Before the Air Conditioner: Designing for Comfort in Indian Homes
The machine should be the last decision, not the first. Here is the order that makes a home comfortable.
Shade, a fan and a verandah, with no air conditioner in sight.
Three pictures in this article are AI-generated concept illustrations of a fictional house and fictional rooms. None shows a completed Team Design Architects project. The diagram was drawn for this article.
Four in the afternoon, in a west-facing room. The curtains are drawn against the glare and the air conditioner is running. The room is cool without being pleasant. Step onto the balcony and the evening air already feels better than the room you are paying to cool.
That room has a design problem, and a machine is being asked to solve it. Heat is arriving through the roof, the wall and the glass faster than it can leave, and the air conditioner is working against all three. A machine can do that every day, at a price. A better house asks it to do less.
This guide is not against air conditioning. In a Mumbai summer and a humid monsoon, most homes will use it, and we install it. It is about order: decide how much heat gets in, then how air moves, and only then size the machine. The numbers come from the sources at the end. Passages marked as our view are opinion.
Start with your climate
The National Building Code divides India into five climate zones, and the advice that suits one can fail in another. The Bureau of Energy Efficiency's Eco Niwas Samhita lists the zone for major cities. Mumbai, Chennai, Kolkata and Kochi are warm-humid. Ahmedabad is hot-dry. Delhi, Jaipur and Hyderabad are composite. Bengaluru is temperate. [1]
A hot-dry city can lean on thick walls and small, shaded openings that keep the afternoon out. In a warm-humid city thick walls are not enough, because the air itself is damp, and moving air does more of the work. The code reflects this. It asks for openable windows of at least 16.66 percent of floor area in a warm-humid zone, against 10 percent in a hot-dry one. [1]
Everything below is written for Mumbai and the coast. On a plot in Jaipur or Bengaluru the order still holds, but the weights change.
Comfort is a range, not a number
People tolerate more than a thermostat assumes. IMAC-R, the India Model for Adaptive Comfort for residences, comes from year-long field surveys in homes in eight cities across five climate zones. More than 80 percent of residents felt neutral at indoor operative temperatures anywhere between 16.3 and 35 °C, while the 30-day outdoor average ranged from 5.5 to 33 °C. [2]
The neutral temperature it finds is, on average, 2 °C warmer than the one in the ASHRAE-55 standard. The authors also found that the PMV model, widely used for air-conditioned buildings, underpredicts how well Indian occupants adapt. [2]
That does not mean everyone is fine at 35 °C. The survey describes a population, not one person, and older people, infants and anyone unwell need more care. That matters in a country that is ageing, which we discuss in our piece on the home in 2035. The model also applies to homes that are naturally ventilated or mixed-mode, where people can open windows and switch on a fan. It is no excuse for sealed glass and still air.
Stop the heat coming in
On a top floor or in a single-storey house, the roof is the surface most exposed to the sun, so we start there. The Eco Niwas Samhita sets a maximum thermal transmittance for a roof of 1.2 W/m²K, a measure of how readily heat passes through it. [1] A reflective finish adds to that. The code's guidance describes a cool roof as one with a solar reflectance of at least 0.6 and an emittance of 0.9, a figure it takes from the earlier ECBC 2017, and it says a cool roof is not a substitute for insulation. [1]
A pilot in Hyderabad reported indoor air temperatures 2.1 to 4.3 °C lower under cool roofs than under conventional ones. [3] That is a pilot result in a different climate zone from Mumbai, so read it as a direction, not a promise.
For walls and glass the code uses RETV, the Residential Envelope Transmittance Value. It counts heat conducted through walls and glass plus the sun coming through glass, over the cooling season, for each square metre of envelope excluding the roof. The limit is 15 W/m², and BEE says it plans to tighten it to 12. [1] You do not need to calculate it for a house to use the idea. Our view is that the west wall and the west glass matter most, and that a small west window with a chajja above it does more than a big one behind a curtain.
The house in the picture puts the usual tools together: deep chajjas over the windows, a timber screen on the upper floor, a mango tree close to the wall and a roof that overhangs. A small air-conditioner unit is also visible on the wall. That is the point of the shade. The unit is there, and it will run less.
Shade does what insulation cannot, which is stop the sun before it touches the building. A chajja or a deep verandah does it. So does a screen, as we describe in The Jaali, Reconsidered, and so does a tree on the west side. A tree takes years to grow, so plant it early and ask where its roots will go.
Ask your architect
- Which walls and windows face west, and how is each one shaded?
- What is the roof made of, what insulates it, and what is its finish?
- How big are the west-facing windows, and could they be smaller or screened?
- Where will a tree go, and is it planted before the house is finished?
Let the air move
Once less heat arrives, the next job is to move out what does. Air movement does this in two ways. When outside air is cooler than inside, usually at night, openings let it in and push the warm air out. The code puts it plainly: openable area lets external air in when it is cooler than the air inside, which improves comfort and reduces cooling energy. [1] And moving air makes people feel cooler even when the room is not, which is why studies find people tolerate higher temperatures where there is appreciable air movement, for example from ceiling fans. [4]
The code's guidance on layout is practical. Put the inlet and the outlet on different walls, either adjacent or opposite. If a room has only one external wall, add an opening high on an internal wall, or use two windows set well apart, or put a ventilator above the window. It also assumes internal doors are closed, because people tend to close bedroom doors at night, so a room cannot rely on its door for airflow. [1]
The bedroom in the picture follows that pattern. It has windows on two walls, a high louvred ventilator over the door and a ceiling fan. One honest note: the illustration shows the door open. At night it would be closed, which is exactly why the ventilator above it matters.
Treat the fan as part of the design, not an accessory. Decide its position when the ceiling is drawn, so it sits clear of beams and lights and over the places where people sit and sleep.
Ask your architect
- Does each main room have openings on two walls, or a high opening where it cannot?
- Can the windows be opened at night and still be secure?
- Where do the fans go, and have they been placed on the ceiling plan?
Then, the air conditioner
In Mumbai an air conditioner also dries the air, which is a real benefit in the monsoon. We covered the moisture side in A House for the Monsoon. The aim is not to ban the machine. It is to make it work less.
A study of 15 Indian homes that use air conditioners together with ceiling fans found that thermal comfort, as predicted by IMAC-R, was maintained with the thermostat at 28 or 30 °C and the fan on its lowest speed. Compared with 24 °C, those settings used 44 and 67 percent less energy. [4] The same study found that inverter air conditioners used 34 to 68 percent less energy than fixed-speed ones. [4]
Our reasoning, not a figure from those studies, is that a machine with less heat to remove can be smaller and will cycle less. So ask your engineer to size it after the roof, walls and glass are settled, not before. Where the outdoor unit goes, and whether someone can reach it to service it, is worth deciding on the drawings.
Ask your architect
- Has the cooling load been calculated after the shade and insulation were decided?
- Is the machine an inverter model, and who sizes it?
- Where does the outdoor unit go, and can it be reached for servicing?
In a flat, and in a house
In a house you control most of this. In a flat you control less. The orientation, the shared walls and the roof were fixed when the building was designed. You can still influence a good deal: the shading on a balcony, whether windows open on two sides, where the fans go, and the machine and its setting.
Before you buy, ask which way the main rooms face, whether they have openings on more than one wall, and what finish the roof has if you are on the top floor. These questions cost nothing, and the answers tell you how hard the air conditioner will have to work.
Where passive design runs out
It has limits. A dense neighbourhood blocks the breeze. Traffic noise, dust and security keep windows shut at night, which is when the cooler air is available. A heatwave can push outdoor temperatures beyond what any wall can answer.
The draft India Cooling Action Plan projects that the nation's cooling requirement will grow about eight times between 2017-18 and 2037-38. [5] That is a projection, and it comes from a draft. It is why we call this guide Before the Air Conditioner, not Instead of It. The better the house, the less that figure weighs on your electricity bill.
The order, in short: know your climate, shade and insulate the roof and the west side, open the house to moving air on two sides, add fans, and size the machine last. To see how we take a project from first conversation to handover, read about our process. For more on the ideas of shade and air, see making a modern home feel Indian. Comfort is felt inside the home, so see our home interiors in Mumbai and the bungalows we have designed, and what an architect costs if you are budgeting.
Terms used in this guide
- Adaptive comfort: the idea that people are comfortable across a range of temperatures because they adjust, by opening windows, using fans and changing clothes.
- Chajja: a projecting sunshade over a window or door.
- Cool roof: a roof finish that reflects most sunlight and gives off the heat it does absorb.
- Cross-ventilation: air moving through a room from an opening on one side to an opening on another.
- Mixed-mode: a home that uses both natural ventilation and air conditioning.
- Operative temperature: a blend of air temperature and surface temperature, closer to what a person feels than air temperature alone.
- RETV: the Residential Envelope Transmittance Value, a measure of heat gain through walls and glass, in W/m².
- Solar reflectance: the share of sunlight a surface reflects, from 0 to 1.
- Thermal transmittance (U-value): how readily heat passes through a wall or roof, in W/m²K. Lower is better.
Sources
[3] The Climate Group. Telangana's cool roof policy: pilot demonstration to policy implementation.
Research accessed 1 October 2026. The Eco Niwas Samhita is mandatory only for larger projects, with a connected load of 100 kW or a contract demand of 120 kVA and above, so its figures are benchmarks for a single home, not rules. The IMAC-R study covers eight cities across five zones, and readers should check the paper for which. The Hyderabad result comes from a pilot. The passages marked as our view are opinion. The pictures illustrate ideas, not completed work.