Boiler vs Tankless HW Heater Help

[Fil Oliveira]

Hi Everyone,

Looking for some help here, we renovated our house top to bottom along with an addition. The addition is a slab on grade with in-floor heating, the rest of the area is heated by radiators. DHW is supplied via indirect hot water tank

My contractor has installed a Navien NPE-180S (Tankless water heater) not a boiler as the heat source. Is this an acceptable practice? My drawings say: “New Boiler: NTI (or equivalent)”.

In my experience, the “or equivalent” reference is referring to an alternate manufacturer, not an alternate source of heat or device”.

I don’t want to accept this product as I think that it voids warranties and above all else, IMO, it’s the wrong piece of equipment!!

 

[WorthFlorida]

I would call the manufacturer. Also your local building department if it would pass inspection.
Tank less water heaters activate on water flow when a faucet is opened. Not sure if it would work with a circular pump.

 

[Sponsor]

 

[Dana]

Hi Everyone,

Looking for some help here, we renovated our house top to bottom along with an addition. The addition is a slab on grade with in-floor heating, the rest of the area is heated by radiators. DHW is supplied via indirect hot water tank

My contractor has installed a Navien NPE-180S (Tankless water heater) not a boiler as the heat source. Is this an acceptable practice? My drawings say: “New Boiler: NTI (or equivalent)”.

In my experience, the “or equivalent” reference is referring to an alternate manufacturer, not an alternate source of heat or device”.

I don’t want to accept this product as I think that it voids warranties and above all else, IMO, it’s the wrong piece of equipment!!

It's possible to design a system that will go the distance using a tankless water heater as the system boiler, but it's a bit silly to do that these days now that more rugged and more appropriate condensing fire tube boilers are available. According to code in my area it's only legal to use a water heater as a hydronic boiler if it's set up as a combi-appliance, heating both domestic hot water and providing space heat. Heating an indirect with the tankless might pass that hurdle in the code language, but if it's not reasonably well set up the tankless may not last very long.

Most hacks using tankless water heaters as the heat source for radiant floors over-pump the tankless, wearing out it's internal plumbing and flow sensor, and operate at too low a delta-T for optimum efficiency. Tankless water heaters are designed to operate at modest flow rates and a delta-T of 25-50C. Most slab radiant heating systems never see a delta-T greater than 10C, often less than 5C. Your radiator zones may see greater deltas than that, but might require over pumping the tankless. The system might be plumbed primary/secondary to get around the flow limitations, but that also lowers the delta-T across the tankless. For this to work well and last for decades it need to be designed as a system.

 

[Fil Oliveira]

Thanks Dana for the technical info

The most frustrating issue is that I paid for a design thats not being followed. The plans clearly state: "New boiler" not generic heating device.

Cheers... ill keep you posted on the progress... should be an interesting week