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How to Check the Temperature of Air Coming Out of Vents in 3 Easy Steps
Keep your cool by measuring air vent temps
Photo: tete_escape / Adobe Stock
Photo: tete_escape / Adobe Stock
SKILL LEVEL
Easy
COMPLETION TIME
10 minutes
COST
Up to $25
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What you'll need:
TOOLS
- Infrared thermostat
- Calculator
Learning how to check the temperature of air coming out of your vents is an easy way to test the effectiveness of your air conditioning unit, which could be a great first step in troubleshooting common HVAC problems. Luckily, the process couldn’t be easier! You’ll only need two tools, and it’ll take just 10 minutes of your time or less. Here’s how to get started.
Prepping to Check the Temperature Coming Out of Vents
It’s important to note your home has supply and return vents. Supply vents are responsible for pushing air from the ductwork into your home. Meanwhile, return vents gather warm, stale air, pulling it through the vents into the ductwork to remove the heat molecules before distributing it again. Because of this, you’ll have two measurements when determining your AC’s effectiveness.
You’ll start by getting an infrared thermostat if you don’t have one on hand. You can buy these through online retailers like Amazon or your local home improvement store. Generally, you can find these for under $20. You’ll also want to have a calculator on hand (you can use the one on your smartphone) to calculate temperature differences.
Angi Tip
If your house isn't cooling down or heating up like it used to, before calling in a pro for air duct maintenance, make sure all your vents and return vents are open and unobstructed.
Locate Vents
You’ll start by locating your supply and return vents. Your supply vents are easy to find since they’re the ones that fan air into your home. If you’re uncertain if a vent is supply or return, you can hold a piece of paper up to it. If the paper blows, it’s a supply vent. If it appears the vent is trying to snag it, it’s a return vent.
Measure Temperatures
Photo: Liudmila / Adobe StockOnce you find a supply and return vent, you can use your infrared thermostat to measure the temperatures of both. Place the thermostat on the supply vent and press the measurement button. It could take a few minutes for the thermostat to calibrate. Once it measures, it’ll tell you the air temperature coming from your ductwork.
Next, locate a return vent and do the same. Measuring this temperature tells you how warm the air that’s being pulled back into your ductwork is.
Calculate the Difference
You’ll want to subtract the temperature reading from the return air from the supply air. Doing this gives you a differential you can use to determine if your AC is effective. Ideally, you want a difference within the 14-degree to 20-degree range. Anything higher than this could indicate a problem with your home’s AC unit.
If you have issues trying to get a measurement or it seems like something is off, a local air duct installer or HVAC pro can help.
What Causes a Large Temperature Differential?
When there’s a large gap in temperature between air blowing from the vents and the air being pulled in by them, there could be several culprits, such as:
Closed Vents
Closing vents in unused rooms may seem practical, but it actually restricts airflow and can create a temperature and humidity imbalance in your ductwork. Remember, your HVAC system’s design is for your whole home, so using it as designed allows for proper airflow.
Dirty Air Filter
Air filters catch dust and other airborne particles to prevent them from blowing through your ductwork and into your lungs. However, when an air filter becomes dirty, it doesn’t have the ability to trap as many particles, resulting in dirty ductwork, air vents, and, worst of all, the air you breathe. Replace your air filters as directed. Usually, this is once every one to three months.
Poor Insulation
Sometimes, a higher differential means your home has insulation issues. If you don’t have them, consider having return air vents installed, as they help balance the humidity and temperature in your home. The cost to add a return air vent runs several hundred dollars.
DIY vs. Hiring a Pro
You can have an HVAC professional visit your home to do the temperature check for you if you don’t have the equipment or time. On average, an initial service call for HVAC repair can cost between $100 and $250, with any repairs adding to the cost. Meanwhile, you can pick up a well-rated infrared thermostat for less than $20 at most retailers. So, if you have time to spare and the ability to do so, it is much more financially feasible to do this on your own.
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