What Does 1 HP Actually Cool? HP to AC Tonnage Conversion in Kerala, 2026

You have a quotation in front of you that says 1.5 HP. Your room, you have been told, needs 1.5 ton. The two numbers look like they match. They do not, and the gap between them is the most common sizing error we find on site visits across Kerala.

The short answer

On an air conditioner nameplate, 1 HP is roughly 0.75 ton, not 1 ton.

So a 1.5 HP unit is about 1.13 TR, closer to a 1 ton AC than a 1.5 ton one. If a dealer has quoted 1.5 HP against a 1.5 ton requirement, you are being offered roughly three quarters of the cooling you asked for.

There is a second answer circulating online that gives a completely different figure. Knowing which one applies to your quotation is what protects you, so the rest of this article shows both, and where each comes from.

Two different things are both called HP

This is the root of the confusion, and almost no showroom explains it.

Mechanical HP is the classical unit of power. It measures the work the compressor motor does, an input:

Nameplate HP on an air conditioner is a shorthand inherited from Japanese and wider Asian practice, where a unit drawing about 735 W was labelled "1 HP". The label then detached from the motor and became the name of a capacity class, an output:

One is power going in. The other is heat coming out. Same two letters, opposite ends of the machine.

Tonnage: the cooling side

Tonnage measures how much heat the unit removes from the room per hour.

The ECBC HVAC tip sheet hosted by Kerala's Energy Management Centre confirms the figure at 12,000 BTU/h, or 3.516 thermal kW. This is heat moved out of the space, not electricity drawn from the socket.

Why the "4.7 HP per ton" figure is wrong

Search this question and you will find a confident conversion that runs as follows: one ton is 3.517 thermal kW, one horsepower is 0.7457 kW, therefore

The arithmetic is flawless. The physics is nonsense. That division assumes the compressor turns 1 kW of input into 1 kW of cooling, as though it were a heater running backwards.

An air conditioner does not manufacture cold. It is a heat pump: it moves heat from inside to outside, and moving heat costs far less energy than creating the equivalent temperature change from scratch. The ratio of heat moved to electricity consumed is the Coefficient of Performance:

Because COP sits comfortably above 1, that 4.7 figure overstates the motor you need by a factor of three or more.

The conversion that is actually correct

Start from the definition of COP and work through to tons. Taking a mid-range inverter at COP 3.0:

Since the two constants collapse to $0.7457 \div 3.517 = 0.212$, any unit can be handled in one line:

Across the COP range of a typical residential split in India:

Reconciling the two answers

You now have two figures for what 1 HP cools: 0.75 TR from the nameplate convention, and 0.53 to 0.74 TR from the mechanical calculation. Both are correct, because they answer different questions.

• If the HP figure came off a product listing or quotation, it is a capacity label. Use $1\ \text{HP} = 0.75\ \text{TR}$.
• If the HP figure is the rated shaft power of the compressor, on an engineering datasheet or the motor's own nameplate, use the COP formula.

For a homeowner reading a quotation it is almost always the first. The two land close enough that the practical rule holds:

1 HP of nameplate rating ≈ 0.75 to 1.0 TR of cooling output

The upper end of that range is dealers rounding 0.75 up to a round ton. In Kerala, where ambient temperatures regularly push 35°C and humidity stays above 70%, assume the lower end. Sustained high ambient and heavy latent load both pull delivered capacity down, never up.

Quick reference table

Every row is $\text{HP} \times 9{,}000$ BTU/h converted to tons. The room sizes assume an average Kerala flat with moderate sun exposure, and they shift considerably with west-facing walls, top-floor slabs, and large glazing.

These remain approximate. The only figure that is not approximate is the rated cooling capacity in kW or BTU/h on the product datasheet.

How to read the spec sheet

1. Find the rated cooling capacity in kW or BTU/h. It is the real measure, and it outranks every HP or ton figure in the brochure.
2. If the listing gives only HP, ask for the capacity in kW or BTU/h. A dealer who cannot produce it is a signal in itself.
3. Treat ISEER with care. It is a seasonal average across a range of outdoor temperatures, which makes it a good efficiency comparator between models and a poor input to a capacity calculation. It is not the COP to put into the formula above.
4. A star rating is a claim with a date attached. BEE tightened the ISEER bands for room air conditioners in 2026, so the same machine can carry a 5 star label in an older listing and a lower one under current bands. Ask for the measured ISEER value and the year it was rated, not just the number of stars.

Size from the room, not from the motor

1. Calculate the cooling load from floor area, ceiling height, sun exposure, glazing, occupants, and equipment heat. Our guide on how to choose the right AC tonnage for your room works through this properly.
2. Convert that load to tonnage. This is the specification that decides comfort.
3. Use HP only as a cross-check on the quotation, via the table above.

What HP-first thinking costs

Oversizing. A buyer reads "2 HP" as a big machine and puts 1.5 TR into a 120 sq ft bedroom. The compressor reaches setpoint quickly and shuts off, which sounds efficient and is not: short cycles never run long enough to strip moisture from the air. The room ends up cold and clammy, which in Kerala's humidity is the complaint we are called out for most often, and the stop-start duty wears the compressor.

Undersizing. A buyer reads "1 HP" and expects it to hold a 150 sq ft room. At 0.75 TR against a load nearer 1.2 TR, the unit runs continuously, never reaches setpoint on a hot afternoon, and ages faster than it should.

Both disappear when you start from the room's load in tons and work backwards to the machine.

Installation decides the real output

The right tonnage on paper still underperforms if the install is poor. An outdoor unit in direct sun, an undersized drain line, or a copper run longer than the manufacturer permits will each cut delivered capacity. Every COP and ISEER figure above is measured under laboratory conditions. Field performance tracks only as closely as the installation allows.

This is why HRS surveys the site before recommending a size, and installs to a standard that holds under Kerala's conditions rather than on the test bench. For sizing, installation, or a second opinion on a quotation, request a site survey or talk to our team.