Paper clip radiators! I'm going to file this under 'appliances'. These colourful radiators become wall art, rather than "clunky ugly utilitarian heating system". And they take up very little depth on the walls.
The Original Morris & Co - Arts and crafts, fabrics and wallpaper designs by William Morris & Company | Products | British/UK Fabrics and Wallpapers | Kelmscott Tree (DM6E230341) | Archive Embroideries