Banning gas boilers in new homes from 2027 is the second-most consequential FHS change after solar PV. It is not an explicit prohibition — instead, the FHS carbon targets are set at a level fossil fuel heating mathematically cannot meet. The practical effect is the same.
Why gas is incompatible with FHS
The {fhsKeyFigures.carbonReduction} CO₂ reduction target in Part L 2026 (vs the 2013 baseline) cannot be achieved using a natural gas combi or system boiler — even paired with a "well-insulated" fabric. The carbon emissions factor for grid gas is 0.21 kgCO₂/kWh; for the 2025–2029 forward-looking grid electricity it is around 0.10. Heating a typical FHS dwelling with gas produces roughly 2× the emissions of a heat pump on the same fabric.
Why hybrid and hydrogen-ready boilers don't pass
Hybrid heat pump + gas boiler systems can be designed to score better than gas-only, but the SAP/HEM modelling assumes worst-case hybrid operation (heat pump down, boiler firing) and so still fails the TER. "Hydrogen-ready" boilers receive no carbon credit because Government has not committed to a hydrogen rollout for domestic heat. Neither route passes Part L 2026.
What replaces gas boilers
Two compliant heating systems remain: air source heat pumps (the default — 80%+ of new builds) and connection to a heat network (typical on dense urban schemes). Ground source heat pumps are technically compliant but rarely economic outside specific scheme types.
Cost impact
The ASHP component of the {fhsKeyFigures.buildCostPremium} per-plot FHS premium is roughly £2,800 — covering the heat pump, hot water cylinder and associated controls. The gas boiler being displaced costs ~£900, so the net incremental cost is ~£1,900/plot. Running costs are 8–12p/kWh vs ~22p/kWh on the grid, so homeowners typically see lower bills despite higher capital cost.
What this means for the gas grid
No new homes added to the gas grid from 2027 onward. Existing homes can continue to install and replace gas boilers indefinitely. National Grid Gas estimates the new-build gas connection rate falls from ~150,000/year (2024) to ~25,000/year by 2030 — driven entirely by the transitional period tail and gas-fired commercial.