Choosing an Inverter for Your Home: Sizing, Batteries and the Mistake Everyone Makes

The mistake: connecting the whole house

This is the single biggest determinant of whether your inverter is useful, and it has nothing to do with the inverter itself.

The intuitive approach is to connect the inverter output back into the main distribution board so that everything in the house runs during an outage. It feels generous and complete. In practice it means that when the power goes, the geyser somebody left switched on, the microwave, the iron and the air conditioner are all connected to a battery designed to run fans and lights.

One of two things then happens. The inverter detects an overload and shuts down, so you have no backup at all. Or it struggles on and flattens the battery in twenty minutes, and repeated deep discharge permanently shortens the battery's life.

The correct approach is a dedicated backup distribution line. You decide which circuits genuinely matter during an outage — fans, lights, television, router, refrigerator, a few charging sockets — and those are wired onto a separate way from the inverter output, with the sockets visually distinguished so nobody plugs a heavy load into them by accident. Everything else stays on mains only.

The difference is dramatic. The same inverter and the same battery, correctly wired, will typically run three to five hours instead of twenty minutes. Retrofitting a proper backup line costs ₹4,500 to ₹12,000 depending on point count, and it is almost always the best money you can spend on an existing inverter installation.

Sizing: the arithmetic

Once you know what is on the backup line, sizing is straightforward arithmetic rather than guesswork.

Total the wattage of everything on your backup line. A typical set for a 2 BHK: six fans at 75 W each (or 30 W each if BLDC), ten LED lights at 9 W, a television at 100 W, a router at 15 W, and a refrigerator at 150 W running. That comes to roughly 900 W with conventional fans, or 630 W with BLDC.

Divide by the inverter's power factor, typically 0.8, to get the VA rating needed. 900 W becomes 1125 VA, so a 1100 to 1500 VA inverter is right. Add margin for the refrigerator's compressor startup surge, which is brief but substantial.

For battery capacity, work from the backup hours you want. Battery Ah = (load in watts × hours) ÷ (battery voltage × efficiency). For 900 W over 4 hours on a 12 V system at 80 per cent efficiency, that is roughly 375 Ah — which in practice means either a 200 Ah battery accepting shorter runtime, or a two-battery 24 V system.

As a practical guide for Surat homes: 900 VA with 150 Ah suits a small flat running fans and lights. 1100 to 1500 VA with 150 to 200 Ah suits a 2 or 3 BHK including a refrigerator. Above 2000 VA usually means either a bungalow, a small office, or an installer who has connected the whole house.

• List only what is actually on the backup line
• Total the wattage, divide by 0.8 to get VA
• Add margin for refrigerator compressor startup
• Battery Ah = (watts × hours) ÷ (voltage × 0.8)
• 900 VA / 150 Ah: small flat. 1100–1500 VA / 150–200 Ah: 2–3 BHK with fridge

Tubular versus lithium

The battery is where most of your money goes and where the running-cost difference lies, so this decision deserves more thought than the inverter brand.

Tall tubular lead-acid remains the best value in Surat's climate. A 150 to 200 Ah unit costs ₹14,000 to ₹20,000, lasts four to five years with reasonable care, tolerates heat and deep discharge better than flat-plate alternatives, and is universally serviceable. Against that: it needs distilled water topping every few months, it must be ventilated because it vents hydrogen during charging, and it is heavy and bulky.

Lithium systems cost two to three times more upfront but are maintenance-free, occupy roughly a third of the space, weigh far less, tolerate partial charging without damage, and last eight to ten years. A 1 kVA lithium inverter system starts around ₹68,000.

The honest comparison is cost per year. A ₹17,000 tubular battery lasting 4.5 years is about ₹3,800 a year. A lithium system's battery portion at roughly ₹45,000 over 9 years is about ₹5,000 a year. Tubular still wins on pure cost, but the gap is narrower than the sticker price suggests, and it closes further if you value the space saving and the absence of maintenance.

Our practical rule: in a compact flat where the trolley sits in a living area, lithium is often worth it. In a bungalow utility room with space and ventilation, tubular usually wins.

Installation details that decide battery life

Several installation details have a larger effect on battery life than the battery brand, and they are frequently got wrong.

DC cable length and size matter enormously. The cable between battery and inverter carries very high current at low voltage, and voltage drop on a long or thin run wastes a meaningful fraction of your stored energy as heat. Keep the run as short as physically possible and use the heavy cable specified, with proper lugged terminations rather than twisted ends.

Ventilation is a safety requirement, not a preference. Lead-acid batteries vent hydrogen during charging, and hydrogen in an enclosed space is exactly as dangerous as it sounds. A proper trolley or open stand with airflow, never a sealed cupboard and never under a bed.

Terminal condition matters in Surat's coastal humidity. Corroded terminals add resistance, which reduces charging efficiency and available current. Clean and grease them at installation and annually thereafter.

Water levels on tubular batteries need checking every two to three months and topping with distilled water only — never tap water, which introduces minerals that damage the plates. Neglected water levels cause plate sulphation, which is the most common reason a battery that should last five years dies in three.

Can an inverter run an air conditioner?

This question comes up constantly and the honest answer is: only with a system substantially larger than what people mean by 'an inverter'.

A single 1.5 ton inverter air conditioner needs roughly 3.5 to 5 kVA of inverter capacity and a large battery bank to run for any useful period. Installed cost for meaningful runtime is well past ₹1.5 lakh, and the battery bank alone requires significant space and ventilation.

For most households, a better answer exists. A high-speed BLDC ceiling fan on the standard backup line draws around 30 W and provides genuine comfort during an outage at a tiny fraction of the cost. Combined with good ventilation, it handles the great majority of Surat's outage situations.

Where AC backup is genuinely required — a medical need, a home office with critical work, a server — it should be specified as a separate high-capacity system with its own sizing exercise, not treated as an upgrade to a domestic inverter. We quote these separately rather than pretending a 1500 VA unit will cope.