A Sustainable Way to Fix Gas Leaks in Water Heaters

Natural gas present in water heating systems escapes through leaks, and also because some of this gas is not combusted by the burner.

According to a new study carried out by Stanford University, such small inefficiencies can certainly add up: The ensuing emissions of methane from water heaters throughout the United States are possibly over three times higher than the predicted limit. Incidentally, methane is a powerful greenhouse gas.

But the good news is that there are simple fixes that can be used across a majority of the global economies.

These appliances are letting less than 1 percent of their gas escape, but so is the natural gas production at the opposite end of the system, and then we have all the leaky pipelines and meters in between. Fixing gas leaks is an iterative challenge. For water heaters, we know what we have to do.

Rob Jackson, Study Senior Author and Professor, Department of Earth System Science, School of Earth, Energy & Environmental Sciences, Stanford University

Natural gas systems, ranging from stovetops to well pads, are often leaky. The gas escaping into the air, be it from a damaged valve on a pipeline or from the moment when a burner has not yet trapped the pilot light, contains 90% methane.

Compared to carbon dioxide (CO₂), methane gas is several times more effective at capturing heat and accounts for nearly a fourth of the Earth’s atmosphere warming caused by all greenhouse gases put together. In the last 5 to 10 years, a majority of the studies have looked at locating and repairing these leaks.

Wasted natural gas from appliances in homes and commercial buildings is probably the least understood cause of climate change from natural gas use.

Eric Lebel, Study Lead Author and PhD Student, Department of Earth System Science. Stanford University

The scientists targeted water heaters because they are responsible for a fourth of natural gas consumption in a typical U.S household that consumes gas for hot water, heating, and cooking purposes. In the United States, nearly 58 million water heaters that utilize natural gas are responsible for the leakage of about 91,000 tons of methane every year in the form of uncombusted gas.

More than two decades ago, considering methane’s relatively higher potency as a greenhouse gas than that of CO₂, 91,000 tons of the methane gas warms the Earth as much as 7.8 million tons of the CO₂ gas.

“That’s a very small part of total U.S. emissions, but it’s the equivalent of 1.7 million cars driving on gasoline for a year,” elucidated Jackson, who is also a senior fellow at Precourt Institute for Energy in Stanford University.

As part of the study, water heaters were tracked in 64 homes based in San Mateo and Santa Clara counties in California from the period of June 2018 to November 2019. While only a few studies have been carried out on methane leakage caused by appliances, one research investigated natural gas water heaters in California and predicted that emissions were approximately 5.4 billion grams throughout the state.

The latest study, performed at Stanford University, includes additional measurements of the on and off pulses in the newer version of tankless water heaters and supplementary measurements of pilot light emissions from traditional storage water heaters. The study predicts that the figure for California is at 17.7 billion grams, which is over thrice as much.

Storage Tank Versus Tankless

The study identified a highly crucial difference in the emission rates between those two simple kinds of natural gas water heaters. While the traditional natural gas water heater preserves the heated water in a tank, the other, newer version of the heater does not have any tank.

Upon opening a hot-water faucet, the tankless water heater instantly fires up the gas to heat the flowing water. A negligible but increasing number of water heaters in the United States are tankless models. In Asia and Europe, about one in five systems does not preserve hot water. At the global level, tankless systems are increasing at a yearly rate of above 7%.

Since that growth trend is expected to continue, we thought it important to compare the two models. On average, we found about twice as much methane emissions from tankless water heaters than from storage water heaters.

Eric Lebel, Study Lead Author and PhD Student, Department of Earth System Science. Stanford University

But tankless heaters are believed to be more efficient because they burn less natural gas for each gallon of hot water when compared to that of traditional systems and hence release less amounts of CO₂. On the whole, tankless water heaters discharge 18% less greenhouse gases when compared to that of the storage water heaters.

Luckily, since tankless water heaters are still turning out to be more famous, particularly in North America, the latest models can be re-designed to minimize uncombusted and leaked natural gas.

Individuals who have been close to a space heater or water heater when it fires up would have heard the burst of combustion at the start of a cycle; this is when a gust of natural gas leaks uncombusted. When the unit shuts down, methane is discharged at that time too. This is applicable to both kinds of water heaters.

However, in the case of tankless heaters, the on and off pulses are responsible for nearly 60% of the discharged methane. Whenever a hot water faucet is opened and shut, tankless models switch on and off, respectively. The stored water is heated or reheated intermittently. The scientists have recommended that the on and off pulses of tankless water heaters can be reduced considerably to minimize the leakage of methane gas, without impacting their performance.

“We find other pretty simple design fixes, too,” added Jackson. “For heaters with tanks, most of the release of uncombusted gas is from the pilot light when the heater is idle. Standard pilot lights should be replaced with electronic igniters.”

The new study also found that the rising popularity of single-handle faucets should be reconsidered, irrespective of the type of heater.

“With single handle faucets, people trigger hot water draws unknowingly by moving the handle straight up and then to the cold side. Or they go for hot water but then decide they’re really not willing to wait for it. It’s a simple but pointless source of emissions of both methane and CO₂ that is multiplied every day,” Jackson concluded.