A home inspector needs two instruments at a gas appliance: a sniffer to check fittings and a CO meter to put a number on the flue gases. These picks were chosen from manufacturer specifications for durability, documentation and the readouts that go into a report.
Sniff the Fittings
Meter the Flue
Write It Down
As an Amazon Associate, Akermin earns from qualifying purchases. Product links on this page are affiliate links.
Inspection work needs a locator for gas fittings and a meter for carbon monoxide; no single consumer instrument does both well. Picks were compared on stated range, alarm points, durability ratings and calibration documentation from manufacturer listings and owner feedback. We did not run laboratory tests.
Two sensitivity ranges, automatic zero and an 18-inch gooseneck from a trade brand.
IP67 ppm meter with NIOSH alarm points, MAX mode and a multi-year battery.
17-inch gooseneck sniffer with a wide stated range and everything in the case.
No pick matches that combination yet. Try a wider budget or a different measurement.
| Product | Job | Range | Readout | Durability / Power | Documentation | |
|---|---|---|---|---|---|---|
| Klein Tools ET120 | Combustible gas sniffer | approx. 50 to 10,000 ppm methane, two ranges | 5 LEDs, 85 dB | Not stated | Auto zero at power-up | View |
| Sensorcon Inspector 2 | CO meter | 1 to 1,999 ppm, 1 ppm | Digital, LED, tone, vibration; MAX mode | IP67, shockproof; CR123A 2 to 4 yr | EN 50271; 2-year warranty | View |
| TopTes PT520A | Combustible gas sniffer | 50 to 10,000 ppm methane | 7 bars, 75 dB | 3 AAA | Manual; 30 s warm-up | View |
| Klein Tools ET110 | CO meter | 0 to 1,000 ppm | Backlit digital with temperature; 35 / 200 ppm alarms, STEL | 4 AAA; 20-min auto off | Pouch included | View |
| Forensics Gas Leak Detector | Combustible gas sniffer | Not stated; methane calibrated | Color LCD with temperature | 10 ft drop test; ABS housing | 7-year sensor life stated; 1-year warranty | View |
| Forensics Carbon Monoxide Meter | CO meter | 0 to 1,000 ppm, 1 ppm | Digital; instantaneous, TWA, STEL; adjustable alarms | IP67, 20 ft drop; 9V lithium, 2-year battery | NIST calibration certificate; 3-year sensor | View |
| Kidde COPDLG (for the buyer) | Plug-in CO and explosive gas alarm | CO ppm display; low-level alert 30 to 70 ppm | Backlit display, 85 dB | 120V + 2 AA backup | UL 2034 5th Ed, ETL; 7-year warranty | View |
| TopTes Guard-101 | 4-gas monitor (H2S, CO, LEL, O2) | Not stated | LED, vibration, sound; alarm record storage | Rechargeable, 14 h stated; waterproof, dustproof | Certification claimed, standard not named | View |
Manufacturer-published figures at the time of research; "Not stated" means the listing gives no number. The Kidde is a residential alarm an inspector might recommend, not an inspection instrument.
Four points decide what goes in the bag:
A combustible gas sniffer finds a leaking fitting; a CO meter measures combustion spillage. Sensors for the two gases are different and no consumer tool does both well.
CO belongs in ppm with a peak-hold value. Gas leaks are usually reported as detected at a location, so LEDs on the sniffer are acceptable.
IP67, drop ratings and a calibration certificate matter when the instrument rides in a truck and its reading may be questioned.
Multi-year lithium cells or AA and AAA packs you can replace on site beat a proprietary rechargeable that is flat at the third house.
Both. A residential CO alarm meets UL 2034 and sounds at thresholds that protect occupants over time; it will not show the 20 or 40 ppm spill at a draft hood that points to a flue problem. A ppm meter such as the Sensorcon Inspector 2 catches that, and the report then recommends listed alarms for the household.
The flexible connector and shutoff behind the range and dryer, the union and drip leg at the furnace and water heater, the valve on a fireplace log set, the regulator at the meter and any accessible joint on the run. Sweep slowly, within an inch or two, and pause at each joint.
Only for confined-space entry: crawl spaces with a sewer connection, pits, tanks or vaults where oxygen deficiency or hydrogen sulfide is plausible. A 4-gas unit needs a bump test before each entry and periodic calibration; for ordinary interior inspections the sniffer and CO meter are enough.
Treat it as a hazard, not a data point. Get the occupants and yourself to fresh air, call 911 if anyone has symptoms, and let the utility or a qualified technician deal with the appliance. Carbon monoxide is odorless and comes from incomplete combustion; a meter reading is the only warning you will get.
An inspector checks the same fittings at every house: the flex connector behind the range, the drip leg and union at the furnace, the valve on the water heater and the shutoff at the meter. The Klein ET120 is built for that repetition. Its two sensitivity ranges, which the manufacturer states as 50 to 1,000 ppm and 1,000 to 10,000 ppm on a methane basis, let you find a faint weep on high and then narrow a strong one on low without the LEDs pinning.
The automatic zero at power-up, signaled by flashing LEDs, means the instrument settles before you sweep, and the 18-inch gooseneck reaches over a water heater or behind an appliance without moving it. The gooseneck clips to the body for storage, which is what keeps a sensor tip alive in a tool bag.
It has no numeric display, so a report says gas was detected at a location, not how much. For most inspection standards of practice that is the correct wording anyway. Our Klein ET120 review goes deeper.
The Sensorcon Inspector 2 is named for the job. Clipped to a shirt or held at a draft hood, it reads carbon monoxide from 1 to 1,999 ppm at 1 ppm resolution, and the manufacturer states a response under five seconds, which is fast enough to watch a furnace come up to temperature and see whether the flue gases are spilling into the room.
The factory alarm points are the NIOSH occupational levels, 35 ppm low and 200 ppm high, delivered as LED, an 80 to 85 dB tone and vibration at once. MAX mode holds the peak so the number that goes in the report is the worst reading, not the last one. The housing is IP67 and shockproof, the CR123A battery is rated by the manufacturer at two to four years, and the instrument carries EN 50271 certification with a two-year warranty.
It is a meter, not a residential alarm: it is not listed to UL 2034 and it does not replace the CO alarms an inspector may recommend to a buyer.
For an inspector who checks gas fittings occasionally, or wants a second sniffer in the truck, the PT520A covers the job at a fraction of the trade-brand cost. The manufacturer states a 50 to 10,000 ppm methane range, a 0.5-second response and a 17-inch gooseneck, which is enough to reach a water heater union or a fireplace valve without disturbing anything.
Seven colored bars and a 75 dB alarm rise together as the tip nears the source, and the listing recommends holding the probe 1 to 5 cm from the suspected leak. Auto power-off after ten minutes and a mute button are the practical touches; the case and three AAA cells are in the box.
There is a single sensitivity range, so at a strong leak the bars fill early and you locate by backing off rather than switching modes. Allow the 30-second warm-up in clean air before every use, and keep it away from aerosols and solvents, which the semiconductor sensor also reads.
Short answer: carry a Klein Tools ET120 to check gas fittings and a Sensorcon Inspector 2 to put a ppm number on carbon monoxide at every gas appliance. The two together cover what an inspection report needs to say about a gas system. If the budget is tight or you want a spare sniffer, the TopTes PT520A does the fitting check for less.
Natural gas and propane are combustible fuels detected by a semiconductor or catalytic sensor. Carbon monoxide is a toxic combustion product read by an electrochemical cell. The chemistries do not overlap, which is why the sniffers on this page say nothing about CO and the CO meters say nothing about gas leaks, and why a CO alarm on a wall does not detect natural gas or propane. The gas leak detector vs carbon monoxide detector explainer covers the split; for an inspector it simply means two instruments in the bag.
Most standards of practice ask the inspector to report a gas leak as observed at a location, not to quantify it. That makes the Klein ET120’s LEDs and two-range design more useful than a number: the high range (50 to 1,000 ppm on the manufacturer’s methane basis) finds a faint weep at a flare nut, and the low range (1,000 to 10,000 ppm) lets you narrow a strong one to a single joint without the display pinning. The PT520A has one range and bars, and locates by backing off from the source instead. Either one needs its clean-air warm-up before the sweep, and both will read alcohol, aerosols and fresh paint, so a hit near a freshly cleaned range is a reason to re-check, not to write it up. The handheld gas leak detector guide compares more sniffers.
A ppm meter is used in three places during an inspection: ambient air in the living space, at the draft hood or vent connector of a furnace or water heater once it has run for several minutes, and in the garage if a vehicle or generator is present. The Sensorcon Inspector 2 reads 1 to 1,999 ppm at 1 ppm and holds the peak in MAX mode. The Klein ET110 covers 0 to 1,000 ppm with a short-term exposure limit alarm and a temperature reading, and the Forensics meter adds instantaneous, TWA and STEL display options with a NIST calibration certificate in the box. For choosing between them, see how to choose a carbon monoxide meter.
A residential CO alarm meets UL 2034 and is designed to sound before occupants are harmed over hours of exposure; it stays quiet at the low levels a meter shows. Low-level CO monitors display ppm below those alarm thresholds, which is closer to what an inspector does by hand. The Kidde COPDLG in the table is the listed alarm an inspector recommends to a buyer, not a tool for the inspection itself. The difference is spelled out in carbon monoxide meter vs CO alarm.
A sealed crawl space with a sewer line, a sump pit or a buried tank can hold hydrogen sulfide or an oxygen-deficient atmosphere. That is confined-space territory, and the correct instrument is a multi-gas monitor reading LEL, O2, H2S and CO, such as the TopTes Guard-101 in the table. It needs a bump test before each entry and periodic calibration, and it is a separate purchase from the two instruments above. Most inspectors will never need one; the ones who enter crawl spaces regularly should not go without it.
Inspection instruments live in a truck. IP67 ratings, drop tests and multi-year lithium cells, all of which the Sensorcon and Forensics meters list, are worth more than an extra feature. A calibration certificate, which Forensics supplies and Sensorcon backs with EN 50271 certification, is what you produce if a reading is ever disputed.
If a CO meter reads high inside a home, or a listed alarm sounds while you are there, the inspection stops. Move everyone to fresh air, call 911 if anyone is unwell and leave the appliance to the utility or a licensed technician. If the sniffer indicates a strong leak the moment it enters a room, do not operate switches; leave and call the gas utility from outside.
Instruments were compared on manufacturer documentation: stated range and resolution, alarm set points, sensitivity modes, probe length, ingress and drop ratings, battery type and life, and calibration or certification documents. Owner feedback was reviewed for false triggering and battery complaints. We did not run laboratory tests and publish no readings of our own. Amazon data supplies images, availability and links only.
An A2L refrigerant leak detector responds to R-32 and R-454B and is rated for use around a mildly flammable gas. Check the listing for the A2L label first.
Read Guide→
PPM is parts per million: gas molecules per million molecules of air. 10,000 ppm is 1 percent by volume, and 50,000 ppm of methane is its explosive limit.
Read Guide→
A heated-diode refrigerant detector with stated sensitivity under 0.03 oz/yr, a 300 hour sensor, IP54, 17-inch probe, tracer gas coverage and 18 hour battery.
Read Guide→