Older mid-century homes often had in-wall electric heaters installed in their bathrooms and other smaller spaces. Unfortunately, original heaters can "burn out" from overused heating elements and transformers (that is, of course, if they weren't already removed entirely during a HVAC renovation). However, working vintage in-wall heaters are affordable and easy to replace or install. 
In-wall electric heaters still make economical and aesthetic sense, too, even if you have central heating in the home. They typically have classic retro styles, featuring chrome or polished aluminum grills and glowing heating elements. They are also perfect if you just need a little warmth in the bathroom on a cool morning without having to heat the entire home. Here are a few examples of some vintage in-wall electric heaters we have rescued and restored over the years.
This Ceil Heat vintage in-wall electric heater is a flush-mount type heater with an attractive retro chrome radiator grill panel cover and an orange glowing ceramic element. This Ceil Heat panel heater was made in Knoxville, Tennessee. A simple black phenolic knob turns the heat on and up, and the heater runs on standard 110v household power. 
The panel measures 19 inches x 11 inches, back panel cover measures 17.25 inches x 8.25 inches x 4 inches (which will be the size of the cutout hole needed in your wall to mount this heater).
Markel Electric is one of our favorite manufacturers of in-wall and portable heaters. This set of three vintage Markel in-wall electric heaters work in pretty much the same way as their iconic Heetair Fan-Glo portable models. Steel spring coil heating elements glow a bright orange when powered on, and a genuine General Electric fan blower forces heat from the front grill panel. The all-metal frames are finished in a tan and dark brown color scheme. 
Two of these Markel H754 in-wall electric heater units were found unused and complete in their original boxes (one was used, but cleaned and restored). One of these unused units has thermostat and power control knobs on the front panel. The other two do not, so they either work in conjunction with the main control unit or will require a separate wall-mounted thermostat control. These particular in-wall heaters are rated at 2000 watts / 240 volts. An included punch out template measures 14.25 inches x 8.5 inches, and the outer frame of the grill measures 17 inches x 10 inches.
This pair of TPI / Markel CB1-10A in-wall heaters have polished aluminum grills and control knobs built-in, so there is no need for an external thermostat unit. These 1000-watt heaters have the classic Markel spring coil heating elements that glow a beautiful orange when turned on. 
The glowing heater doubles as a great night light for the bathroom on cold evenings! These units are newer, probably manufactured sometime in the last 25 years or so, but they look nearly identical to in-wall heaters from the 1960s, complete with classic black phenolic control knob. The panels measure 20 inches x 10 7/8 inches. The unit requires a wall cutout of 17 3/4 inches x 9 inches.