The “Hydrogen Ready Appliances Assessment Report” published by the Northwest Energy Efficiency Alliance (NEEA) in February, 2023, is one of the most recent studies on this topic.  Several key items from the report pertaining to this question include the following:

1.    “There appears to be growing consensus that blends of up to 20% or perhaps even 30% are possible with little to no impact on current equipment. Higher fractions of hydrogen approaching 100% will likely require changes to equipment components and perhaps installation and
maintenance practices.”

2.    “…..there is currently no standardized testing, rating, or labeling program to enable differentiation of equipment manufactured for the North American market that is safe and efficient to operate with hydrogen blended fuels. From a market transformation perspective, this lack of a standardized program with these elements could represent a significant market barrier to the expanded use of hydrogen blended fuels.”

3.    There are “unanswered questions about the long-term use of hydrogen blends on typical materials used in new natural gas appliances. Hydrogen is known to cause some metals and plastics to become brittle over time, increasing the risk of failure of parts made from these materials. It will be important to understand the implications of hydrogen blends over the lifetime of materials used in modern, high-efficiency equipment such as gas-fired heat pumps and condensing heating equipment.”

4.    “Hydrogen integration initiatives are happening all over the world. In the United Kingdom, pilot programs are incorporating 20% hydrogen blends in natural gas in public networks, and in the Netherlands, pilots have replaced natural gas with 100% hydrogen. Utilities in the United States are currently testing up to 20% hydrogen blends within their training facilities, and the Gas Technology Institute conducted laboratory research that indicates that the water heaters and furnaces tested can maintain performance and safety with a 30% hydrogen blend in natural gas.”

However, there are still some safety issues that need to be addressed, such as odor, flammability, and potential skin burns.  A 2021 study* showed how two types of Sulphur-based odorants are compatible with 100% hydrogen gas allowing its identification at the 1% regulatory thresholds of gas in air by untrained participants.” This could help solve concerns in odor detection. High hydrogen concentration blends may also require hydrogen sensors and ventilation systems to maintain safe operations.  Being able to identify the light pale flame, almost invisible to the naked eye, and the lack of infrared heat to avoid skin burns is another consideration.**

See the link below to read more about hydrogen use in residential applications in Europe and the standards in use or under development in Europe and Australia. Current standards and test methods for appliances in the United States (Z21 standards) fail to incorporate hydrogen blends, even as a limit gas. https://neea.org/resources/hydrogen-ready-appliances-assessment-report

*Mouli-Castillo, J. 2021. “A comparative study of odorants for gas escape detection of natural gas and hydrogen,” in
International Journal of Hydrogen Energy, Vol 46, Issue 27, 14881-14893
https://doi.org/10.1016/j.ijhydene.2021.01.211

**PNNL (Pacific Northwest National Laboratory), “Hydrogen Compared with Other Fuels,” Hydrogen Tools,
https://h2tools.org/hydrogen-compared-other-fuels.