My new bedroom mini-split cools the bathroom fine during the recent heat waves. Time will tell if my unheated bathrooms will be chilly if the heat only flows in there from the adjoining rooms.

In Europe wall mounted towel warmers are used as a heat source in bathrooms. I have never taken an interest in how they work so I don't know if it could work in your house.

https://www.warmup.com/blog/can-a-towel-warmer-heat-a-bathroom#:~:text=Of%20course%2C%20if%20you%27re,provide%20heat%20to%20your%20bathroom.

Terrific looking bathroom!

When the coldest months are here - we place a small ceramic space heater on a stacked set of vintage stools by my sons' sink - the room gets crazy warm. Not ideal I know but an easy option in a pinch

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We did this turn on heater in a bathroom we added that is the back of the garage.

You can have a heater/vent unit placed in the ceiling. It warms the room well. In the hot months, keep the door open and let the cool air from other parts of the house in, or use a portable a/c unit and vent it out the window. It's not a permanent placing, you take it out and store it when not needed.

I agree. The only issue is when it gets really cold. The majority of it's fine.

Where are you located? That will make a big difference. We also occasionally use a small space heater in one bathroom and find that works well on the chilliest days--but we're also in California, where cold is just a state of mind. I think the coldest our inside temperature has ever been is the mid-40s, which is balmy winter weather for many parts of the U.S. If you're in an area where you can get by with minimal heat, I'd consider a towel warmer or a fan that has a heater (depending on what fan you have now, you might even be able to swap it out in the same space with a little rewiring). I've used both in other people's homes and while they won't warm up the whole room, they warm it enough to not be freezing in the winter months. Doesn't help with a/c, but honestly that would bother me far less since it's not a room you spend a huge amount of time in unless you're showering (and then you just make it cold if it's muggy out).

The other thing you might be able to consider is a vent in the vanity toekick, if there is one. (I can't see the sink here--obviously not an option if it's a pedestal sink or a wall-hung vanity.) That may not work with mini-splits if you won't be using vents, though.

I find in a smaller bathroom the heater type light/ fan/ radiant het is enogh to heat the space on a chilly day and I agree open the door for the cold air from the rest of the house to cool

I have an exhaust fan with four heat lamps installed. Mounted in the ceiling. Lots of warmth, quick heat!

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