air return. On the other hand, if it is too small, the air return will be too low. 

5. Clogged Filters

When the air return filters are clogged, expect to experience low air return. The ultimate result of clogging will be stuffy air. 

6. Faulty Thermostat

Your thermostat could be the cause of low air return. It could be dysfunctional, probably due to a mechanical problem. Also, it could be poorly placed. 

7. Poorly Working Fan

The condition of the blower motor could be the fundamental cause of low air return. The fun is responsible for controlling the air that enters the air return duct. If it is clogged or dysfunctional, the air return ducts will be ineffective. 

8. Outdated HVAC Design

The design of your HVAC may be the fundamental cause of low air return. The design is important and must be in line with the size of the room. If you installed your HVAC long ago, it could be time you consider renovating it to improve performance. 

What Are the Benefits of Properly Functioning Return Air Vents?

Maintaining the return air vents in top condition comes with a load of upsides. Here are some of the benefits: 

To Maintain Optimum Air Pressure

The HVAC system operates as a closed-loop unit where the air pressure difference is very important. The return air vents maintain the pressure difference. They ensure that there is an equilibrium of air pressure. Thus air is not concentrated on one end of the system. 

Without the return air vents, there would be an accumulation of air from the HVAC. Its air regulation would further be hampered as it would only be directing air in one direction. 

To Trap Debris

An air conditioner system is not only limited to the regulation of the temperatures. It is also useful in trapping the particulate matter in the house via the return air vents. The device is thus crucial in air quality regulation. 

To Save On Energy

The return air vent facilitates the operation of the temperature regulation system. Thus, energy is only applied when necessary, thus saving on costs. In the absence of the return air vents, overheating of the room would be commonplace. 

Can You Shut the Return Air Vents if the Room is Too Cold? 

You should not shut the return air vents to control the temperature of the room. This is irrespective of whether the room is too hot or too cold. Doing so would alter the air pressure difference. 

An air conditioner does not have sensors to detect that the return air vents are closed or dysfunctional. Hence, shutting the return air vents would be pointless, especially regarding regulating the temperatures. 

The air conditioner continues to send the same type of air depending on the indication of the thermostat. Also, shutting this vent may prompt a leak. Therefore, let the system operate without altering the functioning of the return vent. 

Also, avoid placing furniture close to the return air vents. It will block the duct in addition to destroying the furniture. 


In a nutshell, it is important to position a thermostat in the right places for efficient functioning. Avoid placing it close to direct draft areas such as near the doors or windows. Instead, position it where it is uninterrupted. 

There is also no harm in placing the thermostat near the air return vent. The air in this vent is usually at room temperature. It, therefore, cannot cause a false reading on the device. 

Lastly, it would be best if you kept the return air vent in top condition. It is a prerequisite for the efficient functioning of the HVAC system. It aids in the trapping of debris and other foreign materials that can hamper the seamless functioning of the HVAC. Additionally, it is fundamental in the maintenance of air pressure. 

Therefore, as you use your thermostat, put the above-discussed tips into consideration. You will undoubtedly be rewarded with a top-notch performance. 



Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.