Combustible-Gas Leak Detectors

May 01, 2011
May/June 2011
A version of this article appears in the May/June 2011 issue of Home Energy Magazine.
Click here to read more articles about Healthy Homes

You may have heard of houses and neighborhoods exploding due to gas leaks in old pipes under the streets. Inside the home, detecting combustible-gas leaks is an important part of combustion safety testing. Gas connections need to be checked as well. The residents’ health and safety are at stake.

BPI requires that all gas connections, starting at the meter and working out to each appliance, be checked, all the way around, 360º, at every joint you can get to, and it is surprising how many small leaks you will find in the process. If a leak is found, it needs to be verified by applying a dose of bubble liquid, such as Snoop from Swagelock, or All-Purpose Leak Detector from Oatey, or Big Blu from Airsource. Once the leak is verified, the joint can be marked with a surveyor’s tape flag so that it can be repaired. Very small leaks will blow champagne size bubbles. Big leaks will blow serious bubbles. Because natural gas (methane) is odorless, gas companies add a sulphurous compound, such as mercaptan, that smells like rotten eggs.

Paul Raymer is chief investigator of Heyoka Solutions, a company he cofounded in 2006. He has been wandering through the mysteries of building science since 1977. He has multiple BPI certifications and is a HERS Rater. (Paul Raymer)

There is some debate about whether leaks so small that you can’t smell the leaking gas are worth worrying about. They are certainly harder to find and verify, and they are also hard to fix. Some leakage at valves is allowed by industry standards. The gas company may shut off the gas to the building if the alleged leak is not on the company’s side of the line, leaving the customer without heat or hot water. Also, since detection devices sense a wide variety of gases, they are sensitive to cobwebs on the sensor or a rotting mouse as well as a small gas leak. (I had a detector that responded to pasta sauce that the homeowner was concocting in a kitchen attached to the combustion appliance zone.) On the other hand, sensing the presence of gas in places where there are no gas lines may indicate a very serious leak on the gas company’s side. Such a leak can explode the decaying pipes in the street and blow up the whole neighborhood. In a case like this, gas can come through any openings into the house, like the cavity around a water line, and show up on your detector. Combustible-gas testing doesn’t provide clear answers. This is an area where you must use experience and logic to qualify your findings and then decide what to do—always putting your and your client’s health and safety first.

cl-Raymer-Test-process-JrBPI requires that all gas connections, starting at the meter and working out to each appliance, be checked at every joint you can get to.

Every energy auditor needs to have a useful combustible-gas leak detector, and choosing one is a fundamental decision. There is a very wide range of devices on the market, from a bucketful of manufacturers. All of these devices sense many gases other than methane, including acetylene, ethane, ethylene, hydrogen, and acetone, and the presence of gasoline and chlorine. They will react to doping compounds in the pipe joints. Methane, however, is what we are looking for in terms of combustion safety.

Prices vary from less than $100 to thousands. For this article, I am going to focus on products under $300 made by Bacharach, TIF, and UEI (see Table 1). Based on my own informal survey of energy auditors, these seem to be the most popular models. But as I said, there are many other devices in this category. Don’t overlook the instruments made by Testo, Sensit, Extech, TPI, RKI, or others just because they are not included in this article.

In order to meet the BPI protocols, you’re going to need a unit with a flexible probe, because you are going to need to reach around the myriad of connections. A longer probe will make it easier to reach the overhead and crawl space connections, as well. Also, you want to consider the weight of the unit. Weight makes a difference when you’re walking the house to locate ambient sources of combustible gas and you’re carrying a bunch of gear and a clipboard or computer to log the information. Finally, do you need to detect the amount, or simply the presence, of gas? All of these devices provide an indication (visible, audible, or both) of the presence of combustible gas. Not until you get up in the $1,000 range do they provide a digital display of the amount of gas.

Bacharach Leakator 10 and Leakator Jr

The Leakator 10 is a hefty device, 8.5 inches long, 2.25 inches wide, and 1.7 inches thick. It weighs almost 2 lb with 5 C batteries. It has the longest probe at 20 inches, making it possible to reach some pretty out-of-the-way connections. It comes in bright yellow, so that it is fairly obvious when you set it down in a messy basement. The Leakator 10 has a series of ten light-emitting diodes (LEDs) that give a visual indication of the relative level of gas, and a ticking sound that increases in frequency with the relative amount of gas. It also has three operational-status LEDs indicating power, sensor failure, and battery life. (Battery life is rated at 30 hours under normal-use conditions.) The minimum sensitivity is 20 ppm methane.

The number of LEDs and the tick rate are adjustable, and you can use an earphone to monitor the performance in noisy locations. The manual states that after turning the unit on and waiting for it to stabilize, you should rotate the gain control just until the bottom gas level LED turns off. The manual says, “Be sure to always set this control in the same environment you intend to test in.” It is good practice to calibrate the unit in fresh air (outside the house). Since you are looking for sources of combustible-gas leaks and not measuring levels, some auditors feel that if you can’t smell the mercaptan, the air is fresh enough. But since your nose may have adjusted to ambient odors, it is better to follow best practice and calibrate outside.

cl-Raymer-Comb-Gas-Group(left to right) UEI CD200, UEI CD100A, Bacharach Leakator Jr., Testo 361-1, Sensit (Paul Raymer)

The sensor is exposed at the end of the sensor housing with its sides protected. This means that the end of the probe must be pointed at the source of the gas leak, and that can get the sensor covered in dust or cobwebs, which must be cleaned off to avoid false readings. The sensor typically lasts five years, and it is simple to replace. The replacement comes with a matching resistor that must be replaced at the same time. Detailed replacement instructions are included in the manual.

The Leakator Jr is a simpler device than the Leakator 10 and comes in at a bit more than half the cost. It takes four AA batteries; is smaller—just 6 inches long; and has a 12-inch probe. It comes in a lovely avocado green color. Turning it on causes the display light to quickly flash until the unit reaches calibration, at which point it will flash every two seconds unless a source of gas is sensed. The frequency then increases dramatically until it is almost continuous. Pressing the on-off switch twice will reset the sensitivity, increasing it from 20 ppm to 50 ppm to help you to find the source, or verify the presence, of the leak. This feature allows the unit to sense something (maybe a leak) and then quickly increase the sensitivity to verify that there is something worth pursuing further.

There is no way to mute the beeping. If Jr is left on, the unit will shut itself off after nine minutes. Briefly depressing the on-off switch while the unit is operating will restart the timer. The unit has a simple plug-unplug sensor that is easy to replace.

After years of use, the probe connection to the housing may loosen up. There are three screws on the back (plus one for the battery cover and two more inside the battery compartment). The top one of the three screws passes through the base of the sensor probe. Tightening it will tighten up the connection to the housing.

TIF 8800 to 8900

TIF makes a line of combustible-gas detectors: the 8800, 8800A, 8850, and 8900. The 8800 units are all variations on the same theme. According to the manual, the probe is 12.5 inches (other specs suggest that it is 15 inches) long, and the case is 8 inches long by 3 inches wide by 1.8 inches thick. The units weigh about 15.5 oz, including the batteries. They use two 2.4 Ni-Cad rechargeable batteries that have approximately three hours of continuous operating time. These detectors are all brilliant red.

The variations in the 8800 units are small. The 8800 has an on-off switch, a sensitivity adjustment knob, and a low-battery indicator. The 8800A adds a bar graph of six level-indicating LEDs. And the 8850 includes a mute button to silence the ticking. The 8800 units turn on with the slide switch and the sensitivity can then be adjusted to provide a stable, baseline ticking. The warm-up period is 30 seconds.

The 8900 provides the same system in a more ergonomically designed case—it is smaller and has a round hand grip. According to the manual, the probe is 15 inches long. The system weighs 16 oz, including the batteries. The 8900 feels more substantial in your hand than the 8800, and the build quality is better. The primary drawback with the TIF units is their relatively poor sensitivity. At 500 ppm methane, they will overlook many of the smaller leaks.

UEI CD100A and CD200

The CD100A is a simple, one-hand device, wrapped in a protective shell to limit damage if you drop it. It is right handed, in that the adjustment-power knob is on the right side of the instrument, lined up with the right thumb. But once it is powered up and set, it probably won’t be necessary to adjust the setting. Turn the CD100A on in an unpolluted atmosphere and adjust the setting for a steady tick. The warm-up is almost instantaneous. The sensor is on the end of a flexible gooseneck 18 inches long and 11/32 inch in diameter that wraps around the unit for storage. The sensor itself is protected by a lanternlike enclosure with a red LED tip light that helps to pinpoint the location being sensed. Basements and crawl spaces can be dark, mysterious places!

The CD200 is a larger unit. It includes the same 18-inch gooseneck probe with tip illumination and lanternlike cover. The manual says that it takes up to a minute to warm up, but it seems quicker than that. The tick adjust knob is on the face of the unit (for lefties or righties), and the off-on-alarm slide switch is just above it. That slide switch is one of the weaker points of the unit. My test unit arrived with it slid to the on position—which meant that the batteries were dead.

The unit does include an adjustable and mute able alarm. An alarm adjustment knob is located on the heel of the unit. The alarm has a factory-calibrated (click-to-set) setting for 0.5% methane in the air. It is adjustable from 10% to 40% lower explosive limit (LEL) for methane. So as you walk around a house, if the alarm goes off, you will know that there is combustible gas in the air. You can set the sensitivity of the alarm with your thumb. So if you are walking around the house with the homeowner and your red LED tip illuminator is glowing and the CD200 is ticking away and all of a sudden it lets out a warbling alarm sound as well, you might want to warn the homeowner before you go running out of the building!

Table 1. Product Comparison

More on Leak Detectors

The problem with these combustible-gas leak detectors is that it is difficult to manufacture an inexpensive device that senses just methane and/or propane and nothing else, so that when it indicates a leak, you know that it’s something that needs to be addressed. If you call in the gas company for every leak that one of these devices senses, the gas company may shut off the gas to the house, making the leaks difficult to find and making the customer unhappy. It is worth repeating that these devices will alert you that they are sensing something, but you must apply experience and logic in order to decide what to do.

In the process of checking out these devices, I went down into my own basement and quickly found a joint where all of them indicated a leak. I double-pushed the button on the Leakator Jr and increased the sensitivity from 20 to 50 ppm, and it still indicated a leak. Checking it out with bubble fluid didn’t indicate any leak at all, and it is the same joint to a relatively new water heater that I have already had the plumber check out with his gear. So what is causing all these devices to tell me there is a gas leak there? Maybe it’s the excessive amount of pipe dope on the joint. Maybe it’s cobwebs. I chose not to have the gas company or plumber come in to fix it. But how do you do that in a client’s house?

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