Hey everyone, it’s Jake here from the bimetal thermometer supply side. I get so many questions from customers, new and returning alike, and one that’s been popping up nonstop lately is: “Is a bimetal thermometer waterproof?” Let me just cut to the chase first—this is such a common concern, especially for people buying these for outdoor use, food processing, HVAC that deals with moisture, even marine applications. And honestly, I see why it’s confusing, because “waterproof” means different things to different brands, right? I’ve had to explain this to so many folks over the years, and I thought I’d break it down in plain talk, no stuffy engineering jargon that makes your eyes glaze over. Bimetal Thermometer
First, let’s start with what a bimetal thermometer actually is, just to set the stage (quick, I promise). Unlike a digital thermometer that uses a sensor and a display, bimetal ones work on two different metal strips bonded together—like, say, steel and copper, or steel and brass—each with a different rate of expansion when heated or cooled. When the temp changes, one strip grows more than the other, making the whole coil (that’s the curved part inside the case) twist, which moves the needle on the face. Super simple, no batteries needed, which is a big plus for a lot of users. Now, all that mechanical movement means there are tiny gaps, seams, and parts inside the case—so when water gets in, what happens? It’s not just the temp reading that gets messed up; it can corrode the metal strips or the coil over time too. That’s the root of the waterproof question, right?
Here’s the thing: not all bimetal thermometers are created equal when it comes to water resistance. I see a lot of suppliers slap “waterproof” on their cheap, entry-level models, and that’s just marketing fluff. For our part, we categorize our thermometers based on IP ratings—you’ve probably seen that term, right? IP stands for Ingress Protection, and it’s an international standard that tells you how well something is sealed against solids (like dust) and liquids (water). The first number is solids, the second is liquids. So if a model has an IP65 rating, that means it’s dust-tight (6) and protected against low-pressure water jets from any direction (5). If it’s IP67, that means it can even handle being submerged in up to 1 meter of water for 30 minutes.
Let me give you real-world examples, because that’s what matters. If you’re buying a bimetal thermometer for something like a home water heater, or a greenhouse that gets splashed with rain, or a food truck that wipes down equipment constantly, an IP65 model will do the job. It’s sealed well enough that splashes, hose-downs, light rain, even being left in a damp outdoor shed overnight won’t hurt it. But if you need it for submerging—like a well sensor, a marine engine that’s partially immersed, or a process in a factory where it’s fully submerged in water during operation—you want at least IP67, maybe even IP68 if it’s going deeper than 1 meter long-term. Our IP68 models are tested to go down to 5 meters, so they’re totally fine for extended submersion.
Wait, but what about the old myth that all bimetal thermometers are naturally waterproof? No way. The entry-level, no-name models we see sometimes—those cheap ones you pick up at a big box store for $10—they usually have a thin plastic case and a tiny O-ring that’s basically just a rubber band. Leave that out in a rainstorm, and water will seep in within an hour. The coil will rust, the needle will get stuck, and the temp reading will be all over the place. We test every single model we sell, though—before it even gets to our warehouse, we do what’s called a water ingress test: we spray the unit with water from every angle for a set time, or submerge it, then check if the inside is dry and the reading is accurate. If it fails, we send it back to the factory no questions asked.
I also get questions about cleaning. Let’s say you have a bimetal thermometer for commercial kitchen use—you need to wash it down with soap and water, right? An IP65 model is totally safe for that. You don’t need to submerge it, just wipe it off, maybe rinse it a little. But don’t blast it with a pressure washer, that’s way higher pressure than what IP65 is rated for. I’ve seen customers do that and blow the seal right out of the case, which then lets water in. For anything over-the-counter, light cleaning is fine, but pressure washing is a no-go unless it’s a heavy-duty IP68 industrial model made specifically for that.
Another big use case: HVAC technicians. A lot of them use bimetal thermometers for duct work and pipe measurements. Those spaces get super humid, sometimes there’s condensation on the pipes. We always recommend our IP54 models for that—IP54 is dust-protected (no heavy dust, just enough to keep light dust out) and protected against splashing water from any direction. That’s perfect for HVAC, because you don’t have to submerge it, just handle it around damp pipes. I had a tech tell me last month that he’d been using our IP54 model for 2 years, wiping it off every week, and it still reads within 0.5 degrees of the actual temp—way better than the cheap one he had before that died after 6 months.
Wait, what about cold environments? A lot of people think waterproofing stops working in cold weather, because rubber seals get brittle. That’s a good point. We use special, cold-resistant O-rings for all our models rated for temps below 0°C (32°F). I’ve had customers use our IP67 thermometer for ice fishing, leaving it out in -20°C (-4°F) all day, and it works fine—no water seepage, no seal cracking. The key here is to make sure the model is rated for both water resistance and the temp range you’re using it in, because if the seal fails due to cold, the waterproofing goes out the window.
I should also clear up a common mix-up: water-resistant vs. waterproof. A lot of suppliers use these terms interchangeably, but they’re not the same. Water-resistant means it can handle some moisture, but not submersion or heavy exposure. Waterproof means it’s sealed enough to handle full submersion or sustained water exposure. That’s why we always make sure our product descriptions are clear—no vague “waterproof” claims. If a model can’t be submerged, we say “water-resistant, suitable for splashes and rain.” If it can go under water, we specify the IP rating and the maximum depth/time.
Let me give you a bad example, just to make it real. A few years back, a customer bought a bimetal thermometer from a random online supplier, said it was waterproof, and used it to check the temp of his fish tank. Within a week, the inside of the case was fogged up, the needle was stuck, and it read 5 degrees lower than actual. He sent it back, and we took it apart—turned out the O-ring was thin, not compressed right when assembled, so even small amounts of water got in. That’s why we source all our parts from reputable manufacturers, not the cheapest knockoff. Our O-rings are made of Buna-N or silicone, both super durable against water, and we test each unit twice before shipping.
Another thing: what about the stem? The metal part that goes into the liquid or the surface you’re measuring. That’s usually stainless steel, right? Which is corrosion-resistant, but not immune to salt water. Wait, hold on—salt water is way harsher than fresh water. If you’re using a bimetal thermometer for marine applications, salt water can corrode the stem over time, even if the case is waterproof. Our marine-grade models have extra-thick 316 stainless steel stems, which resists salt corrosion way better than 304 stainless. That’s a big difference I tell people—don’t just rely on the IP rating for water; if it’s salt water, make sure the metal parts are compatible too. I once had a fishing boat captain use a regular 304 stem model in the ocean, and after 6 months, the stem had a tiny pinhole where salt got through, even though the case was sealed. Switched to our 316 model, and he’s had it for 3 years no problem.
Now, let’s get back to the original question: is a bimetal thermometer waterproof? The short answer is: only if it’s built to be. If it’s an entry-level, no-name model, probably not. If it’s a model with a clear IP rating, matched to your use case, yes—up to the limits of that rating. And here’s a pro tip for buying: don’t just buy whatever’s cheapest, or whatever says “waterproof” in big letters. Think about how you’re going to use it. Are you just dealing with occasional splashes? IP54 or IP65. Are you going to submerge it briefly? IP67. Are you using it in salt water or full submersion? IP68 with 316 stainless steel.
I get it, if you’re not super technical, IP ratings can seem confusing at first, which is why our team is always here to help. We don’t just sell thermometers—we help people pick the right one for their job, so they don’t waste money on something that’ll break after a month. Last week, a small food processing plant contacted us, needing thermometers for their vats of hot sauce that get washed down every night. We recommended our IP65 models, which are perfect for splashes and hose-downs, and they’ve been ordering 50 units a month since. That’s the stuff we love—helping customers get exactly what they need, no guesswork.
At the end of the day, bimetal thermometers are great for all kinds of applications, but their water resistance depends entirely on how they’re built. A good, quality model with the right IP rating and compatible metal parts will handle way more water exposure than a cheap one with a fake “waterproof” claim. If you’re in the market for a bimetal thermometer and you’re worried about water, don’t overthink it—just tell us what you’re using it for, and we’ll point you to the right model. No hard sell, no jargon, just straight answers.
If you’re looking to source bimetal thermometers for your business, or you have questions about which model is right for your specific use case, feel free to reach out to our team for a procurement consultation. We’re here to help you find a solution that works for your needs and your budget.
Temperature Sensor Accessories References:
- International Electrotechnical Commission. (2013). IEC 60529: Degrees of protection provided by enclosures (IP Code). Geneva, Switzerland: Author.
- American Society of Mechanical Engineers. (2020). ASME PTC 19.3: Thermometers and temperature elements. New York, NY: Author.
- Underwriters Laboratories. (2021). UL 873: Standard for safety for temperature indicating instruments. Northbrook, IL: Author.
- NATIONAL SANITATION FOUNDATION. (2022). NSF/ANSI 2: Food equipment materials. Ann Arbor, MI: Author.
Chongqing Haichen Instrument Co., Ltd.
Chongqing Haichen Instrument Co., Ltd. is one of the most professional bimetal thermometer manufacturers and suppliers in China for over 20 years, featured by good service and competitive price. Please rest assured to buy high quality bimetal thermometer for sale here from our factory. For customized service, contact us now.
Address: No.11 Gusheng Road, Caojie Street, Hechuan District, Chongqing City, P.R. China
E-mail: sales@hcsensor.com
WebSite: https://www.hcsensor.com/
