Six Holiday Rentals, a Rating That Fell From 4.9 to 4.1, and One Word Guests Kept Writing
Last updated: 6 Sep 2026 | 12 Views |
Guests give five stars for the location, the view and the host, then deduct for one thing
Six Holiday Rentals, a Rating That Fell From 4.9 to 4.1, and One Word Guests Kept Writing
Why cleaning between stays is not enough, and why ozone suits a business with only three hours between guests
In a business sold through reviews, losing 0.8 of a star means losing half your visibility on the platform — and the word that causes it is usually short and mild.
Khun Kittipong is 41 and runs six daily-rate holiday houses in Hang Dong, Chiang Mai — Lanna-style timber houses he renovated himself, and the family's main business for five years.
In 2024 his average platform rating was 4.9 out of 5. He held top-tier host status two years running, and annual occupancy averaged 82 percent.
Through 2025 his rating slid to 4.1. Reading back through the three- and four-star reviews, he found that almost every one praised everything — the location, the view, the cleanliness, the welcome — and then ended with the same sentence: but the room was slightly musty.
The story
The one sentence that followed every compliment
What confused him for a long time, he says, is that none of those reviews were angry. Everyone wrote warmly. They praised the view, the house, the airport pickup. Many said they would return.
But in the final paragraph there was always one line. Some wrote that the bedroom was a bit musty. Some wrote that the air conditioning smelled. Some were more direct: I had to keep the window open all night to sleep.
Counting back, he found that of 214 reviews that year, 67 contained the word smell. Reviews containing that word averaged 3.6 stars. Reviews without it averaged 4.9.
What hurt most, he says, is that those guests were not angry with him at all. They were simply being honest — which meant the problem had been real the whole time, and he had never known.
Why a daily rental smells despite being cleaned every single day
He has three housekeepers who clean every house after each checkout: all linen changed, every towel washed, floors mopped, bathrooms cleaned, every surface wiped.
When he asked a friend who runs a boutique hotel in town, the friend asked one question that made everything clear: when a house is empty between bookings, do you leave the air conditioning on or off?
Off, obviously — running air conditioning in six empty houses is electricity nobody is paying for. And some of his houses sit empty for two to five days between bookings, and up to ten days in a row in low season.
His friend explained that this is the whole cause. A timber house in Chiang Mai sealed shut with no air circulation, in humidity that is especially high in the rainy season, is an environment where mould grows freely — in the air conditioning coil, in the mattresses, in the curtains, and in the timber itself.
What losing 0.8 of a star actually costs
On accommodation platforms a rating is not just a number for guests to read. It is the primary variable in search ranking. A 4.9 property appears on the first page of results; a 4.1 property usually falls to page three or four.
His annual occupancy dropped from 82 percent to 54 percent in one year. Six houses at an average 2,800 baht a night is around 1.7 million baht of lost revenue.
He also lost his top-tier host status, which affects both visibility and the confidence of guests comparing options — and regaining it means accumulating new reviews over many months.
He tried cutting prices by 20 percent to pull bookings back. It worked on nights booked and destroyed the margin per night. Worse, the new guests who got the cheaper rate still wrote about the smell.
Three hours between checkout and check-in
The hardest constraint in this business is time. Guests check out at noon, new guests arrive at three. Housekeeping has three hours per house, and on days with four simultaneous checkouts it is tighter still.
Everything he had tried took longer than that. Washing all the curtains took two days. Sunning the mattresses needed a full day of sunshine. Airing the house with the windows open all day was impossible on a day with an arrival.
When he approached an ozone team, his first question was how long it takes. The answer was about thirty minutes per cycle plus ventilation — which fits neatly into the window while housekeeping is cleaning the rest of the house anyway.
He started by treating all six houses in one round to clear five years of accumulation, then set a monthly schedule for every house, plus an extra treatment whenever a house had been empty more than three days before an arrival.
What it actually costs
Losing 0.8 of a star halves your visibility
Rating is the primary variable in search ranking. A 4.9 property is on page one; a 4.1 property falls to page three or four, where almost nobody scrolls. Occupancy fell from 82 percent to 54 percent.
Honest guests hurt you more than angry ones
A review that praises everything and adds one line about smell in the last paragraph looks mild — but it is a three- or four-star review, and it is extremely credible to someone comparing properties, precisely because it sounds fair and sincere.
Cutting prices lifts bookings, kills margin, and changes nothing
Discounting to compensate for a rating is the most common host response. It does increase nights booked and it erases the margin — and the new guests still write about the smell, because nothing was fixed.
You only have three hours between guests
Checkout at noon, arrival at three. Every conventional odour remedy — washing curtains, sunning mattresses, airing the house all day — takes longer than this business has to give.
Why the usual fixes fail
A full clean after every checkout
Housekeeping already does this superbly and must continue. But changing linen, mopping and wiping addresses what guests can see, not the odour living in the air conditioning coil, the mattress foam, the curtains and the timber.
Leaving the air conditioning running while the house is empty
It genuinely helps with humidity, but six empty houses running air conditioning through low season is electricity with no revenue behind it — and it does not remove mould already growing in the coil; it blows it into the house instead.
Air freshener and reed diffusers before arrival
They mask for an hour or two — conveniently while guests check in and take photos. By the time guests close the door to sleep, the original smell is back, now mixed with fragrance, which several reviews describe as feeling like something is being covered up.
Washing curtains and sunning mattresses
Both genuinely work, and both take two days and a full day of sunshine respectively — impossible in a business with three hours between guests, and impossible at all during a Chiang Mai rainy season.
Servicing the air conditioners twice a year
Necessary and worth doing, but it cleans only the coil and removable filters. In a house sealed for several days a week in high humidity, surviving organisms in the ducting repopulate the system within weeks.
This business needs something that genuinely works and finishes inside a three-hour window
A holiday rental has two requirements that must both be met. First, the odour has to be removed at source rather than masked, because the guest is inside that house all night with the doors and windows closed. Second, it has to finish inside the turnaround window between checkout and check-in.
Every conventional remedy fails one or the other. Air freshener is fast and does not fix it. Washing curtains and sunning mattresses works and is far too slow. Servicing the air conditioning helps partially, needs a technician booking, and cannot be done monthly.
Ozone passes both, because it is a gas that spreads through the whole house and into the air conditioning coil, the mattress foam, the curtains, the sofa, the wardrobes and the joints in the timber — everywhere the odour actually lives. Where it meets mould or the bacteria producing the smell, the third oxygen atom breaks away and destroys the cell wall. Then the ozone decomposes back into ordinary oxygen, leaving no chemical in a room a guest will sleep in — and the cycle takes about thirty minutes, exactly while housekeeping is cleaning the rest of the house.
10 reasons ozone treatment solves it
1. About thirty minutes, fitting the turnaround window
The automatic digital timer cycle runs roughly thirty minutes — two to start, twelve to disperse, twelve to purify, twelve to rest. It runs while housekeeping is already working on the rest of the house.
2. It reaches the air conditioning coil, the main source in an empty house
With the air conditioning recirculating during the cycle, ozone travels into the coil and ducting — in a house sealed several days a week, the most certain mould reservoir and the thing that blows the smell at guests the moment they switch it on.
3. Mattresses, curtains, sofas and wardrobes treated at once
Every porous material in the house is an odour sponge. Ozone penetrates mattress foam, curtain and sofa fibres and closed wardrobes in a single cycle, with nothing sent out for laundering and nothing to put in the sun.
4. No chemicals in a room a guest sleeps in all night
Ozone decomposes back into ordinary oxygen — no deposit on the mattress, no film on the floor, and no chemical smell for a guest to write about, unlike air freshener, which guests immediately recognise as a cover-up.
5. It removes the source, so the smell does not return at night
The problem with masking is that it wears off exactly when the guest closes the door to sleep. Ozone destroys the organisms producing the odour, so it does not come back that night or the next.
6. 99.99% removal of embedded mould
Testing confirms 99.99% removal of deep-seated mould in air conditioning systems and furnishings, with virus and bacteria kill an order of magnitude beyond that — the right level for a property with guests turning over every few days.
7. It reduces dust mites, which allergic guests write about
A mattress in a sealed damp house is ideal dust mite habitat. Allergic guests wake congested and mention it in reviews. Ozone reduces both the mites and the allergens they leave behind.
8. It adds no humidity to a house that is often sealed and empty
Washing and steaming add water to a house about to be closed for several more days, feeding mould directly. Ozone is a dry gas and leaves nothing behind for the next cycle.
9. The Master Ozone Generator is certified by the Department of Medical Sciences
WHD uses the Master Ozone Generator, the only ozone brand in Thailand certified by the Department of Medical Sciences, Ministry of Public Health, and tested by Intertek UK.
10. It is a selling point for your listing and your review replies
Stating on the listing that the property is ozone-disinfected monthly with certified equipment is something almost no competing property says — and it gives real weight to a reply on an older review about smell.
Before and after
Before
- Average rating falling from 4.9 to 4.1 in a single year
- 67 of 214 reviews containing the word smell, averaging 3.6 stars
- Occupancy down from 82 percent to 54 percent
- Around 1.7 million baht of lost annual revenue
- Top-tier host status lost after holding it two years running
- A 20 percent price cut that lifted bookings, erased margin, and did not stop the reviews
After
- No review mentioning smell at all across five months of routine treatment
- Average rating back to 4.7 and still climbing
- Occupancy back to 76 percent with the discount promotion withdrawn
- About thirty minutes per house, run while housekeeping cleans the rest
- Five years of odour in mattresses and curtains gone from the first round
- A line on the listing stating monthly ozone disinfection, which guests ask about regularly
How we get you started, in 3 steps
Survey and assessment
The team assesses the number of properties, the size and air volume of each, the porous materials such as mattresses, sofas and curtains, and the air conditioning positions, then sets the cycles and schedules around your check-in and checkout timetable.
Preparation and sealing
Linen is stripped and mattress surfaces exposed. Wardrobes and drawers are opened so the gas reaches inside. The air conditioning is set to recirculate so the ducting is treated, doors and windows are sealed, and everyone leaves.
Ozone cycle, ventilation and check
The machine runs its automatic cycle of about thirty minutes. The house is then fully ventilated, surface moisture is checked, and it is ready to receive new guests the same afternoon.
What a customer says
“I was baffled for a year, because every review was complimentary — the view, the house, me — and then added that the room was a bit musty. I counted: 67 of 214 reviews contained the word smell. Once I understood that leaving the air conditioning off in an empty house was the cause, we started monthly ozone treatment. Five months now and nobody has mentioned smell again. The rating is back to 4.7.”
Khun Kittipong W. — host of six holiday rental houses, Hang Dong, Chiang Mai
Why properties that stand empty smell more than properties in constant use
Most people assume an unoccupied room stays cleaner, because nobody is in it making a mess. In reality the opposite is true. An unoccupied room is a room with no air conditioning running, no windows opened, and no air circulation at all.
In Thailand's climate, with relative humidity at 70 to 85 percent for most of the year and higher in the north during the rainy season, a sealed room without circulation accumulates enough humidity to cross the mould growth threshold within days.
The air conditioning coil is the worst point, because when the unit is switched off after use, condensate remains in the coil and the drip tray. When the house is then sealed for five days, that water sits in the dark, warm and enclosed, for five days.
So when the next guest arrives and switches on the air conditioning, the first thing the machine does is blow everything that grew in those five days directly at them — which is why so many guests write that the smell was strongest in the first hour.
A checklist for hosts who want their rating back
Khun Kittipong now runs five measures, and says the second is the one that changed everything.
One: before every arrival, run the air conditioning for at least thirty minutes before housekeeping starts — both to drive out residual moisture and so you smell the room in the state the guest will actually meet.
Two: ozone-treat every property monthly as a routine, plus an extra treatment whenever a house has stood empty more than three days before an arrival.
Three: stop using air freshener entirely, because guests who recognise it write worse reviews. Four: service every air conditioner twice a year alongside the ozone schedule. Five: state clearly on the listing that the property is ozone-disinfected monthly, because a guest comparing options sees that before they read the older reviews.
Frequently asked questions
How long does one house take?
About thirty minutes following the machine's cycle, plus ventilation — which fits the window between a noon checkout and a three o'clock check-in, and runs while housekeeping cleans the rest of the house.
Can several properties be done in one day?
Yes. The team works through them consecutively and schedules around each property's check-in and checkout times. Six properties are normally completed within a day.
Is there residue on the mattress or linen guests will use?
No. Ozone decomposes back into ordinary oxygen after reacting, leaving no deposit or film on mattresses, sofas or floors, and no chemical smell for a guest to write about.
How often should it be done?
Monthly as a routine, plus an extra treatment whenever a property has stood empty more than three days before an arrival — because the empty period is when mould grows most freely.
Can it really remove years of odour from mattresses and sofas?
Yes, because ozone penetrates the foam and the fibres of the covers. Long accumulation may need more than one cycle on the first treatment, which the team assesses at the survey.
Does it help with dust mites for allergic guests?
Yes. A mattress in a sealed damp house is ideal dust mite habitat, and ozone reduces both the mites and the allergens they leave — the reason allergic guests wake congested and mention it in reviews.
Does it work for small hotels and resorts?
Yes. The same principle applies to boutique hotels, resorts, homestays and monthly rentals, especially rooms with uneven occupancy that stand sealed between bookings.
Is anything included?
For bookings of 15,000 baht and above, WHD includes free hospital-grade CHEMGENE HLD4H spray disinfection — suited to high-contact surfaces such as remote controls, door handles and light switches.
Guests give you five stars for everything, then deduct for the one thing you can fix in thirty minutes
If your rating is sliding while reviews still praise the location, the property and the welcome, search your past reviews for the word smell and count them. The number usually explains everything.
Ozone treatment removes the odour at source in the air conditioning coil, the mattresses, the curtains and the sofas — not a mask that wears off exactly when the guest closes the door to sleep. It leaves no chemical in a room a guest sleeps in all night, and takes about thirty minutes per property, fitting the turnaround window.
For bookings of 15,000 baht or more, WHD includes free hospital-grade CHEMGENE HLD4H spray disinfection.
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Call 065-556-6294 or add LINE @whd268
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