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Indirect System

This system basically combines the Open Direct System with the Closed System. The Indirect System uses a heat exchanger to separate the heating fluid from the domestic hot water. When heat is called for by the thermostat, the heating zone pump and the heat exchanger pump come on at the same time.

Animation illustrating the functionality of an indirect heating system.

Legend for Indirect Heating System animation


  1. Allows for the use of one highly efficient water heater like the Polaris as the source for heating and domestic hot water.
  2. Well accepted by codes because the domestic water and heating water are separated by the heat exchanger.
  3. Allows for anti-freeze to be used in the heating loop for snowmelt applications.
  4. A solar hot water supplement can be added initially or at any time in the future.


  1. Cost and complexity are increased with the addition of the heat exchanger and additional stainless steel pump.
  2. The limited free cooling benefit of the Open Direct System is eliminated.

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Indirect System Example


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Open Direct System
Installing the Closed System
Installing the Indirect System
Installing tubing for a concrete slab
Installing tubing between floor joists
Installing tubing in the ceiling
Installing tubing in the walls
Installing a heated towel rack
Installing Radiantec Controls
Doing your own tubing layout.
Radiantec Basic Solar Domestic
   Water Heater Installation Manual.

Radiantec Basic Solar Domestic
   Water Heater Owners Manual.

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