What Size Air Conditioner Do I Need? Israeli HP and BTU Sizing by Room

The short answer: about ⁦600 BTU⁩ per m² with a standard ceiling, meaning 1 HP up to about 15 m², 1.5 HP for ⁦15–20⁩ m², 2 HP for ⁦20–30⁩ m² and 3 HP for ⁦30–40⁩ m².

This is the table published by the importer Tornado, assuming a 2.5 m (8.2 ft) ceiling:

• Up to 15 m² (160 sq ft): 1 HP, about ⁦9,000 BTU⁩
• ⁦15–20⁩ m² (⁦160–215⁩ sq ft): 1.5 HP, about ⁦13,500 BTU⁩
• ⁦20–30⁩ m² (⁦215–323⁩ sq ft): 2 HP, about ⁦18,000 BTU⁩
• ⁦25–35⁩ m² (⁦269–377⁩ sq ft): 2.5 HP, about ⁦22,500 BTU⁩
• ⁦30–40⁩ m² (⁦323–430⁩ sq ft): 3 HP, about ⁦27,000 BTU⁩
• ⁦35–45⁩ m² (⁦377–484⁩ sq ft): 3.5 HP, about ⁦31,500 BTU⁩
• ⁦40–55⁩ m² (⁦430–592⁩ sq ft): 4 HP, about ⁦36,000 BTU⁩
• ⁦45–60⁩ m² (⁦484–646⁩ sq ft): 4.5 HP, about ⁦40,500 BTU⁩
• Over 55 m²: 5 HP and up, about ⁦45,000 BTU⁩

Tadiran’s capacity calculator is stricter and uses ⁦650–⁦700 BTU⁩⁩ per m², assuming a ceiling of about 2.6 m and average insulation:

• Up to 12 m²: about 1 HP (⁦7,000–⁦9,000 BTU⁩⁩)
• ⁦12–16⁩ m²: ⁦1.25–1.5⁩ HP (⁦12,000–⁦15,000 BTU⁩⁩)
• ⁦16–22⁩ m²: about 1.5 HP (⁦14,000–⁦15,000 BTU⁩⁩)
• ⁦22–30⁩ m²: about 2 HP (⁦17,000–⁦19,000 BTU⁩⁩)
• Up to 40 m²: ⁦2.5–3.5⁩ HP (⁦21,000–⁦28,000 BTU⁩⁩)

Why the difference? Because there’s no single exact formula. A guide by pro.co.il (an Israeli contractors’ site) even gives a lower range of ⁦500–⁦600 BTU⁩⁩ per m². The differences come from different assumptions about insulation, windows and climate. For an average apartment on a mid-level floor, Tornado’s table is enough. On a top floor, in a sun-exposed home or in a particularly hot area, prefer Tadiran’s stricter calculation or add the factors in the next section.

Useful conversions. 1 HP ≈ ⁦9,000 BTU⁩ per hour, 1.5 HP ≈ ⁦13,500 BTU⁩, 2 HP ≈ ⁦18,000 BTU⁩ and 3 HP ≈ ⁦27,000 BTU⁩. If the spec sheet lists capacity in kilowatts, multiply by 3,413 to get BTU per hour. An AC with a cooling spec of ⁦2.6 kW⁩, for example, delivers about ⁦8,900 BTU⁩. A ⁦5.3 kW⁩ AC delivers about ⁦18,000 BTU⁩. Don’t confuse cooling capacity with electricity consumption, which also appears in kilowatts on the spec sheet and is much lower. (Note: the Israeli “HP” label is not the same as a US “ton”; 1 ton = ⁦12,000 BTU⁩, so 1.5 HP ≈ 1.1 tons.)

After calculating by area, add ⁦10–20⁩% for a top floor and strong sun exposure, about 10% per meter of ceiling above 3 m, and about ⁦500 BTU⁩ per additional person regularly in the space.

The factors in detail, according to published sources:

• Top floor or penthouse: about ⁦10–20⁩% extra, mainly when roof insulation is weak (Tadiran calculator).
• Large window or south- or west-facing façade: ⁦10–15⁩% extra (Tornado). Tadiran recommends the same ⁦10–20⁩% range.
• High ceiling: above 3 m, about 10% extra per additional meter (Tornado). If there’s also strong sun and weak insulation, Tornado recommends adding about 20% in total.
• Number of people: pro.co.il suggests adding about ⁦500 BTU⁩ per person regularly in the room. In its example, a family of 5 raises the requirement from 13,500 to ⁦15,500 BTU⁩, hence 2 HP.
• Kitchen and appliances: an oven, fridge, computers and a large TV add heat. A kitchen open to the living room increases the load on the living-room AC.
• Mamad (reinforced safe room): per Tadiran, because of limited airflow it’s worth choosing slightly more capacity than the basic calculation.
• Geographic area: in dry hilly areas like Jerusalem, cooling needs are lower. In humid coastal areas, don’t skimp on capacity, because the AC also works on dehumidifying.

Add the factors together; don’t multiply them. A 14 m² room on a top floor with a west-facing window, for example, gets 14 × 600 = ⁦8,400 BTU⁩, plus about 20% (total for sun and roof), i.e. about ⁦10,000 BTU⁩. Here a 1.25 HP AC, with about ⁦11,000 BTU⁩, fits better than 1 HP.

What reduces the need. Good insulation, double-glazed windows, external shutters (trisim) and a north-facing wall reduce the load. In a new home with thermal insulation to code, or in a shaded apartment on a low floor, you can usually stay at the size the table gives, even at its lower end. External shading on a west window, such as a shutter, awning or tree, can save a ⁦10–15⁩% capacity addition.

In a typical 4-room apartment of about 100 m² (Israelis count the living room as a room, so that’s 3 bedrooms), the usual capacities are 1 HP for a kids’ room, ⁦1.25–1.5⁩ HP for the master bedroom and ⁦2–3⁩ HP for the living room, depending on whether the kitchen is open.

The following examples are based on ⁦600 BTU⁩ per m² and the factors above. They are for illustration only:

• 10 m² kids’ room, third floor of six: ⁦6,000 BTU⁩ base. A 1 HP AC (about ⁦9,000 BTU⁩) is enough with room to spare.
• 14 m² master bedroom, top floor: ⁦8,400 BTU⁩ plus 15% for the roof, about ⁦9,700 BTU⁩. ⁦1–1.25⁩ HP fits. If there’s also a west-facing window, 1.25 HP is better.
• 9 m² mamad used as a study: ⁦5,400 BTU⁩, and a bit more is advisable because of limited airflow. A 1 HP AC will be enough.
• 25 m² closed living room on a mid-level floor: ⁦15,000 BTU⁩, so 2 HP (about ⁦18,000 BTU⁩).
• 25 m² living room plus a 10 m² open kitchen: 35 m² × 600 = ⁦21,000 BTU⁩, plus kitchen and people, about ⁦24,000 BTU⁩. ⁦2.5–3⁩ HP fits, or two smaller units at either end of the space.
• 45 m² living and dining area in a penthouse: ⁦27,000 BTU⁩ plus 20%, about ⁦32,000 BTU⁩. A ⁦3.5–4⁩ HP wall unit fits, or a mini-central AC.

In a long or L-shaped space, one powerful AC at one end will leave the other end warm. In such cases two medium ACs, or a mini-central AC with several outlets, will work better than one large wall unit.

A room in a private house or garden apartment. On a ground floor with a garden, the walls and floor are less exposed to the sun, and the base table is usually enough. In a private house with a tiled or exposed concrete roof, treat rooms on the top floor like a penthouse and add ⁦10–20⁩%. In attic rooms with a sloped ceiling, calculate by the average height, not the lowest point.

The difference between 1 and 1.25 HP is about ⁦2,000 BTU⁩, and in stores it sometimes costs only a few tens of shekels more. So for a room on the borderline, 1.25 HP is the better choice.

What we saw in the spec sheets:

• Tadiran Air One INV 140, marketed as 1 HP, delivers ⁦9,840 BTU⁩ cooling.
• Electra Platinum INV 150, marketed as 1 HP, delivers ⁦9,600 BTU⁩, with an inverter range of ⁦3,100–⁦11,400 BTU⁩⁩.
• Electra A Inverter 140, marketed as 1.25 HP, delivers ⁦11,020 BTU⁩.

Note the inverter range. An inverter AC doesn’t run at its nominal capacity all the time. It can drop to low output when the room is already cool and rise above nominal at peak heat. So an AC with a high upper range gives reserve on heat-wave (sharav) days.

When 1.5 HP? In a ⁦15–20⁩ m² room, or a ⁦13–15⁩ m² room on a top floor with a large window. In stores you’ll find fewer models labeled exactly 1.5 HP. Most manufacturers jump from about ⁦11,000–⁦12,000 BTU⁩⁩ to about ⁦15,000–⁦18,000 BTU⁩⁩, so compare by the BTU in the specs, not the label.

Heating in winter. If the AC will also be used for heating, check the heating figure in BTU and the SCOP. On some models heating is lower than cooling. The Tadiran Air One INV 140, for example, cools at ⁦9,840 BTU⁩ and heats at ⁦8,840 BTU⁩. The Electra A Inverter 140 cools at ⁦11,020 BTU⁩ and heats at ⁦9,365 BTU⁩. In Jerusalem, the Galilee and the Negev, where winter nights are cold, that can be the difference between a comfortable room and a chilly one. So for a room used mainly for heating in winter, compare models by the heating figure and SCOP, not just cooling.

For a closed ⁦20–30⁩ m² living room, 2 HP fits. For a living room open to the kitchen, ⁦30–40⁩ m² in total, ⁦2.5–3⁩ HP fits. 3.5 HP and up suits spaces of 40 m² or more, or penthouses.

What to know at these capacities:

• Price: at one chain we saw 2 HP wall units at about ₪⁦2,200–4,400,⁩ and ⁦3–3.5⁩ HP units at about ₪⁦2,850–5,700,⁩ depending on brand and series.
• Efficiency: a living-room AC runs many hours a day, so SEER matters more than in a bedroom. The Electra Platinum INV 250, for example, reaches SEER 7.3 per the specs.
• Electricity: up to 3.5 HP most models are single-phase. The Electra Platinum INV 250 works with a 16A type C breaker. At ⁦4–4.5⁩ HP there are single-phase and three-phase versions, and with a single-phase connection you need to check the total load.
• Outdoor noise: large ACs with a large outdoor unit are louder. The Electra Platinum INV 250’s outdoor unit reaches ⁦56 dB⁩ per the specs.

If the living room is long, with a dining area at one end and a sofa at the other, consider two ⁦1.25–1.5⁩ HP ACs instead of one 3 HP unit. Installation will cost a bit more, but you’ll get more even distribution and the option to cool only part of the space. For a whole apartment, also look at a mini-central AC.

One large AC or two small ones? An example from the prices we saw: a 3 HP wall unit costs about ₪⁦2,850–5,700,⁩ and two 1.25 HP units together cost about ₪⁦2,500–3,800.⁩ Installing two units costs more, and two outdoor units need space. On the other hand, two units give better distribution, a backup if one breaks down, and the option to run just one on mild days.

An undersized AC runs at full load and can’t reach the set temperature on hot days. An oversized AC cools quickly, but costs more, removes less humidity and can leave the air feeling cold and damp.

An AC that’s too small:

• The compressor runs for long hours at maximum output, which wears it out faster.
• On heat-wave days the room stays hot even after hours of cooling.
• The saving on the purchase price is lost on the electricity bill and in discomfort.

An AC that’s too big:

• A higher purchase price, and installation too (above 2 HP the professional price list rises to ₪⁦1,200–1,800⁩).
• On non-inverter models, an oversized AC keeps switching on and off. With an inverter the problem is smaller, since the compressor can run at low output.
• When the AC reaches temperature quickly, it removes less humidity. On the coast this feels like cold but sticky air.
• A larger outdoor unit takes more space and makes more noise.

The practical rule: use the table, add the factors, and if you land exactly on the border between two sizes, go up only if there’s an exposed roof, a west window or an open space. Otherwise, stay at the smaller size and choose an inverter model with a wide upper range.

Signs your existing AC is too small: it runs all day without stopping, the room doesn’t get below ⁦27–28⁩°C (⁦81–82⁩°F) in the hottest hours, and the air coming out is less cold than before. Before replacing it, have a technician confirm there’s no refrigerant leak or clogged filter. Faults like these reduce performance and look exactly like an underpowered AC.

The calculator on this page gives a quick estimate based on area, floor, sun, ceiling height and open space. For a private house, a double-height space or a mini-central system, have a consultant or installer measure.

To get a good result from the calculator:

• Measure the actual area, including corners and space open to the kitchen or hallway. Don’t rely on a remembered “3 by 4 room”.
• Mark top floor only if there’s a roof above the apartment, not another apartment.
• Mark sun exposure if there’s a large south- or west-facing window without shading.
• Enter the ceiling height if it’s above 2.7 m.

When not to rely on a calculator alone:

• When planning a mini-central AC for several rooms. There you need to calculate each room’s load separately, the duct length and the static pressure.
• In a home with large glass walls, a double-height space or a gallery.
• When insulation is unusual, for example a very old home without insulation or a new home with full thermal insulation.

In any case, before buying, compare the BTU figure in the specs and not just the HP label. Once you’ve chosen a capacity, compare models by SEER, noise, Shabbat mode and warranty. We cover this in our best air conditioner guide and in our Tadiran vs Electra air conditioner comparison.

Questions for the installer before ordering. Does the capacity you chose suit the area, floor and sun exposure? Where will the outdoor unit go, and how long is the piping? Are the electrical line and breaker suitable for the capacity? A good installer will tell you if you chose an AC that’s too small for the room, and also if you chose one that’s too big. If they recommend a capacity much higher than the table, ask for a reasoned explanation. That way you’ll get an AC that suits the room even at the height of summer.