The Strom 11kW Single Phase Heat Only Electric Boiler (SBSP11H) is a compact, wall-mounted electric boiler designed to provide central heating via an existing radiator circuit — with no flue, no gas connection, and no risk of carbon monoxide. It is the most stripped-back form of electric boiler: no integrated pump, no integral expansion vessel, no hot water function — just the essential heating element and controls in a unit measuring just 520 × 235 × 120 mm. This makes it ideal for installations where space is at a premium, where an existing pump and expansion vessel are already in place, or where a system boiler format is not required. The Strom self-modulating heat exchanger supports output from as low as 1 kW, reducing energy consumption during lower demand periods, and the multi-strand element design eliminates hot spots to minimise limescale build-up and extend service life.
from 1 kW
Modulation range
520×235mm
Ultra-compact (120mm deep)
No flue
No gas — install anywhere
⚠ Installer Requirements — Must be installed by a Part P registered electrician. Requires a dedicated 230V single-phase circuit with a minimum 50A breaker and ≥10mm² cable (48A full load). Warranty requires registration within 45 days at stromltd.com. A Part P certificate is required; annual service is recommended but the boiler has no gas-related service obligation.
⚡ Heat Only — What's Not Included
As a heat-only boiler, the SBSP11H provides central heating only — it has no domestic hot water function, no integrated circulating pump, and no integral expansion vessel. These must be supplied separately or already exist in the installation. This is the correct boiler type when replacing a heat-only gas boiler in an existing sealed or open-vented system, or where the pump and vessel are located remotely. If you require integrated pump, vessel, and optional DHW, see the Strom System Boiler or Strom Combi Boiler range instead.
Features & Benefits
✔ No Flue — Install Almost Anywhere
With no combustion and no exhaust gases, the SBSP11H requires no flue penetration through an external wall or roof. It can be installed in any room or cupboard with sufficient wall space and electrical supply — including kitchens, utility rooms, airing cupboards, garages, and roof spaces. There is no planning constraint on flue positioning, no condensate drain, and no annual Gas Safe inspection requirement.
✔ Ultra-Compact — 120mm Deep
At 520 × 235 × 120mm, the SBSP11H is one of the slimmest electric boilers available. The shallow 120mm depth means it fits on walls and in spaces where a conventional boiler would not — it protrudes less from the wall than most combination boilers by a substantial margin, and can be installed inside a slim airing cupboard or recessed into partition boarding.
✔ Self-Modulating — Down to 1 kW
The Strom heat exchanger uses multiple independently controlled heating strands rather than a single element. This allows the boiler to modulate its output from as low as 1 kW up to its full 11 kW, matching heat generation precisely to demand. During mild weather or low-load periods, running at 2–3 kW instead of full power significantly reduces energy consumption — an advantage over electric boilers that only switch fully on or off.
✔ Strom Heat Exchanger — Less Limescale
Heat is transferred across the whole surface area of the element with water kept separate from the heating strands. This eliminates the hot spots that cause localised limescale formation in conventional immersion-style elements — the primary cause of performance degradation and early element failure in hard water areas. The water-separation design also reduces corrosion of the heating strands, extending service life.
✔ Near Silent — Minimal Moving Parts
Without a burner, fan, or combustion process, the SBSP11H operates in near silence. The only moving part in the boiler itself is a basic flow switch or similar; there is no pump or diverter valve within the unit. This makes it suitable for installation in bedrooms, home offices, and living areas adjacent to the boiler location without any noise nuisance.
✔ Zero CO Risk — No Gas Safety Obligation
There is no combustion, so the SBSP11H produces no carbon monoxide and no combustion byproducts of any kind. No CO detector is required by the boiler installation regulations (though always prudent in a property), and there is no Gas Safe registration requirement for the boiler itself. Landlords and building managers benefit from the elimination of one annual safety obligation.
✔ Compatible with Solar PV & Off-Peak Tariffs
An electric boiler is the most straightforward heating appliance to integrate with solar PV self-consumption and time-of-use electricity tariffs (Octopus Go, Economy 7, Agile). The SBSP11H can be controlled by any standard wired room thermostat or programmer — scheduling heating to run during cheap-rate or self-generated electricity hours is straightforward via the external controls.
✔ Drop-In Replacement for Heat-Only Gas Boiler
The SBSP11H uses ¾" male BSP heating connections — the same connection size as most conventional gas boilers. It can replace a heat-only gas boiler in an existing system with minimal pipework modification, using the existing radiators, pump, and expansion vessel. No system redesign is required in the majority of cases — the main work is the electrical supply upgrade and connection.
Technical Specifications
| Manufacturer |
Strom Limited |
| Model / Part No. |
SBSP11H |
| Boiler Type |
Heat only (no pump, no expansion vessel, no DHW) |
| Heat Output |
11 kW (modulates down to 1 kW) |
| Phase |
Single phase — 230V AC |
| Full Load Current |
48 A |
| Minimum Breaker Size |
50 A MCB |
| Minimum Cable Size |
10 mm² |
| Max Flow Temperature |
80°C |
| Min Flow Temperature |
20°C |
| Max Heating Pressure |
1.5 bar |
| Min Heating Pressure |
0.5 bar |
| Heating Connections |
¾" Male BSP (flow and return) |
| PRV Connection |
15mm Compression (½" Female) |
| Efficiency |
~100% (resistive electric — all input converted to heat) |
| ErP Heating Rating |
D (standard rating for electric boilers under EU/UK ERP scheme) |
| Dimensions (H × W × D) |
520 × 235 × 120 mm |
| Integrated Pump |
No — external pump required |
| Integrated Expansion Vessel |
No — external expansion vessel required |
| Domestic Hot Water |
No — heating circuit only |
| Flue Required |
No |
| Warranty |
Up to 5 years — must register within 45 days at stromltd.com; defaults to 1 year without registration |
Frequently Asked Questions
What is a heat-only boiler and when is it the right choice?
A heat-only boiler (also called a regular or heat-only boiler) provides heating output only — it heats the water that circulates through the radiators, but does not heat domestic hot water and does not include a built-in pump or expansion vessel. It is the right choice when: (1) you are replacing an existing heat-only boiler and the pump and expansion vessel are already in situ; (2) space is extremely tight and the smallest possible boiler footprint is required; or (3) the pump needs to be located separately for noise or installation reasons. If you need integrated hot water and you do not have a separate hot water cylinder, a combi or system boiler is more appropriate.
What pump and expansion vessel do I need alongside this boiler?
Any standard central heating circulating pump compatible with your pipework size and system head loss can be used — typically a Grundfos UPS or similar 15–60 unit for a domestic radiator system. The expansion vessel must be sized for the system volume: for most domestic sealed systems up to 10–12 radiators, an 8–12 litre vessel at the correct pre-charge pressure is typical. Your installer will size both components to your specific system. If you are replacing an existing pump and vessel, they can often be reused provided they are in good condition and correctly rated for the existing system.
What electrical supply upgrade is typically required?
At 48A full load on a single phase 230V supply, the SBSP11H requires a dedicated circuit from the consumer unit with a minimum 50A MCB and minimum 10mm² cable. Many UK domestic properties currently served by gas boilers have a 100A single-phase supply available — but the incoming capacity and available consumer unit space must be confirmed before ordering. Your installing electrician will assess the incoming supply rating and consumer unit before proceeding. Properties with a 60A or 80A supply head may need a supply upgrade from the DNO — this should be investigated early in the project.
How does the 11kW single-phase compare to the 14.4kW single-phase model?
The 14.4kW model (SBSP15H) delivers more heating output and is suited to larger or less well-insulated properties, but draws 62A at full load — requiring a 63A MCB and 10mm² cable, and placing a higher demand on the incoming single-phase supply. The 11kW model at 48A is more manageable within typical UK domestic supply constraints. As a guide, 11kW of heating is typically appropriate for a well-insulated 3–4 bedroom property or a smaller property with higher heat loss. If in doubt, a heat loss calculation (BS EN 12831) performed by your installer will confirm the correct output for your property.
