Any way to heat an unheated closet in a 100+ year old home?

Is there a light fixture in there?

There a small portable heaters...some models have thermostats. I have one in my bedroom....45 to 50 degees in the winter with the furnace on. The issue....all the havac vents are 12 inches down from the ceiling. Physics. Cold sinks heat rises.

Could you put in vents that would let the heat in the closet from the heated areas? Perhaps some kind of small heater you can turn on before you go into the closet to warm it up would work.

You could install a wall bathroom heater in the closet.

Will check into finding a way to allow some heat to get into the unheated closet from one of the 2 walls that back on heated areas. My husband is not in favor of using a space type heater of any sort. Thanks to all!

Put a decorative metal panel in the closet door. A small fan in the bedroom, or a ceiling fan will help move the heat into the closet also.

Removing the closet door would be the simplest solution. Since you may redo this whole area in the future, save the door. You can even store the door in the closet on its side, back up against the long wall. That may give you more space since you don't have to leave room for the door to open. Best wishes 😇

Install a bathroom ceiling heating fixture... http://www.homedepot.com/p/Broan-1-250-Watt-Surface-Mount-Fan-Forced-Ceiling-Heater-157/202919950

Change over your light socket to a ceramic one... https://www.amazon.com/Leviton-9726-C-One-Piece-Incandescent-Lampholder/dp/B00002N5FR/ref=sr_1_11?ie=UTF8&qid=1500701562&sr=8-11&keywords=2-1+ceramic+plug+and+socket and then put in a heat lamp bulb

Then put in one of these heat lamp bulbs ,,, http://www.homedepot.com/p/Philips-250-Watt-120-Volt-Incandescent-BR40-Heat-Lamp-Light-Bulb-416743/202768698

And then plug one of these heaters, less dangerous than a space heater yet puts out some real warmth... https://www.staples.com/Cozy-Legs-Heater/product_512953?cid=PS:GooglePLAs:512953&ci_src=17588969&ci_sku=512953&KPID=512953&cvosrc=PLA.google-SALES.Cleaning%20Supplies%20%26%20Facilities%20Maintenance&cvo_crid=45560782422&cvo_campaign=192147462&gclid=CjwKCAjwzMbLBRBzEiwAfFz4geUv_B89zsdS9fov1A3cstwRK0k4Hk4gzeH5LDBSjdOmrYVldm-erBoCO5gQAvD_BwE

You could also put in a radiant floor heating system... http://www.homedepot.com/p/IdealHeat-5-ft-x-36-in-Radiant-Floor-Heat-Film-with-Anti-Fracture-Membrane-IH-AF-36-5/206689289?MERCH=REC-_-PIPHorizontal1_rr-_-205613818-_-206689289-_-N

A couple thoughts come to mind. The first, if it's cold, I'd check to see if there is any insulation in the closet. If not, the easiest way to insulate is to put up sheets of foam on the inside and wallboard over it like a second wall. Then I'd put a grate in the lower portion of the door to let warmed air into the closet. If you don't check for insulation first in a house that old, you will loose any warm air and probably cool the room instead.

I was born and raised in Wisconsin so I know what you are dealing with. You may want to leave the closet door open a crack so heat can enter.