Integrated Heat Pump R134a 245 Litres CoP 3.14 Energy Rating A+ Wi-Fi Control Indirect Coil Plug & Play
The Ariston NUOS Plus Wi-Fi 250I is a large-capacity floor-standing air source heat pump water heater for UK homes needing substantial hot water volumes. The 250I model is the indirect variant — it includes a secondary heating coil for connection to a boiler or solar thermal system alongside its integrated heat pump, giving three separate heat sources in a single floor-standing unit. No outdoor unit is required, and no F-Gas qualification is needed to install. Wi-Fi control via the Aqua Ariston Net app allows remote scheduling, mode switching, and energy monitoring. The titanium-enamelled steel tank is protected by both an active ProTech anode and a traditional replaceable magnesium anode — dual anti-corrosion protection uncommon at this price point.
Recovery & Heat-Up Times
5h 24m
Full heat-up to 55°C — HP only (A7/W55)
~58 min
Via indirect coil at boiler flow 60°C
62°C
Max temp — heat pump only
75°C
Max temp — with heating element
⏱️ Recovery Note: At standard EN16147 test conditions (7°C ambient, 10°C inlet, 55°C target), the 250I heats from cold in approximately 5h 24m on heat pump only. In BOOST mode (heat pump + 2,500W dual element) reheat is considerably faster. The indirect coil enables a connected boiler to heat the 245L cylinder in approximately 58 minutes (at 60°C primary flow, 15 L/min) — ideal for rapid recovery after high-demand periods.
Key Features
- Integrated self-contained heat pump — no outdoor unit, no refrigerant pipework, no F-Gas qualification required
- 245L titanium-enamelled steel tank — 6 bar rated, XL tapping profile, ErP A+
- Indirect coil (250I model) — 0.65 m² surface area; for connection to a boiler, air source heat pump, or solar thermal system
- CoP 3.14 at 7°C (EN16147) — up to 80% more efficient than a direct electric cylinder of the same capacity
- Full heat-up to 55°C in 5h 24m (A7/W55) — one of the fastest recovery times in its class
- Extended operating range −10°C to +42°C — works in cold plant rooms and through winter conditions
- 2,500W dual heating element (1,500W + 1,000W steatite) — BOOST to 75°C for rapid top-up or anti-legionella
- Dual anode: Active ProTech (eddy-current, maintenance-free) + replaceable magnesium anode for superior tank protection
- Super Silent mode at 51 dB(A) — equivalent to a domestic refrigerator; standard mode 55 dB(A)
- Wi-Fi via Aqua Ariston Net app — daily/weekly scheduling, I-Memory self-learning, remote BOOST, energy data
- I-Memory — learns usage patterns and pre-heats proactively at the most efficient times
- Anti-legionella, anti-freeze, and anti-corrosion cycles built in
- 650 m³/h modulating fan — self-adjusts for optimal efficiency vs. noise balance
- Plug & Play 13A — standard 230V socket, no dedicated circuit required
- 150mm or 200mm duct connections — suitable for internal room use or external air supply/exhaust
- SG Ready input for solar PV self-consumption and smart grid integration
No F-Gas Required Dual Anode I-Memory AI Indirect Coil Wi-Fi App SG Ready / PV Silent Mode 51 dB
Operating Modes
AUTO
I-Memory self-learning — pre-heats based on learnt usage patterns, maximising efficiency
HP Only
Green mode — heat pump only, no element, maximum efficiency
BOOST
Heat pump + element simultaneously — fastest possible heat-up to 75°C
Element Only
Element-only — useful for servicing or when HP is unavailable
Programme
Daily/weekly timer — schedule heating around off-peak electricity tariffs
Holiday
Frost protection only — minimises energy during extended absences
Technical Specifications
What's Included
NUOS Plus Wi-Fi 250I cylinder with integrated heat pump
1,500W + 1,000W dual steatite heating element (pre-fitted)
Active ProTech anode + magnesium anode (pre-installed)
Safety group (PRV, check valve, T&P valve)
Tundish
UK installation & user manual
ℹ️ 250I Indirect Coil: The 250I model's 0.65 m² coil at the base of the tank can be connected to a boiler, solar thermal collector, or air-source heat pump via standard ¾" G connections. At a boiler primary flow of 60°C and 15 L/min, the coil transfers ~9.76 kW — heating the 245L cylinder from 15°C to 60°C in approximately 58 minutes. Pressure drop at 15 L/min is approximately 18 mbar.
ℹ️ No F-Gas, Plug & Play: The NUOS Plus heat pump circuit is factory-sealed. No field refrigerant work is needed. The unit plugs into a standard 13A 230V socket — no dedicated circuit required. G3 building regulations and Part P electrical compliance still apply.
⚠️ G3 Compliance: Despite the "Plug & Play" designation, the NUOS Plus is an unvented hot water system. Installation must comply with Building Regulations Part G3 and be carried out by a suitably qualified installer. Local authority notification requirements apply.
Frequently Asked Questions
How long does it take to heat from cold on heat pump only?
At standard test conditions (7°C ambient air, 10°C inlet water, 55°C target, EN16147 cycle L), the 250I heats in approximately 5 hours 24 minutes on heat pump alone. In BOOST mode (heat pump + 2,500W dual element), heat-up is significantly faster. With a connected boiler via the indirect coil, recovery at 60°C primary flow takes approximately 58 minutes.
What is the difference between the 200D and 250I models?
The 200D has a 200L direct cylinder (no secondary coil) and a CoP of 3.10, heating in ~3h 59m. The 250I (stocked here) has a 245L indirect cylinder with boiler/solar coil, CoP of 3.14, and heats in 5h 24m. The 250I is ~25 kg heavier and 260mm taller.
Does it require F-Gas certification to install?
No. The heat pump refrigerant circuit is completely factory-sealed with no field pipework. No F-Gas qualification is required. Standard G3 unvented and Part P electrical competency applies.
How does the I-Memory function work?
In AUTO mode, the NUOS Plus monitors draw-off patterns over time and builds a usage profile. It pre-heats proactively before predicted demand — typically charging overnight on off-peak tariffs and topping up through the day. No manual programming is needed once the learning period completes.
Does it operate in cold weather?
Yes. The heat pump operates down to −10°C ambient — one of the widest ranges in its class. Below this threshold (or during rapid demand periods), the dual 2,500W element provides backup heating to ensure continuous hot water supply.
How loud is it in Silent Mode?
Silent Mode reduces the sound power level to 51 dB(A) — comparable to a standard refrigerator or dishwasher on a quiet cycle. Standard operating mode reaches 55 dB(A). Silent Mode reduces fan speed at a minor efficiency trade-off, suitable for installation close to occupied rooms.
