AC Running Cost: Why Your Electricity Bill Jumped This Month

The complaint usually arrives in the same form: "same AC, same usage, bill up by ₹1,400". Sometimes the tariff changed. More often something in the unit changed, and it changed in a way that costs money without costing comfort — which is why nobody notices until the bill.

The baseline number

A 1.5-ton 5-star inverter split running eight hours a night in Mumbai conditions draws roughly 0.9 to 1.2 units per hour once the room is at temperature, so about 7–9.5 units a night. At ₹9 to ₹12 a unit in most of the Mumbai metropolitan region, that is ₹65 to ₹115 a night.

A fixed-speed 3-star unit of the same size draws closer to 1.5 units an hour — roughly ₹110 to ₹160 a night. Over a five-month season the gap is real money, which is why inverter units pay back their premium in about three years at these tariff rates.

The four faults that raise consumption silently

• Dirty evaporator coil. Restricted airflow means less heat transfer, so the compressor runs longer for the same room temperature. Typical penalty: 15–25%.
• Dirty condenser coil. Same problem on the outdoor side, and it also raises head pressure, which is harder on the compressor. Typical penalty: 10–20%.
• Undercharge from a slow leak. The unit never quite reaches setpoint and runs continuously. Typical penalty: 20–35%.
• Failed run capacitor. The compressor draws higher current to start and run. Typical penalty: 10% plus a much shorter compressor life.

Notice that none of these announce themselves as a fault. The room still gets cool. The unit still sounds normal. Only the meter knows.

How to tell a fault from a tariff change

Two quick checks settle it.

Compare the same month last year. If the increase tracks a tariff revision, it will be proportional across all usage. If the AC is responsible, the jump will be sharper than the rest of the house.

Time the cooling. Switch the unit on after it has been off for an hour and note how long it takes to reach set temperature. If it used to take twelve minutes and now takes twenty, you have an airflow or charge problem, and the extra eight minutes is the bill.

Setpoint and fan speed: free savings

Every degree of setpoint below 24°C adds roughly 6% to consumption. In humid Mumbai weather, 24–25°C with the fan on auto is the comfortable compromise; 18°C does not cool the room faster, it just keeps the compressor running longer at the end.

Running the fan on high all night also costs money for no benefit once the room is at temperature. Auto lets the indoor fan settle as the load drops.

Inverter versus fixed speed, honestly

An inverter compressor varies its speed to hold the setpoint; a fixed-speed unit cycles on and off at full power. In a bedroom running all night, the inverter wins clearly. In a room used for forty minutes in the evening, the advantage shrinks to almost nothing because most of the run is at full load either way.

If your usage is short and occasional, a cheaper fixed-speed unit is not a mistake. If it is nightly and long, inverter pays for itself.

What a service actually recovers

We measure current draw before and after a deep clean on units with visibly blocked coils. A 20% reduction is common, and it shows up in the next bill rather than the one after.

At a ₹1,349 deep dismantle service against roughly ₹400–₹700 a month of avoidable consumption in peak season, the service pays for itself within the season. That calculation is the honest argument for servicing — not comfort, which you rarely notice, but the meter, which you do.