A Thermally Activated Building System (TABS) is a climate control method in which water-carrying pipes are embedded directly within the concrete mass of floors or ceilings to provide both heating and cooling to a building. By using the large thermal mass of the concrete as a heat store, TABS delivers a stable indoor climate with significantly lower energy consumption than conventional HVAC systems.
How It Works
Plastic pipes (typically cross-linked polyethylene, or PEX) are cast into the structural concrete slab during construction. Warm or cool water is circulated through these pipes depending on the season. Because the concrete slab has enormous thermal mass, it absorbs and releases heat slowly and evenly. In winter, water at around 28-30 degrees Celsius gently warms the slab, which then radiates heat into the room. In summer, water at around 16-18 degrees Celsius absorbs heat from the slab, quietly cooling the space.
The system operates at water temperatures very close to room temperature, which makes it exceptionally well suited for pairing with low-energy heat sources such as heat pumps, solar thermal collectors, or geothermal systems.
Advantages
- Energy efficiency: Low water temperatures mean the heat pump or boiler works at peak efficiency.
- Comfort: No drafts, no noise, and very uniform temperatures throughout the space.
- Invisible: No radiators, convectors, or visible ductwork.
- Dual function: The same pipe system handles both heating and cooling.
Application
TABS is most commonly found in commercial buildings such as offices, schools, and hospitals, but it is increasingly used in high-performance residential construction. The system must be planned and installed during the structural concrete phase — it cannot easily be retrofitted. For self-builders planning a concrete slab-on-grade or a concrete upper floor, TABS is worth considering as a long-term, low-maintenance climate solution. Coordination between the structural engineer and the mechanical engineer is essential during design.
Related terms
- Concrete
- Underfloor heating
- Sustainable building
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