testo 860i

The Phone Is the Display

This is the design decision the whole camera follows from, and it’s the same approach Testo takes with the testo 915i temperature probe.

The 860i has no screen and no keypad. It connects to the free testo Smart App over WiFi and Bluetooth, and the app becomes the display, the controls and the reporting tool.

That removes most of the bulk. At 195 grams, the camera clips directly onto a phone or tablet, putting the thermal image and the visible scene in the same hand. It also works on its own, controlled from the phone at up to 10 metres away.

It also means the reporting happens where the measurement does. A thermal survey is as much about documentation as measurement, and creating the record on the phone at the time avoids copying images and readings later. Images can be shared straight away, or sent as a PDF report.

The app needs iOS 17 or later, or Android 14 or later, with Bluetooth 4.0.

Built Around Delta T, Not Absolute Temperature

It’s worth understanding, because it explains both the strength and the limitation of this camera.

Accuracy is ±3°C or ±3% of reading. For an absolute measurement against a threshold, that’s a meaningful uncertainty. For a differential measurement, it matters far less. Both points are read by the same detector under the same conditions, so much of the error cancels, and the difference is more reliable than either number alone.

The 860i is designed around that, with three application specific functions.

DeltaHeat quickly shows the spread between flow and return temperatures on radiators and heating plant.

DeltaCool quickly establishes the temperature difference in refrigeration and air conditioning systems.

Humidity mode helps assess the risk of mould indoors. Readings from an optional testo 605i or testo 625 thermohygrometer transfer automatically to the app.

So the honest way to think about it is a camera for finding what’s hotter or colder than it should be, relative to something else. That covers a lot of practical inspection work, but it isn’t the instrument for certifying an absolute temperature against a limit.

Analysis Functions

Hot and cold spot detection finds the extremes in the image automatically.

Up to ten individual measuring points can be selected, which suits comparing several terminals in a switchboard, or several panels in a string, in one image.

Area measurement gives the minimum and maximum across a selected region, which is the right tool where the target is a surface rather than a point.

For electrical work, readings from the optional testo 770-3 clamp meter transfer to the app automatically, or current, voltage and power can be entered by hand.

The display switches between the infrared image and the real image from the 640 x 480 visual camera. Eleven colour palettes are available, including iron, rainbow, cold-hot, grey, sepia and a dedicated humidity palette for damp and mould work.

Fixed Focus, and What That Means for Range

Two specifications work together here, and they set the practical limits.

The lens is fixed focus, with a 48° x 36° field of view and a minimum focus distance of 0.3 metres. There’s no focus adjustment, so the image is sharp within a range and can’t be optimised for a distant target.

Geometric resolution is 3.3 milliradians, which means one pixel covers about 3.3 millimetres at one metre, and 33 millimetres at ten metres. A reliable temperature needs the target to cover several pixels, so a hot spot ten metres away needs to be roughly 100 millimetres across before the reading can be trusted.

That isn’t a criticism. It’s the selection question. A terminal at arm’s length in a switchboard, a radiator, a coil or a wall is well within range. A connection at height, a panel on a roof seen from the ground, or a busbar behind a barrier needs a camera with more capability.

Where It Sits in the Range

The 860i is Testo’s thermal imager for quick spot checks in HVAC, maintenance and building work.

Fixed focus, ±3°C accuracy, a 9 Hz frame rate and a two hour battery suit that work. For a technician who wants a thermal camera in the van and uses it a few times a week, it’s the right instrument.

Where the output is a formal thermographic survey with absolute temperatures, or the targets are small and distant, the testo 868, testo 872 and testo 883 step up in capability. Our Technical Consultants can help you choose.

Built for the Van

IP54 protection and drop testing to 1.5 metres suit an instrument that lives in a vehicle, not an office.

The built in lithium ion battery runs for about two hours, which is enough for a working session rather than a full day. It charges over USB-C in about 90 minutes, and a 15 minute charge gives 30 minutes of use. That’s worth knowing when planning a large survey.

The testo 860i kit includes a bag for safe transport and a USB-C cable.

Where It’s Used

HVAC commissioning and fault finding. Refrigeration and air conditioning checks. Heating plant flow and return checks. Electrical inspection of switchboards and distribution boards at close range. Motor and bearing checks. Damp, mould and insulation assessment in buildings. Underfloor heating tracing. Blocked pipe and radiator diagnosis. General maintenance and service work. Quick spot checks where a full survey isn’t warranted.