How to choose the tonnage of air conditioner? Square footage comparison table and actual electricity bill measurement (with free computer)

With the same square footage, why do some people buy the right tonnage, while others pay twice as much for electricity?

Many people just ask "how many tons does this room cost" when buying an air conditioner. The master answers a number and places the order directly. As a result, the air conditioner lasts all summer and the electricity bill is half as much as that of the neighbor. The real reason is not the tonnage itself, but the variables other than the tonnage that are often ignored.

Basic formula: 1 ping requires approximately 0.15-0.2 kW

General residential space requires about 0.15-0.2 kW of air-conditioning capacity per ping. When converted into a common tonnage unit, a room of 8-10 ping is about 1 ton. This is the most basic estimation method, and room type variables must be adjusted later.

Room type variables: Western exposure, top floor, and ceiling height all need to be increased

• Western drying room: The sunshine is strong in the afternoon, so it is recommended to increase the tonnage by 1 step
• Rooftop residents: The roof absorbs heat directly, and the room temperature in summer is higher than downstairs. It is also recommended to add tons
• Height space: The volume of the space becomes larger, and the amount of air required for air conditioning increases. For the same square footage, a higher tonnage should be selected

Square footage comparison table (general residential, non-Western)

Real electricity bill calculation: separate type vs window type vs frequency conversion

Based on a 10-square-foot space and 8 hours of use per day, the power consumption of a variable-frequency split air-conditioner is usually about 30 to 40% less than that of a fixed-frequency window type. After long-term use, the difference in electricity bills will accumulate month by month, especially during peak electricity consumption in summer.

Use a computer to calculate the recommended tonnage in 3 steps and 30 seconds

1. Enter the number of square meters of the room and house type (normal/western exposure/penthouse/height)
2. Select a usage time period (day-based/all-day/night-based)
3. Obtain the recommended tonnage range as a reference when making inquiries

You can directly use the Air-conditioning tonnage calculator (/tools/ac-tonnage-calculator) to make a trial calculation. After the calculation, if you want to further confirm the room type variables, if there is a special height or a large area with western exposure, you can also prepare photos of the room and consult a professional air-conditioning technician for on-site evaluation.

Be careful with these 3 words when buying air conditioners

• "The larger the tonnage, the cooler it is": Too large a tonnage will result in poor humidity regulation, and the room will easily get hot and cold.
• "You must buy this latest model": The new or old model does not mean the room type is suitable for you, the square footage is the key
• "The pipelines can be connected at will": Improper pipeline configuration will affect performance and future maintenance difficulty

After purchasing, what should you pay attention to in pipeline specifications?

When installing, it is recommended to confirm whether the copper pipe diameter meets the model requirements, whether the slope of the drainage pipe is sufficient for smooth drainage, and whether the outdoor unit is placed with sufficient space for heat dissipation. These will directly affect the actual use effect and power consumption performance.

When should you ask a master directly for an evaluation

If the room type is special (high floor height, multi-faceted lighting, open space), or the tonnage of the old machine is obviously not suitable for use, it is recommended to arrange an in-house evaluation directly, which is more accurate than a pure online estimate. When the master arrives at your home, he will usually actually measure the wall conditions, confirm whether the power circuit is sufficient, and give a recommended tonnage that is closer to the actual use situation based on the on-site lighting angle.

After choosing the wrong tonnage, can I still make amends

If you have purchased an air conditioner with an inappropriate tonnage, it is not completely irreparable. If the tonnage is slightly smaller, you can use a circulating fan to enhance indoor air flow, or adjust the use time to avoid the hottest periods; if the tonnage is too large, pay attention to humidity control and use it with dehumidification mode in a timely manner to avoid being too dry and uncomfortable indoors. In the long run, if there is a big gap between usage scenarios and square footage, it is still recommended to evaluate and replace with a model of appropriate tonnage, which is more cost-effective than enduring an unsatisfactory usage experience for a long time.

Further reading: For daily maintenance after the air conditioner is installed, you can refer to the "Air Conditioner Cleaning and Maintenance Guide" or "Taipei Summer Air Conditioner Energy Saving Guide" for more energy-saving tips.

FAQ

Q1: The old air conditioner has enough tonnage, but it is still not cold. Is the machine broken?

First confirm whether it is cleaned regularly. Dust accumulation on the filter and condenser will significantly affect the cooling effect. If it is still not cold after cleaning, you need to check whether the refrigerant or the body is faulty.

Q2: Do I have to buy a larger tonnage than the calculated tonnage for the attic?

It is recommended to add one step above the basic tonnage calculated by the computer. The room temperature on the top floor in summer is usually much higher than that on the average floor.

Q3: Does variable frequency air conditioner really save a lot of electricity than fixed frequency air conditioner?

The difference will be more obvious in spaces used for a long time (such as the living room and master bedroom), while the difference in rooms used for a short time (such as a study room) will be relatively limited.

Q4: The tonnage calculated by the computer is different from the suggestion made by the master for evaluation. Which one should I listen to?

The computer provides basic reference values. The in-house evaluation will take into account actual lighting, partitions and usage habits. It is recommended that the in-house evaluation results be the main one. The computer is more suitable for use in the preliminary price comparison or budget planning stage.

Q5: If you want to install air conditioning in a rented house, should you consider window type or split type?

If the lease term is short or the landlord restricts the installation method, the installation and removal of window air conditioners is relatively simple; if the lease term is long and the landlord agrees, split air conditioners usually have more advantages in power consumption performance and noise control, which can be considered based on the actual lease term and the landlord's specifications.

Different usage habits will lead to different tonnage requirements

For a room of the same square footage, if you are at home around the clock and have the air conditioner on for a long time, it is recommended that you choose the upper end of the range in the comparison table for the tonnage. If you only use it for a few hours at night, it is usually enough to choose the lower end of the range. Excessive pursuit of large tonnage will increase unnecessary purchase costs and long-term power consumption burden.

Should old air conditioners be replaced in advance

Even if an old air conditioner that has been used for more than 10 years is still running, its performance and power consumption are usually far behind the current inverter models. If you find that the electricity bill is increasing year by year and the cooling effect is getting worse, it is recommended to evaluate and replace it in advance. The long-term electricity bill savings is often more cost-effective than continuing to use the old model.

For multi-room installation, tonnage planning should be considered together

If you want to install multiple air conditioners for the entire home at one time, it is recommended not to calculate each room separately and place an order directly. Instead, first plan the electricity load of each space as a whole and confirm whether the total power supply capacity in the home is sufficient to support the operation of multiple air conditioners at the same time. This will avoid discovering that the distribution box circuit is insufficient after the installation is completed, and requiring additional costs to update the power distribution system. Planning multiple rooms together makes it easier to negotiate a more reasonable overall quote when purchasing.

Common mistakes in square footage calculation

Many people only calculate the floor area when calculating the number of square feet, but ignore the beams, columns, recessed spaces or areas connected by the open kitchen, resulting in a gap between the calculated tonnage and the actual demand. It is recommended that when determining the number of square meters, try to calculate the actual complete space of the cold room. If the spaces are connected to each other (for example, the guest restaurant is combined), it is recommended to calculate the total square footage together instead of separately estimating and buying one each.

Three on-site conditions to confirm before installation

• Whether the outdoor unit is placed with enough space for heat dissipation to avoid affecting long-term operating efficiency
• Whether the wall is suitable for drilling, some special wall materials (such as water molding, stone) require additional construction evaluation
• Whether the existing power circuit is sufficient to load the new machine, to avoid discovering the need to install additional circuits after installation

New knowledge on air-conditioning power consumption and Taiwan climate maintenance regulations in recent years (2025-2026 current situation)

With the high temperatures in summer breaking historical records and the adjustment of electricity price structure in recent years, the latest statistics from the Energy Administration of the Ministry of Economic Affairs show that air-conditioning equipment accounts for more than 47% of residential electricity consumption in summer. Many people mistakenly believe that if the air conditioner is not cold, they only need to "replenish the refrigerant." However, in fact, refrigerant is not naturally consumed during normal operation in a closed circuit. If the refrigerant is insufficient, it means that there are micro leaks in the copper pipes or joints. Simply replenishing the air conditioner will only treat the symptoms but not the root cause. Refrigerant leakage will aggravate the high temperature overload of the compressor and shorten its service life.

According to Taiwan's standard operating specifications for air-conditioning projects, it is recommended that professional technicians with a refrigeration and air-conditioning decoration technician license perform "full machine high-pressure water washing and evaporator deep sterilization" every 1 to 2 years for detached air-conditioning indoor units. Especially in the humid summer in the Shuangbei Basin, the air drum and water collection tray are easy to breed black mold and jelly-like biofilm. This is also the main reason for the sour smell in the air-conditioning outlet and the backflow of the drainage pipe. Regular maintenance can maintain CSPF (Air Conditioning Seasonal Performance Factor) level one energy efficiency level, which can save an average household 15% to 20% of air conditioning electricity bills every year.

Autonomous simple maintenance vs professional maintenance safety red line

• Homeowners can do by themselves: Remove and clean the nylon filter regularly every 2 to 3 weeks (rinse with clean water and dry in a cool place, do not expose it to the sun to avoid deformation and embrittlement); clean the air outlet blades of the indoor unit with a dry cloth; check whether there is any accumulation of debris within 50 cm around the outdoor unit that hinders heat dissipation.
• Professional technicians must be entrusted according to regulations: Refrigerant pressure testing and leakage repair welding, high-pressure cleaning of indoor unit air drums and aluminum fins with liquid chemicals, reset of the drainage slope of hidden cold water pipes in the ceiling, and 220V dedicated power circuit configuration and leakage circuit breaker replacement.