We have a house that's over 100 years old. It has baseboard hydronic heating which means ugly metal covers that are often dented, rusty, and falling apart. I'd checked into purchasing replacement covers and they aren't cheap. Especially if you have one in every room in the house. We have fourteen.
We've been working on one room at a time and when we painted the living room we painted the metal baseboard heater covers because they were in ok condition and that worked fine. But when we got to the bathroom renovation those covers were rusty due to the moisture in the room. So we decided on wood covers after verifying it was safe for hydronic heaters. The little metal fins on hydronic heaters just don't get hot enough to start a fire even if your curtains or sofa touch them. Even Bob Vila said it was ok!
Please note: this DIY design is only intended for hydronic (oil or water) heaters and NOT electric heaters.