Rinnai hydro - air?

QUESTION

Rinnai Tankless Water Heaters claim they can convert a residential forced air furnace using the Rinnai as the source for hot water usage bathing , dishwasher etc. and to heat a ducted system. They use the fan in the existing furnace, add the Rinnai and a coil. It appears to use the Rinnai instead of a boiler for the comparable result.

I would think this is a hydro air system but I am having trouble finding any information on this except from Rinnai.

I have a 2200 ft2 house located in the foothills of Colorado, elevation at 8,000 feet, current forced air system is fueled by propane.

What prompts this inquiry is I have an old electric water heater 30 years old or more , and it appears the Rinnai conversion would save substantial enery costs for household hot water and forced air heat.

Appreciate your input.

Art