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$1,329.74The Story
The Ariston NUOS Plus Wi-Fi 250L Indirect (250I) is a floor-standing air source heat pump water heater combining a 245-litre titanium-enamelled steel tank with an integrated 0.65 m² solar/boiler coil — making it the system-integration variant of the NUOS Plus Wi-Fi range. A COP of 3.14 at 7°C (EN 16147) and an energy rating of A+ on tapping profile XL make it one of the most efficient domestic hot water solutions available. The built-in Wi-Fi gateway connects to the Aqua Ariston Net app for remote control and scheduling, while Bus BridgeNet enables full integration with Ariston system boilers via a Sensys HD controller. For properties with solar thermal panels, an existing gas or electric system boiler, or planned renewable upgrades, the NUOS Plus 250I delivers a hybrid hot water solution with up to 80% energy savings over a conventional cylinder.
Installation must be carried out by a competent person to current BS 7671, local water byelaws, and the manufacturer's installation manual. A pressure/temperature relief valve and tundish (Type AB air break) are mandatory on the DHW circuit. The secondary coil circuit (solar or boiler) requires its own expansion vessel, safety valve and pump as shown in the Ariston hydraulic schematics. A manual-reset overheat thermostat is factory-fitted; for solar installations, wire it to cut the solar pump in the event of overheating. The unit is rated IPX4 — indoor installation only. Minimum room volume: 30 m³ (non-ducted).
The 250I indirect coil is designed for connection to a solar thermal system or system boiler as a supplementary heat source — primary coil flow/return connections are ¾" G on the right-hand side of the unit. The coil supports up to 6 bar primary pressure and a primary flow rate of 15 l/min (18 mbar pressure drop at rated flow). Maximum primary supply temperature to coil: 65°C. DHW circuit minimum hardness: 12°F; minimum conductivity: 150 µS/cm. Install a water softener in areas above 25°F, maintaining residual hardness above 15°F.
With a Sensys HD Net controller and Ariston system boiler, the 250I operates as a fully integrated hybrid DHW system — the boiler is called via Bus BridgeNet only when the heat pump cannot satisfy demand, eliminating unnecessary boiler cycling. For solar-only integration (without boiler), the AUX contact output can manage a solar pump controller. The Aqua Ariston Net app provides remote access and live energy consumption data independently, with no additional gateway hardware required.
At 7°C ambient the 250I achieves a COP of 3.14, rising to 3.64 at 42°C — generating over 3.6 kWh of heat per kWh of electricity at peak conditions. As an XL-rated product under EN 16147, it is tested against a larger daily draw profile of 333 litres at 55°C in a single intake, suited to larger households or high-demand properties. Annual electricity consumption: 1,299 kWh/year under EU average climate conditions (812/2013).
The 0.65 m² helical indirect coil wound inside the lower tank section accepts pre-heated water from a solar thermal collector array or system boiler, transferring up to 9.76 kW of primary heating power to the stored DHW. At a primary flow rate of 15 l/min the coil heats from 15°C to 60°C in under 59 minutes. The coil is rated to 6 bar primary pressure and fitted with dedicated S2 and S3 temperature probe wells for solar controller integration and safety monitoring.
A Hot-Gas solenoid defrost valve routes high-pressure refrigerant through the evaporator to prevent ice formation, maintaining continuous heat pump operation down to −10°C. Below this threshold the dual steatite elements (1,500 W + 1,000 W) activate automatically. The self-adaptive modulating fan adjusts its speed against measured air conditions, minimising energy use while maintaining adequate evaporator airflow at all times.
The 245-litre steel shell is internally coated with titanium-reinforced enamel fired at 850°C for long-term corrosion resistance. Cathodic protection is provided by both a sacrificial magnesium anode and Ariston's ProTech active eddy-current anode, which generates a continuous protective field without the need for periodic replacement. Both anodes are co-located on the service flange, allowing element and anode access without draining the unit.
The Bus BridgeNet eBUS connector integrates the 250I with Ariston system boilers and Sensys HD Net controllers, enabling the boiler to act as a secondary heat source — called only when the heat pump cannot meet demand alone (parameter P14 set to 3). In a boiler pre-heat configuration (P14 = 2), the DHW temperature set-point is shared between the water heater and the combi generator. A shielded max. 50 m bus cable (min. 1 mm², twisted pair) is required for the BUS connection.
All seven operating modes from the 200D are included: GREEN, COMFORT, FAST, BOOST, PROGRAM, I-MEMORY and VOYAGE, plus HC-HP for time-of-use tariff optimisation. The Anti-Legionella cycle raises stored water above 60°C automatically. In Silent Mode the fan reduces to achieve 51 dB(A) sound power level — equivalent to a domestic fridge-freezer — suitable for properties where noise is a concern.
| Parameter | NUOS Plus 200D | NUOS Plus 250I |
|---|---|---|
| Thermal Performance (EN 16147 @ 7°C / 87% RH) | ||
| COP (A) | 3.10 | 3.14 |
| Heat-up time (10°C → 55°C) | 3h 59m | 5h 24m |
| Heating energy consumption (A) | 2.478 kWh | 3.264 kWh |
| Max. hot water yield @ 55°C | 256 L | 333 L |
| ηwh (812/2013) | 130.0% | 129.0% |
| Energy class / tapping profile | A+ / L | A+ / XL |
| Annual electricity consumption | 790 kWh/yr | 1,299 kWh/yr |
| Standing heat loss | 21 W | 23 W |
| Tank & Construction | ||
| Rated capacity | 200 L | 245 L |
| Internal coating | Titanium enamel at 850°C | |
| Insulation | ≈50 mm polyurethane (CFC/HCFC-free) | |
| Corrosion protection | Magnesium anode + ProTech active anode | |
| Max. DHW pressure | 6 bar (0.6 MPa) | |
| DHW hydraulic connections | ¾" G male | |
| Heating elements | 1,500 W + 1,000 W steatite (dual) | |
| Max. water temp. (HP / element) | 62°C / 75°C (factory set 65°C) | |
| Indirect Coil (250I only) | ||
| Coil surface area | — | 0.65 m² |
| Coil volume | — | 0.0047 m³ |
| Max. primary pressure | — | 6 bar |
| Primary flow rate (rated) | — | 15 l/min |
| Pressure drop @ 15 l/min | — | 18 mbar |
| Primary heating power | — | 9.76 kW |
| Coil heat-up time (15→60°C) | — | 58 min 40 sec |
| Max. primary supply temp. | — | 65°C |
| Coil connections | — | ¾" G (inlet D, outlet E) |
| Air Side, Electrical & Physical | ||
| Ambient operating range | −10°C to +42°C | |
| Air flow (auto-modulating) | 650 m³/h | |
| Available static pressure | 110 Pa | |
| Duct diameters accepted | Ø150, Ø160, Ø200 mm | |
| Sound power (standard / silent) | 55 dB(A) / 51 dB(A) | |
| Refrigerant | R134a (1.3 kg; GWP 1430) | |
| Voltage / frequency | 220–240 V AC / 50 Hz | |
| Protection rating | IPX4 | |
| Dimensions (H × W × D) | 1,737 × 550 × 600 mm | 1,997 × 550 × 810 mm |
| Weight (empty / filled) | 90 kg / 290 kg | 123 kg / 365 kg |
| Min. room volume (non-ducted) | 30 m³ | 30 m³ |
| Min. ceiling height (non-ducted) | ≥ 1,940 mm | ≥ 2,200 mm |
What is the difference between the 250I and the 200D model?
Can the 250I be connected to an existing solar thermal system?
How does Bus BridgeNet integration work with an Ariston system boiler?
What minimum ceiling height is required for the 250I?
Does the NUOS Plus 250I qualify for any UK grants or incentives?
Can the NUOS Plus 250I use surplus solar PV electricity?
Details & Craftsmanship
Every detail has been carefully considered to bring you the perfect product.
Details & Craftsmanship
Every detail has been carefully considered to bring you the perfect product.
Details & Craftsmanship
Every detail has been carefully considered to bring you the perfect product.
Details & Craftsmanship
Every detail has been carefully considered to bring you the perfect product.
Description
The Ariston NUOS Plus Wi-Fi 250L Indirect (250I) is a floor-standing air source heat pump water heater combining a 245-litre titanium-enamelled steel tank with an integrated 0.65 m² solar/boiler coil — making it the system-integration variant of the NUOS Plus Wi-Fi range. A COP of 3.14 at 7°C (EN 16147) and an energy rating of A+ on tapping profile XL make it one of the most efficient domestic hot water solutions available. The built-in Wi-Fi gateway connects to the Aqua Ariston Net app for remote control and scheduling, while Bus BridgeNet enables full integration with Ariston system boilers via a Sensys HD controller. For properties with solar thermal panels, an existing gas or electric system boiler, or planned renewable upgrades, the NUOS Plus 250I delivers a hybrid hot water solution with up to 80% energy savings over a conventional cylinder.
Installation must be carried out by a competent person to current BS 7671, local water byelaws, and the manufacturer's installation manual. A pressure/temperature relief valve and tundish (Type AB air break) are mandatory on the DHW circuit. The secondary coil circuit (solar or boiler) requires its own expansion vessel, safety valve and pump as shown in the Ariston hydraulic schematics. A manual-reset overheat thermostat is factory-fitted; for solar installations, wire it to cut the solar pump in the event of overheating. The unit is rated IPX4 — indoor installation only. Minimum room volume: 30 m³ (non-ducted).
The 250I indirect coil is designed for connection to a solar thermal system or system boiler as a supplementary heat source — primary coil flow/return connections are ¾" G on the right-hand side of the unit. The coil supports up to 6 bar primary pressure and a primary flow rate of 15 l/min (18 mbar pressure drop at rated flow). Maximum primary supply temperature to coil: 65°C. DHW circuit minimum hardness: 12°F; minimum conductivity: 150 µS/cm. Install a water softener in areas above 25°F, maintaining residual hardness above 15°F.
With a Sensys HD Net controller and Ariston system boiler, the 250I operates as a fully integrated hybrid DHW system — the boiler is called via Bus BridgeNet only when the heat pump cannot satisfy demand, eliminating unnecessary boiler cycling. For solar-only integration (without boiler), the AUX contact output can manage a solar pump controller. The Aqua Ariston Net app provides remote access and live energy consumption data independently, with no additional gateway hardware required.
At 7°C ambient the 250I achieves a COP of 3.14, rising to 3.64 at 42°C — generating over 3.6 kWh of heat per kWh of electricity at peak conditions. As an XL-rated product under EN 16147, it is tested against a larger daily draw profile of 333 litres at 55°C in a single intake, suited to larger households or high-demand properties. Annual electricity consumption: 1,299 kWh/year under EU average climate conditions (812/2013).
The 0.65 m² helical indirect coil wound inside the lower tank section accepts pre-heated water from a solar thermal collector array or system boiler, transferring up to 9.76 kW of primary heating power to the stored DHW. At a primary flow rate of 15 l/min the coil heats from 15°C to 60°C in under 59 minutes. The coil is rated to 6 bar primary pressure and fitted with dedicated S2 and S3 temperature probe wells for solar controller integration and safety monitoring.
A Hot-Gas solenoid defrost valve routes high-pressure refrigerant through the evaporator to prevent ice formation, maintaining continuous heat pump operation down to −10°C. Below this threshold the dual steatite elements (1,500 W + 1,000 W) activate automatically. The self-adaptive modulating fan adjusts its speed against measured air conditions, minimising energy use while maintaining adequate evaporator airflow at all times.
The 245-litre steel shell is internally coated with titanium-reinforced enamel fired at 850°C for long-term corrosion resistance. Cathodic protection is provided by both a sacrificial magnesium anode and Ariston's ProTech active eddy-current anode, which generates a continuous protective field without the need for periodic replacement. Both anodes are co-located on the service flange, allowing element and anode access without draining the unit.
The Bus BridgeNet eBUS connector integrates the 250I with Ariston system boilers and Sensys HD Net controllers, enabling the boiler to act as a secondary heat source — called only when the heat pump cannot meet demand alone (parameter P14 set to 3). In a boiler pre-heat configuration (P14 = 2), the DHW temperature set-point is shared between the water heater and the combi generator. A shielded max. 50 m bus cable (min. 1 mm², twisted pair) is required for the BUS connection.
All seven operating modes from the 200D are included: GREEN, COMFORT, FAST, BOOST, PROGRAM, I-MEMORY and VOYAGE, plus HC-HP for time-of-use tariff optimisation. The Anti-Legionella cycle raises stored water above 60°C automatically. In Silent Mode the fan reduces to achieve 51 dB(A) sound power level — equivalent to a domestic fridge-freezer — suitable for properties where noise is a concern.
| Parameter | NUOS Plus 200D | NUOS Plus 250I |
|---|---|---|
| Thermal Performance (EN 16147 @ 7°C / 87% RH) | ||
| COP (A) | 3.10 | 3.14 |
| Heat-up time (10°C → 55°C) | 3h 59m | 5h 24m |
| Heating energy consumption (A) | 2.478 kWh | 3.264 kWh |
| Max. hot water yield @ 55°C | 256 L | 333 L |
| ηwh (812/2013) | 130.0% | 129.0% |
| Energy class / tapping profile | A+ / L | A+ / XL |
| Annual electricity consumption | 790 kWh/yr | 1,299 kWh/yr |
| Standing heat loss | 21 W | 23 W |
| Tank & Construction | ||
| Rated capacity | 200 L | 245 L |
| Internal coating | Titanium enamel at 850°C | |
| Insulation | ≈50 mm polyurethane (CFC/HCFC-free) | |
| Corrosion protection | Magnesium anode + ProTech active anode | |
| Max. DHW pressure | 6 bar (0.6 MPa) | |
| DHW hydraulic connections | ¾" G male | |
| Heating elements | 1,500 W + 1,000 W steatite (dual) | |
| Max. water temp. (HP / element) | 62°C / 75°C (factory set 65°C) | |
| Indirect Coil (250I only) | ||
| Coil surface area | — | 0.65 m² |
| Coil volume | — | 0.0047 m³ |
| Max. primary pressure | — | 6 bar |
| Primary flow rate (rated) | — | 15 l/min |
| Pressure drop @ 15 l/min | — | 18 mbar |
| Primary heating power | — | 9.76 kW |
| Coil heat-up time (15→60°C) | — | 58 min 40 sec |
| Max. primary supply temp. | — | 65°C |
| Coil connections | — | ¾" G (inlet D, outlet E) |
| Air Side, Electrical & Physical | ||
| Ambient operating range | −10°C to +42°C | |
| Air flow (auto-modulating) | 650 m³/h | |
| Available static pressure | 110 Pa | |
| Duct diameters accepted | Ø150, Ø160, Ø200 mm | |
| Sound power (standard / silent) | 55 dB(A) / 51 dB(A) | |
| Refrigerant | R134a (1.3 kg; GWP 1430) | |
| Voltage / frequency | 220–240 V AC / 50 Hz | |
| Protection rating | IPX4 | |
| Dimensions (H × W × D) | 1,737 × 550 × 600 mm | 1,997 × 550 × 810 mm |
| Weight (empty / filled) | 90 kg / 290 kg | 123 kg / 365 kg |
| Min. room volume (non-ducted) | 30 m³ | 30 m³ |
| Min. ceiling height (non-ducted) | ≥ 1,940 mm | ≥ 2,200 mm |
