This guide is for Singapore homeowners replacing a water heater in an HDB flat, condo or landed house, and for anyone deciding between a storage tank, an instant unit and a heat pump. Alpha and Omega Trinity Pte Ltd (AOT) is a licensed M&E contractor and PUB-licensed plumbing firm (Lam Kien Choon, WS16882018) working across Singapore since 2012.
Start with how the hot water is actually used
- How many outlets run at the same time — one shower, or two bathrooms plus a kitchen.
- What is above the ceiling — false ceiling space for a tank, or a solid slab?
- What wiring and pipe the point already has — existing isolator and 15mm or 20mm pipe.
Instant water heater
An instant heater heats water as it flows, so there is no stored tank. It is slim, mounts inside the bathroom, and is the usual choice for a single HDB bathroom.
- Good for: one bathroom in use at a time, limited ceiling space, simple changeout.
- Watch out for: flow and temperature drop when someone opens a second tap; older low-pressure units are fussy about incoming water pressure.
Storage water heater
A storage heater keeps a tank of hot water, usually concealed above the bathroom ceiling or in a service area. A typical HDB installation uses a horizontal tank around 15 to 25 litres; larger homes may run two tanks or a bigger unit.
- Good for: two bathrooms running together, rain showers, steadier pressure and temperature.
- Watch out for: needs ceiling space or a service yard, proper support and drain for the pressure relief valve, and holds heat between uses.
Heat pump water heater
A heat pump moves heat from the surrounding air into the tank instead of using a resistive element. It is efficient, but it needs outdoor or well-ventilated space and a higher upfront budget.
- Good for: landed homes, large households, owners with a yard or utility area and a longer planning horizon.
- Watch out for: space, airflow and condensate drainage must be resolved before quoting.
Quick comparison
| Consideration | Instant | Storage | Heat pump |
|---|---|---|---|
| Space needed | Wall inside bathroom | Ceiling or service area | Outdoor or ventilated area |
| Two showers at once | Not reliable | Yes, if sized correctly | Yes, if sized correctly |
| Typical home | Single-bathroom HDB | HDB with two bathrooms, condo | Landed, large household |
| Changeout complexity | Simplest | Moderate — support, relief drain | Highest — space and drainage |
| Running cost | Heats only what you use | Keeps a tank hot | Most efficient per litre heated |
What a qualified technician checks before quoting
- Cold-water inlet size and pressure at the point.
- Condition of the existing isolator, and whether the circuit is dedicated.
- Anchor points for the tank, and whether the relief valve can discharge safely to drain.
- Whether the old unit can be removed without disturbing tiling or cabinetry.
- Signs of an existing leak: staining under the tank or a drip from the relief pipe.
DIY vs licensed work
Replacing the unit itself is licensed plumbing work. Anything involving the electrical point, the circuit breaker or a tank element belongs to a licensed electrician.
Stop and call a professional immediately if you see water dripping from the tank body or relief discharge, the circuit breaker tripping when the heater runs, burning smell / scorch marks / hot isolator, or a heater that runs hot then cold unpredictably.
Do not open the tank or bypass the relief valve. A storage heater holds hot water under pressure.
How AOT handles a heater replacement
We survey first, then quote. Labour from-prices are on our storage and instant pages; parts and GST are extra. Wider cost tables: aot.com.sg.
Frequently asked questions
Which is better for an HDB flat, storage or instant?
Most HDB bathrooms run one shower at a time, so an instant heater is usually enough and needs no ceiling tank. Choose storage if two bathrooms may run together, or if you want steady pressure through a rain shower.
Can an instant heater serve two bathrooms at once?
Not reliably. One instant unit is sized for one outlet. Two bathrooms in use means a storage tank, or one unit per bathroom.
Why does my storage heater trip the circuit breaker?
Usually a failed heating element or a leaking tank letting water reach the wiring. Stop using the heater, switch the isolator off, and have a licensed plumber and electrician check it together.
Do I need a pressure relief valve on a storage heater?
Yes. Correctly sized pressure and temperature relief valve piped to drain. Seized valve or choked discharge — tank should not be reused.
How long does a heater replacement take?
A straight change of the same type is usually done within a day. Switching from instant to storage is longer because pipework, isolator, relief drain and ceiling support must be run and tested.
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