This 9-inch ventilation stack top kit is a draft hood. It is a necessary / mandatory component if you will be installing and using your heater in an indoor operation setting. This draft hood allows for proper venting and moves heat above and away from the heater. Doing this works to prevent overheating and potential fire hazards. The stack measures 9” and comes with a base and attachment to connect to Raypak heater variants. It fits models: R406A, R407A, R408 Digital Pool Heaters. This stack weighs 19.15 pounds and has dimensions of 32” x 18.5” x 18”.