Walk into any air-conditioner showroom in Bangkok and the first question is "inverter or normal?" The salesperson says inverter saves electricity, the price tag says it costs more, and the stars on the label do not seem to line up with either claim. Most of the confusion comes from a short list of misunderstandings, which this guide clears up.
This guide covers how each type works, what independent studies and Thai government sources say about running costs, how to read EGAT's No. 5 label across both technologies, and a checklist to take to the shop. Every number comes from a linked source, and where we cannot back a number we say so.
The short answer
If the air conditioner will run for many hours a day, such as a bedroom unit that runs all night, a shop or a work-from-home room, an inverter is usually the better buy. The studies point the same way, and long hours give the higher purchase price time to pay back.
If the unit will run for an hour or two a few days a week, as in a guest room or a seldom-used spare room, the saving per year is small and the extra purchase price may never be recovered. A fixed-speed unit with a good label is a reasonable choice there.
Two things matter more than the compressor type. The first is size: a unit that is too big or too small wastes energy whichever technology it uses (see the BTU sizing guide). The second is upkeep, because a rated efficiency is a figure for a clean unit.
How a fixed-speed air conditioner works
Every split air conditioner has the same basic loop. A compressor pumps refrigerant, which absorbs heat at the indoor coil and releases it at the outdoor coil. The compressor is the part that uses most of the electricity.
In a fixed-speed unit, the compressor motor runs at one constant speed. Daikin's technology page explains that a non-inverter air conditioner adjusts the temperature by switching the motor on and off, and describes it as like a runner who sprints, rests and sprints again, which it says wastes energy. When the room is warmer than the set point the compressor runs flat out; when the room reaches the set point it stops; when the room warms a little it starts again.
That pattern has three consequences. The temperature swings slightly around the set point, the compressor starts many times a night, and because it is either at full output or off, the unit can only match a small load, such as a mild evening, by cycling more.
How an inverter air conditioner works
An inverter is a speed controller for the compressor motor. Mitsubishi Electric's explanation of inverter air conditioners says incoming mains power is converted to direct current and then modulated to the frequency needed, and that microcontrollers sample the air temperature and the surroundings to set the compressor speed. Daikin describes the same principle in plainer terms: an inverter adjusts the temperature by changing motor speed instead of switching the motor on and off, which it says means less power loss and some energy saved.
The practical effect is that the compressor rarely switches off. In a hot room the unit works hard at first, and once the room is near the set point it runs at a low speed. Mitsubishi Electric says this allows continuous regulation of the temperature, and Daikin's runner analogy makes the energy point: a runner who keeps a steady, appropriate pace continues without wasting energy. Neither page puts a number on the saving. Mitsubishi Electric also claims a soft start with low rush current, in contrast to the high rush current of conventional units.
ENERGY STAR makes the same contrast for room air conditioners: a conventional compressor works like an on/off switch, either on at maximum capacity or off, while variable-speed compressors vary the motor speed to control the temperature continuously, which it says allows quiet cooling and significant energy savings. A US Department of Energy guide adds a useful detail for sizing, which we return to below: with variable-speed motors and variable-refrigerant-flow compressors, oversizing becomes less of an issue because the equipment can modulate to lower, more efficient speeds when demand is low.
In Thai retail the label says "fixed speed" or "variable speed/inverter", but shoppers say "normal" for fixed-speed units. A survey reported in a January 2021 policy brief by CLASP, a non-profit working on appliance efficiency, found that the English term "fixed speed" was not understood and that only about 45% of consumers knew a fixed-speed unit generally uses more energy than an inverter. The survey predates the current label format, so awareness may have moved on.
What the evidence says about running cost
It is worth being straight about what is and is not known. The Daikin and Mitsubishi Electric pages we read describe the mechanism but quote no saving percentage. Independent evidence exists, but it comes from studies with different methods, so the figures should be read as a range.
- A DEDE-supported simulation for Chiang Mai. A paper presented at the World Congress on Engineering and Computer Science in 2012, with support from Thailand's Department of Alternative Energy Development and Efficiency, compared a fixed-speed and an inverter unit in two identical virtual houses with a design cooling load of 3,500 watts, using Chiang Mai weather and daytime operation. It estimated that the inverter saved 15.38% more energy, with seasonal efficiency of 13.96 against 11.84 for the fixed-speed unit. This is a simulation checked against a standard calculation method, not a metered home.
- A measured office in Sri Lanka. A peer-reviewed paper in the SLEMA Journal measured a standard and an inverter air conditioner of the same capacity in a typical office room for six consecutive weeks, with eight hours of operation a day. The standard unit averaged 13.5 kWh a day and the inverter 8.7 kWh, about 35% less. It is a real measurement but a small one, from one room in a different tropical city.
Those results are 15% and 35%, and nothing in the sources says which is closer to a Bangkok condo. If a salesperson quotes a figure, ask where it comes from; a number without a stated test is marketing. What the sources agree on is the direction and mechanism: the savings come mostly from avoiding cycling and from running efficiently at part load, the condition a bedroom unit spends much of the night in once the room has cooled.
A worked example using the Thai label's own formula
The EGAT label tells you a calculation method, so you can work through a comparison with the label's own rules and then change the hours to match your life. Treat this as arithmetic on published thresholds, not as a prediction of your bill.
EGAT's label brief for air conditioners gives the formula. Electrical power in kilowatts equals the rated cooling capacity in BTU/h divided by the rated SEER multiplied by 1,000, and annual energy equals that power multiplied by the hours of use per year. The label assumes eight hours a day, which is 2,920 hours a year, and a figure of ฿5.00 per unit of electricity as of 2023. A 12,000 BTU/h unit is about 3.5 kW of cooling, so it falls in the label's smallest band, up to 8,000 W (27,296 BTU/h). At the lowest SEER that earns each level in that band, the numbers work out as follows.
| Unit (12,000 BTU/h, lowest SEER for the level) | SEER | kWh per year at 8 h/day | Cost per year at ฿5.00 |
|---|---|---|---|
| Fixed speed, No. 5 | 13.17 | about 2,660 | about ฿13,300 |
| Fixed speed, five stars | 15.85 | about 2,210 | about ฿11,100 |
| Inverter, No. 5 | 17.06 | about 2,050 | about ฿10,300 |
| Inverter, five stars | 24.56 | about 1,430 | about ฿7,100 |
Two things stand out. The first is the gap between the cheapest labelled fixed-speed unit and the cheapest labelled inverter, about 600 kWh a year or ฿3,000 on the label's assumptions. The second is that the label's own rules put the plain No. 5 inverter ahead of the five-star fixed-speed unit, which is the trap we explain below.
Now change the hours. The formula is linear, so a unit used for a quarter of the label's assumed hours has a quarter of the difference.
| Hours of use per day | Annual difference, fixed No. 5 vs inverter No. 5 | At ฿5.00 per unit |
|---|---|---|
| 8 (bedroom, all night) | about 607 kWh | about ฿3,030 |
| 4 | about 303 kWh | about ฿1,520 |
| 2 | about 152 kWh | about ฿760 |
| 1 | about 76 kWh | about ฿380 |
To find your own payback, divide the extra price on your quote for the inverter version of the same capacity by the annual difference for your hours. That is the years to break even, before any change in tariff. We quote no tariff because the label's ฿5.00 is its own planning assumption; check what you pay.
Two cautions. SEER is a lab-tested seasonal rating, and real homes differ in climate, set point, sun and insulation. And prices vary: a CLASP market study published in 2019, from product-level data collected in Thai shops and online marketplaces, found inverter units about 28% dearer on average. That figure is several years old, so use your own quotes. The same study found payback for the most efficient units was shorter for larger ones, just over six months for 48,000 BTU/h but closer to four years for 12,000 BTU/h. Bedroom-sized units take longest to repay a premium, which is why hours of use matter so much.
Thailand's No. 5 label and SEER, explained
The Electricity Generating Authority of Thailand (EGAT) runs the voluntary No. 5 energy label. The EGAT label brief says it covers split-type air conditioners up to 18,000 W of cooling capacity (61,416 BTU/h), in both fixed-speed and variable-speed/inverter types, and that the latest format, with levels from No. 5 up to five stars, began to be applied from 1 January 2024. Before that, as the CLASP policy brief records, EGAT had rescaled the label at the end of 2018 into a three-star rating above No. 5.
The measure behind the stars is SEER, the seasonal energy efficiency ratio, in BTU/h per watt. EGAT's note beside it is simple: the higher the figure, the more electricity is saved. "Seasonal" means the rating accounts for how the unit performs across a range of outdoor temperatures rather than at a single test point, which matters for an inverter that spends much of its time at part load. The 2012 Chiang Mai paper above was in fact a study of whether SEER suits Thailand better than the older single-point rating.
The two-scale trap
The detail that catches shoppers out is that EGAT sets separate thresholds for each technology. This is the same band we used above, for units up to 8,000 W:
| Label level (up to 8,000 W) | Fixed speed, lowest SEER | Inverter, lowest SEER |
|---|---|---|
| No. 5 | 13.17 | 17.06 |
| Three stars | 14.78 | 21.56 |
| Five stars | 15.85 | 24.56 |
A fixed-speed unit can reach five stars at a SEER of 15.85, but an inverter earns even its plain No. 5 only from 17.06. So a five-star fixed-speed unit is, on paper, less efficient than a plain No. 5 inverter. CLASP tested exactly this in a consumer survey: 35% of consumers picked the wrong product when asked which of two labels showed the more efficient unit, choosing a one-star fixed-speed unit over a more efficient inverter with no stars. Among retailers, 26% recommended the fixed-speed unit on the strength of its star count. CLASP recommended that Thailand move to one technology-neutral scale. Its policy brief is dated January 2021 and describes the older three-star label; the 2024 five-star format still uses separate thresholds for each technology, as the table above shows, so the trap remains.
The practical rule is to ignore the star count when comparing across types. Compare the SEER on the label and the estimated annual electricity cost, which the CLASP survey found was one of the label's most useful parts. That cost uses the same eight-hours-a-day assumption, so your bill scales with your hours.
EGAT's article on choosing a No. 5 air conditioner estimates a 12,000 BTU/h fixed-speed unit at ฿917.12 a month at No. 5 and ฿743.53 at three stars, at an assumed ฿3.96 per unit. It covers fixed-speed units only and dates from 2022, so it shows how much stars matter within one type, not an inverter comparison.
Refrigerant also shows up in the numbers
CLASP's market research found R-32 models averaged a SEER of 16.25 against 14.24 for R-410A, which was below the then inverter No. 5 threshold of 15 (CLASP brief). That comes from CLASP's market research published in 2019, under the older label, but it is a reason to check which gas a new unit uses; our R32 vs R410A guide explains the difference.
Comfort and noise
The comfort case for inverters is a steadier room. Mitsubishi Electric describes continuous regulation of the temperature and very low compressor noise at low speed, and Daikin says an inverter holds the set temperature by changing motor speed rather than switching on and off. Both are manufacturer claims with no measured temperature tolerance or decibel figure.
Two things you can check yourself. A compressor that does not keep switching should mean fewer audible changes in the outdoor unit. And the noise that matters most at night is the indoor fan at its lowest speed, so compare quoted sound levels at the quietest setting, measured the same way; a figure for the highest speed tells you little. Comfort also depends on set point and humidity, covered in our guide to the best air conditioner temperature in Thailand.
Repairs, parts and lifespan
An inverter adds electronics between the mains and the compressor, and Mitsubishi Electric's Indian page, for instance, advertises separate warranty terms for the compressor and for the circuit board. That is a prompt to read warranty terms, not a verdict on reliability: we found no independent source comparing failure rates of the two types, so we make no claim either way.
CoolRova's own repair costs, for parts and labour on any compressor type, are ฿1,500 to ฿2,500 for a capacitor, ฿2,500 to ฿4,500 for an indoor fan motor and ฿3,500 to ฿6,000 for a PCB (control board). Compressors are quoted per unit, and sometimes replacement makes more sense, which we say when it is the honest answer. The diagnostic is ฿590, waived if the repair goes ahead, with a fixed written quote first and a 90-day warranty.
Before buying, ask how long the warranty runs on the compressor and on the board, what the installer's workmanship warranty covers, and who services the unit locally. For an older unit with a costly fault, our repair or replace guide sets out how to decide. CLASP's 2019 analysis assumed an average lifetime of 10.5 years, based on manufacturer and importer estimates.
A dirty inverter loses its advantage
The efficiency on a label is a laboratory rating for a new, clean unit. Real units get dirty, and in Bangkok's humid air the indoor coil stays wet, dust sticks to it and a bedroom unit may run eight hours a night.
ENERGY STAR's maintenance checklist says dirty coils reduce a system's ability to cool, so it runs longer and costs more. A laboratory study by Ali and Ismail in HVAC&R Research loaded the evaporator of a room air conditioner with fouling material and found that the coefficient of performance fell from 2.82 on a clean coil to 1.89 after 100 g and 1.23 after 300 g. That was deliberate heavy loading, not a typical home, and not specific to inverters, but it shows the direction. EGAT's savings advice says to wash the air conditioner every six months so dust does not push electricity use up, and credits that with a saving of up to 10%.
If you pay more for an inverter, budget to keep it clean. See what a dirty AC adds to the electricity bill and our AC cleaning service.
Size matters more than technology
The US Department of Energy's right-sizing fact sheet says that when equipment is oversized, efficiency is reduced and energy costs increase, and that correctly sized equipment is especially important in humid climates, where short cycling can lead to poor humidity control. Thailand's EGAT also warns against buying more BTU than the room needs, because the compressor will cut out often and the room stays humid, while too little BTU makes the unit work hard.
An inverter softens that problem: the DOE guide quoted earlier says modulating equipment makes oversizing less of an issue, though it does not say no issue. Size first, then choose the technology; the BTU sizing guide has the Thai room-size table.
Which rooms suit which
This table is our judgement, built on the hours-of-use logic above rather than on a measured study.
| Situation | Usually the better fit | Why |
|---|---|---|
| Bedroom, running most of the night | Inverter | Long hours repay the higher price; steady temperature suits sleep |
| Home office, shop or café running all day | Inverter | Highest hours of use, so the running-cost gap is largest |
| Short-stay rental where guests leave AC on | Inverter | Hours are long and not under your control |
| Guest room used a few times a month | Either; a labelled fixed-speed unit is reasonable | Few hours means a small annual saving, so a lower purchase price may win |
Buying checklist
Take this to the shop or to your installer.
- Check the compressor type on the label, and do not rely on the star count alone when comparing across types.
- Compare SEER and the estimated annual electricity cost, both printed on the label.
- Get the size right first. Measure the room and note sun exposure; do not guess.
- Check the refrigerant. R32 and R410A units differ in service parts and, in CLASP's data, in typical efficiency.
- Ask the price difference for the same capacity, then run the payback arithmetic with your own hours.
- Read the warranty terms for the compressor, the electronic board and the installation, as three separate items.
- Compare indoor-unit noise at the lowest fan speed, measured on the same basis for each model.
- Check where the outdoor unit goes. EGAT advises putting the outdoor unit in shade, out of direct sun and off a bare roof or slab, and avoiding west-facing installation positions where possible.
- Plan the first clean and the schedule so the efficiency lasts.
- Price the installation properly. A good unit installed badly performs badly; our AC installation cost guide lists what a proper job includes.
Buying help from CoolRova
CoolRova's installation service, AC installation in Bangkok, starts from ฿2,500 with a fixed written quote. It includes BTU sizing for the room, brackets, a standard pipe run and trunking, a deep vacuum and leak test before commissioning, commissioning readings in the photo report, and removal and recycling of the old unit. We can supply Daikin, Mitsubishi Electric, Carrier, LG, Samsung or Saijo Denki units at retail price or better, or install a unit you bought yourself. A standard wall-mounted split takes about three hours.
Installation comes with the manufacturer's warranty on the unit plus 12 months on our workmanship, and every new install comes with 15% off a year package. If you are still choosing between technologies, send us the room, its sun exposure and how many hours a day it runs, and we will give you our view. Message us on WhatsApp or use the quote form at /contact.
Sources and further reading
- EGAT: No. 5 label for air conditioners
- EGAT: choosing a No. 5 air conditioner
- EGAT: air-conditioner saving tips
- CLASP: air conditioner labelling in Thailand (2021)
- CLASP: Thailand room air conditioner market (2019)
- Tantakitti et al.: SEER case study, Chiang Mai (WCECS 2012)
- Siriwardhana and Namal: standard vs inverter AC in an office (SLEMA Journal)
- Daikin: inverter technology
- Mitsubishi Electric India: inverter ACs
- ENERGY STAR: room air conditioners
- US DOE: energy renovations HVAC guide
- US DOE: right-size heating and cooling equipment
- ENERGY STAR: maintenance checklist
- Ali and Ismail, HVAC&R Research: evaporator fouling
Frequently asked questions
What is the difference between an inverter and a non-inverter air conditioner?
A non-inverter (fixed-speed) unit runs its compressor at one constant speed and switches it on and off to hold the temperature. An inverter unit changes the compressor speed to match the cooling needed instead of switching the compressor off. Daikin and Mitsubishi Electric both describe the difference as speed control versus on-off switching.
Is an inverter air conditioner worth it in Thailand?
For a unit that runs many hours a day, such as a bedroom or shop, the evidence points to lower running costs that can repay the higher purchase price. For a room used a few hours a week the saving is small, so the extra cost may not be recovered. The payback depends on your hours of use, the price difference in your quote and your electricity rate.
How much electricity does an inverter air conditioner save?
There is no single figure. A DEDE-supported simulation for Chiang Mai estimated about 15% less energy than a fixed-speed unit, and a six-week measurement in a Sri Lankan office found about 35%. Manufacturers' pages that we checked give no percentage, so treat claims without a stated test method with caution.
What does the Thai No. 5 label mean for inverter and fixed-speed air conditioners?
EGAT's voluntary label grades split-type units from No. 5 up to five stars using SEER, where a higher number is more efficient. Fixed-speed and inverter units are graded on separate scales, so compare the SEER figure and the electricity cost on the label rather than the star count alone.
Do inverter air conditioners need less cleaning or servicing?
No. The coil, filter, blower and drain of an inverter unit foul in the same way as any other, and a dirty coil reduces the ability to cool whatever the compressor type. Regular cleaning protects the efficiency you paid extra for.
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Written by the CoolRova Team
We're Bangkok's documented AC crew — everything we write comes from real cleaning, repair and installation visits across condos, homes and short-stay rentals.
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