7 Best HVAC Leak Sealants To Plug The Gaps (2024)

Written By

Josh Mitchell

Expert Reviewed By

Holly Curell

Last Updated On

June 21, 2024

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While R-12 is quite outdated and isn’t being made anymore, a lot of the older, high-quality stuff (manufactured before the Montreal Protocol) still relies on it, which is why this one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

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.

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.

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.

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.

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.

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.

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