Summary
"Electric boiler" specifically means a unit that heats water using an electric resistance element, not a heat pump. This distinction matters because the two are frequently confused by customers and sometimes by tradespeople quoting outside their core trade — a heat pump moves heat and can deliver 2.5-4 units of heat for every unit of electricity in (its coefficient of performance, or COP); a resistive electric boiler delivers, at best, one unit of heat for one unit of electricity. That difference drives almost everything else in this comparison.
Electric boilers have a real place in the UK heating market. They avoid combustion entirely, which means no flue, no carbon monoxide risk, no annual Gas Safe service requirement and no gas supply infrastructure — genuinely useful where a flue route is impossible or where a property has no mains gas connection and a heat pump isn't viable on cost or space grounds. They're also simpler mechanically, with fewer moving parts than a gas combi, which tends to mean a longer service life and lower maintenance overhead.
Where they lose out is running cost. Because the electricity-to-gas price ratio in the UK has consistently sat well above the ratio needed to make resistive electric heating cost-competitive with gas, an electric boiler on a property with an existing gas connection is very rarely the sensible choice on bills alone. The exception is where the customer's priority isn't running cost but avoiding fossil fuel combustion in the building, has no realistic heat pump option, and accepts the cost trade-off — that's a legitimate but different conversation from "which is cheaper."
Key Facts
- How it works — an electric boiler heats water directly via a resistive element submerged in the flow, similar in principle to an immersion heater but plumbed into the central heating and/or hot water circuit; coefficient of performance (COP) is approximately 1
- No flue required — a major practical advantage for flats without a viable external wall run, some listed/heritage buildings, and park homes
- Typical domestic sizes — roughly 3kW to 15kW for combi/system electric boilers; larger heat loads need either multiple units, three-phase supply, or a thermal store approach with off-peak charging
- Electrical supply demand — a 12kW electric boiler draws in the region of 50A+ at 230V single phase; larger units commonly need a dedicated three-phase supply or split-load wiring, and the property's incoming supply capacity must be checked before specifying
- Notifiable electrical work — installing the dedicated circuit and consumer unit modification for an electric boiler is notifiable work under Building Regulations Part P in England and Wales; must be certified via a registered competent person scheme or through Building Control
- BS 7671:2018+A2:2022 — the IET Wiring Regulations govern circuit design, cable sizing and RCD/RCBO protection for the dedicated boiler circuit
- No Gas Safe registration needed — because there's no gas or combustion involved, but the electrical connection must be carried out or certified by a competent, Part P-registered installer
- Boiler Plus does not apply — the Boiler Plus efficiency and controls requirements (Building Regulations Part L amendment, in force since April 2018) apply specifically to gas combi boiler replacements, not electric boilers
- Running cost gap — grid electricity has consistently priced at roughly 3-4x mains gas per kWh under the Ofgem price cap in recent years; because a resistive electric boiler delivers only ~1kWh of heat per kWh of electricity (versus a condensing gas boiler's ~90%+ efficiency, still burning cheaper fuel), annual running costs for a typical household are materially higher on electric resistance heating
- No Boiler Upgrade Scheme (BUS) grant — the £7,500 government BUS grant applies to MCS-certified air/ground source heat pumps and biomass boilers, not resistive electric boilers
- Unvented cylinder rules unchanged — if paired with an unvented hot water cylinder, Building Regulations Part G3 requirements (competent person certification, expansion vessel, safety valves) apply regardless of the heat source
- Standing losses — electric boilers have very low standing/idle losses compared with some older gas systems, since there's no pilot light or continuous flue loss, though modern condensing gas boilers have largely closed that gap
- Servicing — no annual combustion service or CP12-equivalent landlord safety check is required, since there's no gas appliance; periodic checks of the element, contactors and controls are still sensible, typically every 1-2 years
- Best-fit scenarios — off-gas-grid properties without space, budget or suitability for a heat pump; flats with restricted or communal flue arrangements; annexes, garden rooms and holiday lets with low, occasional demand; landlords needing a straightforward compliant swap where flue routing is the blocker
Quick Reference Table
Quoting a heating job? squote turns a 2-minute voice recording into a professional quote.
Try squote free →| Factor | Gas Combi/System Boiler | Electric Boiler |
|---|---|---|
| Heat source | Combustion (natural gas) | Resistive electric element |
| Efficiency/COP | ~92-94% combustion efficiency (SEDBUK, condensing) | ~99-100% conversion, but COP ≈ 1 |
| Typical running cost, 3-bed home | Lower — mains gas priced well below electricity per kWh | Higher — grid electricity price per kWh, no heat multiplication |
| Flue required | Yes — Approved Document J clearances apply | No |
| Competent person scheme | Gas Safe Register (mandatory for gas work) | Part P-registered electrician (for the circuit) |
| Annual servicing | Recommended annually; CP12 mandatory for landlords | No combustion service; periodic electrical/element check |
| CO risk | Present — CO alarm required | None |
| BUS grant eligible | No | No — grant is for heat pumps/biomass only |
| Typical unit lifespan | 10-15 years | 15-20+ years (fewer moving parts) |
| Notifiable work | Gas Safe notification (gas work) | Part P notification (electrical circuit) |
Detailed Guidance
How Electric Boilers Actually Work
An electric boiler passes water through or around an electrical resistance element, which heats it directly — mechanically similar to a kettle or an immersion heater rather than to a heat pump's refrigerant cycle. There's no combustion, no flue gas, and no requirement for outdoor terminal clearances. This simplicity is the source of both its main advantages (no flue, no CO risk, fewer failure points) and its main disadvantage (no efficiency multiplication — every kWh of electricity in produces, at best, one kWh of heat out).
Running Cost Reality — Why Electric Rarely Wins on a Gas-Connected Property
The comparison that matters to most customers is cost per unit of delivered heat, not just appliance efficiency. Because electricity has consistently been priced several times higher than gas per kWh on the UK domestic price cap, and because a resistive electric boiler doesn't multiply the electricity it consumes the way a heat pump does, the maths rarely favours electric on a property that already has mains gas. Be specific with customers: this isn't a marginal difference, it's typically a multiple. If a customer's priority is genuinely lower bills, and mains gas isn't available or wanted, a heat pump is very likely the better recommendation than a resistive electric boiler — check current Ofgem price cap figures before giving firm numbers, as they move twice a year.
Electrical Supply and Part P Compliance
Electric boilers of any meaningful size draw serious current — a 12kW unit is in the region of 50A+ at single-phase 230V, which is a substantial addition to a domestic consumer unit and often requires either a dedicated three-phase supply, split-load wiring across two circuits, or confirmation from the district network operator (DNO) that the incoming supply has capacity. This is notifiable electrical work under Part P and must be designed and installed in line with BS 7671:2018+A2:2022, then certified through a registered competent person scheme or Building Control. Don't treat this as a simple swap-in — check supply capacity with the DNO before quoting.
When Electric Genuinely Makes Sense
The strongest cases for an electric boiler are: no mains gas connection and a heat pump isn't viable (space, budget, or property suitability); no safe or permitted flue route (certain flats, listed buildings, park homes); low and occasional heat demand where the higher running cost per kWh is offset by genuinely low total consumption (annexes, holiday lets, garden offices); or a landlord/customer decision to avoid gas combustion in the building entirely and accept the running cost trade-off as a known compromise ahead of a future heat pump.
Electric Boiler vs Heat Pump — Don't Confuse the Two
This is the most important distinction to get right when advising a customer. A heat pump moves heat from outside air (or ground/water) into the building and typically delivers a COP of 2.5-4.0 — several times the heat output per unit of electricity that a resistive electric boiler achieves. If a customer says "I want to go electric to cut my bills," they almost always mean a heat pump, not a resistive electric boiler, and should be advised accordingly. Resistive electric boilers are the right answer to a different question: "I can't have gas or a heat pump here, what are my options."
Sizing and Installation Practicalities
Size electric boilers to actual heat loss (BS EN 12831 methodology) or hot water demand for combi units, in the same way you would a gas system — don't oversize just because there's no flue constraint, as oversizing causes short-cycling regardless of heat source. Confirm the property's electrical supply capacity and any three-phase requirement early in the quoting process, since electrical infrastructure upgrades can materially change the job cost and are easy to miss if you're approaching this from a plumbing/heating background rather than an electrical one.
Frequently Asked Questions
Is an electric boiler cheaper to run than gas?
Not usually, if the property already has mains gas. Grid electricity has consistently priced several times higher than mains gas per kWh under the Ofgem price cap, and a resistive electric boiler doesn't multiply the electricity it uses the way a heat pump does, so annual running costs for typical household heat demand are materially higher on electric than gas. Always check current price cap figures before giving a customer firm numbers.
Do I need Gas Safe registration to fit an electric boiler?
No — there's no gas or combustion involved, so Gas Safe registration isn't relevant to the appliance itself. However, the dedicated electrical circuit required to power the boiler is notifiable work under Building Regulations Part P and must be installed or certified by a registered competent person (or signed off via Building Control).
Can I get the £7,500 Boiler Upgrade Scheme grant for an electric boiler?
No. The Boiler Upgrade Scheme grant is aimed at MCS-certified air source heat pumps, ground source heat pumps and biomass boilers — resistive electric boilers are not eligible.
What size electrical supply does an electric boiler need?
It depends on the boiler's kW rating — a 12kW unit draws in the region of 50A+ at single-phase 230V, which is a significant load. Larger domestic units often need a three-phase supply or split-load wiring across two circuits. Always check the property's incoming supply capacity with the district network operator before specifying, particularly on older properties with limited fuse ratings.
Is an electric boiler better for the environment than gas?
It depends entirely on the carbon intensity of the grid electricity supplying it, and on whether the alternative is genuinely gas or a heat pump. As the UK grid decarbonises, electric heating's carbon footprint falls — but a resistive electric boiler still uses roughly 2.5-4 times more electricity than a heat pump would to deliver the same heat, so from a pure carbon-per-kWh-of-heat perspective, a heat pump is the lower-carbon electric option where one is viable.
Regulations & Standards
Building Regulations Part L — conservation of fuel and power; efficiency requirements apply to the heating system regardless of heat source
Building Regulations Part P — electrical safety; the dedicated circuit and any consumer unit modification for an electric boiler is notifiable work
BS 7671:2018+A2:2022 — IET Wiring Regulations; governs circuit design, cable sizing and protective device selection for the boiler's electrical supply
Boiler Plus (Building Regulations etc. (Amendment) Regulations 2018) — efficiency and controls requirements for gas combi boiler replacements only; does not apply to electric boilers
Building Regulations Part G3 — unvented hot water storage system requirements, applicable if the electric boiler feeds an unvented cylinder
Boiler Upgrade Scheme rules (gov.uk) — MCS-certified heat pump and biomass eligibility; electric resistive boilers excluded
Ofgem — Energy price cap — current electricity and gas unit rates
gov.uk — Boiler Upgrade Scheme — eligibility and grant rules
gov.uk — Building Regulations Approved Documents — Part L, Part P
Energy Saving Trust — heating system comparisons — running cost and efficiency guidance
heat pumps — Air source heat pump COP, MCS sizing and BUS grant detail — the usual answer when a customer says "cheaper electric heating"
combi vs system vs regular boiler — Gas boiler type selection by property and bathroom count
boiler to heat pump migration — What changes structurally and on pipework when moving off a boiler onto a heat pump
heat pump wiring — Electrical connection requirements relevant to sizing electric heat sources generally