Why a Johor Bahru unit nobody has stayed in needs more than a turnover clean

A unit that has sat empty for a few weeks smells musty because Johor Bahru air is humid, the water seals in the floor drains slowly dry out, the aircon has been off, and everything fabric has been shut in a closed room. A normal turnover clean wipes surfaces. It does not fix any of those four things, so the smell comes back the day after the cleaner leaves.

This is the sixth article in our homestay series. The first covers what a turnover costs. This one is about the other situation: the unit nobody booked, and the first guest who walks into it.

Why does an empty unit smell worse than an occupied one?

Because an occupied unit is constantly being aired, run and flushed, and an empty one is not. Guests open doors, run the aircon, use the showers and flush the toilets. An empty unit does none of that, so moisture just sits there.

Moisture is the root of almost every musty smell. The US EPA says indoor relative humidity should be kept below 60 percent, ideally between 30 and 50 percent, and that wet materials should be dried within 24 to 48 hours to prevent mould. Timeanddate lists the average humidity in Johor Bahru at around 84 percent. A closed unit with no aircon running has no way to get anywhere near the EPA's number, and 24 to 48 hours is not something a shut-up room can do.

So the smell is not a sign the last cleaner did a bad job. It is what a closed room does in this climate.

Where exactly does the smell come from?

From four places, and each one needs a different fix. The table also tells you which ones are a health matter and which ones are only unpleasant.

The honest ranking: the floor traps and the aircon are the two that people notice in the first thirty seconds, and the aircon coil is the only one that is more than cosmetic.

What is a dry floor trap, and why does it make an empty unit smell like a drain?

A floor trap or basin trap holds a small plug of water in a bend of the pipe, and that water is what stops drain gas coming up into the room. When a drain is not used for a long time the water evaporates, and the gas comes straight up. A plumbing reference describes this as water seals evaporating "over time in infrequently used floor drains", after which sewer gas can escape into the building.

The fix takes about a minute per drain: pour a jug of water down every floor trap, basin, kitchen sink and shower drain, and flush every toilet. That refills the seal.

If the smell comes back within a day of refilling, the problem is not the water seal, and that is when to call a plumber and not a cleaner.

How do you air out an empty unit before the guest arrives?

Open it, run it, flush it and dry it, in that order, ideally the day before check-in and not the morning of. Here is the order we would follow.

1. Open the windows and the balcony door for as long as the weather and the security of the building allow. Moving air is the cheapest dehumidifier.
2. Refill every drain. Jug of water into each floor trap, basin, sink and shower. Flush each toilet twice.
3. Run the aircon in cool mode with the fan on for a few hours. If the first blast smells sour, that is the coil, and the filter and coil need cleaning before a guest sleeps under it. Wash the filter at the same time.
4. Open the wardrobes, drawers and the space under the sink. Leave doors open while the aircon runs.
5. Take the linen out, and wash it again. Towels and sheets that spent weeks in a closed cupboard pick up the room's moisture even though they were clean when stored. Shake out pillows and look at the mattress protector for spots.
6. Wipe the bathroom and look at the silicone line and the grout. Anything black that returns after wiping is mould and needs a proper clean, not another spray.
7. Smell the unit again an hour later. If it is clean, you are done.

Doing all seven takes one person roughly one to two hours on site (our own estimate), most of it waiting for the aircon. It costs nothing but time and a jug.

When is it worth paying for a warm clean?

When the unit has been empty long enough that the airing routine above does not clear the smell, when you can see mould, or when nobody can get there to do the routine at all. A warm clean, which is what we call the clean for a long-empty homestay, is a turnover clean plus the extras an empty unit needs: reaching every drain, the aircon check, the cupboards and the bathroom seals.

Being straightforward: if you live near the unit, or have a cleaner already visiting every week, the routine above does most of what a warm clean would do, for free. The case for paying is the owner who lives across the Causeway in Singapore, the owner who is out of town, or the unit that went from a booking every few days to nothing for a month.

Why can't a warm clean have a fixed price?

Because what it takes depends on what the unit is like when we walk in, and two units empty for the same number of weeks can differ by hours. The things that change the work are how long the unit was shut, whether there is visible mould, how many drains and aircon units there are, how many cupboards, and whether the linen needs to go to the dobi.

That is why a warm clean is quote-on-request with us, and not one of the fixed turnover prices. For reference, a normal turnover starts at RM50 for a studio and RM10 per bed on top (see what a turnover costs). A warm clean is more than that, and we would rather tell you so than show you a number that is wrong for your unit. Photos of the bathroom and the aircon help us tell you what to expect.

How do you stop it happening again?

Do not let a unit go fully dead. A short visit every week or two, even without a booking, costs far less than a warm clean. Refill the drains, open the windows, run the aircon for an hour, and leave the cupboard doors ajar. If you cannot do it yourself, ask us what we can arrange. For a unit you are not listing for a few months, the answer is different, and we would look at the unit first.

If you would rather not deal with it, send us the unit details on /services and we will tell you honestly what it needs.