This Youtube video Engineering With Rosie interviews a chemical engineer who talks about the problems of replacing some or all of the natural gas with hydrogen. Hydrogen has higher energy per unit weight, but it is much less dense than methane so it has much less energy per unit volume.
The natural gas system has a large amount of leakage. Half is in production and the other half is leakage in distribution. Hydrogen has a smaller molecule and leaks even easier than methane.
After the 11 minute point he has some important things to say about the need for eliminating CO2 from the atmosphere.
