It’s that time of the year again when temperatures start increasing, and you can’t help but think, “At what temperature should I put my AC”? From experience, we know that it takes a few tries to get that ideal temperature, as you either put it too low or too high – however, what’s the “just right” temperature that your AC should be putting out during warmer months? And how, in general, calculate what temp should AC blow?

Understanding AC Output Temperature

To answer how cold should AC blow, we need to do a little bit of simple math. According to several researches, the best situation for your HVAC system is when the difference between supply and return air temperature is between 16 to 22°F. This is also called evaporator Delta T. However, before we start doing the calculations, let’s talk about what supply and return air are.

Supply and Return Air

Each air conditioning system has two types of vents – return vents and supply vents. Return vents take the warm air from your home and suck it into the AC system, where it gets cooled down and reintroduced to your home through supply vents.

If you’re unsure which are which in your home, there’s a very simple way of checking it – grab a paper towel, and place it near the vent – if the vent tries to suck it in, it means that it’s a return vent.

Why Should You Calculate Evaporator Delta T

Calculating this is very important for keeping your HVAC system in the best condition possible. If the evaporator Delta T is too high, your air conditioner has to work significantly harder to provide the desired results and will, therefore, wear out faster. It also shows whether your air conditioner is working properly or whether it’s time for HVAC maintenance.

How to Calculate Evaporator Delta T

The process and calculations are very simple. First of all, you need to locate which ones are supply vents and which ones are return vents – we already explained how to do it. Once you know, you should:

Go to a return vent and record the temperature of the air being sucked in using a temperature probe.
Go to three supply vents and record the temperature from each of them. Add the results, and divide them by three to get an average temperature.
Subtract the return vent temperature from the average supply vent temperature.

Again, it’s a very simple math. Let’s see how it works in practice.

Example 1. After measuring the temperature from the return and supply vents, you recorded the return air temperature of 80°F. For the supply vents, you’ve done three measurements, getting 61°F, 59°F and 63°F, which gives an average temperature of 61°F. To calculate the evaporator Delta T, you need to:

80°F – 61°F = 19°F

There you have it – your AC’s evaporator Delta T is 19°F – right in the middle of the acceptable results. This means that your AC is working well and not overworking itself.

Example 2. After measuring the return vent temperature, you recorded 89°F. For the supply vents, you recorded three temperatures – 56°F, 59°F, and 61°F, which gives an average of about 59°F. The formula for calculating evaporator Delta T would be:

89°F – 59°F = 30°F

As you can see, in this case, the evaporator Delta T is way too high compared to what it should be. This actually brings us to our next point – what does it mean when the evaporator Delta T falls outside of the acceptable range?

What Does It Mean When the AC Delta T Is Outside the Range

If the temperature differential does not fall within the acceptable range, it means that something is wrong with your air conditioning – what it is can be determined based on whether the difference is too low or too high.

AC Temperature Differential Too Low

If the difference between input and output air is too low (less than 16°F, that means that the air is not being properly cooled. There could be several causes of that, including:

Refrigerant issues – Without enough refrigerant, your HVAC system is not able to absorb enough heat from the input air, leaving it quite warm. Refrigerant restrictions, such as faulty components or clogs, can also cause issues.
Excessive airflow – If there’s too much air being sucked into your AC, your unit probably doesn’t have enough contact time to cool it down properly, which results in warm air being released. Common causes of that include wrongly sized blower fun or improperly designed ductwork.
Component malfunctions – Issues with the compressor, metering device, or evaporator coil can also cause high AC output temperature.
High outdoor temperatures – Sometimes, the cause of high output temperature is not something with the AC itself, but the very high outdoor temperature reducing the AC efficiency.

AC Temperature Differential Too High

If the difference between input and output air is very high, chances are that your AC is actually cooling the air too much – and while many people would consider it to be a blessing, in the long run, it can take a toll on your system.

Again, there could be several reasons for that, but the most common one is reduced airflow. If the air cannot move freely when in contact with the evaporator coil, it might cause it to stay there a little too long, making it significantly cool down, more than it should. Dirty air filters, clogged evaporator coils, and blocked ductwork are the most common causes of reduced airflow.

Restricted airflow can potentially cause the evaporator coil to freeze up – the coil becomes so cold that the condensation on it freezes.

Maintaining Optimal AC Performance

If you want your air conditioner unit to serve you for years to come, you need to take care of it properly – and there are two sides to this. First, you need to maintain it properly. Second, you should consider energy-efficient practices, which can not only help your AC live long but also lower your energy bills.

Regular Maintenance Tips

Wondering what your regular AC maintenance should involve? Here are a few ideas:

Change the air filter regularly – Believe it or not, but a lot of AC issues could actually be prevented by simply replacing the air filter every once in a while – or at least cleaning it, if you don’t want to replace them too often.
Make sure the outdoor condenser unit remains clean – By that, we mean that no debris should be able to enter it. A good way to ensure it is by cleaning about 2 feet around the unit for proper airflow.
Clean condensate drain – While it doesn’t have to be done often, the condensate drain should be cleaned every once in a while.
Schedule regular maintenance – While you can perfom a lot of maintenance tasks youself, scheduling a professional service can help you detect issues before they become a bigger problem and require an expensive repair.

Energy Efficient Considerations

When it comes to energy-conserving tips, here are some things to consider:

Increase the thermostat temperature whenever you’re away from home.
Consider investing in a smart thermostat.
Don’t set the thermostat too low, as big differences between input and output air can consume more energy.
Use ceiling fans when you’re home in addition to the AC, and turn them off when leaving.
Seal any air leaks as soon as they appear.
Make sure that your home is properly insulated – if it’s not, your AC will be working harder to keep up the desired temperature.
Close your blinds or curtains during the hottest parts of the day.
Consider planting trees around your home to shade it.

The Bottom Line

Coming up with the answer to “What temp should my AC be blowing” might require a little bit of math, but at least it’s a very simple equation – and after reading our article, you should be able to do it with no issues.

Keep in mind, however, that while evaporator Delta T is a good base for deciding on the temperature, falling out of range doesn’t necessarily mean that there’s something wrong with your AC. Is it a good reason to have a professional inspect it, however? Very much so.

Scheduling a professional HVAC service can help prevent issues from developing into bigger problems, which often require costly repairs. At Meadow Air, we’ve got you covered if you’re located in the Phoenix area – just give us a call, and our technicians will be with you as quickly as on the same day. Sounds good, doesn’t it?

What Temperature Should My Central AC Be Putting Out?