How do i make a downstairs bathroom at the back of the house warmer

How about installing heated flooring?

Do you have anything but concrete on the floor

Cover the floor with rugs, if your feet are warm, the rest of you may feel warmer.

Why not insulate the floor and overboard.......

Could you put cooper tubing on the concrete floor and add more concrete. I'm not sure how it's done, but I lived in an apartment in the midwest, where it was the only heating. Hot water or air ran thur the tubing.

Have you considered an overhead ceiling fan/heater? Do you have room for a baseboard heater? Short of covering up the concrete floor or tearing out the concrete, some type of accessory heat is an easy DIY option. Also, throw rugs will help some.

You could try a space heater with a thermostat. OR.. install a heat lamp light fixture. http://www.bathroomheater.org/bathroom-heat-lamps.html

I would suggest using a carpet to help reduce the cold

She said clearly a space heater has to be on 24/7 and it’s very expensive. And she’s absolutely right. You do NOT want to walk into a freezing cold bathroom and have to then wait for the space heater to heat the room AKA toilet seat or bath/shower floor. It’s also $1 an hour. 24hrs is $24 per day x 30. Been there done that. I wouldn’t give advice that I wouldn’t take myself.

if you can put siding on the exterior of the room without it looking weird, even if it is over brick that wild help. But I think it is the concrete floor that is the main culprit. You might check into the cost of having cork flooring installed, and or check into putting in heated flooring. If there is a window involved, make sure it is as insulated as you can get. Leave the door going into that bathroom open at all times. That will help keep it from becoming a fridge, at least a little.

oh and a ceiling heat/vent system would be nice too. My parents have one and it has a safety timer switch.

if you don't have damp proof contact on rising cavity block work would this make a 9'x6' room cold?