Cassette, ducted or wall split: cooling a shop or a small office

Updated September 4, 2026 · Claude AC · 2 sources cited

Contents (6)

The four answers on the table
Sizing: forget the residential rule of thumb
What the energy label covers
The three practical constraints
Running cost, and the door
Frequently asked questions

A home and a shop ask an air conditioner for very different things. A bedroom holds two people, one tube light, and stays shut for eight hours. A 700 sq ft showroom holds a dozen customers, thirty spotlights and a glass frontage, and opens its door every ninety seconds. The machine that cools the bedroom beautifully will run flat out in the showroom and still lose. The shop-and-office question is therefore not “which brand” but “which type, and how much of it”.

The four answers on the table

Indian light-commercial cooling comes down to four form factors, and the choice is usually decided by the ceiling before it is decided by anything else.

Type	What it needs	How the air moves	Where it fits
Wall-mounted split	A wall, a drain fall, a pipe run to the outdoor unit	One direction, from high on one wall	Small offices, cabins, clinics, back rooms
Ceiling cassette	A false ceiling with real depth above it, and a drain pump	Four ways from the centre of the ceiling	Square shops, waiting areas, conference rooms
Ducted (concealed)	Ceiling depth plus space for supply ducts and a return path	Through grilles you place where you want them	Multi-room offices, restaurants, anywhere the machine must be invisible
Tower / floor-standing	Floor space and a wall behind it	A long vertical throw across a room	Shops with no false ceiling, showrooms, halls

The trap is choosing on appearance. A cassette looks like the professional answer, but in a long, narrow shop it cools the middle and abandons the ends, because its four-way throw assumes a roughly square plan. A ducted system solves that — the grilles go where the people are — but it needs a return air path, and a ducted unit installed without a proper return will be noisy, weak, and permanently blamed on the brand.

Sizing: forget the residential rule of thumb

The familiar Indian shortcut — roughly a ton per 100 to 120 sq ft — is a residential number. It assumes low occupancy, modest lighting, and a room that is not opening onto the street. Commercial spaces load up on all three counts, and the honest ranges are considerably tighter.

Space	Indicative area per ton	What drives it
Back office, few people, LED lighting	Around 100–120 sq ft	Close to a residential load
Open-plan office, one person per 80–100 sq ft, screens	Around 80–100 sq ft	People and equipment
Retail shop, glass frontage, spotlights, door opening constantly	Around 60–90 sq ft	Solar gain through glass, lighting, infiltration
Restaurant seating near a kitchen pass	Under 60 sq ft in the worst cases	Kitchen heat, high occupancy, high fresh-air need

These are indicative planning figures, not a substitute for a heat-load calculation. For any space above roughly 500 sq ft, or any space with a kitchen, a glass front or a server cupboard, ask the supplier for the load sheet: occupancy, lighting watts per square foot, equipment load, glass area and orientation, fresh-air quantity. A vendor who quotes tonnage without asking what is inside the room is quoting from a table, not from your building. Our tonnage guide sets out the logic for rooms; a commercial space adds the loads a home does not have.

The fresh-air question nobody quotes for

A sealed bedroom needs no ventilation allowance. A shop full of customers does, and the outside air brought in to keep it breathable arrives at 38 °C and has to be cooled from there. That is the largest single reason commercial spaces need more tonnage per square foot than homes, and the item most often missing from a cheap quotation.

What the energy label covers

India's Standards and Labelling programme is mandatory for room air conditioners, and its scope is wider than most buyers assume: split and window units, but also cassette, tower and floor-standing machines. What differs is the schedule they are rated under — cassette and ducted units are assessed against their own thresholds, so a five-star cassette and a five-star wall split are not making the same claim. Compare ISEER within a category, never across categories, for the reason our guide to BEE star ratings and ISEER explains: the star is a ranking inside a schedule, not an absolute score.

Above the room-AC range, labelling gives way to building rules. The Energy Conservation Building Code applies to buildings and complexes with a connected load of 100 kW or a contract demand of 120 kVA or more, and it sets minimum efficiencies for the HVAC system as a whole rather than for one appliance. Most single shops sit well below that threshold; a whole commercial building does not, and a tenant fitting out a unit inside one may inherit its requirements.

The three practical constraints

Ceiling depth

Cassettes need meaningful clearance above the false ceiling for the body and the drain pump; ducted units need more, plus a route for the ducts. In an older shop with a low structural slab, the false ceiling that makes a cassette possible may cost you a foot of headroom you cannot spare. Measure before you shortlist.

Electrical supply

Beyond roughly two tons, three-phase supply becomes the norm, and the connected load of several machines running together will often exceed the sanctioned load on the commercial connection. Enhancing sanctioned load with the distribution company takes time and money, and finding out during commissioning is the expensive way to discover it. The circuit, breaker and earthing side is covered in our guide to AC wiring, MCBs and sanctioned load.

Outdoor unit space

Commercial jobs concentrate several condensers in one place — a rear service area, a terrace, a shaft. Packed too close, they recirculate their own discharge air and every unit loses capacity at the hour you need it, so clearances matter more here than in a flat; our guide to outdoor unit placement sets them out.

Running cost, and the door

Commercial tariffs are higher than domestic ones and frequently include a demand charge based on peak kVA, so several machines starting together at ten in the morning cost you twice — once for the energy, once for the peak. Inverter machines soften that, and staggering start-up across units costs nothing at all.

Then there is the door. A retail unit that props its entrance open in May is buying cooling for the pavement, and no amount of tonnage fixes it — the load simply rises to match. A closer, an air curtain or a double-door lobby returns more comfort per rupee than upgrading the machine. To turn running hours into a bill, our guide to what an AC adds to an Indian electricity bill gives the arithmetic; for a shop, use the commercial tariff and add the demand charge.

Frequently asked questions

Is a cassette AC better than a wall split?

Not inherently — it is better suited to a roughly square room with a false ceiling, because it throws air four ways from the centre instead of one way from a wall. In a long narrow shop, two wall splits at opposite ends will often out-cool one central cassette of the same total tonnage. Cassettes also cost more to install and need a drain pump, which is one more part that can fail.

How many tons does a 500 sq ft shop need?

As an indicative starting point, a retail unit of that size with a glass frontage and display lighting typically lands somewhere between five and eight tons of installed capacity — a wide range precisely because glass area, lighting load, footfall and door discipline move the number more than floor area does. Treat any figure quoted without those inputs as a guess, and ask for the heat-load sheet.

Do commercial ACs carry a BEE star rating?

Room air conditioners do, including cassette and tower types, and the label is mandatory. Cassette and ducted units are rated under their own schedule, so stars are comparable within a type but not across types. Larger central plant sits outside appliance labelling and falls under building-level rules such as the Energy Conservation Building Code instead.

Can I use ordinary residential ACs in a shop?

Technically yes, and many small shops do. The catch is duty cycle and warranty: a machine running twelve hours a day at high ambient in a dusty street-facing unit ages faster than the same model in a bedroom, and some warranties distinguish domestic from commercial use. Read that clause before buying — our guide to what an Indian AC warranty covers explains where the exclusions usually sit.

Ducted or VRF for a multi-room office?

Ducted suits a floor plate that can be treated as one or two zones. Once you have many rooms used at different times — cabins, a conference room, a server room — a variable refrigerant flow system earns its higher cost by modulating each indoor unit independently, and by letting an empty cabin stop consuming anything. The break-even is about zoning and occupancy patterns, not about floor area alone.