Aircon size calculator

How the number is worked out

Floor area sets the starting point. Everything else on the form is heat arriving from somewhere the floor area cannot see: the sun through a west window, the roof above a second-floor bedroom, the people sitting in it, the rice cooker. Each of those adds a percentage to the cooling the room needs, and the total decides which band it lands in.

A shaded 14 square metre bedroom with two people lands on 1.0 HP. Put the same room under the roof with the afternoon sun on it and it wants 1.5. That is the whole reason a floor area on its own gives the wrong answer often enough to matter.

Aircon HP by room size

1. 1 Find your room, not your budget. Measure the floor and read up. The squares are the rooms at one scale, so the one that looks like yours is yours.
2. 2 Five times the room is only twice the width. Area grows as the square of the side, so stepping up a size buys less floor than the horsepower figure suggests. It is also why guessing from the look of a room goes wrong so reliably.
3. 3 The room is the start and not the whole answer. Sun on the wall, the ceiling height, how many people are in it and what else in it is hot all move the real figure, which is what a visit settles.

Room sizes assume a normal ceiling, ordinary sun and two people. The calculator above applies the adjustments for you.

Tons, BTU and horsepower

Commercial equipment and older paperwork talk in tons. A refrigeration ton is 12,000 BTU per hour, so it converts straight onto the same sizes above.

Watts and amperes by size

1. 1 The ranges barely overlap. Which size you fit decides what you pay to run it, far more than anything you do with the remote afterwards.
2. 2 The steps get expensive at the top. Going from 2.0 to 2.5 HP adds about as much draw as going from 0.5 to 1.5 does. An oversized unit is paid for twice, once at the shop and then every month.
3. 3 A range, not a figure. The spread within each size is mostly inverter against non-inverter, which is the other decision worth making before the room gets its unit.

Two numbers people usually want next. Running watts is what the unit draws once it is working; an inverter varies its draw and settles lower once the room is cold, which is where its saving comes from. Amperes are the running figure on 230 volts, and starting current on a non-inverter is several times that for a moment.

Typical ranges for units sold in the Philippines. Models differ, so read the nameplate before sizing anything electrical from these.

What breaker does an aircon need?

The amperes above are what a unit typically draws while running. They are not breaker ratings. For example, the 1.5 HP row shows 5.7 to 7.0 A, but that alone cannot tell you which breaker to buy. Check the unit's nameplate and installation manual; a licensed electrician can then assess the circuit, wire and breaker together.

In Philippine shops you may see a safety breaker with a universal aircon outlet. The outlet and the rating printed on the product still have to suit the unit and the wiring behind it. Do not use an aircon without proper circuit protection or keep resetting a breaker that trips. Leave breaker selection and electrical wiring to a licensed electrician.

Questions people ask

How many square metres can a 1.5 HP aircon cool?

Around 16 to 22 square metres in an ordinary bedroom with a normal ceiling and no strong afternoon sun. A room that takes the sun from the west, sits directly under the roof, or holds several people for hours will need the next size up even at the same floor area.

How many HP of aircon do I need per square metre?

Roughly one horsepower for every 12 to 16 square metres in a shaded bedroom. It is a starting point rather than a rule, because heat comes in through the roof, the windows and the people as well as through the floor area.

How many amperes does a 1.5 HP aircon draw?

A non-inverter 1.5 HP unit typically runs at about 5.7 to 7 amperes on 230 volts. Starting current is several times higher for a moment, which is why the breaker is sized above the running figure. The nameplate on your own unit is the number that counts, and an electrician sizes the breaker and the wire from it.

Is a 0.6 HP aircon enough for a bedroom?

For a small bedroom up to about 8 square metres, usually yes. Above that it will run continuously without ever getting the room properly cold, which costs more in electricity than the larger unit would have.

Does an inverter unit need a different size?

No. Size it for the room exactly the same way. The inverter changes how much electricity it uses to hold that temperature, not how much cooling the room needs.

What happens if the aircon is too big for the room?

It cools quickly, switches off, and leaves the air damp, because the unit never runs long enough to pull moisture out. The room feels cold and clammy at the same time, and the compressor wears from the constant stopping and starting.