Harvia KIP is a traditional wall-mounted heater with a separate control unit, which corresponds to a modern design. In the Harvia KIP heater, price and quality correspond to each other, which is beneficial for sauna users. The large space for stones ensures optimal heat output.

https://www.harvia.com/en/products/HEK900230/kip90e-90-kw-black 
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The model is available in three colors: steel, black and white. Switching between the colors of the outer casing is done using the Material modifier, where:
1-steel option
2-white version
3-black
the modifier is made for convenience, materials can be switched in the usual way by assigning the corresponding id to the element (see screenshot)
Corona uses legacymtl