Direct vent vs. B vent requirements

[Brandon Whitmore]

Does anybody know why a direct vent does not have to follow the same requirements as a B vent when venting adjacent to a sidewall?

I assumed the clearance requirements were in place so that air currents would not cause venting issues, but perhaps I'm mistaken?

I just looked up something that I was sure would be wrong, only to find out it was perfectly acceptable. I had a direct vent fireplace venting through a roof line, about 4' from a dormer wall. With a B vent, the vent would have to be 2' above the roof line since it is within 8' of the sidewall. On this particular fireplace, only a 20'' clearance was required. Requirements- page 12

[patt]

Lower BTU rating?

[Brandon Whitmore]

Lower BTU rating?

That would make sense.

[Richard Moore]

BTU rating probably enters into the equation. The codes basically say to manufacturer's specs for direct vent.

This is just a WAG off the top off my head but perhaps the consistent, steady draft isn't quite as important for a, glassed in, gas fireplace. It's not like you can blow a lot of combustion gases back into the room. Obviously, draft is necessary, but maybe they decided that clearances to eddy creating walls, etc, can be less with with sealed, direct vent appliances?

[Chad Fabry]

What Richard or maybe because the direct vent gasses are tempered?