The UK policy on hydrogen as a route to decarbonize domestic and industrial heat is reviewed. The alternative of using zero carbon electricity for heat is shown to be currently unviable, due to the lack of zero carbon electricity supply and consumer resistance to heat pumps. Repurposing the gas grid for hydrogen is the practical and lowest cost solution to the decarbonization of heat, which is achievable by 2040 if we make a start in 2025. The combustion properties of hydrogen in comparison with natural gas (NG) are discussed and the implications for the design of burners. It is advocated that dual fuel NG/hydrogen burners are used for both domestic and industrial applications now, so that when hydrogen arrives in the gas grid the heating equipment does not need modifying. This paper concentrates on 100% hydrogen operation, where UK guidance requires the hydrogen to be produced with <20 gCO2/MJ and hydrogen from NG can be generated today at <5 gCO2/MJ, but a heat pump operated in the 2023 electricity grid will emit about 42 g/MJ compared with 62 g/MJ for a current NG boiler. Hydrogen by electrolysis from the grid will have at least 42 g/MJ and is not viable unless wind/solar/hydro are connected directly to electrolysis plants and not via the electricity grid. Electrolyzers can cope with the varying electricity supply from wind, but the grid cannot and requires NG gas turbines to give a stable grid. Once hydrogen is available the gas turbines can be modified to operate on hydrogen and only then will the grid electricity be zero carbon and this will not happen until 2046 at the earliest (National Grid). The gas grid was originally built for coal gas, which had typically 40–50% hydrogen and so supplying 100% hydrogen in the grid and to end users is not an insurmountable technical or financial challenge. Extensive work on the safety of hydrogen operation has shown that the explosion risk is the same as with NG, as explosions only occur when there is a large leak and the energy flow from a large leak is the same for both fuels. For both fuels explosions can be prevented from large leaks by fitting excess flow shut-off valves, which are being installed now as they are required for NG operational safety. The explosion risk for NG and hydrogen in the gas grid is about the same as the risk of being struck by lightning or being electrocuted in the home and there is no safety reason to prevent hydrogen from being supplied to homes. However, as hydrogen has no CO emissions the deaths due to CO in natural gas heating are eliminated and so hydrogen is a safer fuel to use than natural gas. A standard gas pipeline can transfer up to ten times as much energy as a 380 kV twin overhead power line with a rating of 1.5 GW, at about one-fourteenth of specific cost. This is why decarbonizing energy by repurposing the existing gas grid for hydrogen is the lowest cost and quickest route to the widespread decarbonization of domestic and industrial heat. The gas grid exists at the required capacity to distribute hydrogen, in contrast to the electricity grid that requires major modification and extensions at high cost, if domestic heat, road transport energy and steel-making energy are to be transferred to the electric supply system. Also, hydrogen can be burnt in existing gas turbines (after a combustor change) to generate zero carbon electricity and to enable more variable power from wind and solar to be accommodated by the grid. Thus, hydrogen is essential for the grid to be zero carbon as an electricity grid cannot operate only on wind/solar/hydro as their variable power has to be balanced with electricity from gas turbines to achieve a stable grid operation. It is shown that premixed combustion of hydrogen is not possible in burners due to flash back, so that all burner designs have to be diffusion burners. It is shown that hydrogen diffusion burners are clearly visible and orange. Dual fuel hydrogen burners designed for natural gas at Ø = 0.95 and operated at the same air flow and the same fuel pressure will operate at Ø = 0.7 on hydrogen, with the same burner power but a lower mean temperature and this will result in lower NOx. Hydrogen diffusion burners have to rapidly mix fuel and air, and this can be done by impinging the gas jet on a ceramic (gas fires) or metal flame stabilizer (industrial burners). The velocity of a hydrogen jet is three times that for NG, for the same gas pressure and hole size, and this gives better impingement jet mixing with air, which produces lower NOx emissions. Prompt NOx is non-existent in hydrogen flames as there are no hydrocarbons and this contributes to lower NOx than for NG. HO2 levels are lower in hydrogen flames than NG as there are no hydrocarbons to form HO2 and this leads to a lower proportion of NO2 in the NOx emissions. Thus, hydrogen burners can be designed to have lower NOx and a lower proportion of NO2, than when the same burner is operated on NG. Thus, hydrogen burners will be better for the environment. Examples of domestic and industrial burners with lower NOx emissions on hydrogen than NG are given to demonstrate this and to show that the common assumption that NOx emissions from hydrogen flames will always be higher than for NG flames is incorrect, and in most cases where this is stated there is no supporting evidence given.