hmmm

[Ronald P. Bero]

They said it's ok its a power vent

[Steven Taylor]

Well that makes sense. The fan would push out the gases instead of relying on natural draft.

[gkay]

I’m sure Dave has explained this before, but no one else is touching it so here goes. (Where’s Ben Dave???) LMAO

Short answer it is acceptable to be vented horizontally with a maximum downward (yes downward) pitch of ¼ inch per foot.

Long answer…
Ronald if the gas appliance is using B-Vent it is a Cat I Appliance and in this case would be a Fan Assist Cat I Appliance. The "power vent" of a Cat I doesn’t create a positive vent pressure to exhaust and therefore still relies on the buoyancy of the hot flue gasses to vent them horizontally to the exterior.
You can vent them horizontally with a maximum downward pitch of ¼ inch per foot when AHJ allow it. You also have limitations with horizontal distances that cannot be exceeded as per manufacturers’ specs along with termination points.

Definition of a Cat I Appliance is one that operates with a nonpositive vent static pressure and a flue loss not less than 17%. Flue gas temperature 140F above its dew point so it won’t (shouldn’t) condense.

Steve the only time flue gasses are pushed out is with Cat IV high efficiency furnaces and are vented with plastics like PVC, ABS or 636 or Cat III Appliances that are vented with stainless steel all of which are a sealed venting systems to contain the products of combustion under a positive vent pressure.
The fan assist of a Cat I has say a two inch exhaust port. When you attach a 4 inch or 5 inch vent to the two inch port it becomes a non positive pressure at that point.
Hold a match to any screw hole on C vent and it will pull the flame in, nonpositive vent pressure.

Definition of a Cat III Appliance is one that operates with a positive vent static pressure and with a flue loss not less than 17%. Flue gas temperature 140F above its dew point temperature won’t (shouldn’t) condense.

Definition of a Cat IV Appliance is one that operates with a positive vent static pressure and with a flue loss less than 17%. Flue gas temperature is less than 140 F above its dew point moisture in flue gasses will condense.