Heating with Tankless Water Heater & Hydronic Air Handler vs. Gas Furnace


I've looked around online and haven't found a lot of good information on home heating with hydronic air handlers used in conjunction with tankless water heaters (TWH). I would be interested to hear from anyone who has experience with these "combined" or "integrated" space- and domestic water heating systems.  I'd like to know a few things, especially as they compare to a condensing gas furnace:

- How efficient are these systems?  I've read that they match the efficiency of the water heater, so if you have a 94% efficient condensing TWH, your home heating is then 94% efficient as well. Of course, this does not mean that they necessarily heat as effectively as a condensing gas furnace, since the heated air from these systems is not as warm as that from a gas furnace, correct? 

- What are your thoughts on ease of installation and ongoing maintenance requirements? I have heard of issues with scaling, and a need for very frequent cleaning of the inlet strainer to the TWH.

- When the water from the air handler is returned to the TWH it is much warmer than typical incoming water to a TWH.  It is my understanding that higher incoming water actually reduces the efficiency of a condensing TWH - is this still true with current condensing TWH models?

- Bottom line, would you put in one of these systems, or opt for a separate condensing gas furnace?  Are there situations when you would choose one over the other?

I'm interested to know more about these systems in general, but also have a specific home in mind: a 2400 sf home in Portland, OR built in 1928 (currently with little insulation), that has a condensing TWH already installed.

Thanks for any insight you can offer!

- Chris

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When it costs the same price as 2 separate systems there is no juice regardless of how hard you squeeze.

Only a nightmare for future service techs, there will never be a part on the truck to fix the system, maybe not even at the supply house. Parts for tankless water heaters are special order, and not every tech can work on them.

I've looked at tankless water heaters and I'm not seeing any juice for the squeeze there either. They simply don’t' save enough energy to justify their high upfront installed cost and more complex maintenance/parts availability.

As you have pointed out, on a tight house is it even worth paying an ever increasing monthly fee for the gas meter charge, or just go all electric? Our local electric company gives cheaper rates in the winter, cheap enough that 3/4 of all-electric homes use RESISTANCE HEAT as a primary heating method.


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