This page shows the different variations of the Kotłownia from an Icons8 icon pack. Feel free to resize and recolor the icon, and then download the icon in PNG format for free. Icons are available in PNG and vector.
A square with rounded edges, except where the top side of the square would be there is instead the roof. The shape overall resembles a simple house. Inside there are three curvy lines that run towards the roof of the house to the bottom of the square. Each of the curvy line is next to each other.