Print this page as PDF

Send this page via e-mail

Add it to Favorites

Share OSO Hotwater on Twitter

Share OSO Hotwater on Facebook

Share this page with others

OSO Optima Coil Inside - EPCI

  - The ideal choice for heat pumps

The EPCI’s unique construction (pat.) provides optimal working conditions for heat pumps up to 12kW with the possibility of prioritizing domestic hot water (DHW) production. Integrated buffer tank functions as energy storage for space heating requirements. The Optima Coil Inside provides consistent space heating temperature while DHW usage is high.

The unique tank-in-tank construction provides optimal working conditions for heat pumps up to 12 kW. The large buffer tank (> 100 l.) is suitable for space heating such as under-floor heating or wall mounted radiators. The water in the buffer tank transfers heat to the domestic hot water tank. This reduces return temperature to the heat pump and maximizes COP. 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.


Once there is domestic hot water use, the variable valve in the heat pump switches its flow into the 1,8m² heating coil in the DHW tank, providing maximum heat transfer and domestic hot water production. During this time, the buffer vessel continues to provide consistent temperature to the space heating system, without compromising performance. The 3kW immersion heater heats the water up 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, 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 - EPC
Optima Twin Coil - EPTC
Technical Specifications
Quick Facts
Choose volume

Optima Coil Inside 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
8,000,277 Optima Coil Inside EPCI 360 - 3+15 kW/1/3x230V + coil 1,8m² 5,0 pers. 470 l. Heat Source Heat Source 2,97 kWh ø580x1990 90
Product Data Sheet
  - click to expand   - click to collapse
Indirect Unit Type
Product Optima Coil Inside EPC 360
Product No. OSO no. 8,000,277
Product Capacity Persons 5,0
Product Segment   Domestic
Weight - Net kg 90
Height - Max mm. 1990
Diameter mm. 580
Volume - Actual ltr. 240
Usable hot water draw off at 40°C (ltr) ltr. 320
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 2.90
Dimensions - Cardboard Box LxWxH mm. 595x625x2000
Volume - Cardboard Box 0.74
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   Heat Pump
Type - Secondary   -
Temperature - Primary / Lower   Low Temp.
Temperature - Secondary / Upper   -
Heating Coil(s)
Surface area - Primary / Lower 0.25
Surface area - Secondary / Upper 1.80
Recommended Flow Rate ltr./min. Heat Pump
Heat Source Buffer Volume ltr. 110
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 -
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) 4x1 - Female
Sensor Connection w/ PG nipple mm. 2x8mm
Safety Valve - Opening Pressure +/- 5 % Bar 9/3
T&P Valve - Opening Pressure/Temp. Bar/°C -
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