Wow... "power direct vent" was a new one for me. I had to look it up. It looks like a power vent (uses fan to exhaust) with a coaxial outside air intake to draw combustion air from outside.

Of the two, I would use a power direct vent since it's getting air from outside instead of inside the heated space.

The answer to your question about hot water if power goes out is "no".

The odd thing is that the efficiency ratings aren't great (.67).

Consider a condensing gas tankless for the same amount of money and .92 energy efficiency.

They are horribly horribly LOUD. Surely there are other options?

jake, thanks for pointing out the differences! i could not find info on explaining that anywhere!!

livewireoak, do you think i would be able to hear it from the first floor if it is in the basement? would insulation help at all? unfortunately because we want it in the basement, we have to do a direct vent model, but the title 24 forces us to do one that is at least .67 efficient and the only models that have that minimum efficiency rating are for power models...

Most power vents I've heard, you could hear them all over the house. Loud doesn't begin to describe that whistling piercing shriek.

Can you not do a direct vent tankless? You don't have to worry about freezing pipes in CA, so you could even do it external to the house entirely.