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Optima Twin Coil - EPTC

  - The ideal choice for multiple energy sources

The EPTC’s unique construction (pat.) provides optimal working conditions for heat pumps up to 12kW without the possibility of prioritizing domestic hot water (DHW) production in combination with solar collectors up to 12m². Integrated buffer tank functions as energy storage for space heating requirements. The Optima Twin Coil provides consistent space heating temperature while increasing DHW production significantly.

The unique tank-in-tank construction provides maximum COP (Coefficient of Performance) for heat pumps up to 12 kW in combination with solar collectors up to 12m². The large buffer tank (> 140 l.) is suitable for space heating such as under-floor heating or wall mounted radiators. The upper heating coil in the buffer tank pre-heats DHW before shifting it to the DHW tank in the top. In addition, the water in the buffer tank transfers heat to the domestic hot water tank. Both features reduces return temperature to solar collectors / heat pump and maximizes COP like no other solution on the market. There is no heat transfer from the DHW to the buffer tank due to carefully designed features. Should the heat pump fail, there is full electric back up through the 15 kW electric heater.


In the DHW tank, the 3kW electric heater increases the water temperature to 70°C. Separate ½” sensor pockets for precise control from the energy source is factory fitted. Low heat loss is provided by OSO ECO Foam, with impressive key figures for GWP of 1 (Global Warming Potential) and ODP of 1 (Ozone Depletion Potential.)

Key advantages:

  • The ultimate tank-in-tank unit for heat pumps up to 12kW and solar collectors up to 12m², providing both DHW & space heating
  • Unsurpassed energy efficiency with minimum heat loss and maximized COP
  • Impressive DHW production compared to traditional tank-in-tank units
  • 10 year warranty on the stainless steel inner cylinder & OSO ECO Foam insulation
Optima Coil Inside - EPCI
Optima Triple Coil - EPTRC
Technical Specifications
Quick Facts
Choose volume

Optima Twin Coil is available in 1 volume, suitable for the no. of people designated in the table below. The table is based on experience from average hot water usage in a normal household. Hotwater capacity is calculated by instant tapping at 40°C. at 40°C a normal shower uses approx. 60 l., bathtubs 180 l. and bubblebaths 400 l. Capacity is also dependant upon the heat source's size and performance.



Prod. nr. Product description Capacity Hot water - 40°C Hot Water / hour - 40°C  Heat-up Time - 15 - 75°C: Heat loss - 24 hours Dia x H mm. Weight
8,000,279 Optima Twin Coil EPTC 400 - 3+15 kW/1/3x230V + coil 0,8+0,7m² 7,0 pers. 550 l. Heat Source Heat Source 3,30 kWh ø580x2250 95
Product Data Sheet
  - click to expand   - click to collapse
Indirect Unit Type
Product Optima Twin Coil EPTC 400
Product No. OSO no. 8,000,279
Product Capacity Persons 7,0
Product Segment   Domestic
Weight - Net kg 95
Height - Max mm. 2250
Diameter mm. 580
Volume - Actual ltr. 210
Usable hot water draw off at 40°C (ltr) ltr. 550
Hot Water / hour at 40°C (ltr) ltr. Heat Source
Heat Up Time - 15°C - max Temp. hours Heat Source
Standing Heat Loss - 24 hours kWh/24 hours 3.30
Dimensions - Cardboard Box LxWxH mm. 595x625x2250
Volume - Cardboard Box 0.81
Inner Cylinder Stainless Steel Duplex
Coil(s) Stainless Steel Duplex
Electric Element(s) Stainless Steel Incoloy 825
Electric Box and Lid(s) Plastic V0 Plastic
Insulation PUR ECO Foam
Outer Casing Steel Epoxy Coated
Energy Source   Suggested
Type - Primary   Solar
Type - Secondary   Heat Pump
Temperature - Primary / Lower   Low Temp.
Temperature - Secondary / Upper   Low Temp.
Heating Coil(s)
Surface area - Primary / Lower 0.70
Surface area - Secondary / Upper 0,80+0,25
Recommended Flow Rate ltr./min. Heat Source
Heat Source Buffer Volume ltr. 190
Immersion Heater Booster - Capacity kW 3.0
Immersion Heater Backup - Capacity kW 15.0
Immersion Heater - Phase Phase 1/3
Immersion Heater - Voltage Volt 230/400
Thermostat Type   Surface
Upper Working Thermostat - Temp. Range °C 60-90
Upper Working Thermostat - Set Temp. °C 75
Lower Working Thermostat - Temp. Range °C 30-60
Lower Working Thermostat - Set Temp. °C 45
Electrical Installation   Regulations
IP Classification   IP 21
Cold Feed / Hot Water Draw Off Location Top
Cold Feed / Hot Water Draw Off Compression 15mm
Safety Valve (Drain Connection) " (inches) 3/8 - Female
Safety Valve (Overflow Connection) " (inches) 3/4 - Female
T&P Valve (Overflow Connection) Compression 15mm
Secondary Return / Hot Water w/o mixing " (inches) 3/4 - Female
Immersion Heater(s) " (inches) 5/4
Primary Coil Flow / Return " (inches) 3/4 - Female
Buffer Volume Flow / Return " (inches) 6x1 - Female
Sensor Connection w/ PG nipple mm. 2x8mm
Safety Valve - Opening Pressure +/- 5 % Bar 3
T&P Valve - Opening Pressure/Temp. Bar/°C 10/95
Safety Thermostat - Cut-out Temp. °C 98/75
Inner Cylinder - Design Pressure /Temp. Bar/°C 10/99
Coil(s) - Design Pressure Bar 10
Certifications / Approvals
Product Certifications Certificates CE / NEMKO / KIWA / WRAS
Manufacturing Plant Approvals Standards ISO 9001:2008 / ISO 14001:2008 / OHSAS 18001
Environmental Declaration 100 % Recyclable / >60 % Recycled Materials / ODP of 0 / GWP of 1
Warranty - Water Quality EN 98/83EC
Water - Chloride Content Max - Cl ppm 250
Water - Sulphate Content Max - So4 ppm 250
Water - Chloride/Sulphate Content Max ppm 250
Warranty Period - Inner Cylinder / Parts Years 10 / 2