How Do You Keep a Mumbai Flat Cool in October?
Stop the sun before it reaches the glass, keep the AC at 24 degrees or above with a fan, and air the flat early, not in the evening. October is hot because the monsoon clouds have gone while the air stays humid, so shade and airflow beat a colder setting.
Heat through the glass, and heat in the air. In October the clouds clear, so far more sun reaches west- and south-facing windows, while the air still holds the monsoon's moisture. The first problem is solved before it enters the room, with shade. The second is handled by the AC and a fan, not by pushing the AC colder. Most October discomfort comes from treating both as one problem.
Every Mumbai household knows the feeling: the rain stops, everyone is relieved for about a week, and then the flat is warmer at 4pm than it was in August. It is not your imagination, and it is not only the temperature. The weather record shows exactly what changes.
Why is October so hot in Mumbai?
Because the sky clears faster than the air dries. The India Meteorological Department's averages for the Santacruz observatory, over thirty years from 1991 to 2020, show three things moving at once between September and October: cloud cover roughly halves, the average daily high rises by close to three degrees, and humidity, while falling, is still high.
On the hottest day of a typical October, the Santacruz high averages 36.4 degrees. And November, which feels easier, is actually warmer by day. It feels easier because the air is much drier.
What do IMD's own numbers show for September to November?
These are the long-term averages from IMD's Climatological Tables of Observatories in India, 1991 to 2020, for Mumbai (Santacruz).
| Month | Average daily high | Humidity at 8:30am / 5:30pm | Cloud cover | Rainy days |
|---|---|---|---|---|
| September | 30.9 degrees | 85% / 76% | 6.0 oktas | 14.4 |
| October | 33.6 degrees | 75% / 63% | 3.3 oktas | 3.9 |
| November | 34.1 degrees | 66% / 54% | 1.7 oktas | 0.6 |
Cloud cover is measured in oktas, eighths of the sky: 6.0 means three quarters of the sky covered on average, 3.3 means well under half. That is the whole story of October in one column. The sun is back on your windows, and the air has not yet dried out to November levels.
Where does the heat actually get into a flat?
Mostly through the glass. In a Mumbai flat, windows on the west side take the afternoon sun at its strongest, south-facing glass takes sun for much of the day, and a top-floor flat also takes heat through the roof. Once sunlight has passed through the glass and warmed the floor and furniture, the heat is inside, and the AC has to remove it.
That is why the order matters: stopping the sun outside the room is cheaper than removing its heat afterwards. The US Department of Energy's guidance on energy-efficient window coverings puts a number on it: medium-coloured curtains with a white plastic backing, closed over a window in direct sun, can reduce heat gain by about 33 percent. The catch is in the word closed. Open curtains do nothing, and curtains drawn at 5pm have already let the afternoon in.
Our guide to curtains for the living room covers the linings and fit that make the difference, including why the edges matter as much as the fabric.
What temperature should the AC be set to in October?
24 degrees or higher, with a fan. The Bureau of Energy Efficiency's portal states that "increasing the air-conditioner temperature setting by just 1 degree Celsius can save about 6 per cent of electricity consumption", and 24 degrees is now the default setting on new star-labelled ACs.
October makes the fan more useful, not less. The air is still humid, so a room at 26 degrees with still air feels close, while the same room with a fan moving the air feels noticeably cooler. Setting the AC colder instead makes the compressor work harder for a feeling a fan delivers for far less power. We go through the numbers on a real Mumbai bill in AC at 24 degrees in Mumbai.
When should you open the windows in October?
Early in the morning, not the evening. IMD's October averages for Santacruz put the air at about 27 degrees at 8:30am and about 31 degrees at 5:30pm. The evening breeze feels welcome after a hot afternoon, but on average the air coming in at 5:30pm is warmer than the air you could have let in at breakfast.
So the rhythm that works in October is simple. Air the flat first thing, close the windows and the sunny-side curtains before the sun reaches the glass, and keep them closed through the afternoon. Humidity is lower in the evening, so if you want fresh air later, the late evening is better than 5pm, but the morning is still the coolest air you will get.
What does a smart home change in October?
Everything above only works if someone does it at the right time, every day, including the days nobody is home at 1pm. That is the part automation takes over. A study by the Illinois Institute of Technology at Chicago's Willis Tower found that automated shades cut energy use by roughly a quarter over a ten-month test. The point of automating them is simple: they move on schedule, not when someone remembers.
- Curtains that close before the sun Motorised curtains can close the west-facing side on a schedule before the afternoon sun reaches it, and open again in the evening. In the morning, Goodmorning Mode opens them 10 percent every 5 minutes instead of all at once
- The AC at your temperature An IR controller brings the AC you already own onto the system. Grand Welcome switches it on at your chosen temperature when you unlock the door, and you can switch it on from the app on the way home
- The fan with the AC An RF controller puts a BLDC fan into the same scene as the AC, so 26 degrees with the fan on is one button, not two. BLDC fans draw up to 60 to 65 percent less power than induction fans
- Drying the room Cleaning Mode's double click runs the AC for a short while to dry a room after mopping, useful while the air is still this humid
- Who does what Your electrician mounts and wires the hardware to our plan, and our technicians configure and commission it. We do not do the mounting and wiring ourselves
As a scope estimate, a fully automated bedroom, including AC and fan control and one curtain set, is around ₹85,000, an estimate rather than a quote. How we plan this across a whole Mumbai flat is on our page for the home automation company in Mumbai.
What will this not fix?
- An inefficient AC. Automation decides when the AC runs and at what setting. It does not make an old unit more efficient.
- A hot roof. In a top-floor flat, much of the heat comes through the ceiling. Curtains and schedules help with the windows, not the roof.
- A power cut. The hub runs scenes without the internet, but not without power. When the mains goes, scenes stop until it returns.
- Induction fans. The RF controller works with BLDC fans. A standard induction fan cannot join the scene without being replaced.
- A curtain with no power point. Curtain motors run on mains power, so a window with no point at pelmet height needs one first, and an IR controller needs a clear line of sight to the AC.
If your flat is already finished, most of this can still go in without breaking walls, and our guide to home automation without breaking walls shows exactly which parts need nothing and which need one wire.
What do people ask us next?
Why is it so hot in Mumbai in October?
Because the monsoon clouds clear while the air is still humid. On IMD's 1991 to 2020 averages for Santacruz, cloud cover falls from 6.0 oktas in September to 3.3 in October, the average daily high rises from 30.9 to 33.6 degrees, and morning humidity is still 75 percent.
What temperature should I set my AC to in October?
24 degrees or higher. The Bureau of Energy Efficiency says each degree higher saves about 6 percent of the AC's electricity, and 24 is the default on new star-labelled ACs. With a ceiling fan running, many people find 26 comfortable, and it saves more.
Do curtains really reduce heat in a flat?
Yes, if they are closed before the sun reaches the glass. The US Department of Energy puts the reduction at about 33 percent for medium-coloured curtains with a white backing, closed over a window in direct sun.
When should I open the windows in October?
Early in the morning. On IMD's October averages for Santacruz, the air is about 27 degrees at 8:30am and about 31 degrees at 5:30pm, so airing the flat first thing and closing up before the sun reaches the windows keeps more heat out than opening up in the evening.
Can a smart home keep my flat cool while I am out?
It can stop the heat building up. Motorised curtains can close on a schedule before the afternoon sun reaches the glass, and the AC can be switched on at your chosen temperature from the app on the way home, or the moment you unlock the door with Grand Welcome. Remote access needs the internet.
Does a BLDC fan help in October?
Yes, alongside the AC. Moving air makes a warmer setting feel comfortable, and AHA's RF controller brings BLDC fans into the same scenes as the AC. It works with BLDC fans only, not standard induction fans.
The short version: October is hot because the clouds leave before the humidity does. Close the sunny-side curtains before the sun reaches them, keep the AC at 24 or above with a fan, and let the morning air in instead of the evening air.
If you want to feel the difference a scheduled room makes, both our experience centres, in Santacruz West and Lower Parel, are open daily 11am to 7pm. Walk in, or book ahead.
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