Planning a technical room for a home battery

Give a large home battery its own dry, ventilated technical room. It needs a solid wall and floor, close to the main board. Reserve about 1.3 m of floor width for the battery towers, about 1 m of wall for the inverters, and room to grow. Plan the space around the real home battery dimensions, not around a brochure. Lay the cables and conduits while the walls and floors are still open.

You are building or renovating a large home. The architect has drawn a technical room for the heat pump, the ventilation unit and the boiler. The battery "comes later". One renovator on a Dutch-language forum dug cables to his garage for the heat pump. He added a thick battery cable too: "I do not want to dig again in two years."

What most plans leave out is the second cable. A battery with back-up needs a cable to the main board and a cable back for the back-up circuits. One owner found his battery on the other side of the house from the meter box. His installer said a new line through the whole house for back-up would be "a very expensive job", so he did without. A room drawn only for the heat pump often ends the same way. The battery lands in a cold garage, far from the board, on a wall that cannot carry it.

In Kortenberg we installed our typical three-phase battery with full back-up in off-grid mode: 30.8 kWh and 9 kVA. "Quality deserves a nice finish," as the project page puts it. A finish like that starts with a room that was planned for it.

What goes into the technical room of a home with a large battery?

More than the battery: inverters, a control unit, fuses, often a back-up board, and cables to the meter, roof and router. The heat pump and the boiler often share the room.

Do you want the whole house on the battery in a power cut, as in Wetteren? Then the back-up board is large, and the wiring changes. Our article on how a full no-break house is wired covers the switchboard and the changeover.

How much wall and floor space does a large home battery need?

For about 30 kWh with three-phase back-up, plan roughly 1.3 m of floor for the battery and 1 m of wall for the inverters. Add working space in front and room for one more tower.

Take the BYD Battery-Box Premium LVS, a modular LFP battery, as an example. One module stores 4 kWh and weighs 45 kg. A tower of four modules (16 kWh) is 1,227 mm high, 650 mm wide and 298 mm deep, and weighs 199 kg. A single tower goes up to 24 kWh; above that you place towers side by side, with up to four modules each.

The inverters hang on the wall. One Victron MultiPlus-II 48/5000 measures 565 x 320 x 149 mm and weighs 30 kg. For three-phase you use three units of the same model, one per phase. That is about 1 m of wall and 90 kg, before the fuses, the control unit and the back-up board.

Those are example products, not a quote. Your size follows from your consumption: read how big a battery a large home needs. Want to start smaller? Then reserve the floor for the second tower now. Our guide on expanding a home battery later explains what grows with it and what does not.

Which walls and floors can carry a home battery?

A solid wall of concrete or masonry, and a floor that takes a concentrated load. Both the battery maker and the inverter maker ask for that.

The BYD manual asks for "a solid support surface", concrete or masonry, suitable for the weight and dimensions. The tower stands on its base 12 to 19 mm from the wall and is fixed to it with a wall bracket. Victron asks the same for the MultiPlus-II: a solid surface such as concrete or masonry, and no flammable materials close by.

• Timber-frame house or plasterboard walls? Plan one solid, non-combustible wall section for the battery and inverters before the finishing starts.
• Floor: two towers of 199 kg stand on about 0.4 m². That is roughly one tonne per square metre, locally. A concrete slab carries it; on a suspended or timber floor, ask your structural engineer first.
• Access: a module of 45 kg goes down stairs by hand, but check doors, corners and stairs for the towers and the inverters. The same access counts when the battery leaves again, as explained in what happens to a home battery at the end of its life.

How warm, cold and dry should a battery room be?

Between 0 and 50 °C, as constant as possible, dry and ventilated. Outside that range the battery switches itself off.

The location we specify for a battery must be watertight, with constant temperature and humidity and minimal dust. It must stay at least 2 m from a heat source and 0.5 m from the ventilation of the inverter. The room needs ventilation, and children and pets stay away from it.

Both ends of the range cost you something. The BYD datasheet notes that charging is reduced between -10 °C and +5 °C. The MultiPlus-II 48/5000 gives 4,000 W continuous at 25 °C, but 3,700 W at 40 °C. So a frost-free, cool room keeps both charging and power at their best.

The inverters also make heat. At full power, one MultiPlus-II 48/5000 at its best efficiency of 96% loses at least about 170 W. Three of them give off about 500 W: a small heater. A Belgian forum member put it plainly. Inverters often end up "in a small technical room" with fridges, the dryer and the boiler, where it is warm. Put the battery room on the cool side of the house, and give it an air inlet and outlet.

Where should the technical room be: near the meter, the roof or the garage?

Keep the battery and the inverters together, and let the room sit as close to the main board as possible. Distance to the roof or the garage is easier to bridge than distance on the battery side.

The reason is current. One MultiPlus-II delivering 4,000 W draws about 83 A from a 48 V battery, against about 17 A on the 230 V side. Victron recommends 70 mm² battery cables for a MultiPlus-II 48/5000 up to 5 m, and 120 mm² from 5 to 10 m. Its manual adds: do not lay battery cables in a closed conduit. The data cable between a BYD battery and the inverter may be at most 10 m.

So in a new build, draw the technical room next to the main board, or put the main board in the technical room. In a renovation, the board is often in the hall or the cellar. Then the AC cables to the room are the part to plan, not the battery cables.

Which cables and conduits should you lay now, even if the battery comes later?

Lay empty conduits and the cables that are hard to add once floors and walls are finished. It costs little during the works and saves breaking open finished rooms.

• Main board to technical room: a supply cable for the battery system, plus a second cable back for the back-up circuits. At least lay a spare conduit for it.
• Roof to technical room: a conduit for the solar cables, with room for more panels later.
• Technical room to garage or driveway: a cable or conduit for the car charger, also for a second car.
• Network: one or better two network cables from the router to the technical room. A forum member gave exactly that tip.
• Outside wall: a spare conduit for a generator inlet. Then you can recharge the battery with a generator in a long power cut.

Why a network cable? The control unit sends the data of your system to the free VRM app and portal, where you follow and adjust it. BYD also highly recommends connecting its battery to the internet for remote service. A cable is usually more reliable than wifi through thick walls.

The renovator who dug to his garage got one more tip. Bury a spare conduit, and decide later what goes in it. A conduit you do not use is cheap; a missing one means digging again.

What does fire safety ask from a home battery room?

A place outside escape routes and bedrooms, a smoke detector, ventilation, and where possible a separate space with fire-resistant walls. Belgian fire services give that advice, even though Belgium has no specific placement rule for home batteries.

The Walloon fire zone of Hesbaye advises a dedicated battery space "if your space allows it". EI60 fire-resistant walls separate it from the rest of the building. It calls automatic fire detection "indispensable". For large batteries it also advises a pressure relief vent, a warning sign and an action sheet outside the room.

Brandweer Zone Rand, a Flemish fire zone, asks for a working smoke detector in the room with the battery and good ventilation. It adds: never on your escape route. In a new build, fire-resistant walls and a detector cost little when they are on the plan from the start.

Is a home battery a real fire risk, and what does your insurer ask? Read our article on whether a large home battery is a fire risk. No room inside at all? Then see whether a large home battery can stand outside.

New build or renovation: what changes for the technical room?

In a new build you choose the room; in a renovation you mostly choose the cable route. The rules for the battery itself are the same.

Every home battery is registered with the grid operator. In Flanders you do that in Mijn Fluvius, with a valid AREI inspection and a single-line diagram of the battery. Our article on registering a home battery explains the steps. Working with an architect on a larger building? Our guide on designing a building with a battery is written for the design team.

Is it a business site rather than a home? Then read battery container or technical room for a business.

How do we plan the technical room with you?

We plan the room together with the battery, not after it. Our team includes three certified battery experts, and we take a future extension into account from the start.

In Lokeren we powered a new home that was built without any grid connection. In the preliminary study we determined the battery capacity it needed, and that capacity can be expanded afterwards. That is the logic for every new build: size now, leave room to grow.

1. Step 1: We measure or estimate your consumption, including the heat pump, the cars and anything planned.
2. Step 2: We check your floor plan: the technical room, the walls, the floor, the distance to the main board and the cable routes.
3. Step 3: We tell you which conduits and cables to lay during the works, so the battery can come now or later.
4. Step 4: We install, commission and follow the system with you in the free VRM app and portal.

Want to see what our home batteries can do for a large home? Or send us your plans first.