[Silver Judge]

I have a 2-story 1927 home that originally had a garage with carriage style doors.
When I bought it, the garage area had been re-framed and a man-door was put in, effectively de-commissioning it as a garage. This garage is on the ground level with two floors above. I’ve gutted parts of the basement and garage (all on same level) and have created a larger space for a new garage that I’m working on slowly.

What is the best practice and what codes apply if I must keep a natural gas furnace in the same space as a car?

In another part of the US, there’s a requirement to have the furnace installed on a concrete pad 3 or 4 inches above the level of the rest of the space.

I found some access to city of seattle building codes but cannot find a reference to this in the codes for existing buildings