Q&A: Marking on Energy Storage Systems for Residential Use

07 Jul.,2025

 

Q&A: Marking on Energy Storage Systems for Residential Use

Question

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The International Residential Code (IRC) and NFPA 855, Standard for the Installation of Stationary Energy Storage Systems, both have criteria for lithium-ion battery energy storage systems (ESSs) intended for use in residential applications. How can I verify that an ESS is certified for residential use? Which ESSs are certified for use inside the habitable space of a dwelling unit? 

Answer

The installation codes and standards cited require a residential ESS to be certified to UL , the Standard for Energy Storage Systems and Equipment, and may also specify a maximum stored energy limitation of 20 kWh per ESS unit. The current edition of UL limits the maximum energy capacity of an individual electrochemical ESS for residential use to 20 kWh (72 MJ). Currently, there is no requirement in UL for these units to be marked “Residential Use,” but such a marking has been proposed for UL for the next edition. However, current UL Marks may or may not include reference to residential use. Marks may or may not include reference to residential use.   

Goto CHANGINGTECH to know more.

UL also requires an electrochemical ESS intended for use in the living or habitable space of a residential dwelling unit to meet the cell level performance test requirements in UL A, which basically means the battery cells cannot be forced into thermal runaway or produce flammable gases. Any ESS complying with these requirements may include the marking "Suitable for Use in Residential Dwelling Units Where Permitted." However, to date, there are no lithium ion based ESS units that we have tested and found to comply with UL A’s stringent cell level performance requirements. Also, due to potential confusion between other certified residential use ESSs, the marking “Residential Use” has been proposed for inclusion in UL when an electrochemical ESS complies with the unit level residential large-scale fire test performance criteria in UL A. This marking will distinguish these residential systems from the rare situation in which an ESS meets the cell level criteria of UL A and can be marked as being suitable for use in residential dwellings.

An additional revision to UL has been proposed that will require installation instructions for indoor residential electrochemical ESSs to indicate that the units are only intended to be installed in specific locations. Permitted locations would include attached or detached garages, detached sheds, enclosed utility closets, basements, storage or utility spaces within dwelling units. Prohibited locations for an ESS would include habitable spaces and livings spaces in dwelling units, except when large-scale testing demonstrates that the cells that make up the ESS did not go into thermal runaway or vent flammable gas during the cell level test. For this rare exception, an ESS that meets the cell level criteria of UL A (no thermal runaway or flammable gas) can be considered to not present an additional fire hazard from the batteries as there is no added flammability hazards from the cells.

There has also been a proposal for UL that the instructions for residential ESSs indicate that they be installed only in enclosed utility closets, basements, storage or utility spaces with walls and ceilings finished with gypsum wallboard or be of noncombustible construction. If the walls and ceilings are unfinished, wood-framed construction, they must be covered with no less than 5/8-inch Type X gypsum wallboard.

Note:

If you want to learn more, please visit our website Residential ESS Manufacturer.

ESS (energy storage system) sizing in residential garage

Watts Happening

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I've been poking around each aspect of my install to ensure I'm not going to upset an inspector in the near future and when it comes to ESS, I'm confused.

Per this well written article, which sums up the codes relating to ESS, I'm trying to define what the "20kWh max each" means:

Fire Codes and NFPA 855 for Energy Storage Systems — Mayfield Renewables

Fire codes and standards inform energy storage system design and installation and serve as a backstop to protect homes, families, commercial facilities, and personnel, including our solar-plus-storage businesses. It is crucial to understand which codes and standards apply to any given project...
Is this a single battery with a max of 20kWh, or a stack of server rack batteries totaling 20kWh? IE, if it was a max in one location such as a server rack, we couldn't have more than (3) standard server rack batteries in one location without going over the 20kWh mark (we'd barely be over, but that .3kWh will matter to someone I'm sure).

So again, is it a single battery, or combination of batteries in one location without spacing? I'll be fine with the 80kWh total in the garage, but I want to ensure I'm not stacking six server rack batteries right next to each other and creating a violation right out of the gate.

Rednecktek

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It appears that any combination of batteries, whether 1 big battery or 10 little ones, counts towards the limit.

It's a real pain in the ass...

Watts Happening

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It appears that any combination of batteries, whether 1 big battery or 10 little ones, counts towards the limit.

It's a real pain in the ass...
Very annoying.

So, if that is the case, would it be fair to say that any/all EG4 server racks with six of their batteries is "illegal" or maybe I should say, "not code compliant"?

I'm not picking on EG4 by any means, they're just a well known battery/rack for the purposes of this discussion. I assume the same would be true for the SOK rack with five batteries or any other similar brand/rack setup.

That sure does seem dumb, and also would seem to nullify the entire point of one of those racks. They're super handy yet, apparently "not allowed"??

Or, is the fact that they have different listings such as UL/UL/ULA a determining factor of some sort. IE the EG4 LL batteries have a fire suppression system inside, maybe that somehow excludes them from said 20kWh max?

Dumb that I can park my 75kWh car anywhere and nobody bats an eye but if I set four batteries next to each other I'm a rebel..

Oldphile

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I've also been poking around trying to understand this. How would HomeGrid be allowed to have a stack of more than 20 KWH?

zanydroid

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I believe those diagrams show the standard rules but there are exemptions if the listing cert indicates that it is tested for closer spacing.

Watts Happening

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I've also been poking around trying to understand this. How would HomeGrid be allowed to have a stack of more than 20 KWH?
My guess is simply that if you go above the 20kWh in one location, or max per area (say 80kWh in a garage) then this line is what becomes relevant:

  • The maximum energy rating per ESS unit is 20 kWh. The maximum kWh capacity per location is also specified—80 kWh when located in garages, accessory structures, and outdoors and 40 kWh in utility closets or storage spaces. For storage capacities that exceed these limits, non-residential requirements come into play (NFPA 855 Chapters 4-9).
I've not read or reviewed anything relating to NFPA 855, so I can't intelligently comment (I'll look at it now). Maybe those requirements are met by the products we're talking about. IE maybe they need to be in a rack that can't easily be accessed by children, or they must have a fire suppression system or whatever is required. Being that most of the article I linked talked about fire, I imagine the requirements are biased towards that.

Maybe a server rack full of batteries is totally code compliant. I just want to make sure I handle it all correctly, I'm not looking to have an insurance claim later denied.

DIYrich

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So, if that is the case, would it be fair to say that any/all EG4 server racks with six of their batteries is "illegal" or maybe I should say, "not code compliant"?
Correct. You can put 3 in a rack, and have a 2nd rack 3 feet apart. You can also add one more battery 3 feet from that.

I'm guessing they designed the racks prior to UL . What's dumb is that NEC didn't set the limit at 21k, so you can put four 5.1kWh batteries in a rack.

DIYrich

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So again, is it a single battery, or combination of batteries in one location without spacing? I'll be fine with the 80kWh total in the garage, but I want to ensure I'm not stacking six server rack batteries right next to each other and creating a violation right out of the gate.
No, it is 40kWh in the Garage. The combined Garage, Accessory Structure, and Outdoors cannot excess 80kWh.
In addition, you get 40kWh in Utility Closets and Storage Spaces (inside the house).
Total of 120kWh per house.

DIYrich

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I've also been poking around trying to understand this. How would HomeGrid be allowed to have a stack of more than 20 KWH?
They are capable of being stacked to 38.4 kWh per stack.

UL itself limits the stack to 20kWh.

Watts Happening

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No, it is 40kWh in the Garage. The combined Garage, Accessory Structure, and Outdoors cannot excess 80kWh.
In addition, you get 40kWh in Utility Closets and Storage Spaces (inside the house).
Total of 120kWh per house.
I'm certainly not here to say you are wrong, as I don't know the rules well enough to determine, but based on that article and the image I posted from said article, it's stating 80kWh in the garage.

timselectric

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Seems pretty simple.
1. 3 batteries per rack.
2. Pass inspection.
3. Add 3 more batteries per rack.
Problem solved.

And just for me.
4. Get 3 more racks. lol

Watts Happening

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Seems pretty simple.
1. 3 batteries per rack.
2. Pass inspection.
3. Add 3 more batteries per rack.
Problem solved.

And just for me.
4. Get 3 more racks. lol
I'm all for that, I just don't want to have an unrelated fire or something down the road and have my batteries become a point of contention for an insurance payout.

Also, any reason the batteries "need" to be in a rack? I've got mine on top of a gun safe, it's a convenient location, keeps my child from being able to reach them and efficient use of space. Not sure that would make any difference?

zanydroid

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Presumably the UL/ destructive testing was done with a particular configuration for the equipment.

Also, code says you need to follow the installation instructions.

timselectric

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I'm all for that, I just don't want to have an unrelated fire or something down the road and have my batteries become a point of contention for an insurance payout.

Also, any reason the batteries "need" to be in a rack? I've got mine on top of a gun safe, it's a convenient location, keeps my child from being able to reach them and efficient use of space. Not sure that would make any difference?
That would depend on what your inspector wants.
I would think that if everything is covered and protected from contact, it should be fine. But, it's really up to your inspector.

Watts Happening

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That would depend on what your inspector wants.
I would think that if everything is covered and protected from contact, it should be fine. But, it's really up to your inspector.
It pays to have a nice inspector haha!

Now, for someone like you that has 76.8kwh of DIY batteries, are you just "not code compliant" in their eyes?

God I get tired of the rules!

timselectric

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It pays to have a nice inspector haha!

Now, for someone like you that has 76.8kwh of DIY batteries, are you just "not code compliant" in their eyes?

God I get tired of the rules!
I'm definitely not code compliant. lol

DIYrich

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I'm certainly not here to say you are wrong, as I don't know the rules well enough to determine, but based on that article and the image I posted from said article, it's stating 80kWh in the garage.
Must have changed since I learned about it. I can find a edition that has the 40 + 80 you mentioned, plus 80 on exterior wall, and another 80 "outside".

Watts Happening

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Must have changed since I learned about it. I can find a edition that has the 40 + 80 you mentioned, plus 80 on exterior wall, and another 80 "outside".
Gotcha. I’m still bummed about how this is written. I’ve got PLENTY of room on top of my gun safe for 7-8 batteries, yet now I’m restricted to 3. Certainly not convenient.

Oldphile

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My state NH has not adopted NFPA 855, so I'm not going to limit myself to 20 KWH per ESS. Hopefully that doesn't change before I have batteries installed. Last code adoption was July .

Edit: oops, just found an amendment to NH adoption of NFPA 1 to include NFPA 855. Last edited: Aug 15,

Danke

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Seems pretty simple.
1. 3 batteries per rack.
2. Pass inspection.
3. Add 3 more batteries per rack.
Problem solved.

And just for me.
4. Get 3 more racks. lol
Quiet You!


So where is the best place (via USA) to order Grade A 320/302/280ah EVE/CATL batteries from?

Looking to build a few sets of 16 cells 48v setups for home. Are there any sellers in US that sell brand new.. reputable, and you dont end up with bloated or lied about batteries? Is it worth the price taking the risk on Alibaba or Amazon?

mbox

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Has anyone gone through inspection with one of these? I am conflicted especially with new DC-ESS systems. Seems to me that if the individual batteries are DC-ESS and the rack is ULa tested to have the spacing be less than three feet then it would be okay?

I believe 15.3.1 says as much in NFPA855 which is that the spacing must be 3ft unless specified otherwise in testing (ULa). So if the manufacturer says it passes that in a rack, I believe it should pass. But of course AHJ has final say and they can just decide they don't agree or don't care.