Large flats are constrained by ceiling height and equipment platform space, so Five-Constant depends on three prerequisites: at least 2.6 m of clear height inside the ceiling void, a load-bearing outdoor position for the equipment, and exterior windows with airtightness of grade 6 or better. If any one is missing, the design has to change or the performance targets come down.
What matters is not the structural ceiling height but the clear height once the finishes are in. A Five-Constant system usually takes 250–320mm inside the ceiling void, and with insulation and the ceiling itself the comfort floor for a home is 2.6 m. At a structural height of 3.0 m, roughly 2.65–2.75 m remains, which works; at 2.8 m, the system should go in selected areas or the design should change.
The figure is worked backwards. Inside the ceiling void a Five-Constant system carries fresh-air ducts, water pipes, refrigerant or air ducts, and control cabling; with insulation and the ceiling itself, the usual allowance is 250–320mm. Add ducted central air conditioning and the allowance grows.
So the test is not "how high is the ceiling" but "how much clear height is left after finishes". The comfort floor for a home is 2.6 m; below that, even a well-built system feels confining to live under. A home with a 3.0 m structural height ends up at about 2.65–2.75 m after Five-Constant, which is workable; at 2.8 m, install in selected areas or choose a system that takes less space.
Yes, but three questions have to be answered: where the equipment goes (a balcony corner, the kitchen ceiling void, or a bracket on the exterior wall), how the heat is rejected (air-cooled units need room to draw and discharge air), and how noise is isolated (anything within 5 m of a bedroom needs treatment). If none of the three can be solved, we recommend room-by-room air conditioning with independent fresh air and dehumidification.
Yes, but three questions must be answered: where the equipment goes, how the heat is rejected, and how noise is isolated.
The usual alternatives are a corner of the balcony, the kitchen ceiling void, or a bracket on the exterior wall.A wall bracket needs approval from both property management and the structural engineer, and load capacity and service access have to be considered. On heat rejection, an air-cooled unit needs enough space to draw and discharge air, or its efficiency drops sharply in summer. Noise depends on the distance between the equipment and the bedroom; anything within 5 m needs acoustic treatment.
If none of the three can be solved, our advice is to skip whole-home Five-Constant and use room-by-room air conditioning with independent fresh air and dehumidification. The metrics are lower, but the experience is still far better than an ordinary fit-out.
It depends on whether the ceiling can be opened and the floor can be touched. A light-gauge steel stud and plasterboard ceiling can be opened locally and worked on in zones; a complex shaped ceiling costs nearly as much to remove as a full refit. The pragmatic route is to leave the underfloor heating alone, add fresh air and dehumidification inside the ceiling void, and upgrade part of the smart control, which delivers about 70% of the gain in experience.
How much a finished home can be changed comes down to two things: whether the ceiling can be opened and whether the floor can be touched.
If the existing ceiling is light-gauge steel stud and plasterboard, access panels can be cut locally, work can proceed in zones, and most of the finish kept. If it is a modular ceiling or a complex shaped ceiling, removing and rebuilding it costs close to a full renovation. On the floor side, dry underfloor heating or capillary mats can be added; building up on top of an existing screed, however, means checking door opening heights and floor loads.
The pragmatic approach:leave the underfloor heating alone, add fresh air and dehumidification inside the ceiling void, and upgrade part of the smart control. That delivers about 70% of the gain in experience for about 30% of the work.
They are not on the same level. Central air conditioning plus underfloor heating handles heating and cooling; Five-Constant handles heating and cooling plus humidity, oxygen, cleanliness, and noise, five things in all. The difference is greatest in homes with a pronounced plum rain season, on a street, or near an elevated road. The main differences also include ceiling space and night-time noise.
They are not the same kind of thing. Central air conditioning plus underfloor heating solves "cold" and "heat"; Five-Constant solves "heating and cooling + humidity + oxygen + cleanliness + noise". In central or southern China, with a plum rain season, on a street, or near an elevated road, the difference Five-Constant makes is most obvious.
| Item | Central AC + underfloor heating | Full fresh-air Five-Constant |
|---|---|---|
| Temperature control | Temperature varies between rooms; floor temperature is fairly even | Whole-home temperature held within 2℃ |
| Humidity control | Incidental dehumidification while cooling; limited in the plum rain season | Independent humidity control, stable at 50±5% |
| Oxygen / CO₂ | Not addressed; rooms go stale once the windows close | Continuous full fresh-air exchange; CO₂ held under 800ppm |
| Cleanliness | Relies on indoor unit filters, of limited grade | Centralized filtration, with high-efficiency filters available |
| Noise | Indoor units are audible, up to 35–40dB(A) at night | No indoor units; below 30dB(A) at night |
| Ceiling space | Smaller | Larger, typically 250–320mm |
| Maintenance | Clean filters, service the refrigerant circuit | Replace filters, inspect ducts and units |
This comparison describes general technical differences. Actual performance depends on equipment selection, installation quality, and the condition of the home, and is not a verdict on the merits of any single approach.
The intake has to avoid kitchen exhaust outlets, bathroom exhausts, garage entrances, and the road-facing side. Keep at least 3 m of horizontal distance from the exhaust, or put the two on different facades. If holes can only be made on the same side, use a height difference and the louver orientation to prevent short-circuiting. Cutting an exterior wall requires property management approval.
Where the intake sits decides how clean the incoming air is. The basic rule: avoid kitchen exhaust outlets, bathroom exhausts, underground garage entrances, and the side facing the road.
In high-rise homes the usual approach is to draw air through an opening in the equipment balcony or the exterior wall, keeping the intake at least 3 m horizontally from the exhaust and placing it upwind of the exhaust or on a different facade. If holes can only be made on the same side, a height difference and the louver orientation prevent short-circuiting.
Not impossible, but it means lowering the design targets or covering part of the home. Options include slimline fresh-air units, fewer duct crossings in the ceiling void, or Five-Constant only in the main living areas with independent fresh air and air conditioning in the bedrooms. It depends on the clear height measured on site.
Not necessarily. Fresh-air ducts do have to run in a ceiling void, but partial ceilings and holes through beams reduce the area covered. The trade-off is higher duct resistance and a unit with more static pressure.
Yes. Adding an independent fresh-air system alongside existing central air conditioning is the most common retrofit. The two must not share a return path, or the air conditioning return will cancel out the fresh-air supply.
A Five-Constant system usually draws less power than whole-home air conditioning of the same area, but it needs dedicated circuits and enough distribution capacity. In older developments or homes with a limited supply, this has to be calculated at the design stage.
Common restrictions cover working hours, lift use, exterior wall openings, and noise. They affect the schedule, so before work starts we register the project with property management together with the owner.
To find out whether your house is a fit and how a scheme would work, call us or add us on WeChat. We answer one to one.