Tag: recovery

Recovering refrigerant sounds like an easy task at first, especially with digital recovery machines and large hoses at our disposal. Unfortunately, we all know that filling the tanks is more complicated than it seems. 

If you want to recover refrigerant and store it in a tank safely, you’re going to have to do some math. The math isn’t easy, either. You must pay careful attention to the numbers on your tank, understand the density differences between refrigerants at a given temperature, and make sure you only reach 80% capacity. All of those variables fit into an equation, and it can get confusing very quickly.

There is some good news, though. The HVAC School mobile app has a feature that does the math for you. All you have to do is plug in some numbers and select your refrigerant from a drop-down menu, and our calculator will give you the total weight and maximum refrigerant fill.

This article will walk you through the Recovery Tank Fill tool on the HVAC School app. Before we dive straight into the app usage, we’ll cover the safety basics of recovery tanks.


Tank weight and capacity

Tank weight is perhaps the most critical element of safe and effective refrigerant recovery. The keys to evaluating tank weight and capacity are usually stamped at the tank’s top rim or handle, as you can see in the image above. Those values are tare weight (TW) and water capacity (WC).

Tare weight (TW) is the weight of the empty tank. The total weight of the tank is everything inside the tank plus the tare weight. Scales only measure the total weight, so you must remember to include tare weight when you determine your maximum recovery fill.

Water capacity (WC) is the total weight of liquid water that fills the tank to 100% capacity.

As you can see in the image above, the tare weight is 16.6 lbs, and the water capacity is 47.6 lbs. However, that does NOT mean that our maximum tank weight should be 64.2 lbs.


Refrigerants and temperatures

There’s one glaring problem with using water capacity to determine the maximum refrigerant fill. We aren’t filling the tanks with water.

You’ll most likely fill your tank with R-410a or R-22, though all refrigerants are possible. These refrigerants have different densities under variable temperature conditions, so it’s incorrect (and potentially dangerous) to use water to make those calculations.

The other major issue with water capacity is that it represents 100% tank fill. When you recover refrigerant, you don’t want to exceed 80% capacity because hydrostatic pressure can build up and explode the tank if it has nowhere to go.

The tricky thing about achieving 80% capacity is that the refrigerant capacity may fluctuate as the ambient temperature affects its density. Most tanks are rated at 77° F, and AHRI bases their refrigerant fill guidelines on 77° F. However, the backs of our vans can get a lot warmer than 77° throughout the year. We base our calculations on 130° F out of an abundance of caution. 

In short, calculating the maximum tank weight is not as easy as adding the WC to the TW. You also have to factor in the refrigerant’s specific gravity (the density at a given temperature, which you must multiply by the WC). You also have to multiply that product by 0.8 to determine an 80% fill. Then, of course, you add the tare weight to get the maximum number you should see on your scale.

Smash all those together, and you’re working with an equation that looks like this: 

0.8 x WC x SG +TW

Again, WC and TW stand for water capacity and tare weight, respectively. SG represents the refrigerant’s specific gravity under the temperature conditions.


How to use the HVAC School recovery tank fill calculator

We understand that equations make some people’s heads spin. It’s also a bit of a hassle to look up the refrigerant’s density and temperature to find the specific gravity. Luckily, the HVAC School app’s Recovery Tank Fill calculator allows you to plug in a few numbers and not worry about doing math.

With the recovery tank fill calculator, all you need to do is supply the tare weight and water capacity, adjust the maximum temperature to your conditions, and select the type of refrigerant you’re using from a drop-down menu.

If you haven’t installed the app yet, you can download it for free from the iOS App Store on iPhones and the Google Play store on Androids. It’s also a good idea to check if you have the latest version of the app or need to update it.

1. Open the HVAC School app and go to “Tools”

When you open the app, you’ll see the main menu with four options. The “Tools” option is the third one down, and it has a wrench beside it. Select that option from the menu.

2. Scroll through the menu and go to “Recovery Tank Fill”

The HVAC School app has several different calculators built into it, and recovery tank fill is one of them. It’s the last option on the menu. Scroll down to it and select it.

3. Type your corresponding numbers into the first three fields

We only require you to type in three values: tare weight (TW on your tank), water capacity (WC on your tank), and the ambient temperature (default is 130° F). For the sake of an example, I have used the tare weight and water capacity listed on the example tank we used earlier (TW – 16.6 lbs, WC – 47.6 lbs). I have left the temperature at our default value.

4. Select your refrigerant type from the drop-down menu

The default refrigerant listed is R-22, but you can select all sorts of refrigerants by pressing the drop-down menu. If we don’t have your refrigerant listed, you can select the “User Defined” option and input the density yourself. 

The right side of the image above shows the expanded drop-down menu. For the sake of an example, we have selected R-410a.

5. Select “Calculate” to receive the total weight and refrigerant weight

When you finish inputting your information and select the “Calculate” button, you will receive your recovery tank fill result. You will see two different values that are slightly grayed out. 

The top value is the total weight, which is your fill weight plus the tare weight. That’s the highest number you should see on your scale. According to our example, our R-410a recovery tank’s total weight should not exceed 49.97 lbs on a scale.

The lower value is the refrigerant weight. That’s just the fill weight and tells you how much refrigerant you can store in the tank to reach 80% capacity at the temperature you provide. In terms of our example, we can keep up to 33.37 lbs of R-410a in our tank.


A few other things to mention about tanks and recovery

Another thing we should mention about tanks is that they can only handle so much pressure. Like the tare weight and water capacity, the service pressure should also be stamped near the tank’s top. Look at an example below:

If you’re having a difficult time seeing it, the stamp says DOT-4BA400.

The stamp represents the service pressure standard. The Department of Transportation (DOT) regulates and oversees the production and handling of tanks; that’s why the service pressure stamp begins with DOT. You’ll also want to look at the number at the end. The 400, in this case, means that the tank has been designed to withstand a service pressure of 400 PSIG. However, it has been tested to withstand double that: 800 PSIG.

Tanks can explode under excessive pressure, so be sure to avoid high-pressure conditions or extreme temperatures with high-pressure refrigerants. It’s also a good idea to maintain tanks well and discontinue use if there are dents or other signs of damage.


In the end, be safe and sensible with your tanks. Read the tanks and pay attention to them, but don’t get too stressed out by the math involved in tank weight and refrigerant capacity. The HVAC School app can take care of that for you.


To start with I'm going to cut straight to the part that most of you want to know. This is based on calculations I have done personally based on typical Mastercool DOT tanks but feel free to come to your own conclusions based on your own calculations. I prefer to stay on the safe side.

30 lb recovery tank – Fill with no more than 17lbs of R410a or 21 lbs of R22 – total tank weight will be about 35lbs for R410a and 39lbs for R22

50 lb recovery tank – Fill with no more than 32lbs of R410a or 39 lbs of R22 – total tank weight will be about 60lbs for R410a and 67lbs  for R22

Now for the details.

First, you should look for the Tare Weight of the tank. It will be stamped on the top rim of the tank or handle with TW- and then the # like shown below on a common propane tank

Tare weight is simply the empty weight of the tank and must be factored for whenever you are weighing the total weight of the tank.

Next look for a stamp that says WC, this indicates the water capacity of the tank, the total weight in liquid water to fill the tank 100%.

You also need to consider a few more things before you start filling

  1. You cannot fill above 80% with liquid or you risk building up the hydrostatic pressure and exploding the tank (That's a bad day).
  2. Refrigerant does not have the exact same weight to volume ratio as water so you must compensate based on the refrigerant type.
  3. Refrigerant weight to volume ratio changes based on temperature, so to be safe you would calculate the refrigerant volume at the maximum ambient the tank will be exposed to in the back of your van. I figure 130° but there is a caveat….

It has been pointed out to me by Steve Mazzoni that AHRI Guideline K 2015 states that we should use the liquid density at 77° which means you can often fill the tank quite a bit more than what I'm suggesting here.

I am definitely not going to say AHRI is wrong but I still feel it's better to use 130° as the number because it never hurts to be on the safer side. When we fill a tank the tank heats up and when we store a tank it is often very hot in the back of the van and I feel 77° puts us in the danger zone in certain circumstances.

There are a few different ways to do the math. Some use the specific gravity of the refrigerant but I just use cubic foot per pound at 130°Fto calculate just to be certain I am on the safe side of the range.

Water has a liquid density of 62.42 pounds per cubic foot, R22 is 66.17 and R410a 54.70. You can find other refrigerants by looking up their datasheets.

a 30lb(13.6kg) Mastercool 400 PSI(27.57 bar) recovery tank has a water capacity of  26.2 lbs. Divide that by the water density of 62.42 and you get 0.419 cubic ft of space in the tank  (25.2 / 62.42 = 0.419)

If you are filling the tank with R410a you would then multiply the space in the tank (0.419 cubic ft) by the cubic feet per lb of liquid R410a at 130 degrees (54.70) and you get 22.95 lbs to completely fill the tank.

However you cannot completely fill the tank, you must only fill it to 80%, so you multiply the 100% full weight (22.95 lbs) by .80 which gives you 18.36 lbs rounded down to 18 lbs of total internal R410a weight (I go down to 17 just to be extra conservative).

If you then want to calculate the total weight of the tank + the refrigerant inside the tank you would need to add the tare weight. For this Mastercool 30lb tank, the TW = 17.99lbs for a total tank weight of 34.99 lbs

So in order to know for sure that you are not overfilling a tank, you must have the following –

  • A scale under the tank at all times
  • The tare weight of the tank
  • The water capacity of the tank
  • Either the liquid volume per pound or the specific gravity of the refrigerant you are removing

For R22 and 410a I came up with some quick (conservative) cheat numbers to simplify the math a bit (again, this is at 130°).

For R410a just multiply the WC by .65 to find a safe fill weight, for R22 multiply WC by .82

You would still need to add in the tare weight to calculate total tank weight and if you are using a different refrigerant you need to start the math from scratch.

When in doubt, err on the safe side… and for heaven's sake… use a scale and read the information on your tank.

— Bryan

P.S. – Tech Daniel Green made a really cool spreadsheet calculator to get max fill for various refrigerants HERE




Most techs know that you shouldn't fill a recovery tank more than 80% with liquid based. Many know that the WC rating stands for “water capacity” and that you need to adjust for the density of the actual refrigerant rather than just using 80% of WC.

I hope most of you know that the TW marking stands for “Tare Weight” and tells you empty weight of the tank.

But do you know the service pressure your tank is designed for? 

Because R-410a is one of the higher pressure refrigerants in common use today most modern recovery tanks are built to handle R-410a pressures. The standard they are built to is called DOT-4BA400 and will be stamped on the tank collar. The DOT (department of transportation) is the governing body in the USA that has the rule making and enforcement authority on tanks, tank handling and tank shipment.

Tanks listed as DOT-4BA400 are designed for a service pressure of 400 PSIG with a test pressure of 800 PSIG. This means that R410a is safe in the tank at a tank temperature of up to 116°F which equates to 400 PSIG for typical use but that the tank is tested not to fail until over 800 PSIG. 

If a tank has any physical signs of damage it is to be taken out of service and tanks must be re-certified via hydro-static test and visual inspection forma certified facility every 5-years.

— Bryan



If you don't use a scale every time you add or remove refrigerant I would suggest you begin doing so immediately if not sooner. Weighing in while charging is fairly obvious and is useful so you can keep track of what you are using and how much to charge a customer.

When you have a system that has just been repaired it is a good practice to weigh in the charge to factory specs plus or minus adjustments for the line-set if it is a split system. This is all pretty evident, but why would you weigh a charge out? There are many reasons but one good example is whenever you have a failed compressor, weighing out the charge can help indicate whether possible undercharge or overcharge may have contributed to the failure. With any significant failure on an older system, weighing out the refrigerant can indicate whether a leak is likely. When possible on major failures you could even weigh out the refrigerant at the time of diagnosis just to ensure that a leak or a compensatory overcharge may be at play.

Using refrigerant recovery as a means to find possible cause or even diagnose leaks on non-functional systems is next level diagnosis in my book. Use your scale.

Weigh in when adding charge

Weigh out as a diagnostic aid and to ensure you don't overfill your tank.

— Bryan

This topic came up because I was testing out the new MR45 digital recovery machine and that machine goes off by itself when it hits a 20″ Hg vacuum. This is a cool feature but it is good to know when that level of vacuum is overkill and when it's not enough according to EPA requirements.

Why would you need to recover into a vacuum you might ask? Well, so long as you are above a PERFECT VACUUM (and you always do) there are still molecules of refrigerant in a system even at 0 pisg (14.7 PSIA at sea level). In low pressure systems like centrifugal  chillers the entire system charge can often be in a vacuum when the system is off, this means that recovery on these systems means you START below 0 PSIG and go down from there. 

First off let's pretty much assume that none of you are using recovery machines OLDER than 1993 so really only look at the right side of the chart above.

If you are working on an air conditioning system with UNDER 200 lbs you are safe taking your recovery to 0 or atmospheric pressure. If the system you are working on has OVER 200 lbs of refrigerant or if you are working on a medium pressure or low pressure system you will need to pull the system into a vacuum.

The EPA does make an exception if the system has a know leak and pulling into a vacuum will result in contamination of the recovered refrigerant. Here is an excert from the EPA final rule summary from 1995 (still in force)

Also let me clarify that 25mm hg absolute is another way of saying 25 torr or 25,000 microns, it's just a finer scale and it goes from 760 torr (760,000 microns) down as the vacuum gets deeper whereas inches of mercury (“hg) goes up as the vacuum gets deeper.

— Bryan

We get a lot of questions about both evacuation procedure and TXVs so last week we produced videos on both topics including –

  • Before and after testing of piston vs. TXV
  • Using the Bluvac Measurequick app
  • Use of core remover tools for evacuation
  • flowing nitrogen process
  • creating an external equalizer port and much more

If you haven't hit subscribe on our YouTube channel yet would you mind taking the time to do it today? it would be greatly appreciated. You can do that HERE 

P.S. – I will be at the Rectorseal booth 2545 in Chicago at the AHR conference on January 23rd at 2PM demonstrating the new Pro-Fit flaring tool. If you are at AHR come by and see me and sign up for a chance to win a free Pro-fit!

Adolfo Wurts from Arbiter Incorporated, designer of the UEI WRS line of Bluetooth scales comes on the podcast and we talk about scales including.

  • When to pull a scale off of the truck
  • Opportunities you may be missing to be a better diagnositician
  • Features of a good scale
  • All about the industry leading WRS110 and WRS220 from UEI

You can find these scales for sale at TruTech Tools by going HERE

And don't forget to use the coupon code “getschooled” for an 8% discount at Trutechtools.com

Find out more about the WRS line by visiting the UEI website 

In this episode of the podcast Jeremy Arling from the EPA comes on and answers some common questions about the new rule changes that affect recovery, leak repair, record keeping and evacuation on HVAC and refrigeration systems. You can find the complete rule update HERE
s well as Jeremy's presentation slides HERE as well as a quick sheet for technicians HERE

If you want an app to help you keep record of recovered refrigerant I would suggest looking at the R-Log app HERE

If you have an iPhone subscribe to the podcast HERE and if you have an Android phone subscribe HERE

Recovery is the removal of refrigerant from a system to either store and send in for recycling or to reintroduce back into the same system.

Here are some top tips –

  • Make sure your tank is empty and evacuated to 300 microns if you plan to return the refrigerant back into the system.
  • Never mix refrigerants.
  • Purge hoses before recovery.
  • Use a flare line drier on the inlet of the machine to increase the life of the machine and to filter and dry the refrigerant. These must be replaced regularly.
  • When recovering into a tank using the standard method invert the tank and pump into the vapor port on the tank.
  • Remove Schrader cores before recovery for faster recovery and a cooler tank.
  • Use larger gauge hoses with no core depressors for faster recovery.
  • Check Recovery machine inlet screens regularly and clean or replace as needed.
  • Some machines require oil to be run through the machine from time to time. Read manufacturer specifications.
  • If your tank becomes hot you can either place it in a bucket of water or run water over the tank.
  • Do not leave refrigerant in your machine during storage. If your machine has a purge mode make sure to purge the refrigerant out of the condenser (see manufacturers specs on your machine).
  • Most HVAC systems holding under 200 lbs of refrigerant are not required to be pulled into a vacuum during recovery. See this chart from the EPA.
  • Weigh the refrigerant out and do not fill the tank to more than 80% of the REFRIGERANT capacity, not just the water capacity.

We cover all of this and more in this video –

— Bryan

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