Air conditioners are only available in sizes for 6, 10, and 14 tatami mats | Why catalog specifications can't be trusted

table of contents

1. Why you can't trust the "room size" indicated on air conditioners.
2. Rated capacity vs. maximum capacity: Which is the truly important indicator?
3. There are essentially only three types of air conditioners—the truth behind the catalog.
4. What is APF? Don't be fooled by catalog fuel efficiency figures.
5. You'll regret it in winter if you don't know the heating capacity correction factor.
6. Smart ways to buy an air conditioner at a mass retailer without losing money

Why can't you trust the "room size" indicated on air conditioners?

The room size rating for air conditioners has not been revised since it was established in 1964. This rating was based on the standards of wooden, uninsulated, single-story houses of that time, and is therefore far removed from the performance of modern homes.

Modern homes have significantly improved insulation performance. As a result, for heating purposes, a smaller unit than indicated by the room size is often sufficient. On the other hand, for cooling, depending on the conditions of solar shading and ceiling insulation, a unit with the capacity corresponding to the room size may be necessary.

What is the 1964 standard?

In 1964, the standard for uninsulated wooden houses was around 20 on the Q-value, which indicates insulation performance. This is fundamentally different from the performance of modern, highly insulated houses. If you simply trust the room size (in tatami mats) indicated, you'll end up choosing a house with significantly excessive specifications for heating purposes.

Reasons why mass retailers want to sell larger models

The moment you say, "It's a 16-tatami mat room," smaller models will no longer be shown to you. This is because larger models are more profitable for mass retailers. There is only one solution: don't mention the room size, and instead specify the model number when making your purchase.

Rated capacity vs. maximum capacity: Which is the truly important indicator?

When choosing an air conditioner, you should look at the "maximum capacity," not the "rated capacity," which is merely a number used for catalog listings. The rated capacity is neither an intermediate nor a standard capacity; it's simply a value set for convenience in order to list the room size in the catalog.

The rated capacity listed in the catalog is approximately 2.5kW for a 6-tatami room and approximately 2.8kW for an 8-tatami room, and it increases steadily as the room size increases. However, when you look at the maximum capacity, a completely different fact emerges.

The true nature of rated capacity

The numbers in the model number correspond to the rated cooling capacity. For example, an air conditioner with "22" in the model number has a rated cooling capacity of 2.2kW. Multiplying this number by 10 gives you the rated cooling capacity (kW). However, this is merely an indicator shown in the catalog.

What are the differences between the higher-end and lower-end models?

Even among air conditioners designed for a 6-tatami room, the maximum heating capacity of higher-end models reaches 6.3kW (equivalent to more than 10 kotatsu tables). Lower-end and mid-range models are limited to around 3-4kW. In other words, the difference between high-end and lower-end models is not only in fuel efficiency, but also in their maximum capacity.

You can calculate the amount of storage capacity you need for your home using a free tool .

There are essentially only three types of air conditioners—the truth behind the catalog.

The catalog lists 9 to 10 different models ranging from 6 tatami mats to 26 tatami mats, but if you sort them by maximum heating capacity, there are effectively only 3 models. Air conditioners are a technology that separates heat into a "cold side" and a "warm side," and ideally, cooling capacity and heating capacity should increase symmetrically like a mirror. However, in reality, a limiter is set by the circuit board.

To use a moped analogy, it's like putting a 60km/h speed limit on an engine that's originally capable of 80km/h. By applying different limiters to the same engine, it's simply creating the illusion of many different speed categories.

A system that classifies heating capacity into three categories.

In one manufacturer's high-end models, the maximum heating capacity for 6-tatami, 8-tatami, 10-tatami, and 12-tatami rooms is almost the same (approximately 6.0-6.9kW). However, for a 14-tatami room (200V), it jumps sharply to over 11kW. This difference represents the practical boundary of performance.

Why are these three models for 6, 10, and 14 tatami mat rooms "must be bought"?

Within the same performance group, the lowest-priced models are the flagship models for each group (6, 10, and 14 tatami mat rooms). Other models (for 8, 12, and 16 tatami mat rooms, etc.) may be more expensive despite having the same maximum capacity. The large price difference immediately after release, and how it narrows towards the end of the model's lifecycle, indicates high profit margins.

What is APF? Don't be fooled by catalog fuel efficiency figures.

APF (Annual Performance Factor) is an index that indicates the energy efficiency of an air conditioner, and all manufacturers have included it in their catalogs since 2010. It is equivalent to "fuel efficiency" in cars, and a higher number indicates better energy efficiency.

Before 2010, heating COP and cooling COP were listed separately in catalogs. APF integrates these, showing the total efficiency under certain conditions during annual operation. Top-of-the-line models as of 2025 have reached an APF of around 7.3.

The gap between catalog fuel efficiency and actual fuel efficiency

The APF (Annual Performance Factor) is structured exactly the same way as the Prius's catalog fuel efficiency. Even though the catalog states 40 km/liter, the actual fuel efficiency can range from 15 to 30 km/liter depending on the driver and road conditions. It's important to use APF only as a reference value and not rely on it too much.

Why "driving slowly" is the most inefficient method

Running an air conditioner that's too large for the room's capacity at low power is like idling in traffic. The engine is running, but the car isn't moving forward—it's the worst-case scenario where you're just consuming energy with little effect. The most efficient way is to run an air conditioner of the appropriate size at the appropriate load.

You'll regret it in winter if you don't know the heating capacity correction factor.

The maximum heating capacity of an air conditioner is based on tests conducted at an outside temperature of 7°C. Actual heating capacity decreases significantly as the outside temperature drops, so it is dangerous to apply the catalog value directly.

The cooling test conditions were set at 35°C, but at 30-32°C, the unit actually performs better than its catalog maximum. On the other hand, the heating test condition of 7°C is an outside temperature that is consistently lower than that in Tokyo every year. The correction requirements are significantly stricter for heating.

Guidelines for heating capacity reduction based on outside temperature

According to correction factors based on national textbooks, the fan achieves approximately 8% of its maximum capacity at an outside temperature of around 5°C. Below 4°C, defrosting occurs, and the time when warm air is not being emitted increases. At -2°C, the maximum capacity drops to approximately 50%.

Situations where you should choose a higher-end model or an air conditioner designed for cold climates

If you're worried about whether you can get through winter with just air conditioning heating, the best option is to choose an air conditioner designed for cold climates (with an outdoor unit heater) or a top-of-the-line model from any manufacturer. Top-of-the-line models not only have higher maximum capacity, but also better performance retention in low-temperature environments than mid-range or lower-end models.

Smart ways to buy an air conditioner at a mass retailer without losing money

When buying an air conditioner at a mass retailer, the golden rule is to absolutely never mention the room's size in tatami mats. The moment you mention the size, they will stop recommending smaller models.

The most reliable method is to find the product number beforehand and then specify "I'd like this product number" when making a purchase. If you specify the product number, any mass retailer will be able to assist you.

You should not trust the listed price of an air conditioner.

Air conditioners are among the home appliances where the difference between the list price and the actual selling price is the greatest. Air conditioners are practically the only products where prices can be discounted by as much as 8%. Profit margins are particularly high for models outside the standard room size range (e.g., for 16 tatami mats), and prices tend to plummet towards the end of a model's production cycle.

The idea of ​​designing a house based on a 200V model for a 14-tatami room.

One approach involves designing a house so that a single unit can heat the entire house, using the maximum heating capacity of a 200V model designed for a 14-tatami mat room as the upper limit. This approach is directly related to the design philosophy of "underfloor air conditioning heating." This reverse-engineering approach, which incorporates the capabilities of the air conditioner into the house design, is key to maximizing cost performance.

The conditions for heating and cooling an entire house with air conditioners are summarized in the frequently asked question, " Can I heat and cool an entire house with just two air conditioners?"

Summary: 5 points to avoid making a bad choice when selecting an air conditioner

To avoid regretting your choice of air conditioner, there are five key points to keep in mind.

1. The tatami mat size measurement is based on the 1964 standard—it shouldn't be directly applied to modern housing.
2. Check the maximum capacity, not the rated capacity.
3. You can essentially choose from three types (6 tatami mat size, 10 tatami mat size, and 14 tatami mat size, 200V).
4. Heating capacity needs to be adjusted—at -2°C, it drops to about 50% of its maximum capacity.
5. At mass retailers, you don't specify the number of tatami mats you're buying; you just specify the product number.

Start by checking the "Maximum Capacity" section in the catalog. You should start to see facts that you hadn't noticed before.

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