Key points
- Duct losses can exceed 30% of heating and cooling energy when ducts run through unconditioned space (such as above an uninsulated roof).
- Splits allow room-by-room control, but their washable mesh filters capture little and need cleaning about every two weeks.
- Connecting more than 3 indoor units to one outdoor unit is generally not recommended in multi-zone systems.
- An oversized unit short-cycles, wasting energy without controlling temperature and humidity; size each space to its load.
The choice of AC type affects the electricity bill, comfort and maintenance for many years. This guide compares the common home systems and complements the AC and efficiency label guide.
1) The basic difference
- Ducted (central or concealed): one centrally located air handler blows conditioned air through a duct system1.
- Ductless split: small indoor units installed in the rooms themselves1.
- Single or multi-zone: one outdoor unit for one indoor unit, or several; the source says more than 3 indoor units on one outdoor unit is generally not recommended1.
- Short-run ducted: a concealed unit with short ducts serving several nearby rooms1.
2) Comparison
| Item | Ductless split | Central or ducted |
|---|---|---|
| Distribution losses | No ducts, so no duct losses1 | Duct losses can exceed 30% of heating and cooling energy in unconditioned space1 |
| Control | Each unit runs independently at its own temperature1 | Depends on the zoning in the design |
| Filtration | Many have washable mesh filters with poor filtration1 | A higher-MERV filter can be fitted depending on the system. See indoor air and dust |
| Dehumidification | Some newer high-efficiency units dehumidify less well1 | Depends on the design |
| Space | No bulky ducts; convenient for retrofits1 | Needs room for ducts and the air handler (false ceilings) |
| Appearance | Units visible in rooms | Hidden; only grilles show |
3) Size: bigger is not better
Sizing the outdoor unit and each indoor unit to the space load is imperative; an oversized unit short-cycles, wasting energy without proper temperature or humidity control1. Ask a technician or engineer for a load calculation instead of a "one ton per room" rule (practical advice).
What goes into a load calculation, and what to prepare
We give no per-square-metre figure because the load varies a lot between homes. A proper calculation combines these factors for each room:
| Factor | Why it changes the result | What to prepare |
|---|---|---|
| Area and height | The volume of air to cool | The drawing or measurements |
| Orientation and sun | West- and south-facing rooms gain more heat | The orientation of each wall and window. See Sun protection |
| Windows | Their area, glass type and shading | Window sizes and glass type. See Windows |
| Insulation | Uninsulated walls and roofs let more heat in | Whether the roof and walls are insulated, and with what. See Thermal insulation |
| People, appliances and lighting | Each adds heat inside the room | How the room is used (majlis, kitchen, bedroom) and the usual number of people |
| Air leakage and ventilation | Hot air coming in needs cooling | How well doors and windows seal |
| City climate | Design temperature and humidity differ between cities | The city name |
Ask for the calculation in writing for each room and keep it with the house drawings; it helps when replacing units later.
4) Maintenance
- Split mesh filters: clean about every two weeks1, more on dusty days.
- Deep cleaning of indoor units (blower and coil): every 1 to 3 years depending on use, with a technician's equipment1.
- Condensate line and pan: make sure both are installed correctly. The design of most wall-mounted units lets moisture collect on the blower wheel in cooling mode, so dust and mold build up on it1. See AC problems.
5) Before buying
- Compare the Saudi energy efficiency label of the specific model, not the brand name. See the AC guide.
- Ask for a load calculation for each space.
- For ducted systems: where will the ducts run, and how will they be insulated and sealed?
- For splits: where does the condensate drain? See water around the building.
- In very dry places and for large open spaces, an evaporative cooler may be a complementary option.
Sources
The number next to a statement points to its source in this list. Sources back the general information; anything marked “practical advice” is editorial experience, not a quoted source. Anything that affects safety, structural design or electrical installations needs a licensed professional, and in Saudi Arabia the binding reference is the Saudi Building Code.
- 1Ductless (Mini-Split) Heat Pumps (Building America Solution Center) — Pacific Northwest National Laboratory / U.S. DOE