The local AHJ is saying that the bathroom requires heat? I think it would be a poor design not to have heat, but I think it would be a stretch to say it's required, unless they have a local ordinance. I assume you have plans, and I assume the plans are in plan check which is bringing up these questions. Do you have a designer or are you doing the planning work as well as the building?
I am making a bunch of assumptions because I don't know your scenario, but if they are telling you this is required, they need to provide you a code section. When you say "title 24" I assume you mean energy code, correct? (Title 24 is actually the entire building standards code, but is commonly used to reference part 6, energy code.) Are you using an energy consultant who is creating an energy report? If not, then you would theoretically be creating the compliance documents yourself?
Assuming you are using the 2022 CA Residential Code as the basis for your design then you would want to review R303, and in particular, R303.10. You will notice that required heating references "habitable" rooms. Go to chapter 2 (definitions) and you will find that bathrooms are not considered habitable.
I think you want heat though. Review the exceptions that
@mark handler referenced, one of those might work. Electric resistance is an expensive solution, but for the relatively infrequent use in a bathroom, it might not be too bad. You can use radiant heat, but you may find it difficult to produce the compliance documents yourself, consider hiring an energy consultant to do so.
