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Title 24 question


Feb 7, 2024
I am building a bathroom that is detached from the main house’s HVAC. They are requiring a permanent heat source. It is 70 sf. I would like to do a 500 watt wall heater but I fear that wouldn’t pass Title 24.

Anyone know of an economical product to get this through?
California Green Building Code 2022
A5.207.2.2 Electric Resistance Heating

Electric resistance heating systems shall not be used for space heating.
  1. Where an electric-resistance heating system supplements a heating system in which at least 60 percent of the annual energy requirement is supplied by site-solar or recovered energy.
  2. Where the total capacity of all electric-resistance heating systems serving the entire building is less than 10 percent of the total design output capacity of all heating equipment serving the entire building.
  3. Where an electric resistance heating system serves an entire building that is not a high-rise residential or hotel/motel building; and has a conditioned floor area no greater than 5,000 square feet; and has no mechanical cooling; and is in an area where natural gas is not currently available and an extension of a natural gas system is impractical, as determined by the natural gas utility.

A bit expensive but, You could use a Heat pump

Mini Split Heat Pump
I agree with what mark says. I don't do MEP work personally, but the MEP engineers my firm works with have told me that the changes the state made in the 2022 code make it much harder to use devices that aren't heat pumps for applications like this. I was told that the State is going all in on heat pumps.
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.
A thru-wall heat pump might be your best bet. Even the smallest 6000 BTUH unit would be oversized for such a small space.