What is Superheat, and Why Does it Matter?

Have you ever heard the term superheat? Unless you study thermodynamics, or you’ve been reading our website, or talking to our technicians, then probably not. Don’t feel alone though. It’s sad to admit, but many heating and air conditioning companies don’t even know what superheat is, why it’s important, or even how to check it. This is another, of many, reasons why AirPro is the most trusted heating and air conditioning company in Eastern Arkansas!

What is Superheat?

Superheat is the only truly accurate way to measure the refrigerant (freon) levels in your air conditioning system.

Technically speaking, superheat is the temperature of a gas or vapor, above the boiling point for that liquid.

Let’s take water, for example. Under normal conditions (at sea level, etc) water will boil at about 212 degrees Fahrenheit. When we heat water to this temperature, it results in a physical change of state in which the water turns from a liquid into a gas (steam). If we continue to heat this gas — the steam — it will cause it to go above water’s boiling point of 212 degrees. This increase in temperature, above 212 degrees, would be the superheat. In other words, if we increased the temperature from 212 to 215 degrees, we would have superheated the steam 3 degrees.

How does Superheat Apply to Air Conditioning?

Given the above example, where water boils at 212 degrees, you may have wondered what this has to do with air conditioning. One of the key things to making your air conditioner work is the liquid refrigerant inside of it, often called freon. This refrigerant, unlike water, has an extremely low boiling point. Where water boils and turns into a vapor (gas), at 212 degrees, most refrigerants boil at a frigid negative 40 degrees Fahrenheit, or colder!

Inside of your air conditioning system, liquid refrigerant is pumped through copper tubes into a piece of equipment known as an evaporator coil. At the same time, a fan passes hot air from inside of your house through this same evaporator coil. Since the air from your house is much hotter than the refrigerant’s boiling point of around -40 degrees Fahrenheit, as it passes through the evaporator coil, the refrigerant starts to boil and is converted into a gas. As this happens, the gas “absorbs” the latent heat from the air, resulting in the air being cooled down before being delivered back into your home.

The path of refrigerant in your air conditioning system

Why is Superheat Important to Me, the Customer?

As a customer, the main thing you should know is that superheat is the only truly accurate way to measure the refrigerant (freon) levels in your air conditioning system.

Having the precise amount of refrigeration that your air conditioning unit requires is crucial. If you don’t have enough, your system can’t function correctly. If you have too much, there is a risk of liquid freon being transported back to the compressor, resulting in permanent damage!

By measuring the superheat of your air conditioner’s refrigerant, a skilled technician can ensure that your system has the precise amount of refrigerant needed to operate correctly.

Let AirPro Inspect and Service Your Air Conditioner Today

Letting AirPro check your superheat and service your air conditioner is a great way to ensure that it’s running safely, and at peak efficiency. Don’t wait until it’s too late — schedule to have your air conditioner inspected and serviced today!

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13 Comments on “What is Superheat, and Why Does it Matter?”

  • Robby Sclafani January 16th, 2013 7:23 am

    I work for Hill Phoenix in CA, I came across your superheat write up and wanted to say thank you. So many young techs have no idea what it is, and I have shared this with a lot of techs.

    Thank you guys
    Great work!!
    Robby Sclafani
    Journeyman technician

  • Poelee Polly September 19th, 2013 7:31 am

    Thank u so much. I gained a lot of knowledge.
    Thank u.

  • Kadav October 1st, 2013 4:54 am

    Well explained in simple way

  • vic January 19th, 2014 10:33 am

    Thanks , its always good to do alittle refreshers course on superheat. Ive been in the refrigeration business for years

  • Raul CastaƱeda March 28th, 2014 8:11 am

    Thanks for the refresher. Only a good company would explain that to a customer

  • evaporatormanufacturer April 10th, 2014 6:04 am

    I read your blog.. its amazing. you having very good content. very helpful to all.

  • Mohamed Rashid May 1st, 2014 2:25 am

    I have been trying to adjust the expansion valve to bring a control to liquid flowing back to the compressor but there is no change by adjusting the expansion valve in both side.

    could you please give some

  • admin May 1st, 2014 5:29 am

    Since you are using a TXV (expansion valve) you will be measuring Sub Cooling not super heat, unless your dealing with a Freezer.

    To properly answer your question I would need more info.
    Refrigerant type?
    How are you adjusting? (small turns)

  • LD June 19th, 2014 7:31 pm

    Very simple, yet very informative explanation, thank you.

  • John August 11th, 2014 7:57 am

    Isn’t “subcooling” a better judge of freon quantity levels in systems having txv valves due to the variable office size of the txv valve regulating superheat to an extend?

    I understand this is a very simplistic and effective way of explaining the general process of cooling, it is the integrity of the integrity of the conclusions I feel there should be further clarifications. I am a begginer Hvac learner from a customers side. Thanks.

  • Emerson October 14th, 2014 6:10 pm

    My unit is a 1 ton misubishi Muz-FE12NA1.In heating mode my suction pressure is 520 PSI line temp is188.6 F and condenser temp 137.3 F ,superheat is 51.3 F,note this is on test mode constant for 30 minutes.my unit is precharged for 25 feet of lineset however my total lineset is only 10 feet.In spec’s for every 5 feet add 1.62 oz of R410A,in my case I should remove 4.86 oz…15 feet too much,am I correct in saying this,thus lowering suction pressure,inside temp was 66.2 F and outside temp was 63.5 F.Unit works fine but im scared of suction pressure being to high,……looking forward for your reply.

  • admin October 15th, 2014 6:25 am

    Your suction pressure is way to high for heat mode and cooling mode. Remove refrigerant to stated charge then check again. This Mini Split should have a TXV (expansion valve) as the metering device. You will need to check subcooling not superheat.

    Check the subcooling in the AC mode only, connect a temp meter to liquid line side and hook gauges to system. I am not sure what the manufacture recommended Subcooling is, but usually you can go about 13 degrees and be safe. I recommend checking their website to get the exact number.

    Why is the pressure so high, improper charge causes improper metering.

  • admin October 15th, 2014 6:27 am

    subcooling is done with TXV metering devices, If the system has a fixed orfice you will use superheat…. Also all refrigeration equipment measures subcooling with TXV valves. That is a different animal tho….

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