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Thermia Diplomat Optimum G3 - Soil-Water


  • Reduce your energy consumption by up to 80%
  • Optimum technology for higher annual efficiency
  • Superb hot water production (TWS and HGW technology)
  • Flexibility – for new-builds or refurbishments
  • One solution – heating, domestic hot water and cooling
  • Low sound level
  • Online – control your heat pump from anywhere



Efficient performance in all seasons

The Thermia Diplomat Optimum G3 is a ground-source heat pump that offers you superior annual efficiency thanks to its unique technical solutions. With an impressive coefficient of performance (COP) of 4.8 (G3 10 at B0/W35 according to EN14511), the Thermia Diplomat Optimum G3 enables you to reduce your energy consumption by up to 80%.

COP is a measure of the heat pump’s efficiency and indicates the relationship between the amount of energy produced and the amount consumed. The higher the value, the better the system.


Intelligent control system

The controller coordinates and controls the heating system. Thermia heat pumps work with complete precision to give your home the best possible indoor climate at the lowest possible cost. Our controller is very easy to use.

The controller displays visualized heat curves and, once it is set, you never need to think about it again. Raising or lowering the temperature can be achieved at the touch of a button.



Most common European heating systems are water-based, with heat being distributed via radiators or hydronic floor heating. The output temperature of the water distribution system is usually 30-35°C for floor heating and 45-55°C for radiators. Thermia heat pumps offer a low-carbon alternative to traditional boilers in modern buildings, whether for new-builds or refurbishments and regardless of the temperature required in the heating system.


Cool in the summer

The heat pump provides heat during the winter while in the summer the process can be simply reversed. The heat pump collects heat from the house and deposits it into the ground borehole to provide cooling. That is more cost-efficient than traditional air conditioning. The Diplomat Optimum G3 with an optional accessory can also provide efficient cooling for your home during the summer.


Exceptional hot water production

With HGW (Hot Gas Water heater), Thermia has developed a unique patent-pending method for producing hot water. At the same time as water is heated for distribution through the house’s heating system, hot water is produced at very high temperature through an extra de-superheater. This means that during the part of the year when the house is heated, you get lots of hot water at a very low cost. Thermia heat pumps equipped with HGW technology and with a built-in 180-liter hot water tank can produce 419 liters hot water (40°C) on tap, enabling up to nine people to take showers at once.


More hot water, faster

The hot water tank is fitted with our TWS (Tap Water Stratification) technology, which means that hot water is produced faster and at higher temperatures than with traditional technology. Because the hot water is diluted to tap water temperature, the volume of usable hot water is considerably higher due to the high temperature.


Thermia versus other brands in terms of hot water production:

Thermia with TWS technology

Recharging from 40°C to full load for a water heater using TWS technology: just 21 mins.

Time to fully recharge tank after peak consumption: 21 mins.

Typical traditional water heater

Recharging from 40°C to full load for traditional water heater: 50 mins.

Time to fully recharge tank after peak consumption: 50 min.


Optimum technology

Optimum Technology is a technology that constantly monitors your system and adjusts the pump’s performance accordingly. The controller continuously monitors the system and, if needed, automatically adjusts the speed of the circulation pumps to maintain the defined temperature delta for brine and heating circuit. Speed-controlled Class-A circulation pumps guarantee that daily operation is always adjusted according to the user’s requirements and conditions. This means that you can be sure your heat pump is always running at its most efficient level.



Thermia Diplomat Optimum G3 is available in five output sizes: 6kW, 8kW, 10kW, 13kW, 17 kW and is available in three-phase version (400V). G3 has a built-in 180-liter hot water tank but Thermia Diplomat Duo Optimum G3 is a version without hot water tank, ready to work with the Thermia MBH hot water tanks with a volume of 200 or 300 liters, or any other hot water tank. With a wide range of accessories, G3 can also provide cooling, heat a pool and work in combination with solar panels or additional heat sources.


Thermia Online

The Thermia Online app enables you to check that your heating system is working properly, reduce the temperature when you are on holiday, or receive a notification if anything unexpected comes up. Our online system provides installers with comprehensive diagnostics data and also enables them to respond promptly to notifications or access a live feed on system performance. The Thermia Online app is available for both Android and iPhone.


Pool heating

G3 can easily be supplemented to heat your pool, all year round. In this way, you can enjoy your pool in all seasons while substantially reducing the cost of heating it.


The essence of Scandinavian design and durability

Thermia heat pumps are designed, tested and manufactured in one of the harshest climates in Europe. Swedish winters can be extreme. February is usually the coldest month, with temperatures dropping as low as -30°C or even lower in the north and heating is essential from September to May. The Thermia Diplomat Optimum G3 is built on 40 years’ experience of developing and supplying heat pumps and has been one of Thermia’s best-selling products since 2012.