Thermax Semi-Storage Calorifiers


GMS Storage Calorifier

The 'Thermax' Range of Semi-Storage Calorifiers are designed to meet high DHWS (domestic hot water service) demands on a compact and cost effective way. Hot water is available within a few minutes of a cold start, temperature control is excellent and - thanks to the built-in thermal store - the primary input power requirement is much lower than for instantaneous water heaters.

Why choose a Thermax unit?

  • A compact design
  • A flexible water heater design to suit any demand
  • Utilises steam, LTHW or MTHW primary medium
  • Gives virtually instantaneous hot water
  • Optimises peak input power
Description of Operation

The Thermax unit pumps cold water from the bottom of the thermal storage vessel through a powerful heat exchanger. This heats the water to the set temperature. The heated water flows over a temperature sensor at the heat exchanger outlet. This adjusts primary fluid flowrate via a proportional valve to maintain temperature. After this the heated water is returned to the vessel near the top. The vessel contains special baffles to prevent excessive stirring. The hot water now at the top of the vessel can be drawn off for use. Peaks of demand, which exceed the heat exchanger output, are met from the hot water stored in the vessel. The vessel is then re-charged with hot water during the subsequent lower demand. When demand is low the water in the vessel is heated from top to bottom, preventing growth of legionella bacteria

Thermax standard specification
  • Thermal storage vessel: Materials:- Copper or copper lined steel. Each vessel is designed to suit the particular application, its working pressure and whether open- or un-vented.
  • Heat exchanger: U-tube type, 2 tube passes, 2 shell passes. Copper tubes, copper baffles, brass tube-plate, Steel header.
  • Loading pump: Bronze, in-line.
  • Intermediate pipe-work: This links vessel, pump and heat exchanger. Material:- copper.

GMS manufacture Thermax semi-storage calorifiers using the following standard materials:

  • Solid Copper
  • Copper-Lined Steel
  • Galvanised Steel
  • Stainless Steel
  • Glass/Polymer Lined Steel
Information Pages


     Primary Heat Source

     Some System Considerations

     Ancillary Items

     Thermal Insulation

     Design Standards

     Unvented Packages

Technical Documentation

     Download Data Book

     Download O&M Manual

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