A 388-Unit Condominium Lost 26 Residents in One Year Because Mosquitoes From the Treatment Tank Reached the Eighth Floor Every Evening
Last updated: 7 Sep 2026 | 7 Views |
A true story from a 388-unit condominium in Bang Na, Bangkok
A 388-Unit Condominium Lost 26 Residents in One Year Because Mosquitoes From the Treatment Tank Reached the Eighth Floor Every Evening
When mosquitoes from a treatment tank reach the eighth floor, and the lost service fees become everybody's problem
A 388-unit condominium in Bang Na lost 26 residents in a single year, and the management office was receiving an average of 19 mosquito complaints a month. The real cause was not building hygiene. It was the underground sewage treatment tank and the beautifully designed landscaping. Here are the real numbers, and how the AIROFOG AT35 thermal fogger resolved it within two months.
Siriporn, 44, is the building manager for a 24-storey, 388-unit condominium in Bang Na. Thirteen years in property management, and she says the complaint that has weighed on her hardest is not noise and not parking. It is mosquitoes.
Over the past year the office logged an average of 19 mosquito complaints a month, peaking at 34 in September, and four residents were diagnosed with dengue in that same year. One was a seven-year-old who spent five days in hospital.
What genuinely alarmed the committee was the vacancy figure. Twenty-six units turned over that year, and 11 of them named mosquitoes and insects as the reason on the move-out questionnaire — ranking above service fees as the leading cause.
The eighth-floor resident who photographed mosquitoes every week
One resident on the eighth floor sent the office photographs of mosquitoes he had killed in his unit almost every week. The team initially assumed it was specific to that unit — open windows, perhaps plants on the balcony. But when they compiled a year of complaint records, the complaints clustered on floors 2 to 9 and all faced the same direction.
So Siriporn walked the building at six in the evening instead of during office hours, and that was the first time she saw it clearly: clouds of mosquitoes around the ventilation openings of the underground sewage treatment tank behind the building, on exactly the side the complaints came from.
The team investigated further and found several tank covers not seated properly, with gaps mosquitoes could pass through, and seepage pooling around the tank. They also discovered that the aeration pump on one chamber had been broken for months without anyone reporting it, leaving that chamber's water completely still.
Siriporn says the sentence that made everything click came from the building technician: mosquitoes do not fly up from the ground to the eighth floor — they ride the air that rises along the building wall in the evening.
Why mosquitoes really do reach the upper floors
The most common misconception in high-rise management is that mosquitoes cannot fly high, so upper floors are safe. In truth Aedes cannot fly very high on its own — but flying is not how it gets there.
A tall building generates an upward air current along its walls in the evening and at night, because the facade sheds the heat it absorbed all day, and that warm air rises along the wall. Mosquitoes at the base are carried to the eighth or tenth floor without expending any effort.
The second route is lift shafts and fire stairs — vertical channels with constant air movement. A mosquito that enters the lobby or lift hall can be carried up and released onto any floor.
The third factor is balconies with potted plants and saucers, which become small breeding sites on the upper floors themselves. Once mosquitoes arrive and find somewhere to lay, an upper-floor population can sustain itself independently of the ground.
The costs the committee had never seen laid out
When Siriporn presented her report, she opened with the number everyone cared about: 26 units turned over in one year, 11 of them citing mosquitoes and insects. Vacancies affect collectable service fees, resale prices and rental values across the whole building.
She then totalled what the building was already spending on the problem: monthly contracted spraying, 14 electric insect traps, and maintenance on those traps — roughly 260,000 baht a year, with the complaint count not falling at all.
The cost that is hardest to measure and heaviest in practice was staff time. Each complaint means receiving it, inspecting the unit, explaining, and responding in writing — about ninety minutes each. At 19 a month, that is nearly four working days lost every month.
And there was a relationship cost Siriporn calls the worst of all: residents had stopped believing the office actually did anything, which spread into everything else, from service fee collection to the atmosphere at the annual general meeting.
What the committee approved after seeing the report
Siriporn proposed a three-part plan. First, repair and properly seal every treatment tank cover, fix the failed aeration pump, and eliminate the seepage pooling around the tank — cutting the breeding source at the origin.
Second, a systematic monthly survey of breeding sites across all common areas: plant saucers in the gardens, gutters around the building, the decorative pond that had been switched off, storerooms holding water, and the roof deck where pools form after rain.
Third, and the part the committee hesitated over: buy a thermal fogger for the building rather than continuing to contract the work out. Her comparison was simple — three years of monthly contracted spraying costs more than the machine and equipment, and ownership allows twice-weekly fogging through the rainy season at no cost beyond chemical.
The committee approved it at that meeting and chose two AIROFOG AT35 units, because they are shoulder-carried units building staff can operate, the stainless body suits work near the treatment tank, and service and genuine parts are available inside Thailand.
What it actually costs
Vacancies and the value of the whole building
Twenty-six units turned over in one year, 11 citing mosquitoes and insects. Vacancies hit collectable service fees, resale prices and rental values across the entire building — a loss every co-owner shares without realising it.
Residents' health, especially children and older people
Four residents were diagnosed with dengue in a single year, one a seven-year-old hospitalised for five days. When several cases occur in one building, the management office is immediately asked what it has actually done.
Workload and the credibility of the management office
Nineteen complaints a month consumes nearly four working days of staff time, and when the problem never resolves, residents stop trusting the office on everything else — which reaches from service fee collection to the tone of the annual general meeting.
Budget already spent with nothing to show for it
The building was spending roughly 260,000 baht a year on contracted spraying, insect traps and their maintenance, with no reduction in complaints. Money spent without visible result is the hardest thing to explain at an annual general meeting.
Why the usual fixes do not work
Installing electric insect traps around the building
Traps work within a limited radius and draw mosquitoes toward a light source, which can concentrate them nearby. More importantly they do nothing about the breeding and resting sites, which were the treatment tank and the garden shrubbery.
Contracted spraying once a month
The contractor comes on his own schedule, usually during daylight hours convenient to him, when mosquitoes are sheltering in shade. And monthly is far too infrequent against Aedes, which goes from egg to adult in seven to ten days.
Posting notices asking residents to cooperate
Asking residents to manage the saucers on their balconies is worth doing and genuinely helps, but it is not enough, because the principal breeding sites are in common areas residents cannot access — and pushing responsibility onto residents alone damages the relationship.
Aerosol cans in the lobby and corridors
These cover a tiny area and dissipate within hours. A 24-storey building with common areas and surrounding gardens needs equipment that covers wide areas and reaches into shrubbery and ventilation openings.
Waiting for the district or city authority to spray
Local authorities cover very large areas and prioritise communities with reported cases. Private condominiums are rarely near the top of the list, and even when they come it is a few times a year — nowhere near enough for continuous control.
A condominium needs to fog weekly on its own, and reach the treatment tank and the landscaping
Once the source is identified as the sewage treatment tank, the landscaping and the ventilation openings around the building base, the requirement is clear: keep the adult mosquito population in the base zone continuously low, so there is no source to be carried up the facade.
A thermal fogger is the right tool, because the fog drifts into the treatment tank ventilation openings, into garden shrubbery, under mature trees, along the boundary, and into the plant rooms and dark, damp basement parking — resting sites that aerosols and traps never reach.
The machine must belong to the building, because the frequency that actually works is twice a week through the rainy season, which is expensive to contract and impossible to schedule. Ownership means fogging at the right hour: early evening, once residents are back in their units.
And it has to survive working near a treatment tank, with humidity and corrosive gases. That is why the committee chose the AIROFOG AT35, with its 100 percent stainless steel body.
10 reasons the AIROFOG AT35 thermal fogger solves it
1. Fog reaches treatment tank vents and garden shrubbery
The source of mosquitoes in a condominium is the underground treatment tank, the garden shrubbery, the space under mature trees, and dark damp basement parking. The AIROFOG AT35 produces a fog that genuinely drifts into these places — which insect traps and aerosol cans cannot do at all.
2. A 100 percent stainless steel body that survives work near the treatment tank
The area around a treatment tank combines high humidity with gases that corrode metal. Coated-metal and plastic-bodied machines fail quickly there. Full stainless lasts for years, which matters to a management committee spending common funds it must account for.
3. Carried on the shoulder to every zone of the property
A condominium has many areas no vehicle can reach: the gardens, narrow walkways, plant rooms, the basement and the roof deck. The AT35 is light enough for building staff to carry anywhere, including up in the lift to treat upper floors and the roof.
4. Building staff can operate it without an outside crew
Most management offices already have technicians and housekeeping staff. The AT35 is simple enough to train two or three of them as responsible operators, which turns fogging into a weekly maintenance routine at no additional labour cost.
5. Runs both water-based and oil-based formulations
A building with residents must be careful about chemistry and should use properly registered products. Accepting both formulation types lets you follow the health officers' recommendations and rotate products to slow resistance.
6. Fog at the hour that suits residents
The most effective window is early evening, around seven, when residents are back inside and mosquitoes are active. Owning the machine means choosing that hour, rather than a contractor arriving during office hours — the least effective time of all.
7. Covers all common areas in well under an hour
The common areas of a 388-unit building — gardens, treatment tank, parking and ground-floor lobbies — take roughly 40 to 60 minutes with the AT35. Short enough to genuinely do twice a week without disrupting anything else.
8. Certified to German and British standards
For a management office reporting to a committee and co-owners, using internationally certified equipment is something that can be explained and audited — rather than simply buying the cheapest item that satisfies a procurement rule.
9. Compliant with Thai government standard equipment specifications
For buildings owned by government agencies, the National Housing Authority, or any body procuring under public procurement regulations, meeting the official standard equipment schedule makes budgeting and acceptance inspection straightforward.
10. A Thai service centre with genuine parts and 10-plus years of technician experience
A management office cannot stop fogging for a month waiting on parts, because the complaints return immediately. Domestic service and genuine parts should weigh ahead of purchase price — particularly when spending common funds you must account for.
Before the thermal fogger
- An average of 19 mosquito complaints a month, peaking at 34
- 4 residents diagnosed with dengue, including a seven-year-old
- 26 units turned over, 11 citing mosquitoes as the reason
- Roughly 260,000 baht a year on contracted spraying and traps, with no result
- Nearly 4 working days a month of staff time absorbed by complaints
- Treatment tank covers not sealed and an aeration pump broken for months
After the thermal fogger
- Complaints down to an average of 2 a month within two months
- No reported dengue cases among residents the following year
- Turnover clearly down, with mosquitoes gone from the move-out questionnaire
- Outside spraying contract cancelled, saving over a hundred thousand baht a year
- Twice-weekly fogging through the rainy season using existing staff
- A fogging report presented to the committee every month
The three-step process
1. Survey the building in the early evening, not during office hours
Walk the property with the building technician between six and seven in the evening, when mosquitoes are genuinely active. Mark where density is highest, and inspect the treatment tank covers, ventilation openings, garden plant saucers, gutters, the disused decorative pond, storerooms and roof-deck pooling.
2. Fix the source first, then fog systematically
Seal the tank covers, repair the aeration pump, eliminate seepage pooling and remove every water-holding container from the common areas. Then fog with the AT35 in the early evening — daily for the first two weeks to break the cycle, then twice a week in the rainy season and weekly in the dry.
3. Report to the committee and the residents every month
Record every application — date, time, area, product and operator — alongside the monthly complaint count, and summarise it on a single page for the notice board and the committee. Letting residents see the work actually happening is what changes the relationship most.
From someone who uses one
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The breeding sites management offices most often miss
The underground sewage treatment tank is the most common and the most serious, particularly in buildings where the aeration pump has failed or is underperforming, leaving the water still. Covers that do not seat properly, and ventilation openings without insect mesh, become a direct doorway. Checking covers and mesh belongs on the monthly maintenance list.
Decorative ponds and fountains that have been switched off are the next most common. Many buildings shut the fountain off to save electricity without draining it, creating a large body of still water in the middle of the property. Either drain it completely or stock it with larvivorous fish if you want to keep the water.
Plant saucers in the common gardens and on residents' balconies are the most numerous sites even though each is tiny. Buildings with attractive landscaping often have hundreds of them. Switching to a drainage system instead of saucers, or a weekly emptying check, solves it.
The last is the roof deck, which nobody goes up to look at. Pools form after rain where the slab has settled or drains are blocked, and there are air-conditioner drip trays and water tanks with poorly seated lids. Inspecting the roof after every heavy rain should be a standing instruction.
Why showing residents the work matters as much as doing it
The lesson Siriporn stresses most is that many management offices genuinely do the work but residents never see it, which produces the feeling that nothing is being done — a harm greater than the original problem, because it spreads into everything else.
The cheapest and most effective remedy is a one-page report on the notice board each month: which days fogging happened, which areas, how many breeding sites were found, how many were fixed, and the complaint count against last month.
What happens once residents see the numbers falling consistently is that they start cooperating on their own — managing balcony saucers and reporting where they see mosquitoes so the team can check. That makes the whole programme more effective still.
Over time the same record is excellent evidence at the annual general meeting when continued budget approval is needed, because the committee and co-owners can see the relationship between the money spent and the result achieved.
Frequently asked questions
Is fogging safe in an occupied condominium?
Yes, with the right procedure: notify residents in advance via the notice board and messaging group, treat only exterior common areas and enclosed spaces with nobody present, cover anything that needs covering, and allow roughly 30 to 60 minutes before people re-enter.
When should we fog?
Early evening, around seven to eight, works best — mosquitoes are active, the air is calm, and most residents are back inside. Some buildings choose before six in the morning instead, which works equally well and disturbs fewer people.
Do we need to fog the upper floors as well?
In principle concentrate on the base zone, which is the source. But where complaints cluster on a particular floor, treat that floor's lift hall, corridors and fire stairs too, along with the roof deck, which often holds pools after rain.
How many machines does a building of my size need?
A single tower under 300 units with surrounding gardens is fine with one machine. Buildings of 300 to 600 units, or multi-tower developments, should have two — so a full pass finishes within an hour and there is a spare when one goes for service.
How often should we fog?
Daily for the first two weeks to break the cycle, then twice a week in the rainy season and weekly in the dry. Let the monthly complaint count drive the decision — a number the management office already tracks.
Can building staff operate the machine?
Yes. Designate two or three responsible operators and train them fully on mixing ratios, protective equipment and cleaning the machine after every use — that last step being the biggest factor in how long the machine lasts.
Is buying really better value than contracting?
For any building that needs one or two applications a week, clearly yes. The per-visit contract cost multiplied by the frequency actually required exceeds the machine's price within one to two years, and ownership also gives you control over timing and frequency.
If the machine fails, how long is the wait?
AIROFOG maintains a service centre and genuine parts in Thailand with technicians of more than 10 years' experience, so there is no overseas wait. Larger buildings are advised to keep a spare machine or the common wear parts on hand so fogging never stops in the wet season.
Mosquitoes are a small problem, until 26 units move out
The clearest lesson here is that a small problem experienced daily by several hundred people always becomes a large problem — and it usually shows up in the financial statements before anyone connects it to the cause.
Walking the building at six in the evening instead of during office hours took one hour and revealed what had been invisible for a year. That lesson applies to every building.
And for a management office, buying a thermal fogger is not a new expense. It converts money already being paid to a contractor into a capability the building controls, together with a monthly report that can be explained to every co-owner.
Talk to the World Health Disinfection team about a mosquito control plan for your building — machine count, chemistry and a fogging schedule matched to your development.
See the machine and pricing — click here
Call 065-556-6294 or add LINE @whd268
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