Questions about a furnace in my garage remodel
 

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

My furnace is in the garage..its up on a wood and drywall platform guessing 18 inchs off the ground with the gas water heater..

I sometimes work in a fuel environment around aircraft all eletrical connections ( drop lights) are at least 18 inchs off the ground in a class A hanger

Thats figured the safe limit considering fuels vapors are heavier than air and collect on the ground also in order to obtain a good draft up the heaters exhaust pipe to outdoors you will need a couple small vents in the room so incoming air can replace exhausted so CO. doesnt accumulate from the furnace and its best to have them low to vent out any combustable vapors from autos or cleaning fluids or just stored combustables in the garage

call and ask , just don't tell them your name just say your thinking about it and whats involved , when we built my buddys garage we put the furnace outside the garage in a little insulated room with a outside door and vents so it draws its burning air from outside and not the garage so it was less suseptable to drawing in explosive vapors and made it easier to service and it doesn't make a draft in the garage by burning the heated air .

Are you dead-set on a furnace or would you consider a radiant heat system?

I think that they are fairly reasonably priced (under $1000) BUT they operate more economically than the furnace AND warm the objects rather than the air. If you are going to be working in the garage any it makes the area more comfortable plus recovers more quickly to the set temp if the door is opened, etc.

We have one in our barn and it is nice. I can't be more definite on the price as I allowed a local contractor to use my building as a project. He charged parts only a few years ago and took pics to document step by step instructions. Was a good deal.

I'm in the midwest and you being in Seattle where it doesn't get as cold should work out even better for you.

CF

There is a working Lennox furnace in my garage now, it's to heat the house and not necessarily the garage. I'm trying to figure out if I have to elevate the furnace and put it on a pad of concrete or another non-combustible material.

The flame needs to be at least 18" about the floor. Also the furnace needs to have some sort of guard around it to prevent it from being hit by a car. If its boxed in you need to allow for proper combustion air and the return must be ducted and sealed to the furnace. If the garage is small and the furnace is big enough BTU wise you may also need to provide some outside air for combustion.

I install gas furnaces every day almost and as far as I am aware you dont need to elevate it. If the flame is less than 18" which I doubt, the manufacturers purposely design them that way so that the flame is above that. If you have a Lennox 90% your good because that is sealed combustion. If it concerns you heed the advice above or do what I do and put it up on bricks and cork pads. If you already have concrete on your floor it is so not worth it to retrofit to radiant floor heat, unless you do concrete for a living and have a buddy that does hydronics for a living.

Thank you for the input on furnaces and heating in garages here