OSO AquaSustain 260 Integrated Heat Pump Cylinder R290 | 260L | Exhaust Air MEV DHW Heat Pump

The OSO AquaSustain 260 (DHP) is a fully integrated domestic hot water heat pump cylinder designed for properties where underfloor mechanical extract ventilation (MEV) is installed, or where external air can be ducted in and out. The heat pump unit sits in the upper section of the cylinder and extracts thermal energy from the incoming air stream, concentrating it to heat the 260-litre stainless steel storage vessel in the lower section. Using R290 (propane) refrigerant — with a Global Warming Potential of just 3 and zero Ozone Depletion Potential — the AquaSustain achieves a Coefficient of Performance of up to 3.55 in warm climates and 3.24 in average conditions, meaning it delivers up to 3.55 kWh of heat for every 1 kWh of electricity consumed. The cylinder reaches up to 60°C on heat pump power alone, with a 1.5 kW auxiliary immersion for boost or backup. A complete G3 Building Regulations kit (24L expansion vessel, inlet control valve, tundish) is supplied factory-fitted, simplifying compliance and reducing installation time.

• Integrated single-footprint design — heat pump and cylinder in one unit, no separate plant room required
• R290 (propane) refrigerant: GWP of 3, Ozone Depletion Potential of 0 — future-proof low-carbon solution
• CoP up to 3.55 (warm climate) / 3.24 (average climate) — delivers over 3× the energy input as useful heat
• Heats to 60°C on heat pump alone — no need to use backup immersion for pasteurisation
• A+ energy rating — ideal for Building Regulations Part L compliance and SAP calculations
• NCM (SAP) identifier 108964 — listed on government energy database
• 1.5 kW auxiliary immersion heater for backup and boost operation (max 70°C with element)
• Complete G3 kit factory-fitted: 24L expansion vessel, inlet control valve, tundish
• Stainless steel cylinder with ULTRAWELD construction — 5-year manufacturer's warranty
• INCOTEC immersion heater — high durability in hard water areas
• Designed to work with MEV (Mechanical Extract Ventilation) systems — draws stale warm air from kitchen/bathroom
• Can also connect to external air supply via 150–200mm duct connections
• Fully insulated cylinder body to minimise standing heat loss
• Suitable for domestic properties in both new build and retrofit installations

1. Survey and siting: Confirm the installation location can accommodate the unit dimensions (1907 × 584 × 624mm). Allow a minimum of 400mm clearance above the unit. The floor must be capable of supporting the full weight (352 kg when full of water).
2. Ductwork design: Calculate total pressure drop for supply and extract ductwork. OSO recommends insulated ductwork (min. 0.625 m²K/W). Include all components — flexible connections, anti-insect grids — in pressure drop calculations. Connect using 150mm, 160mm, or 200mm duct adapters.
3. Cold water supply connection: Connect the mains cold water supply to the inlet control valve (supplied). Ensure supply pressure is within system limits. The G3 kit components (strainer, PRV, expansion relief, tundish) are factory-fitted.
4. Hot water outlet connection: Connect the hot water outlet to the distribution pipework. Add a mixing valve if required to limit draw-off temperature.
5. Electrical connection: Wire the unit to a dedicated 230V / 13A fused spur. Do not share with other high-load appliances. Connect the immersion heater thermostat wiring as per the wiring diagram in the installation manual.
6. Fill and commission: Fill the cylinder with cold water and check all connections for leaks. Bleed any air from the cylinder. Power up the unit and set the operating mode (ECO for heat pump only, AUTO for heat pump + immersion). Allow up to 8 hours for initial heat-up from cold.
7. Handover: Advise the homeowner not to switch the unit off completely during normal use. The unit manages its own temperature automatically. Provide all documentation including the installation guide and G3 compliance record.