You have moved into your new flat and brought your AC with you. You set it to 24°C as usual, but the AC is not cooling properly. Even though the filter is clean, the gas has been topped up, and the technician also says the unit is fine. Still, the room never gets close to the 24°C setpoint — it just feels somewhat less hot than outside. Most people assume that something inside the unit is malfunctioning — a slow gas leak, a faulty compressor, or a coil that needs cleaning.
However, the AC not cooling may come down to the tonnage and the room size. Heat accumulates in a room through the roof, walls, appliances, and glass. Two bedrooms with identical square footage can have different heat loads; that’s why their cooling capacities can differ.
This becomes a problem when you relocate to a different place. When you move, the cooling capacity remains fixed, but the room changes. So, a unit that was suitable for the old bedroom may fall short in the new one. Anyone renting an air conditioner can choose a different tonnage as the room changes.
AC Tonnage for Room Size Doesn’t Give the Whole Picture
Matching the AC tonnage to room size starts with one thing – 1 ton of cooling capacity removes 12,000 BTU of heat per hour. That is a rate of removal, not a floor area.
| Room Size | Baseline Capacity |
| Under 120 sq ft | 1 ton |
| 120-180 sq ft | 1.5 tons |
| 180-280 sq ft | 2 tons |
Note: These are commonly used approximate guidelines, not fixed standards — actual requirements vary by climate, insulation, and heat load.
The runtime is crucial, just as the capacity is. Since January 2020, the Bureau of Energy Efficiency has mandated that room ACs default to 24°C because each degree higher saves about 6% of electricity. The setpoint helps when the unit can reach it.
A correctly sized AC reaches the setpoint and cycles normally. An oversized AC gets there too quickly, switches off before it can properly dehumidify the air, and leaves the room feeling cold and clammy
Five Reasons for AC not Cooling Properly in the New Flat
The floor area sets the baseline. Beyond that, there are still a few reasons your AC is not cooling, even when every component checks all the boxes.
1. The Floor You Are On
If your new room is on the top floor and under a slab that absorbs the sunlight all day. Then the room radiates the heat after sunset. Roof heat can noticeably raise the effective cooling load — often estimated at an additional 3 to 5°C equivalent — compared to the same layout a few floors below, though the exact figure depends on roof insulation and slab thickness. While taking the room size into account, you may want to add half a ton more.
2. Which Way the Windows Face
West-facing glass takes the harshest afternoon sun and can meaningfully increase cooling load — commonly estimated at an extra 10-20%, which would be roughly 0.15 to 0.3 tons on a 1.5-ton base
3. Ceiling Height
An air conditioner cools a volume of air, not a floor area. As a rough estimate, a 12-foot ceiling may require around 15% more cooling capacity than the same footprint at 10 feet, though this varies with airflow.
4. Who and What’s in the Room
Every person adds heat, and you should consider half a ton per five people. A shared wall with the kitchen or a room with appliances like a router or desktop also constantly increases the load.
5. What Happened During the Move
With each reinstallation, the scenario changes. A longer copper line or an outdoor unit boxed into a shaft where it cannot reject heat – these all become differentiating factors. If a drain line lacks a slope, it may also prevent the AC from cooling properly.
Air Conditioner Running but Not Cooling: Capacity or Condition?
The causes for the AC not cooling fall into two categories;
1. The unit is already in condition
2. The unit is working fine but outmatched
If the AC is working but not cooling during the afternoon, it is a different problem that has been fading over a month.
| If you notice this | It means this |
| Fine overnight, loses ground 2–6 pm | Capacity, against peak solar load |
| Runs continuously, never reaches set temperature | Capacity — heat gain matches removal |
| Cools fast, then cycles on and off, feels clammy | Oversized; too little run time to dehumidify |
| Weak airflow, or cooling faded over weeks | Condition — filter, coil or refrigerant |
| Worse from the first day in the new flat | Capacity or installation |
If nothing has degraded, all the components may be working fine. What changed was the room only. Before concluding it as an AC malfunction, it is better to reduce the load. It can be a cheaper alternative to adding capacity. Thermal curtains for the window may work; keep the door gap sealed. If the room sits directly under the roof, applying a reflective coating on the terrace above can also help reduce heat gain.
What a Rental Changes if the AC Tonnage to Room Size is Wrong
If the AC tonnage for room size is slightly off, you have two options – either you change what the air conditioning unit puts out or change the unit
A convertible AC may address the first concern, within limits. An inverter compressor allows a 1.5-ton unit to operate as a 1-ton unit during light use. If it is boosted to around 110-116% of its rating, often for about 40 minutes, the boost cools the room.
In the second concern, ownership is what matters. Changing an AC might not suit someone who bought the unit 18 months ago and relocates within a year. Rental platforms, like Rentomojo, list air conditioners for rent with services such as delivery, installation, and maintenance — check current terms, as inclusions like free relocation may vary by plan or city. When the apartments change, renting in metro cities can be specified against your room instead of being respecified at the next move.
Final Thoughts
While the air conditioner provides a fixed rate of heat removal, the room experiences variable heat gains. When you relocate, the room changes, but the AC doesn’t. If you own the unit, you can measure the new room before anything. Ensure the unit is serviced and runs on clean filters. When the AC does not cool well in the first week of the shift, the issue may lie in its capacity and not require a repair.
Frequently Asked Questions
1. Why is an AC not cooling properly in a new flat when it worked for the old place?
The cooling capacity should match a room’s heat load rather than the room layout. Where the windows are situated, how high the ceiling is, or where the room is – these all change the equation. The same can work for one room, yet it may be undersized for another room of the same dimensions in a different building.
2. Does the top-floor room require a bigger AC?
Usually, yes. A top-floor room sits directly under the slab, which absorbs heat throughout the day and radiates it downward after sunset. This may be the reason the room temperature may also increase. Generally, half a ton is added for top-floor rooms.
3. What is a 5-in-1 convertible AC?
A convertible air conditioner uses an inverter compressor that operates at multiple capacity levels rather than a single fixed output. A 1.5-ton unit can be set to behave like a 1-ton in light use, or boosted above its rating for a short spell. It adjusts output, not installed capacity.
4. What does an air conditioner running but not cooling properly indicate?
Continuous running without reaching the set temperature indicates that heat is entering the room at or above the set rate. It indicates that the capacity is not enough. If you notice weak airflow or cooling issues, you may need to check the coil, filter, or refrigerant.
5. Is a 1.5-ton AC enough for a 200 sq ft room?
At 200 sq ft, the room sits above the 120-to-180-square-foot band that a 1.5-ton unit covers comfortably. On a middle floor with modest glazing, it may cope. On a top floor or with west-facing windows, the requirement exceeds 2 tons.
