I bought a new -ometer. It measures temperature - but it measures over 75,000 discrete points of temperature, and displays them on a screen!
Yes, I now own an HTI HT-19 thermal imager! And it is every bit as awesome as I hoped it would be.
It’s a $450 bit of Chinesium - so the obvious question is, “Is it any good?” And, “Is it useful?” The answers are “Yes” and “Yes.” The next answer is “Not if a friend has one” - to the question, “Should you buy one?”
If you’re reading my blog, you probably know what a thermal imager is. They’re a device that takes pictures of temperature, not of visual light - and they’re incredibly fun to play with. They’re also incredibly useful for a wide range of troubleshooting around the house and property, and if you’re doing anything that involves heat or electricity, you would probably benefit from occasional access to one. They’re also incredibly useful for doing things like “finding out where your house leaks energy” by finding the hot or cold sections (depending on the season).
But, historically, they’ve been very expensive, and so they have been fairly uncommon outside some pretty expensive and high end versions used in industry. But, as of late, the price of them has been coming down - either the cell phone modules, or even the full standalone handheld imagers. While I was beating my head against the wall troubleshooting some solar string issues, I knew very well that an imager would help find my problems - and so, after some research, I bought one. And it pointed out my problem within the first half hour of having it!
Why Not Cell Phone Attachments?
Lately, the common sort of thermal imager are the gizmos that attach to a cell phone as an external camera, with an App(TM) that Does Stuff.
And there’s a very simple reason that I didn’t buy one of those: I don’t trust them to last long term.
It’s not the device, so much. They’ll probably last. It’s that I don’t trust the connectors on phones to remain stable, or the software ecosystem to remain stable. How many of you have gotten rid of some 30 pin iPod accessory or another over the years as the connections moved away from them? How many of you have discovered that some game or app you liked won’t run after an OS update? I’m just not OK with that for an expensive imaging tool, so I’d rather get a standalone one that will work regardless of what happens to OSes. If I can’t read files off a USB mass storage device, I’ve got bigger problems - and even if I can’t do that, this thing will work in purely standalone mode.
The HTI HT-19
The HT-19 is a reasonably modern thermal imager, with a thermal resolution of 320x240, and a visual camera as well that supports a “fusion” image containing both a visual and thermal representation of what you’re looking at. This can be useful to help distinguish exactly what’s hot, though I’ve found the resolution generally sufficient to not have to bother with this very often.
No, HTI, this is not a “high-definition color screen.” It’s 320x200. It’s exceedingly low resolution, though at least it’s color. Box features are standard Chinesium and worth ignoring.
They do support multiple different types in this box - the “gun type” and the “camcorder type.” I’m not sure why you’d use the other one, but the box covers both, should you be interested in what one of their other models looks like.
Inside the box, the imager comes with a handy enough carrying case. It’s got some loops for an included shoulder strap, and for reasons I don’t quite grasp, uses zippers for corners - despite not having a zipper pull anywhere on the case. They don’t seem to come open, so… it’s fine, I suppose. Just weird.
Inside the case, of course, is the imager! It looks roughly like any other trigger-based point-and-shoot sort of thing you might find. However, if you’re bored, it also looks an awful lot like most people’s impressions of a radar gun. So you might slow traffic down nicely while also managing to get thermal images of people’s cars! Are you interested in their radiator performance? Now you can find out while slowing them down in the process.
All the sensors are hidden behind the flip up cover.
And, finally, sensors! The big one on the left (bottom) is the thermal imager, and the small round opening on the right (top) is the camera for visual processing. Anyone who’s sighted in a rifle will immediately see the problem with this approach - and you’d be right. There is an offset in the overlay of the two images, and while one can set the offset, it’s not automatic based on range. However, it mostly works.
This is clearly inspired by the Death Star main laser.
The back has the screen (super low resolution), and the keys, well enough labeled. No, I’ve not removed my screen protector. I don’t see a good reason to remove those from tools like this, and it works just fine with it on.
And, excitingly, an accessible, replaceable battery! Seriously, how cool is this? It’s a boring standard 18650, though the wiring is a bit funky (you’ll need to do some soldering to tabs to replace the battery), but it’s accessible. To access it, you slide the grip down away from the trigger, and it will unlock. You can also just pry on it and squeeze things out, but there’s no reason to do that unless you’ve no idea about how to release it because the manual doesn’t say anything about it. Anyway, I’m very, very happy to see this - it means that this tool is likely to last, because replacing a dead 18650 (even with a bit of custom wiring) just isn’t a big deal.
Turn it on, and you get the UI! Top left is the center point temperature, top right is the current emissivity setting and battery. In the bottom, min and max temps (my blanket here is clearly fairly uniform in temperature), the time, and on the right, the thermal scale for reference. On bright, the screen is visible even outside (though you may want to shade it a bit with a hand).
Finally, on the side, a rubber cover guards the micro USB port. I don’t like this port. It’s a bit too recessed for most normal USB cables - and while the unit comes with one that fits, a lot of your random micro USB cables won’t make good contact. Keep the cable that it comes with around. The problem is that the top end of the port from this angle is too close to the raised wall. Add a fraction more width and it wouldn’t be a problem in the slightest.
Power it on, set it up, and you’re away, thermally imaging all the things!
And that’s it for the overview. No, I didn’t tear it all the way apart. First, I bought it as a tool to use, not tear down. Second, I’m not actually sure how to get it further apart. There are a few screws I’ve seen, but the path is far from clear, and it’s not cheap enough I’m going to pry on it a ton trying to find which will pop open for me. Sorry!
Menu Options and Configuration Settings
The on-device menu is fairly straightforward and there just aren’t many settings to change. Hit the Menu button and navigate your way around!
“Image registration” allows you to adjust the alignment of the optical and thermal image. The two sensors are offset by a bit, so if you want the images to line up, there’s a bit of tweaking to do. If you’ve ever had to deal with bore/sight offset in a rifle, you’ll know exactly what the problem is. You can set it up for long range (10+’) if you’re mostly doing long range work, or you can set it up to overlap closer if you’re doing things like PCB inspection. Unfortunately, there’s no auto-ranging option that will detect range based on the camera focus or something.
“Images” and “Videos” allow you to view and edit previously recorded images and videos.
Color palette allows you to select what colors you want to use to reflect heat. I’ll cover the options later, but I find “iron” useful, and “white” is also of some use. The others, I just don’t find terribly useful.
The emissivity menu allows you to (surprise!) set the emissivity of the surfaces you’re measuring. This is a complex topic, and there are entire courses on properly compensating for it, but just know that polished surfaces reflect heat as well as light. If you’re trying to measure the temperature of a shiny metal object, you’re going to measure the background reflecting it far more than the surface. The emissivity theoretically lets you compensate for this, though if you’re aware of how heat reflects, it’s perhaps somewhat less useful. You’re the one interpreting results - so if you find that a spot in your window is a few hundred degrees, you’re probably measuring the sun.
Finally, you can adjust a few settings - set your preferred units, set the date/time, and you’re probably done in here.
To take a picture, squeeze the trigger. Then press Menu if you want to save it, or Select if not. Pretty simple. They come out as standard looking JPG images - but they’re special, and I’ll cover that more when I explain the software.
In normal “point at hot things” use, the up arrow will toggle the status bar (min/max temp, time) along the bottom. The left/right arrows adjust the “optical/thermal” blend in quarter steps - so 0%, 25%, 50%, 75%, 100%. Whatever shows on the screen is what the image will appear when you load the image.
You can select from a range of thermal palettes on this unit - and, with the software, can adjust them after-the-fact in post. I’ll be honest, only two of them make the slightest sense to me - Iron and Whitehot. But for completeness:
The default option is “Spectra” - which seems to mostly append white to the red end of a rainbow and use that for coloring. I can’t say it’s particularly intuitive, though it does have the advantage of “using all the colors.” It’s pretty, I just don’t find it useful.
The “Iron” representation seems to correlate mostly to the colors of a bar of iron as you heat it with some blue modifications at the low end - starting at black, glowing blue, then into the reds, yellows, and finally white hot. I like this option, and it’s my default option, because it means something of value to me. I’ve spent long enough with various things I’ve heated in flames to be familiar with the red/yellow/white spectrum, and the addition of the blues to the bottom end of it makes sense to me.
This spectrum… is an option. It gets somewhat “brighter” as things get hotter, but I really can’t make much sense of it. Sorry. You probably shouldn’t use this one.
This spectrum is very simple: It smashes everything to greyscale and the brighter it is, the hotter it is. Quite useful, really!
If you invert the previous spectrum, you get this one. I have nothing to say about it beyond, “This exists as an option.”
All the ads for the imager talk about the software that comes with it and gives you additional analysis options. What you can’t find anywhere is an actual download link to the software - because the software doesn’t come from the web. It comes on the device, lurking in the USB storage region from which you download the files. I’ve run the various forms of it through VirusTotal, and it seems clean, though for anything of this nature, I tend to run it in a virtual machine. Win10 is fine for that, Win11 will probably complain about your VM, but… whatever. Or it seems to run just fine in wine, though you’ll need the 32-bit version of wine installed, which… you may as well use a VM, I hate polluting my filesystem with multiarch stuff these days.
The jpeg files coming off the imager are “special,” and I’ve not fully worked out the details. They’re an entirely valid JPG image of the current settings as shown on the screen. But they are also a blob containing the IR raw data, and the visual image - and you can then manipulate these with the provided software package.
Load an image into the software, and you’ll see the thumbnail you saved in the lower right corner… and then the image in a potentially different thermal palette, and a bunch of options on the right. Fiddle with them, and the image on the left changes to match your settings - so this file isn’t just the image in the lower right. It’s the whole data collection!
You can set the “Fusion” slider anywhere you want, not just the 0/25/50/75/100% points that the handheld unit allows - so you can set things where you need to highlight things. And you can change the palette to whatever you want. Here, I’ve got the “Iron” palette (which I prefer) overlayed with the image to really highlight that hot set in the #2 panel on my north array.
But you can do more. You can draw lines that mark the hottest and coldest point, put markers that show temperature in new areas, draw circles, scribbles, etc. These will show you the hot and cold points within that region. The “Undo” button and “Trash” button do what you’d expect, removing either the last annotation or all of them. I’ve never played with thermal imaging analysis software before, but this does everything I’d expect and a bit more in the deal. The “save” button exports a screenshot of the current status.
We’re still working with low enough resolution images here, but they’re useful. Am I going to take a photo I can blow up to wall size with this unit? No. Can I tell what’s hot, well enough to figure out if there are problems? Absolutely. And I’m simply not too concerned with ultra-resolution for an extra zero on the price.
Unfortunately, all this functionality is only present with the images. The video file seems to be a straight up video file of the screen with none of the neat additional data for later analysis.
Want a copy of the software? It’s on my Github along with some sample images to mess with.
What to Use a Thermal Imager For
By this point, if you’re still reading, you probably have a mental list of “Oh, I could use this for that!” things in which a thermal imager would be very useful. If you’ve got any projects in which understanding, visually, “which bits are hotter,” then something like this would be useful. Resolution varies, but I’ll argue that you don’t need a particularly high resolution to get useful data.
If you’re in the business or hobby of solar panels, buy one. “Hidden faults” in solar have a way of showing up, blindingly brightly, in thermal imaging. That’s why I picked this up - I was running out of ideas for solar faults. They literally glowed brightly when I got the imager.
This is a junction box.
This is a junction box with a corroded internal connection that’s still working perfectly, but “a problem waiting to happen”:
And we’re not going to talk about Bruno. I mean, that totally corroded box covered in another post.
You’re hunting a weird overheating issue on your vehicle. Is it a thermostat? Is it a water pump? Could it be the radiator?
Being able to see the thermal pattern of your cooling system opens up a lot of insights. If you’ve got a partly clogged radiator, it will be exceedingly obvious! A properly working radiator has a smooth gradient across it. A clogged one? Not so much.
Do you have a hot wheel bearing? A weirdly hot differential? Point an imager at your various parts and see!
Electrical uses are an extension of solar, but you can point it at various things and see if they’re “abnormally hot” from some distance. The offset is a bit wrong here from being closer than I have things set for, but my PV breakers are running “warmer than the rest of the panel.” Except, the whole panel is pretty hot, it’s 90F outside, and PV is producing well. I have no concerns about this. Were the breakers up past 150F, I’d have the front off looking for loose connections. Faults are high resistance. High resistance is hot. You can identify these at a distance with even a cheap thermal imager!
Actually, no, you shouldn’t use it for this. You’re probably hunting yourself.
If you have some ferrets that like to sleep well out of the way in dark spots, as they reasonably should, they can be hard to find. A thermal imager will absolutely let you figure out where the ball of ferrets is curled up! You can, similarly, find a child hiding in a dark room. A few of us are probably going to get together some moonless night and play “Thermal Imager Flashlight Tag” or something.
Home Efficiency Improvement
Want to know how your insulation is doing? Do you have regions that aren’t insulated? One of these will certainly show it in a hurry! I took it to a friends place, and we discovered that a section of their living room ceiling was at 90F on a hot, sunny evening. The rest of the ceiling was at a far more sane 75F. Guess which section doesn’t have insulation?
If you want to seal a house to improve efficiency, one of these is a God’s Eye View into the thermal condition of a house. In the winter, go outside and look for “hot areas” or look inside for “cold areas.” In the summer, stand inside and look for “hot areas” or go outside and look for “cold areas.” You will find weird places leaking you had no idea were a thing - and that’s great! If the difference is minor, maybe it’s not worth bothering. But when you discover that some corner of the attic has no insulation, or that outlets are leaking, or that something else is leaking, you can fix it. With the price of energy lately, that’s time well spent.
They also can be very useful for poking and prodding your HVAC - if one of your vents is blowing significantly warmer or cooler than the rest (not in terms of volume, but in terms of absolute temperature), you might go find the missing insulation. I’m not too worried about our air conditioner out here - it’s working fine. But I did flip a few vents to blow on the wall, in an attempt to make a bit more use of the thermal mass. Vents blowing away from the wall don’t cool the drywall in the slightest.
Should You Buy One?
No. At least, probably not. Think of them like a boat.
You don’t need a personal thermal imager. You need access to a thermal imager in your social circle. If you’re “that guy” who has the neat tools, then, yes, you should buy one and be prepared to loan it out regularly. But I don’t think it’s hugely useful to buy as a “I’m going to use this thing weekly!” sort of device. I just think you should have access to one for troubleshooting.
This is a companion discussion topic for the original entry at https://www.sevarg.net/2022/08/14/hti-ht-19-thermal-imager-review/