Buying your first air conditioner: sizing, inverter vs non-inverter and what to check
By Janice · Updated 2026-07-03
Buying a first air conditioner involves more decisions than it looks like from the shop floor: capacity, inverter or not, and which installer to trust with the piping and wiring. Getting the first one wrong is the most expensive mistake, since an undersized or oversized unit is hard to fix without reinstalling.
Once you have a rough idea of what you need, installation providers in this area are listed and scored on this directory, which is useful for comparing before you commit to a quote. The home page has every category on this directory if you are also weighing up servicing or warranty support at the same time.
Getting the size right
As a rough starting point, capacity generally scales with room size, but sun exposure, ceiling height, and occupancy all push that number up:
| Room size | Typical starting capacity | Adjust up if… |
|---|---|---|
| Small bedroom, up to around 10 sqm | 1.0 HP | Top floor, west-facing, or more than one occupant |
| Medium bedroom or study, 10 to 15 sqm | 1.0 to 1.5 HP | Direct afternoon sun or high ceiling |
| Living room, 15 to 20 sqm | 1.5 to 2.0 HP | Open-plan layout or large windows |
| Larger open-plan space, 20 sqm plus | 2.0 to 2.5 HP | Multiple heat sources, high occupancy |
A unit that is too small runs constantly on hot afternoons and never quite catches up. A unit that is too big cools the room fast but cycles on and off often, which leaves the air feeling cold but humid rather than properly dry. A contractor who measures the room, checks which way it faces, and asks how many people usually use it will size this more accurately than a rule of thumb alone.
Inverter vs non-inverter
Inverter units adjust their compressor speed to hold a steady temperature, rather than switching fully on and off. That generally means lower electricity use over time, quieter running, and less temperature swing in the room. Non-inverter units cost less to buy but use more electricity for the same cooling output and cycle more noisily.
For a room used most of the day, like a living room or a home office, inverter tends to be worth the higher upfront cost. For a guest room or a space used occasionally, the electricity savings take longer to add up, so a non-inverter unit is a reasonable way to save on the initial purchase.
What to check before you commit
- Warranty terms. Ask how long the compressor warranty runs separately from the general parts warranty, since compressors are the most expensive part to replace.
- Workmanship warranty. This covers the installation itself, not the unit. Ask what it covers and for how long.
- Noise rating. If the bedroom is small or the wall is shared, a quieter model is worth the small premium.
- Spare parts availability. A well-known brand with a local service network is easier to get serviced years down the line than an obscure one.
Getting a fair quote
Professional, skilled workmanship is one of the most common praise points across reviews on this directory, which is a reasonable baseline to expect. Get at least two quotes for a like-for-like comparison, same capacity, same brand tier, and ask each one to break down unit cost, labour, and piping separately rather than quoting one bundled number. That makes it far easier to see where the price difference actually comes from. For typical price ranges by unit capacity, the aircon installation cost guide breaks down what a fair quote should include.
After the purchase
Once installed, a new unit generally does not need its first chemical wash for six months to a year, but a general filter clean every three to four months keeps it running efficiently from day one. Registering the warranty with the manufacturer, if required, is worth doing in the first week rather than leaving it until something goes wrong. Keeping the original invoice, warranty card, and installation receipt together in one place also saves a lot of hassle if a claim comes up years later.
More on how providers are ranked on this directory, including how installation feedback factors into scoring, is on the methodology page.
FAQ
- Is inverter always better than non-inverter?
- For a room used several hours a day, inverter usually pays for itself over time through lower electricity use. For a room used only occasionally, the price gap may not be worth it, since non-inverter units cost less upfront.
- What size unit do I need for a bedroom?
- It depends on floor area, ceiling height, sun exposure and how many people usually sleep in the room, not floor area alone. A contractor should size it after seeing the room rather than guessing over the phone.
- Does brand matter as much as capacity?
- Capacity and installation quality matter more day to day. Established brands tend to have easier access to spare parts and local warranty support, which matters more over the unit's life than the badge on the front.
- Should I buy the unit myself or let the installer supply it?
- Either can work. Buying through the installer often bundles a workmanship warranty with the unit warranty, which is simpler if something goes wrong. Buying separately can save money if you find a good deal, but confirm the installer will still honour their workmanship warranty on a unit they did not supply.