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Is An On-Demand Gas Water Heater Considered "Central Heating Equipment?"

What I find interesting is that immediately after the section in question in the NEC is the section on Storage-Type Water Heaters.

I don't believe the section on Central Heating Equipment was intended for on-demand water heaters to be included; however, what is the difference between an on-demand water heater providing hot water to sinks, tubs, and showers, or for a hydronic heating system? What I am seeing in the comments is that if it provides heat to a house, then it is Central Heating Equipment, but if it doesn't, then it is not.
 
jar546 said:
What I find interesting is that immediately after the section in question in the NEC is the section on Storage-Type Water Heaters.
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I spotted that immediately.

jar546 said:
I don't believe the section on Central Heating Equipment was intended for on-demand water heaters to be included; however, what is the difference between an on-demand water heater providing hot water to sinks, tubs, and showers, or for a hydronic heating system?
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It is difficult to imagine using an on-demand water heater to provide heat for a building. The duty cycle is completely different. I can't imagine anyone doing such a thing except possibly on an emergency basis.

jar546 said:
What I am seeing in the comments is that if it provides heat to a house, then it is Central Heating Equipment, but if it doesn't, then it is not.
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Exactly.
 
jar546 said:
So what I’ve discovered is that they actually make these dual gas units that actually do both.
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That's news to me. I don't even see many of them being used for water heating around here, but I think they are gaining in popularity. In my late wife's native country, that's ALL they use. And they don't even leave the pilot running. When not in use, they shut off the gas supply. When they want hot water -- there's a box of kitchen matches next to the water heater.
 
Yankee Chronicler said:
I don't even see many of them being used for water heating around here
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They make more sense for low temperature hydronic systems, e.g. radiant hydronic floor heat, where the desired water temperature is circa 120F. If you have old school radiators that are designed for 180F water, a boiler is more typical. Although some wall hung boilers also can provide domestic hot water, I think via a built-in heat exchanger.

Cheers, Wayne
 
Yankee Chronicler said:
That's news to me. I don't even see many of them being used for water heating around here, but I think they are gaining in popularity. In my late wife's native country, that's ALL they use. And they don't even leave the pilot running. When not in use, they shut off the gas supply. When they want hot water -- there's a box of kitchen matches next to the water heater.
Click to expand...
Italy uses a dual system with one side of the on demand controlling domestic hot water and the other side controlling the temperature of the radiators.
 
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