Chemical Wash Every Aircon or Just One? Deciding Unit by Unit in Singapore

One unit starts to smell. Usually it is the master bedroom, the one that runs every night. The question that follows is almost always the same: "Do I need to chemical wash all of them, or just that one?"

There is no single answer for a whole flat, because aircons in the same flat do not get dirty at the same speed. The right way to decide is unit by unit. And once you put the published prices next to each other, two things become clear: doing one unit properly is cheaper than most people expect, and splitting a whole-flat wash across separate visits costs more than doing it together.

Here is how to decide, with the actual figures from our price list.

First: what counts as a unit

For cleaning, count the indoor units — the ones on your walls. A System 3 is one outdoor unit and three indoor units, so a chemical wash on a System 3 is priced as three units, not one.

Gas top-up is the exception people mix up with this. That is priced per outdoor circuit, not per indoor unit, so indoor units sharing one outdoor unit share one top-up. Cleaning does not work that way: every indoor unit has its own coil, its own blower wheel and its own drain pan, and each one fouls on its own schedule.

Ducted units have their own rates on the price list. Everything below is about wall-mounted units.

Four questions to ask about each unit

Go room by room. For each indoor unit, answer these four honestly.

1. Is it showing any of the signs?

These are the signs that a unit has gone past what a general service can reach:

• A musty, sour or wet-cloth smell when it first switches on
• Cooling has weakened — the room takes longer to get cold, or never quite does
• Water dripping from the indoor unit
• Visible mould, black spots or slime on the coil fins or the louvres

A unit with none of these, which cools the room the way it always has, is not asking for a wash yet.

2. How hard does it work?

For a typical home, a chemical wash every 6 to 12 months is the sensible interval, on top of general servicing every 3 to 4 months. Where a unit sits in that range depends on the room, not the flat. Go closer to every 6 months if the unit runs 8 or more hours a day, if anyone sleeping in that room has allergies or asthma, or if there are pets. A lightly used guest room or study unit can stretch closer to 12 months.

This is why the master bedroom is so often the first to smell. It is the unit that runs longest, every night, with the door shut.

3. When was this unit last deep-cleaned?

Not the flat — this unit. People often remember "we did a chemical wash last year" when it was two of the four. If you have an old invoice, check how many units it lists. If you cannot remember at all, treat that unit as overdue.

4. Is it actually a cleaning problem?

This is the question that saves the most money, because a wash only fixes dirt. Three quick tells that it is something else:

• Run the smelly unit on fan only for ten minutes. A coil smell fades noticeably. A smell that does not change, or is there with the unit off, is not coming from the coil.
• One room warm, the others fine? Switch every other unit off and run that one alone for half an hour. If it cools on its own, the problem is capacity sharing, not dirt. Our guide to why one room never gets cold walks through it.
• Water dripping again every few months, even after cleaning, usually points at the drain pipe's fall rather than dirt.

There is one more tell, and it points the other way — to a bigger job than a wash. Black specks on the wall or bedsheet below the unit, or a previous wash that helped for only a few weeks, means the build-up is on the blower wheel. The photo above shows one taken out of a wall-mounted unit. A chemical wash cleans around that barrel; only a chemical overhaul takes it out. The blower wheel explained sets out how to tell. For everything a wash cannot fix, see what a chemical wash cannot fix.

What each choice costs

These are the published rates. The price you see is the price you pay.

• General servicing: $45 for 1 unit, $70 for 2, $95 for 3, $115 for 4, $25 per unit from 5
• Chemical wash (booked as its own visit): $135 for 1 unit, $245 for 2, $345 for 3, $425 for 4, $100 per unit from 5
• Chemical clean when we are already on site for another job: $100–$150 per unit
• Chemical overhaul: $200 for 1 unit, $370 for 2, $515 for 3, $640 for 4, $150 per unit from 5

Now take a flat with four indoor units, where one bedroom unit smells and the other three are behaving normally. Here is how the options compare.

Two things stand out.

If the other units are fine, you do not need to wash them to fix the one that is not. The middle option — routine service where it is due, deep clean only where it is needed — is what most flats with one problem unit should book. The already-on-site rate is published as a range, so ask for the exact figure for that unit when you book.

If all the units are due anyway, do them in one visit. The per-unit price drops with every unit you add, and that saving disappears the moment you split the job. Washing one this month "to see if it helps" and the rest next month is the most expensive way to arrive at the same place.

When washing every unit makes sense

• Two or more units are already showing signs. At that point you are no longer dealing with one problem room, and two units washed together is $245, against $270 if each were booked as its own visit.
• None of the units has been deep-cleaned in over 12 months and they all get daily use. They are all due, whether or not they have started to smell yet.
• You have just finished renovating. Construction dust goes through every unit that was running, not just one. Read servicing after renovation first, because heavy dust can push a unit past a wash.
• You would rather take one morning off than two. A chemical wash takes about 60 to 90 minutes per unit, so four units in one visit is four to six hours, and someone should be home for it.

When washing just one makes sense

• One unit has the signs, and the others cool normally and smell fine.
• The other units have been kept on general servicing every 3 to 4 months.
• The problem unit is the one that works hardest — the nightly bedroom, the unit near the kitchen — so it has fouled first.
• The fan-only test confirms the smell is coming from that coil.

In that case, book a general service for the flat and ask for the chemical clean on that one unit during the same visit. Then note the date. That unit will likely need its next deep clean before the others do, and it helps to know that in advance rather than find out from the smell.

Let the pre-check settle it

You do not have to get this exactly right from the outside. Every service booking includes our 9-point pre-check, and one of the nine points is a filter and coil dirt assessment. On a multi-unit visit, that is what tells you which unit needs a wash, which just needs its general service, and whether any of them has gone as far as an overhaul — before any money is committed to the wrong job.

If a unit has gone years rather than months without attention, read what the first service on a neglected aircon involves, because that one is often an overhaul, not a wash.

What to tell us before we come

A short list per unit makes the quote accurate the first time:

• Which room it is in, and roughly how many hours a day it runs
• What it is doing: smell, dripping, weak cooling, black specks, or nothing
• When it was last serviced, and whether that was a general service, a wash or an overhaul
• Whether anyone sleeping in that room has allergies or asthma
• Whether there has been renovation in the flat recently

The short version

Decide unit by unit, not flat by flat. Count indoor units. A unit with no signs that is on its normal servicing rhythm does not need a wash just because another room does. If only one unit is the problem, a general service for the rest plus a chemical clean on that one ($100–$150 while we are on site) is usually the right booking. If most of them are due, wash them together in one visit — splitting it costs $55 to $65 more on a four-unit flat. And before paying for any wash, make sure the problem is actually dirt.

Not sure which of your units need it? WhatsApp us on 9107 2601 — tell us how many indoor units you have and what each one is doing, and we will tell you which job each unit is likely to need before anyone comes out. The full cleaning options are on the chemical wash page.