Blaze Through the 2026 TSSA Gas Technician II Test – Fuel Your Future Success!

The stacking effect happens because water temperature creates density differences in the tank. Hot water is less dense and tends to rise, while colder water settles at the bottom. When you repeatedly draw small amounts of hot water, you remove the top hot layer, and the incoming cold water at the bottom doesn’t mix quickly. Over time this produces distinct temperature layers from top to bottom—hot water on top, cooler water below—rather than a uniform mix. That layered, stratified arrangement is the stacking effect. Sediment buildup, tank wall corrosion, or air pockets are separate issues and aren’t what this phenomenon describes.