What Temperature Should an Oxalic Acid Vaporizer Run At?
Ask this question in any beekeeping group and someone will tell you, with total confidence, that oxalic acid breaks down above 375°F, so a vaporizer that runs hotter than that is destroying your treatment. It is one of the most repeated claims in American beekeeping. It is also a misreading of a number, and the measurements published over the last year point the other way: within reason, a hotter pan delivers more intact oxalic acid to your bees, not less.
Here is where the number came from, what actually happens inside a vaporizer, and what the data says.
The short version
375°F is the temperature at which dry oxalic acid melts, not the temperature at which it starts to break down. Breakdown begins well below that and is governed by how long the acid sits on hot metal, not by crossing a line. A pan that flashes the charge off in ten seconds destroys less of it than one that slowly cooks it for a minute. Every InstantVap model runs at 445°F, and the Turbo at 500°F, both set at the factory. There is nothing for you to adjust and nothing you need to change about how you treat.
Where the 375°F figure comes from
It traces back to a single, honest sentence. Years ago Randy Oliver, writing at Scientific Beekeeping, looked up oxalic acid in a chemistry reference and reported that it begins to sublime around 315°F and that at 372°F any acid that has not yet sublimed decomposes. Equipment vendors copied those two numbers onto their product pages, the second one got rounded to 375°F, and a reference-book melting point turned into a rule about vaporizers.
Look up what 372°F is and the problem becomes obvious. Anhydrous oxalic acid melts at 189–191°C, which is 372–376°F. Chemistry references print it as “melting point (decomposes)” because oxalic acid happens to fall apart at about the same temperature it melts. That annotation is describing what melting looks like for this particular compound. It is not announcing a threshold below which the acid is safe.
Two things follow, and both are inconvenient for the myth.
Breakdown starts long before 375°F
Oxalic acid vapor decomposes into carbon dioxide and formic acid across roughly 257–347°F, well under the melting point. There are two competing routes, one water-assisted and one not, and the balance between them shifts as temperature climbs. None of this waits for a magic number.
That has an awkward implication for the “keep it under 375°F” advice. When Oliver went back and measured a vaporizer properly with his co-author János Fenyősy, capturing the output in chilled traps and titrating it, they found that most of the acid leaves the pan in the 374–410°F window and that this is precisely where most of the thermal destruction is happening too. They could ignite the exhaust gas coming off the device in that range. A vaporizer carefully held at “safe” 375°F is not avoiding the decomposition zone. It is parked in the middle of it.
It is time on the metal, not the number on the dial
Chemical decomposition is a rate. It goes faster as things get hotter, and the total amount destroyed is that rate multiplied by how long the acid sits there. Both halves matter, and the second half is the one the 375°F rule ignores completely.
A pan at 392°F takes about 65 seconds to clear two grams. At 446°F it takes 25 seconds. At 500°F it takes 10. The cooler pan is gentler per second and still destroys more acid overall, because it holds the charge in the danger zone six times longer. Beekeepers running low-temperature vaporizers have reported charges sitting in the pan for three and four minutes, which is a long time to slowly cook your medicine.
There is a limit in the other direction. Past about 554°F, a thin layer of vapor forms between the melted acid and the metal and insulates the two from each other — the same effect that makes a water droplet skitter around a hot skillet instead of boiling instantly. Residence time creeps back up, formic acid production climbs, and above roughly 932°F you are recovering less than a tenth of what you loaded. Very hot is not better. Fast is better, and there is a window where fast happens.
What the honest numbers look like
| Pan temperature | Time to clear 2 g | Roughly what comes out intact |
|---|---|---|
| 392°F (200°C) | ~65 seconds | 30–35% |
| 446°F (230°C) | ~25 seconds | rising |
| 465–535°F (240–280°C) | 10–20 seconds | 70–75%, the peak |
| Above 554°F (290°C) | climbing again | falling; formic acid rising |
| Above 932°F (500°C) | very fast | under 10% |
The number nobody likes is that no vaporizer delivers everything you put in. Oliver’s independent titrations put the practical ceiling at somewhere around 50–60% of the charge recovered as intact acid, and less than that actually reaching the bees once some condenses on cold woodenware. That is not a knock on any particular device. Vaporizing oxalic acid and decomposing it are the same event happening at the same time, and the best any design can do is get the acid out of the pan before the heat finishes it off.
A word about who did this work. The temperature measurements above come from Randy Oliver, who has no commercial stake in any vaporizer, working together with János Fenyősy, who designs the InstantVap. We sell InstantVaps, so read the second name with that in mind. The work is published openly, the method is described in enough detail to repeat, and Oliver reports his disagreements and his outliers rather than hiding them. It is also not peer-reviewed, which we would rather say plainly than have you find out later. The physical constants — melting points, decomposition products, decomposition temperatures — are from NIST, PubChem and NIOSH and are not in dispute.
So what should you actually do?
If you own an InstantVap: nothing. Every model runs at 445°F, and the Turbo at 500°F. Both are set at the factory and neither is user-adjustable. At 445°F a 2 gram charge is gone in roughly 25 seconds, which is well clear of the slow-cook zone below 428°F where the most acid is destroyed. The Turbo’s 500°F sits inside the range where the most intact acid was measured coming out, and clears the same dose in about ten seconds. That is the whole reason the Turbo exists. Load the dose, run it, and get on with your day.
If you own something else: check whether the manufacturer publishes a temperature and whether anyone has ever titrated the output. Most have not. A vaporizer that takes two or three minutes to clear a charge is telling you something about how much acid is surviving the trip, and if your device has a dial, the manufacturer’s setting is still the one to use — we are not suggesting anyone rewire a vaporizer based on a blog post.
One thing this article is not an argument for: using more acid. Temperature and dose are separate questions. If 2 grams has been knocking your mites down, keep running 2 grams — see how much oxalic acid per hive for the dosing side.
And whatever you run, the honest check is the same one it has always been. Do a mite wash before you treat and another two to three weeks after. Mite counts do not care about internet arguments.
Tools We Use (and Recommend)
- InstantVap oxalic acid vaporizer: cordless, runs on the 18V or 20V tool battery you already own, and the temperature is set at the factory so there is nothing for you to dial in. See the Lite, Compact, Original and Turbo. Lorob Bees is the primary US seller, with stateside phone support and a two-year warranty.
- Oxalic acid: EPA-registered EZ-OX, 97% oxalic acid dihydrate with no sugar carrier to caramelize in the pan.
- Mite monitoring: the Easy-Check mite wash, because the only way to know a treatment worked is to count before and after. How to do a wash.
- Respirator: a full-face respirator with acid-gas cartridges. The EPA label requires one.
Related reading
- How much oxalic acid should you use per hive?
- Does oxalic acid vaporization actually work? What the studies show
- How to use an oxalic acid vaporizer safely
- Which oxalic acid should you use?
Sources
- Oliver, R. & Fenyősy, J., “The How and Why of Oxalic Vaporization, Part 1”, scientificbeekeeping.com, American Bee Journal, 2025
- Oliver, R. & Fenyősy, J., “Part 2”, scientificbeekeeping.com, 2026
- Fenyősy, J., “Milyen hőmérsékleten szublimáljunk” (What temperature should we sublimate at), instantvap.hu, 2026
- Oxalic acid, melting point and thermochemistry, NIST Chemistry WebBook
- Oxalic acid, physical properties and decomposition products, PubChem CID 971
- Oxalic acid pocket guide, NIOSH
- Higgins, J. et al., “Theoretical Study of Thermal Decomposition Mechanisms of Oxalic Acid”, J. Phys. Chem. A 101:2702, 1997
- Oliver, R., “Oxalic Acid: Heat Vaporization and Other Methods” (the earlier article the 375°F figure comes from), scientificbeekeeping.com
- EZ-OX Tablets label, EPA Reg. No. 101743-2, accepted 27 January 2026, US EPA
Happy Beekeeping from the Lorob Bees Team
General beekeeping information, not a substitute for the product label. Always read and follow the label of any product you use in a hive.
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