7 Best HVAC Leak Sealants To Plug The Gaps

Josh Mitchell

Written By

Josh Mitchell

Expert Reviewed By

Holly Curell

Last Updated On

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HVAC leak sealants are my go-to solution whenever I suspect a leak in a system.

Any sealant worth its salt will fix the issue and save you quite a bit of money on costly repairs.

That said, I've encountered numerous products over the years, but only a select few stand out.

In this article, I’ll recommend 7 different HVAC leak sealants that I've personally found to be very effective in plugging those pesky untraceable gaps.

Quick Glance - My Recommendations

BlueDevil Products Red Angel 49496 A/C Stop...

BlueDevil A/C Stop Leak

Editor's Choice

InterDynamics Car Air Conditioner, Certified...

InterDynamics A/C Pro Refrigerant Leak Stop Kit

Recommended Seal Kit for Cars

Rectorseal 45316 AC Freeze PRO Nano Leak...

Rectorseal 45316

Easy To Use Option for Central ACs

7 Best Leak Sealants HVAC Professionals Use

1 - BlueDevil 49496 Sealant

4.7

Overall Score


Sealant Performance

4.75

Current Progress
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Ease-of-Use

4.25

Current Progress
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Value for Money

5.0

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Best For: Central HVAC systems, vehicles
Refrigerant Compatibility: R-12 or R-134a

Pros
  • Providing durable and long-lasting solutions
  • Works with R-12 and R-134a refrigerants
  • Non-clogging formula
  • Excellent price-to-quality ratio
CONS
  • It is not ideal for larger leaks
  • Requires an injector
  • Not compatible with modern-day refrigerants

BlueDevil's Red Angel sealant has been my go-to over the years because, back in the day, you had to use an injector for this kind of work.

However, I still use it because it's reliable, and old habits die hard.

In a nutshell, I've used Red Angel to deal with more than a handful of leaks in central air conditioning systems and a vehicle's AC system that used the old CFC R12 refrigerant.

On a more "technical" side, the chemical weld Red Angel offers is quite impressive. While I wouldn't call it "permanent," I've consistently seen over four years of reliable function.

For instance, back in 2021, I was called to seal the malfunctioning evaporator coil on this early-90s system.

After a few months, the owners called me back to say that the system had been working better than ever.

Now, unlike Nu Calgon's Direct-Inject sealant, which is more of a broad-spectrum solution, this one is reserved for very minute leaks, so keep that in mind.

Also, don’t stress about the compatibility.

While R-12 is quite outdated and isn’t being made anymore, a lot of the older, high-quality stuff (manufactured before the Montreal Protocol) still relies on it, which is why this one comes in handy quite a bit.

R-134a is the most common refrigerant currently used, so you'll likely be able to fix most existing leaks with this tool in your toolbox.

The only real drawback I see is that you need an injector. It is not as simple to use as Leak Saver, but the price difference you get with Red Angel is massive.


2 - InterDynamics 325PL A/C Pro Kit

4.6

Overall Score


Sealant Performance

4.5

Current Progress
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Ease-of-Use

5.0

Current Progress
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Value for Money

4.25

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Best For: Vehicles
Refrigerant Compatibility: R-134a

Pros
  • Seals leaks in various vehicles
  • Very easy to use
  • Works for both metal and rubber components
  • Compatible with most automotive refrigerants
CONS
  • R-134a refrigerant only

InterDynamics's Leak-Stop kit is one of the best sealants I've seen used for automotive purposes.

It effectively seals metal and rubber components, which is vital for a vehicle-specific AC leak sealant.

I'm not a mechanic, but as far as I know, that's the only thing used in automotive HVAC systems, so you're good on this front.

Now, its compatibility with just R-134a can be tricky.

While most cars, vans, or trucks rely on the R-134a refrigerant, some newer models use R-1234YF, so you should check before you use it in your car.

However, if you need R-134a, you’ll get a reliable seal that’ll last several years.

The main advantage of the A/C Pro Kit, in my opinion, is the recharge hose. It makes using it so simple and effortless.

You just connect the hose, open the valve, turn the can around for the sealant to come out, and you’re done.

The whole process takes a minute, and there’s no spilling at all. You can’t do that with BlueDevil's Red Angel.


3 - Rectorseal 45316

Safest Option for Central ACs

4.5

Overall Score


Sealant Performance

4.75

Current Progress
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Ease-of-Use

4.5

Current Progress
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Value for Money

4.25

Current Progress
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Best For: Central HVAC systems
Refrigerant Compatibility: All refrigerants

Pros
  • Polymer-free formula that doesn’t clog the system
  • Compatible with a wide range of refrigerants
  • Quick and easy application process
CONS
  • A bit on the pricier side

Rectorseal 45316 is your safest bet if you don't know which type of refrigerant your air conditioning system uses.

It is compatible with all refrigerants, just like Leak Saver, mainly due to its polymer-free composition, so it won't randomly gel up or clog your AC unit or heat pump system.

Now, I don't know about the "nano-technology-based formula" and how much of that is just marketing lingo.

Still, I've never had any mishaps with it, so I would wholeheartedly recommend it.

One of the biggest advantages for me is the Rectorseal's ability to work without the need for system evacuation or major downtime.

Basically, you can just thread the female end of your sealant onto the low-side port of your AC and finish the job in several minutes.

That said, there may be better choices for larger, more visible leaks, where a product like Nu Calgon EasySeal can help you gain a few months before you replace the part.

As for drawbacks, I really can’t name any other than the fact that it is on the pricier side when compared to your average sealant.


4 - LEAK SAVER LS-05 Direct Inject

4.5

Overall Score


Sealant Performance

4.25

Current Progress
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Ease-of-Use

5.0

Current Progress
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Value for Money

4.25

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Best For: HVAC systems, vehicles
Refrigerant Compatibility: All refrigerants (except ammonia)

Pros
  • Excellent price-to-quality ratio
  • Super easy to use thanks to the direct-inject method
  • Across-the-board compatibility
CONS
  • Often only available in multi-packs

Leak Saver has consistently proven to be one of the top leak sealants on the market. Any HVAC technician, myself included, will recommend this product, and for a good reason.

Leak Saver is very versatile and very effective when it comes to sealing small leaks across a myriad of systems.

It works with central HVAC systems up to 60,000 BTU, so you could even find its use in a residential setting.

Even if you wanted to use it with ductless mini-splits, like 15,000 BTU, you could do it.

What’s more impressive is that Leak Saver is universally compatible with all refrigerants except ammonia, just like Rectorseal 45316.

However, what truly separates the Leak Saver from the bunch is its ease of use and package quality.

The direct injection method is a game changer.

It allows everyone to do this job, compared to traditional methods that might require additional tools or steps, like Red Angel.

Also, don’t be spooked by the price tag. What you often see is a 3-for-1 price, which also makes this one of the most budget-friendly options out there.


5 - RED TEK ProSeal12

4.4

Overall Score


Sealant Performance

4.0

Current Progress
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Ease-of-Use

4.25

Current Progress
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Value for Money

5.0

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Best For: Vehicles
Refrigerant Compatibility: R134a, R12, R502

Pros
  • Best used for automotive HVAC systems
  • Compatible with R-12 refrigerant
  • Very affordable compared to competition
CONS
  • Not the best refrigerant compatibility

RED TEK ProSeal12 is known for its reliable performance, to say the least. I’ve seen instances where ProSeal12 has worked for more than five years without any touch-ups.

Granted, I have yet to see it used in many residential HVAC systems (although you can use it).

However, this sealant is wildly popular with folks riding heavy-duty machinery, like tractors or combines, or those with a passion for older cars.

Why? Most of those machines rely on the R-12 refrigerant, which is no longer made because of its horrid environmental impact.

When there’s no new refrigerant, there’s also no need for the appropriate sealant, so getting your hands on products like ProSeal12 and Blue Devil is pretty much the only way to go about fixing tractor AC leaks nowadays.

Also, the sealant can seal leaks in metal and rubber components, so you don’t have to worry about that.

I actually used this one to repair leaks in the evaporator behind my ‘89 Chevy C1500, and now I have cool air in my truck.


6 - Nu Calgon 4050-08

4.3

Overall Score


Sealant Performance

4.25

Current Progress
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Ease-of-Use

4.5

Current Progress
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Value for Money

4.0

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Best For: HVAC systems
Refrigerant Compatibility: Works with all refrigerants and oils

Pros
  • Suitable for a wide range of HVAC systems and refrigerants, including commercial systems
  • Beginner-friendly and super easy to use
  • It can handle larger leaks, unlike many other sealants
CONS
  • A bit on the pricier side

I like Nu Calgon 4050-08 for two reasons. First, it is compatible with all refrigerants, unlike the RED TEK ProSeal12.

Secondly, it can handle larger seals and postpone expensive repairs and replacements for the time being.

It is suitable for both residential and commercial applications, as it can handle up to 10 tons or 120,000 BTUs, so whenever I’m called to handle a leak in a commercial setting — this is what I bring.

Actually, there's a third thing I like: the no-pump-down feature for R-410A units.

It simplifies the sealing process and saves both time and effort compared to some more traditional sealants that require system evacuation.

In other words, it's tailor-made for people who lack experience with this sort of work.


7 - Red Devil 0841DX F-Seal 181

4.1

Overall Score


Sealant Performance

4.25

Current Progress
Current Progress
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Ease-of-Use

3.75

Current Progress
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Value for Money

4.25

Current Progress
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Best For: HVAC ductwork (metal and flexible)

Pros
  • Provides a long-lasting, durable seal
  • Suitable for both indoor and outdoor applications
  • Adheres to both metal and flexible ducts
CONS
  • Can get a bit messy

Just in case you were looking for ductwork or an HVAC pipe sealant, here’s one I often use - the Red Devil 0841DX F-Seal 18. It is great for ductwork maintenance, fixing leaks, and installation.

You can use it for joints and for both rigid and flexible ducts. In other words, you can’t go wrong.

Its fiber-reinforced formula offers excellent sealing capabilities, lasting upwards of 10-15 years without the need for a re-do.

It is resistant to mold, temperature fluctuations, weather, and every other environmental factor you can imagine.

As a result, the F-Seal 181 is effective on both indoor and outdoor ductwork, which made it my go-to product for numerous projects.

Pair this one up with some great HVAC mastic tape, and you have everything you need for a leaky ductwork repair or installation.

Just so we’re clear — this is not intended for refrigerant leak repairs. You can’t use this to seal a leaky coil and you can’t inject this into an HVAC unit. This is for ductwork only.


Best HVAC Leak Sealants Compared

Preview

Name

Rating

Metric

Metric

Price

BlueDevil Products Red Angel 49496 A/C Stop...

BlueDevil A/C Stop Leak

4.7

Value

Value

InterDynamics Car Air Conditioner, Certified...

InterDynamics 325PL

4.6

Value

Value

Rectorseal 45316 AC Freeze PRO Nano Leak...

Rectorseal 45316

4.5

Value

Value

Leak Saver Direct Inject AC Leak Sealer...

LEAK SAVER LS-05

4.5

Value

Value

RED TEK ProSeal12 A/C Seal Treatment (4 oz....

RED TEK ProSeal12

4.4

Value

Value

Nu Calgon 4050-08 EasySeal Direct Inject...

Nu Calgon 4050-08

4.3

Value

Value

Red Devil 0841DX F-Seal 181 Fiber Reinforced...

Red Devil 0841DX F-Seal 181

4.1

Value

Value


How to Choose a Quality HVAC Sealant

When it comes to sealing leaks, here are some of the questions I consider when choosing the right sealant.

What Types of Leaks Am I Sealing?

The term HVAC sealant is quite broad, so buying the wrong thing is easy. So, use this as your guide.

Injectable sealants (the ones we’re discussing, like BlueDevil or Leak Saver) are designed for small, hard-to-find internal refrigerant leaks within the refrigerant lines or coils.

While made for interior work, you can’t use these bad boys for larger or visible cracks.

Basically, if you can spot the crack, call your local HVAC guy and have him repair your air conditioner.

Now, suppose your ductwork is leaky, or you're installing ductwork and want to prevent future leaks from happening over time.

In that case, you have to use mastic sealants or HVAC tape. 

Please do not use regular duct tape. That thing will fall off in three weeks, and you’ll have to do it all over again.

TL;DR: Different types of leaks and systems require different types of sealants.

What’s The Application Method?

Using injectable AC leak sealer is straightforward, and you can get by on your own if you read the instruction manual.

I’ll give you a detailed rundown in a second, but for now, let’s cover the basics.

Typically, the sealant is injected into the air conditioning system's refrigerant line, where it circulates through the system to locate and fix leaks from the inside.

How does it do that? In simple terms, the chemicals inside these things are set to “go off” if the conditions aren’t “ideal.”

Basically, the pressure, moisture, and even oxygen presence are different around the microcrack you’re trying to gap.

When the sealant reaches those spots, it reacts to those differences, creates a polymer barrier, and seals the crack.

Now, external sealants like mastic HVAC sealant tape or an HVAC sealant putty are either spread over or taped around the ductwork connection joints.

TL;DR: Injectable AC leak sealants are easy to use and are injected directly into the AC system. HVAC sealants tapes, on the other hand, are put externally. 

Effectiveness (Obviously)

This one’s important, so don’t skip this part.

Choosing the correct HVAC sealant is crucial because using an incompatible product can lead to system failure or decreased efficiency.

Example: A sealant designed for R-22 refrigerant might not seal effectively in a system using R-410A. Best-case scenario — you don't fix the issue.
However, I have seen homeowners ultimately damaging their systems. Different refrigerants operate under varying pressures and have different chemical compositions, potentially leading to thousands in repair costs.

You also have to mind the material the sealant is used for.

For instance, a sealant effective on metal may not stick properly to plastic components.

Metal surfaces can handle sealants that undergo a certain degree of thermal expansion and contraction, while plastic components may require a sealant with more flexibility.

I'm just painting you a picture and simplifying things, but using a "for metal" sealant with plastic could damage the internals.

The sealant might not flex with the plastic during temperature changes, leading to cracks or gaps.

TL;DR: You must choose the right sealant for your HVAC system. Make sure that it is compatible with your refrigerant.

Always Consider Safety

Most of these products are toxic, flammable, and not even remotely environmentally friendly, so you must be careful around them.

Wear gloves and a face mask. 

That's the least you can do. Also, don't dump these wherever. Dispose of them appropriately. It takes minutes.

TL;DR: Sealants are toxic chemicals hence it is of paramount importance to observe safety measures.


Leak Sealants 101 – Application Guide

As promised, here’s a step-by-step guide on how to use the best HVAC leak sealant.

I’ve broken it down into simple steps so you can follow along even if it's your first time.

To prep, get your HVAC system up and running in cooling mode, and make sure the compressor is working by using a multimeter.

Set the multimeter to continuity and check the terminals (the one with three differently colored wires labeled C, R, and S).

If the multimeter shows sub-30 ohm readings, you’re good to go.

ACLAB Note:

If the prep sounds too difficult, it’s time to stop here and call an HVAC expert.

Before you inject the sealant, make sure the valves (there are two, low- and high-side) on the manifold are closed. If all that’s clear, do the following:

  1. 1
    Thread the female end of your sealant onto the low-side service port of your system. It’s that one “open” port at the bottom with nothing attached to it.
  2. 2
    Connect the high-side hose (the red one) to the high-side port (the one above the low-side port) on your HVAC system. You need to do this to make sure the sealant goes into the correct circuit.
  3. 3
    After you’ve done all that, quickly open and close the high-side manifold valve to let any trapped air out of the hoses.
  4. 4
    Connect the center hose (the yellow one) to the male fitting of your injectable leak sealant.
  5. 5
    Finally, open the high-side manifold valve for a brief moment to let the sealant flow into the system. This will be over in an instant, and you'll know it's done when you see the tube is clear.

In the end, just give it a minute to let everything settle down.

Then, carefully remove the sealant tube and dispose of it properly.

Also, keep your system running for at least an hour afterward to ensure sealant flows throughout the system.

How We Review & Rank Our Product List

At Air Conditioner Lab, our team follows a similar process when evaluating all products reviews before formulating our final lists for readers.

We begin by gathering data sources directly from brands, e-commerce platforms, online retailers and press releases.

These are then added to a master file we use to compare features specifications from all HVAC products. You can access this HVAC Product Sheet Here.

Next, we narrow down all the products on the market by evaluating user reviews, ratings and feedback from a wide variety of online and in-person sources.

Our team then discusses and co-ordinates our first hand experiences using these products, as well as gather independent opinions and feedback through Youtube and customer reviews.


FAQs

Do HVAC Leak Sealers Always Work?

HVAC sealers work in most cases if they’re used properly. If they don’t work, it is because you’re trying to plug a bigger leak or solve an issue that requires a hands-on approach.

Is Refrigerant Leak Sealer A Permanent Fix?

Refrigerant leak sealers are not a permanent fix. However, if you're only fixing small leaks, they can last several years.

How Long Does It Take For AC Sealer To Work?

Most AC leak sealers begin to work within the first 24 hours.

How Long Does Home AC Sealant Last?

On average, you can expect your leak sealant to last anywhere from 1 to 5 years, depending on the leak severity.

So, Which HVAC Sealant Is The Right Choice for You?

As you can see, there are more than a handful of HVAC sealants that can help fix refrigerant leaks and improve the performance of your HVAC system.

You can use all of these without prior experience by following the manufacturer's instructions.

They are a reliable solution for an affordable price.

That said, safety is paramount. If you're ever unsure, then I recommend calling an HVAC technician.

My #1 Recommendation
BlueDevil A/C Stop Leak

  • Providing durable and long-lasting solutions
  • Works with R-12 and R-134a refrigerants
  • Non-clogging formula
  • Excellent price-to-quality ratio
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Josh Mitchell

Founder

Josh Mitchell
My name is Josh and I am obsessed with home appliances. From portable AC units to heaters and air purifiers, I enjoy testing, learning and using these devices to improve the air quality inside my family home.

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Midea U Shaped Window Air Conditioner

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