Radiator heating is the most common HVAC system in multi-occupancy housing and small commercial buildings. Yet balancing is often neglected, leading to recurring complaints: radiators close to the boiler room are scorching while those furthest away stay lukewarm.
How a two-pipe system works
In a two-pipe system, each radiator is fed in parallel from a flow header and a return header. Flow naturally takes the path of least resistance (the circuits closest to the pump). Balancing means adding pressure drop to the favoured circuits to redistribute flow to the disadvantaged ones.
Balancing by temperature
- 1. Set all thermostatic radiator valves to maximum (or remove the heads temporarily).
- 2. Open all balancing valves 100% and let the system stabilise (30 min).
- 3. Measure the ΔT (flow/return difference) on each radiator with a contact thermometer.
- 4. The target ΔT is the one specified by the design engineers (generally 10 to 20°C depending on the water temperature regime).
- 5. Gradually close the balancing valves on radiators with too low a ΔT (excessive flow).
- 6. Repeat until the ΔT is even across all radiators.
Balancing by flow rate
If the radiators are fitted with balancing valves with pressure test points (e.g. TA-STAD), use a hydronic balancing instrument to measure and set the exact flow rate for each radiator. This is more accurate but requires specific equipment.
In multi-occupancy housing, always start with the risers (primary balancing) before setting individual radiators (secondary balancing). An imbalance between risers cannot be compensated for at radiator level.
Special case: the one-pipe system
In a one-pipe system, the radiators are in series. The water gradually loses heat as it passes through each radiator. Balancing is done by adjusting the diverter tees that control the flow diverted to each radiator. The inlet temperature is inevitably lower at the last radiators — this is normal and allowed for in the sizing.