I’m currently living in my tack/feed room while my house is being renovated. This is the heater that we have in the room where we sleep: Stiebel Eltron 074058 1500W, 120V CK 15E Wall Mounted Electric Fan Heater. It is wall mounted, not plugged in.
We bought in on Amazon and you can set the temp on a dial from low to high. Our room is 12x14 with a 14’ sloped ceiling (I think it slopes up to about 15’). The room is well insulated and 2 of the 4 walls are 2x12/insulation/2x12, so about 5" thick.
Two of our 9 dogs stay in the room during the day when we are at work and we leave it set on low. When we arrive home the room is always toasty warm. During the night when we are sleeping, we set it at medium. We don’t have a thermometer in the room, so I don’t know for sure the temp, but it’s well above freezing.
We have an identical room that has a wall mount AC/heater and we felt like it was overkill for the size of the room and how well insulated the room is so we bought the separate heater for the second room and will install a wall mount AC when it gets warm in the spring. The room we live in has water, but the pipes aren’t in the concrete foundation, they from the outside of the building, so if it gets really cold we have to completely shut off the water supply. We live in Texas, so thankfully that doesn’t happen very often.