Dedicated Circuits for 120V heat Pump Water Heaters

[samthebikerider]

Preface: I am a researcher who is hiring contractors across the US to install 120V heat pumps and heat pump water heaters

I've had some pushback from electricians in various corners of the country regarding installing 120V heat pump water heaters on shared circuits. Some say their AHJ will take issue, and some have seemed to not notice a problem. The question is: can 120V HPWHs that are designed and UL-listed for use on a shared circuit be installed on a shared circuit according to NEC? The concerns are that dedicated circuits are required for "critical-use" equipment, and electric water heaters fall into that category. I haven't found the code references yet, and surely this will be somewhat AHJ-dependent, but what are the general thoughts? UL and manufacturer approval is good enough to not worry? With the recent and ongoing push to bring 120V heat pump equipment for water heating and space conditioning to market, I see this question breaking out eventually.

Example product: https://images.thdstatic.com/catalog/pdfImages/08/08663254-cda3-4820-bc09-2789a7a20b2e.pdf

 

[tortuga]

Can you post a photo of the nameplate that says voltage & amps or watts ? That spec sheet only says 'average wattage'.

 

[Tulsa Electrician]

What does the name plate say for current draw. I seen nothing in the link.
Sorry, posted same time.

 

[wwhitney]

NEC 422.13 indicates that a storage type water heater of 120 gallons or less shall be considered a continuous load, which requires a 125% continuous use factor for load calculations.. And NEC 210.23(A)(2) says that on a multi-outlet branch circuit, the rating of cord-and-plug connected equipment fastened in place (like a water heater) shall not exceed 50% of the branch circuit rating, where lighting units or portable cord-and-plug connected equipment are also supplied from the branch circuit.

So to plug the water heater into a branch circuit that supplies "general use" receptacles, or that also supplies lighting, the water heater nameplate would need to indicate 6A or less at 120V to plug into a 15A branch circuit. Or the nameplate would need to indicate 8A or less to plug into a 20A branch circuit.

If the nameplates comply with those limits, then the code references above should be sufficient to convince a reasonable AHJ that there's no problem with this "shared use". On the other hand, if the name plate amperage exceeds the above limits, then the AHJs are correct that it is an NEC violation, regardless of the manufacturers' marketing.

BTW, if the nameplate says "MCA" or minimum circuit ampacity, that figure already includes a 125% factor, so the limits would be 7.5A on a 15A circuit, 10A on a 20A circuit.

Cheers, Wayne

 

[samthebikerider]

NEC 422.13 indicates that a storage type water heater of 120 gallons or less shall be considered a continuous load, which requires a 125% continuous use factor for load calculations.. And NEC 210.23(A)(2) says that on a multi-outlet branch circuit, the rating of cord-and-plug connected equipment fastened in place (like a water heater) shall not exceed 50% of the branch circuit rating, where lighting units or portable cord-and-plug connected equipment are also supplied from the branch circuit.

So to plug the water heater into a branch circuit that supplies "general use" receptacles, or that also supplies lighting, the water heater nameplate would need to indicate 6A or less at 120V to plug into a 15A branch circuit. Or the nameplate would need to indicate 8A or less to plug into a 20A branch circuit.

If the nameplates comply with those limits, then the code references above should be sufficient to convince a reasonable AHJ that there's no problem with this "shared use". On the other hand, if the name plate amperage exceeds the above limits, then the AHJs are correct that it is an NEC violation, regardless of the manufacturers' marketing.

BTW, if the nameplate says "MCA" or minimum circuit ampacity, that figure already includes a 125% factor, so the limits would be 7.5A on a 15A circuit, 10A on a 20A circuit.

Cheers, Wayne

Thanks for that, Wayne. That is confirmation enough for me. The Rheem model I posted (sorry to the other two commenters, for some reason the spec sheets I've found online are missing amperages) recommends 7.5A of a 15A shared circuit, which I am almost certain is reported as a MCA (will of course find out). Will need to work with these manufacturers to clarify and improve spec sheet reporting. As long as it isn't prohibited by some "critical-use" requirements that I'm not finding in the code, then I think we are meeting NEC.

Thanks!

 

[Tulsa Electrician]

Does this mean you can not use a 20 amp shared circuit.

 

[Tulsa Electrician]

Would 422.60 apply to this?

 

[samthebikerider]

Another question I have is regarding the definition of “fastened in place.” A 120V HPWH is plug-in, not wired. It is technically fastened in place by plumbing and whatnot, but is that the same “fastened in place” as is mentioned in the code?

 

[wwhitney]

A 120V HPWH is plug-in, not wired. It is technically fastened in place by plumbing and whatnot, but is that the same “fastened in place” as is mentioned in the code?

Yes. 210.32(A)(2) is specifically about cord and plug connected equipment fastened in place. Roughly speaking, I'd say fastened in place means not moveable without tools.

Cheers, Wayne

 

[mtnelect]

Yes. 210.32(A)(2) is specifically about cord and plug connected equipment fastened in place. Roughly speaking, I'd say fastened in place means not moveable without tools.

Cheers, Wayne

Check out Section 400.7 Uses Permitted, and Section 400.8 Uses Not Permitted.

 

[tortuga]

Would 422.60 apply to this?

I think so, the nameplate should comply with 422.60