Options for Extreme Series Extreme Ducting Plenum. Sizes available for the Platinum 3500ti, 5000ti, and 8000ti. This plenum allows either side of the unit to be ducted. Duct the cold air through a vent into the cellar, duct the hot exhaust air out of the home. This plenum allows for total installation flexibility. The Exterior Grille protects the exhaust side of the system from the weather elements when installed through an exterior wall.