Gas leak detection has advanced far beyond the days of canaries in coal mines. Today’s detectors allow a tradesperson the ability to provide accurate readings for methane (CH₄), propane (C₃H₈), carbon monoxide (CO), hydrogen sulphide (H₂S), and natural gas. There's a huge range of detectors available for any setting or situation — no worms required.
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- How do gas leak detectors work?
- How to use a portable gas leak detector
- Types of gas leak detectors
1. How do gas leak detectors work?
If you work with gas-powered systems, you know one thing: at some point, leaks happen. Finding and fixing them quickly is key to being a good plumber or HVAC technician. Gas leak detectors pinpoint leaks in pipelines, appliances, and enclosed spaces, reducing risks of fire, toxic exposure, and equipment failure.
Gas leaks can be dangerous (and expensive). Left unchecked, they can lead to:
- Reduced efficiency and increased energy costs.
- Equipment damage and breakdowns.
- Exposure to harmful gases like carbon monoxide (CO) or hydrogen sulphide (H₂S).
- Fire or explosion risks from gases like methane (CH₄) or propane (C₃H₈).
Gas leak detectors generally fall into two main categories:
Portable gas leak detectors
These are the go-to tools for HVAC technicians, plumbers, and any tradesman who needs to check the security of a gas connection. Designed to check for leaks in gas lines and appliances, they’re small, easy to carry, and cheaper than permanent versions.
- Their flexible probes help reach tight spaces along pipelines.
- Sensitivity adjustments detect the smallest leaks.
- Either audible or visual alarms go off when gas is detected.
Fixed gas detectors
These are typically installed in industrial settings where continuous gas monitoring is needed. If a gas leak is detected, they trigger alarms, ventilation systems, or even automatic shut-offs to prevent dangerous situations.
2. How to use a portable gas leak detector
First, protect yourself! Gas leaks can be dangerous, so avoid any open flames and use your PPE, including gas masks — particularly if the area has poor ventilation.
- Test in a well-ventilated area
- Note any strong air currents, as these may disperse gasses.
- Move the probe slowly to allow the sensor to detect small leaks.
- Adjust the sensitivity settings. Start with high sensitivity for initial detection, then shift to lower to pinpoint the leak.
- Check gas lines after repairs or installations—never assume a new connection is leak-free.
- Maintain your detectors. Most sensors degrade over time and will need regular calibration or replacement.
3. Types of gas leak detectors
There's no one-size-fits-all solution to finding gas leaks. The type of sensors you use will depend on the use case, your environment and what types of gas you'll be looking for.
Best for HVAC technicians: Heated diode gas detectors
Most effective for detecting HVAC refrigerant leaks, heated diode gas detectors operate using a ceramic sensor heated to high temperatures (typically 600–800°C). When refrigerant gases pass over the sensor, thermal decomposition occurs, releasing chlorine or fluorine ions. These ions generate an electrical signal, the more gas registered, the more electricity produced. This sets off an alarm proportional to the gas concentration.
Used for:
- Detecting leaks in residential HVAC refrigerant lines (e.g., R-410A, R-32, R-22).
- Pinpointing micro-leaks in AC evaporators, condensers, and refrigerant piping.
- Useful in crawl spaces, attics, or near coils where refrigerant leaks often occur.
Limitations:
- Not effective for natural gas or propane detection.
- Sensitive to moisture and wind, which can reduce accuracy outdoors
Best for plumbers: Catalytic bead gas detectors
For plumbers working with natural gas and propane, catalytic bead gas detectors can register combustible gases due to exposure to a heated catalyst. They contain two wire coils embedded in ceramic beads—one is coated with a platinum catalyst, and the other serves as a reference. When combustible gases (methane, propane) contact with the heated catalyst bead, they oxidise, producing heat. This changes the resistance of the sensing bead and sets off an alarm.
Used for:
- Detecting methane (natural gas) and propane leaks in residential gas lines.
- Testing joints and connections in water heaters, furnaces, and gas appliances.
- Checking outdoor propane tanks and underground gas lines for leaks.
- Ideal for pre-service checks after new gas installations or repairs.
Limitations:
- Requires oxygen for operation—won't work in inert environments (e.g., nitrogen-purged lines).
CO and toxic gas detection: Electrochemical gas detectors
Used as an emergency response in CO poisoning risk situations, electrochemical gas detectors detect leaks by registering a chemical reaction. They contain a liquid electrolyte and electrodes, so when target gases (e.g., carbon monoxide, hydrogen sulphide) diffuse through a porous membrane, they undergo a redox reaction at the sensing electrode. This reaction causes a measurable electrical current which triggers an alarm.
Used for:
- Detecting carbon monoxide (CO) leaks from furnaces, water heaters, and boiler exhausts.
- Ensuring adequate oxygen levels in confined residential HVAC spaces.
- Identifying hydrogen sulphide (H₂S) in sewage-related plumbing issues.
Limitations:
- Electrolyte depletes over time, requiring sensor replacement every 2–3 years.
- May produce false positives in high-humidity environments.
Low-cost, multi-purpose leak detection: Semiconductor gas detectors
The cheapest option, semiconductor gas detectors, have a metal oxide (MOX) semiconductor sensor built within it that interacts with gas molecules. When gases (e.g., methane, propane, refrigerants) contact the heated semiconductor surface, they alter its electrical resistance, setting off the alarm.
Used for:
- Affordable alternative for detecting natural gas, propane, and refrigerant leaks.
- Often used in household gas alarms and continuous monitoring devices.
- Ideal for detecting gas buildup in basements, attics, or mechanical rooms.
- Backup detection method when pinpointing leaks manually.
Limitations:
- Less precise than catalytic bead or heated diode detectors.
- May register false alarms from high humidity or cooking fumes.
Ideal for on-the-spot leak detection: Electronic combustible gas detectors (Sniffers)
These handheld detectors use a heated filament sensor or semiconductor chip to "sniff" combustible gases (e.g., methane, propane). When a gas is present, the sensor resistance changes, triggering an alert.
Used for:
- Checking for leaks in gas-powered stoves, fireplaces, and water heaters.
- Verifying underground gas line safety.
- Quick leak location in tight crawlspaces and wall cavities.
Limitations:
- May not differentiate between gases (e.g., methane vs. propane).
- Sensors require regular calibration.
For gas line testing: Negative pressure testing
In this method, a sealed gas system is pressurised and monitored for unexpected pressure drops. If the pressure declines over time, it indicates a leak.
Used for:
- Pre-commission testing of new residential gas lines.
- Checking for duct leaks in HVAC systems.
- Ensuring airtight connections before activating gas service.
Limitations:
- Cannot locate the exact leak position—only confirms its presence.
- Requires specialised equipment for accurate pressure measurement.
Backup: Soap bubble testing
A soapy water solution is applied to suspected leak areas. This method relies on gas displacing liquid to form bubbles. When a soapy water solution is spread over a suspected leak site, any escaping gas pushes through the liquid film, reducing surface tension and creating visible air pockets. The bubbles confirm an active leak.
Used for:
- Simple, cheap verification of gas line and refrigerant leaks.
- Effective for confirming leaks in threaded gas fittings and pipe joints.
- Works as a final test after repairs before electronic detection.
Limitations:
- Not effective for very small leaks or fast-dissipating gases (e.g., refrigerants).
- Requires manual application and may miss leaks in hidden areas.
Industrial gas leak detectors
Heard of a gas leak detector not included in the list above? There are more options to find escaped gasses, many of which are too complex, expensive or difficult to use in most residential settings. These include:
- Infrared imaging gas detectors
- Uses thermal imaging to visually detect gas leaks — but it is too expensive and better suited for industrial-scale applications like oil refineries and large HVAC systems.
- Infrared point gas detectors
- This detects gas concentration by measuring infrared absorption, but it is expensive and requires complex calibration requirements.
- Ultrasonic gas leak detectors
- High-frequency sound waves are produced by gas escaping under pressure, but this test is ineffective for low-pressure residential gas leaks (e.g., HVAC refrigerants or household natural gas lines).
- Photoionisation detectors (PIDs)
- UV light is used to detect volatile organic compounds (VOCs), however, it does not work for refrigerants, methane, or propane—making it irrelevant for HVAC and plumbing.
- Holographic gas detectors
- It is possible to use holograms to identify gas leaks, but it is still an experimental technology with no current application in residential settings.
- Thermal conductivity gas detectors
- These measure how different gases conduct heat to detect leaks but are mainly used in lab environments and are not practical for HVAC or plumbing work.
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