Right after Midsummer, on June 30th, Boverket's new battery rule became fully mandatory. In one sentence: more than 20 kWh of battery inside that room must be built as its own fire cell. If you already have a battery, relax, the rule is not retroactive. But if you are buying solar and storage now, walk through the house with me. It takes five minutes and can save you real money when you buy.

Why exactly 20 kWh?

20 is not a magic number. A 25 kWh battery burns like a 20, only more of it. What the line measures is time, not size but how long a family needs to escape the smoke. And kWh is an honest measurement, printed on every datasheet where anyone can check it in ten seconds.

But a normal villa fuse of 20 to 25 amperes carries 14 to 17 kW, and a battery that should work properly and earn on grid services wants half its size as power. That math points to 28 to 35 kWh, not 20. So I asked Boverket in writing why exactly 20.

Their impact assessment gives three reasons. A typical villa battery sits at 5 to 15 kWh, so the line spares normal installs and catches large ones. Above 20, the toxic and flammable gases from a battery fire demand a fire cell, a fire lock and smoke ventilation. Up to 20, the risk is judged manageable with normal building protection. Fair enough. But that line was drawn where yesterday's typical battery ended. Tomorrow's, sized for grid services and effect tariffs, starts above it, at least in my experience.

What happens if you ignore it?

Nothing today. No inspector rings your doorbell. The rule surfaces later, at two moments.

First one is if there ever would be an accident the question is will insurance pay if the battery installation broke the rules? Insurers judge case by case, but my opinion is they will look for a way not to pay in full. And a tip is to ask your insurer for a written statement on your exact setup before installation because that paper is your ace if something ever happens or when you sell.

The second is if you sell your house. Solar and a battery usually lift the price, but a faulty installation gives the buyer leverage to negotiate because their insurance company will need to take the risk.

Now that the basics are covered let us take a quick tour in the house to see what to think of when buying an energy system.

Room one: the utility room

A convenient spot: easy installation and protected from weather. At 20 kWh or less it works, but anything higher than that is a no go. Just keep in mind that even if the battery is silent the inverter can make noise.

Want more than 20? Then this room must be a real fire cell. The ten second check: a label on the door frame, EI30 or EI60. The number is minutes, and EI30 is enough for a villa. No label, no fire cell, no big battery.

Room two: the garage

The question everyone asks: my EV sleeps here with 75 kWh inside, why does a 21 kWh wall battery need a fire cell when the car does not? Not because regulators forgot cars, the real answer is that the garage is already on the regulation's list of rooms that must be their own fire compartment, in the same sentence as big batteries.

One caveat: not every garage was built as one. Houses from the last ten to fifteen years usually have it, older ones often not. Same check, same label on the door. If it is there, this is in my opinion the battery's best installation point because the steady temperature, no heating cost, no construction, no noise by your bedroom.

Last stop: outside

Out here the rule does not apply at all, and this is where I believe more and more installations will go. But here there is another aspect - the weather. Three things to think of before placing the battery outside.

The IP class: many outdoor batteries stop at IP65, tested with 12.5 liters of water per minute; IP66 is tested with 100 liters under high pressure, a real autumn storm, with tighter gaskets against the damp air a battery breathes in as it cools.

The corrosion class: C3, normal town air, must survive 480 hours of salt fog in the test chamber. C5, harbor air, must survive 1,440, sixty days. In the Nordics I would say that the weather demands C5.

The heating: below zero degrees a lithium battery cannot not charge, so without heating it cannot refill until the cold breaks. With heating it works all winter, for a small energy cost.

Lastly, make sure you follow Svensk Solenergi's placement guideline when installing outside, two meters to anything that burns, or a fireproof board behind the unit. The latter is often cheaper than digging a cable trench, so ask your installer to price both.

And if you need a fire cell without building one, Swedish cabinets like PowerSafe Box and Voltguard offer EI60 boxes for up to 75 kWh.

Where would I place mine?

Garage first, if the label allows. Outdoors second, because I would go above 20 kWh. And as I am the Regional Manager Nordics for Solis, I would of course pick our FlexHome, which has all three things, IP66, C5 and heating to minus 20. But Solis or not, those are the three words to look for.

Three things to take with you

If placing indoors, never above 20 kWh in the same room.

Before installation, get a written answer from your insurer.

If placing outdoors: IP66, C5 and heating on the datasheet.

Sources and disclosure

Built on: Boverket BFS 2024:7 and its impact assessment (energy storage section, page references to be confirmed), Boverket's written reply to the author, Svensk Solenergi's fire protection guideline, MSB fire statistics 2018 to 2022, IEC 60529 and ISO 12944-6 test parameters, and manufacturer documentation including Solis FlexHome, PowerSafe Box and Voltguard. The author is Regional Manager Nordics at Solis. This is general information, not legal advice; get written answers from your municipality and insurer for your specific installation.