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Inspecting Hydro-Air Heating Systems

Hydro-Air Boiler System

 Heat Pump Geo-Thermal System

A hydro-air system employs hot water coils in an air handling system. Basically, it is a forced air system with coils (Hydronic Coil) heated by hot water running through them. The hot water in the coil is supplied by a hydronic boiler. Some geo-thermal systems employ hydro-air if forced hot air distribution is desired. It could also be integrated in one air handler using the same coils for an air conditioning system. This is basically a heat pump employing a compressor. This configuration uses refrigerant. If supplied by a boiler; these units are very efficient in the winter months. The inspection on hydro-air units are different than a conventional forced hot air furnace. What should a home inspector be looking for:

  • There may be a timed delay when the thermostat calls for heat to allow the coils to heat up. The timed delay will be shorter on a heat pump system.
  • The unit will either have a dedicated zone valve, circulator, or pump / check valve installed in the air handler (see diagram above). This must activate properly for the system to respond.
  • Keep in mind that the hydronic supply from the boiler will most likely be used for domestic hot water and should be separated from the coils used for the Hydro-Air system.
  • A mixing or tempering valve (can be seen in detail above) should be installed if the unit is also producing domestic hot water. The water for the heating coils will be considerably hotter than the domestic hot water should be. The mixing valve will ensure the temperature is lowered to an acceptable level.
  • If possible the air handler should be positioned below the water heating source to prevent thermosiphoning; (mixing of hot and cooled water), if a circulator or pump is not employed.
  • The heat pump should be inspected as normal.
  • The duct system should be well insulated.
  • If integrated with the air conditioning system (heat pump), a condensate discharge should be present.
  • Obviously there is no flue pipe or carbon monoxide issue to be concerned with at the air handler.
  • The boiler or heat pump supplying the unit should also be inspected at this time.

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