With the upper and lower heat exchanger

With the upper and lower heat exchanger (stainless steel)

It allows you to connect an additional low-power energy sources (heat pumps, solar collectors). Used for DHW (domestic hot water, shower, bathroom, kitchen)

With the upper and lower heat exchanger (black steel)

It is used for underfloor heating. It allows you to connect additional sources of energy (gas, electric, diesel boilers)