What would cause white smoke, with a burning smell, to come out from under the hood, and through the air vents?

is the oil cap on?

Just keep a close eye on all of your fluids for a while. If the smoke smelled sweet would be anti-freeze. If it smelled like oil could have gotten a little oil on the manifold from the service work. And yes check oil cap..................

Yes, the oil cap was on. There was oil on the dipstick. The Subaru service center went over all of it. The tow truck msn said it smelled like a burned out electrical component like an alternator. What would air conditioning fluid smell like?

Thanks, I will look at all the fluids. I was wondering if something from the environment might have gotten in the engine.

A/C gas is pretty much invisible with a very strange odor not likely the A/C. I can't see anything from outside the engine getting inside to cause this.

Thanks. The engine was cold, and I had just started it, so it's hard to imagine any fluids leaking and causing smoke right away. I have just heard stories about small animals getting under the hood, and I guess, not inside the engine block, but somewhere on the outside. My next guesses are that something in the fuel regulating system might have stuck briefly. There had been a recall for an update to the computerized system that regulates all of that, as much as I understand, and they had changed something there, Or perhaps the clutch, as I have a standard, stuck briefly for a moment. I'm going to take it in for it's 30,000 mile checkup.

Is your windshield washers working? and is the fluid still in the resivoir?

Head gasket leak when cold. leaks anti freeze into the combustion chamber and results in white smoke but should be out the exhaust system unless had a backfire which might then come out the intake system under the hood. This is an hypothesis only