When buying an AC, what should be compared? How to choose between fixed-speed and inverter units
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When choosing between a fixed-speed and an inverter AC, first confirm the appropriate cooling capacity and installable model, then compare the Hong Kong Energy Label, unit price, installation fee and actual usage time. Without data on electricity use and prices for two specific models, no one can promise that an inverter unit will pay for itself in a few years.
Buy a budget unit or an inverter unit?
If the unit is used for longer periods, the savings from a more energy-efficient model may be worth considering; however, regardless of whether it runs for a few hours a day, payback depends on the actual model's power consumption, price difference and electricity rate, so it cannot be said that it will always pay back in one to three years.
How to estimate the difference in electricity cost and the payback period?
First find two models with similar cooling capacity, then check the power consumption data on the energy labels and the actual purchase and installation quotes. If the estimate assumptions differ, they cannot be compared directly.
Price difference for buying a unit (initial cost)
- Low-cost fixed-speed AC units usually have a lower unit price and a lower initial investment.
- Grade 1 energy-label inverter air conditioner: higher upfront price, but better operating efficiency and energy-saving performance.
- The actual price difference should be based on specific quotes for the same cooling capacity, and installation plus necessary accessories must also be included.
Electricity bill calculation basis (calculated using the local power company’s tariff)
Electricity use should be estimated based on the actual model label data, usage periods and conditions; the number of days of use differs from household to household each year, so May to September cannot be treated as a fixed 120 days.
- Fixed-speed unit: refer to the rated power consumption of the selected model, and take into account that the compressor will start and stop as needed; do not assume any one model represents a fixed hourly power use for all fixed-speed units.
- Estimate using comparable energy-label annual consumption data or the same test conditions, then adjust for actual usage habits. Do not multiply unverified daily power use by a fixed number of seasonal days.
- Total summer electricity bill: calculated by multiplying the power consumption of a fixed-speed unit running at full load by the local electricity tariff.
- Inverter model: check the model’s energy label and test conditions. Inverter operation can adjust to load, but you cannot assume a fixed power use per hour or a fixed savings percentage.
- Compare the two models under the same conditions, then calculate the difference; do not use one example to estimate the seasonal electricity use of all households.
- Total summer electricity bill: calculated by multiplying the power consumption of an inverter unit running in energy-saving mode by the local electricity tariff.
Payback period result:
- Annual electricity savings: depending on daily usage time and ambient temperature, the running cost of inverter models is usually lower than fixed-speed models.
- Payback period estimate = additional purchase and installation cost ÷ estimated annual electricity savings; if power consumption, electricity rate or usage pattern has not been verified, the result should only be shown as a conditional estimate.
For heating use in a heat-and-cool unit and the efficiency of different appliances, comparison must be made separately according to each model's label and actual use; you cannot assume it will definitely shorten the payback period.
Debunking buying myths: 4 common misconceptions about AC value for money and energy savings
Many people buy an air conditioner based only on the slogan on the promotional poster, while overlooking the practical details of how it actually works:
Myth 1: "As long as I buy a Grade 1 energy label, it will definitely be the most energy-efficient?"
A recognised Grade 1 energy label in Hong Kong indicates that the model meets a high energy-efficiency standard within the same cooling-capacity category.
- Compare the label grade and power consumption data of models with similar cooling capacity; different capacities or usage conditions cannot be judged better value from numbers alone.
Myth 2: "If I buy a smaller air conditioner capacity (for example, 1 HP for 1.5 HP use), the unit will be cheaper and save electricity?"
Some people think that choosing a smaller-capacity model means lower power and therefore lower electricity use.
- Insufficient capacity may reduce cooling performance or lengthen running time, but not all units will be in 100% overload or inevitably break down for a long time; choose the unit according to the room load.
Myth 3: "Turning an inverter air conditioner on and off uses more electricity, and leaving it on for half an hour before going out saves power?"
It is often said that inverter ACs draw a very large current when starting up, so leaving them on briefly instead of switching them off saves more power.
- Whether to switch off the AC when leaving briefly depends on the model, the indoor-outdoor temperature difference and the actual time away; there is no universally applicable 10, 15, 30 or 40 minute threshold, and no method can be guaranteed to save more electricity.
Myth 4: "Fixed-speed units are already obsolete and completely not worth buying?"
Variable-speed models are heavily promoted in the market. Are fixed-speed models completely useless?
- Fixed-speed and inverter units differ in price and energy performance, so failure rates or repair costs should not be inferred solely from the compressor type; compare the maintenance and total cost of specific models.
Fixed-speed and inverter: what should you compare when buying?
For the same capacity, compare the label information, unit price, installation fee, noise level, after-sales arrangement and room usage. Without standard testing, do not give stars for safety, comfort or energy saving.
Seek help from a professional team
The installation location, capacity matching, and the cleanliness inside the unit are all worth noting, but you should not treat '30% machine, 70% installation' as test data, and we cannot promise that cleaning will definitely improve energy efficiency.
Related reading and services
- Related service scope and current charges
- Back to AC encyclopedia
- Electrical and Mechanical Services Department: air conditioner energy label
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