Best combustion analyzer for HVAC service: furnace & boiler picks

Cold house, full calendar: choose a combustion analyzer that makes the tune-up and the paperwork easier. The useful finish is a report tied to the furnace or boiler, the customer and the work you did.

Our picks: Fieldpiece CAT85 for the complete wireless-report workflow, UEi C163 for residential furnace service, CAT45 for a rugged touchscreen, and Testo 310 II for a straightforward starter. Start with the measurements you need, then choose how the report gets back to the office.

Quick picks for furnace and boiler tune-ups

Your priority	Our pick	Why it earns the spot
Best wireless-report workflow	Fieldpiece CAT85	Job Link reporting plus live draft, a built-in manometer and automatic water return
Best for residential furnaces	UEi C163	Combustion readings, differential pressure and temperature, with wireless report output
Best rugged touchscreen	Fieldpiece CAT45	Rubberized casing, magnetic back and a large screen, with Job Link reporting
Best straightforward starter	Testo 310 II	Four measurement menus and Smart App documentation; maker publishes a base-unit price

Both Fieldpiece models use Job Link. CAT85’s extra appeal is the pressure and water-handling workflow, rather than exclusive access to wireless reports. The table below separates those features from the gas measurements.

What the maker specs actually give you

Analyzer	Gas measurement	CO measuring range	Draft / pressure	Report route
Fieldpiece CAT85	Replaceable electrochemical O₂ and CO sensors; calculated CO₂	0–4,000 ppm	Live draft plus built-in dual-port manometer	Job Link app → emailed report; optional CATPR printer
UEi C163	Measures CO and CO₂; calculates O₂	0–2,000 ppm	Draft and differential pressure	Kane Wireless Printer App; optional IR printer
Fieldpiece CAT45	Replaceable electrochemical O₂ and CO sensors; calculated CO₂	0–4,000 ppm	Draft; CAT85 is the built-in-manometer model	Job Link app → emailed report; optional CATPR printer
Testo 310 II	O₂ and CO measurements; NOx-filtered CO channel	0–4,000 ppm, without H₂ compensation	Draft and pressure	testo Smart App / email; optional Bluetooth printer

Spec sources: CAT85 manual, CAT45 manual, UEi C163 page, C163 manual and Testo 310 II data sheet and US product page.

Keep measuring range separate from overload protection. Fieldpiece’s manual lists a 10,000 ppm maximum CO overload, while the specified measuring range is 0–4,000 ppm. Use the measuring range when choosing the tool and reporting readings.

Fieldpiece CAT85: best wireless-report workflow

Why you’ll like it: Live draft lets you watch pressure while running the analysis. The built-in manometer keeps pressure measurements in the same instrument, and the HydroCycle pump separates accumulated water and returns it to the flue. A 5.5-inch touchscreen and magnetic back keep the display where you can work with it. Those are the practical differences in Fieldpiece’s CAT85 overview.

Turn on Job Link, open the analyzer’s current job in the mobile app, and email the report from the phone. The CAT85 manual documents that one-way analyzer-to-app reporting and roughly 1,000 jobs of internal storage. Use the customer and equipment identity consistently so the office gets the right record first time.

Good to know: This pick is the base CAT85. The CAT85K2 is the separate printer kit.

UEi C163: best for residential furnace service

Why you’ll like it: The C163 combines combustion measurements with differential pressure and temperature, includes two thermocouples and a case, and protects its CO sensor with a purge pump. You can record and email results with the free Kane Wireless Printer App, or use an optional IR printer. The C163 product page lays out that service-call package.

Its sensing approach is different from the Fieldpiece pair: C163 measures CO₂ directly and calculates O₂. That distinction is explicit in the maker’s manual. Label the channels accurately when comparing tools and saving the report.

Good to know: UEi’s service programme starts with a one-year warranty and extends it through qualifying annual recertification, up to ten years. Plan that service rather than treating the headline as ten years of maintenance-free use; see UEi Service+.

Fieldpiece CAT45: best rugged touchscreen

Why you’ll like it: The rubberized case, magnetic back and 5.5-inch display suit a tool that comes out on every heating call. You still get field-replaceable gas sensors and Job Link reporting. Choose CAT45 when you want that interface and reporting route and already have the separate pressure tools your work needs. Fieldpiece’s CAT45 page describes the construction and controls.

Its manual gives seven hours of typical battery life, versus five hours for CAT85, both with the pump running 80% of the time. Both ratings use the same stated pump-duty condition; the CAT45 and CAT85 manuals state them separately.

Good to know: CAT45 uses a conventional water-collection setup; CAT85 adds HydroCycle and the built-in manometer.

Testo 310 II: best straightforward starter

Why you’ll like it: Four menus cover flue gas, draft, ambient CO and pressure. The Smart App adds documentation, customer-data management and emailed results; a magnetic back frees your hands at the appliance. Testo’s US manufacturer page lists the base 0563 3104 01 at $999, checked 2026-10-23 (maker page and price). Budget separately for the printer if you want a paper copy at the house.

The data sheet lists no internal memory, so make the app report part of the finish-the-job routine. The base unit and the with-printer kit are different purchases.

Good to know: Testo recommends an annual check at an authorized service centre in its 310 II manual; it does not publish a fixed sensor lifespan in the reviewed page/manual.

NOx, sensor cover and calibration: buy the right capability

A NOx filter is different from a nitric-oxide sensor. The filtered CO channels listed on these service analyzers do not add an NO measurement. If the work requires NO, UEi’s C165+N is a distinct model fitted with that sensor. Order the NO-equipped version when your work requires that measurement.

Keep warranty and calibration on separate lines in the tool budget:

• Fieldpiece: four-year O₂/CO sensor warranty, with field-replaceable sensors. The manual recommends annual recalibration; Fieldpiece’s calibration guidance directs owners to authorized third-party centres.
• UEi: yearly recertification maintains the Service+ warranty extension. Actual sensor replacement follows service findings.
• Testo: a supplied calibration protocol and an annual authorized-centre check, per the manual.

Record flue CO, CO air-free and ambient CO under their own labels. CO air-free is a calculated value referenced to oxygen; it is a different report field from the measured sample. Fieldpiece identifies CO at 0% O₂ as CO air-free in its test-parameter table.

For CO safety, follow the appliance manufacturer’s service specifications; if a CO alarm sounds, move everyone outside, call 911 and stay out until responders allow return (CPSC guidance).

Get the combustion report into the job and invoice

Finish the call with a record the office can use: customer, appliance model/serial, fuel, date, measured channels, before/after findings, work completed and the next repair or return visit. Use a simple filename such as Smith-furnace-combustion-before and keep the original exported report.

Jobber: save the report with the work

Put the combustion report in Jobber before leaving the call, so the measured result stays with the work being quoted or invoiced.

Add the exported report or a clear photo to the job’s Notes and Attachments, then link the note to the related quote or invoice where useful. Internal notes are for the team; customer-facing invoice attachments are a separate, select-plan feature. Jobber’s attachment guide explains that distinction. Choose the report you want the customer to receive rather than assuming an internal upload appears on their invoice.

HCP alternative: choose the attachment you send

Open the job or estimate, find Attachments, and use + to upload the report. When sending the invoice or estimate, edit the Attachments section in the preview and select the report to include. That is the workflow in HCP’s sharing guide.

The connection is export, then upload. Job Link, testo Smart App and Kane report output give you a document to retain; Jobber or HCP gives it a home beside the customer and follow-up work.

Building the rest of the service kit? Pair this guide with our HVAC clamp meters, thermal cameras and refrigerant leak detectors. Each solves a different part of the call.

For the room-air side of the call, use our ambient CO meter and personal-monitor guide. It covers handheld versus wearable picks, separate from flue-gas analysis.

For the pressure side of a furnace visit, our HVAC digital manometer guide compares wireless probes and handhelds for static-pressure and gas-valve checks.