Alde Flow Continuous Hot Water The Alde Flow is our latest ingenious invention, expanding the heat exchange surface to pre-heat the water entering the Alde 3020 Compact HE boiler. This provides continuous hot water. The Alde Flow is more compact and lighter weight than conventional marine calorifiers, and integrates seamlessly with the Alde 3020 Compact HE system, so no manual switches or valves are required. The Alde Flow has an integral pump, so when the boiler's circulation pump is inactive, continuous hot water is still available. Indeed once fitted, your hot water is limited only your fresh water and gas supply!