Quick question... The picture I attached shows the ceiling of a small 29"w X 29"d water heater closet that has access from the exterior of the house. The vent exited directly through the center with a metal firestop. It also had two of these grates right next to the vent that were probably there to allow hot air to escape up into the attic. I now plan on installing a tankless in the same closet venting through the same center hole (replacing existing with proper vent material), but wonder if I need these grates up in the ceiling? Does it pretty much make the firestop useless being so close to the vent? The whole closet will be covered with proper 5/8" drywall, before I put the new water heater in. So what do you think? Does the extra heat of a tankless require that I keep the venting grates up there to keep the heat from collecting in the ceiling?