Balancing a Heating System and Using Thermostats

If one room's radiator is hot and another's is cold, the problem is often not the boiler but uneven water distribution. Balancing and thermostats fix that.

A familiar picture at home: the radiator in the room nearest the boiler is so hot that the window gets opened, while in the far bedroom only the top of the radiator is lukewarm. The usual reaction is to think about a bigger boiler or a higher temperature. In most cases, though, the system has enough capacity; the issue is that hot water is not shared evenly between radiators. The fix is hydraulic balancing.

Why a system becomes unbalanced

Water always follows the easiest path. Radiators close to the boiler on short pipe runs have little resistance, so most of the water flows through them. Distant radiators, especially upstairs or at the end of a long run, receive little. The first rooms overheat and the last ones stay cold.

Raising the boiler temperature in this situation warms the distant rooms a little but overheats the near rooms even more and increases energy use. Turning up the pump speed can cause noise and whistling in pipes and valves.

How hydraulic balancing is done

Balancing means giving each radiator or underfloor loop the flow of water it needs. The process runs roughly as follows:

• the heat loss of each room is calculated or estimated from available data;
• the required flow for each radiator is determined accordingly;
• the regulating valves on radiator return pipes (or pre-settable thermostatic valves) are set to the calculated position;
• the pump's operating mode is matched to the system's real demand;
• the system is started, radiator flow and return temperatures are checked, and adjustments are made if needed.

Valves on nearby radiators are throttled more, while those on distant radiators stay more open. Water is then shared evenly and all rooms warm up at roughly the same time.

In underfloor heating, the same work is done at the manifold. Using the flow meters on the manifold, each loop's flow is set according to its length and the room's needs. Long loops need more flow, and short loops are restricted.

Bleeding air and keeping the system clean

There must be no air in the system before balancing. A cold top and warm bottom on a radiator, or a gurgling sound in the pipes, are signs of air. It is released through the bleed valve at the top of the radiator, after which the system pressure is checked and topped up if needed.

In older systems, sludge builds up in pipes and radiators and restricts flow. Flushing the system first and fitting a dirt separator filter greatly improves the result of balancing.

Thermostats: matching heat to need

Balancing shares water evenly; thermostats then control each room according to its own needs.

Thermostatic radiator valves automatically reduce flow to a radiator once the room reaches the chosen temperature. A sunny living room, a room full of people or a kitchen with cooking under way all produce extra heat, and the valve takes that into account. They also make it easy to keep bedrooms cooler.

A room thermostat controls the boiler or heat pump. It should be installed on an internal wall that represents the typical temperature of the house, at around eye level, not near a radiator, a window, direct sun or a cooker. A programmable thermostat lowers the temperature automatically at night and when nobody is home.

Weather-compensated control with an outdoor sensor adjusts the heating water temperature to the outdoor temperature: cooler water on a mild day, hotter on a frosty one. This is particularly efficient for condensing boilers and heat pumps.

Balancing is more reliable when done by a specialist with measuring instruments, because valve positions are set to calculated flows rather than by eye. After the first heating season, it is normal practice to observe room temperatures again and make small corrections where needed. Writing down the final valve settings, on paper or next to the manifold, avoids having to set the system up from scratch during future work.

Common mistakes

• A thermostatic valve hidden behind heavy curtains, a decorative cover or furniture, so it senses the wrong temperature.
• Turning every valve to maximum in the hope the room will "heat faster".
• Fitting thermostatic valves on radiators in the same room as the room thermostat, so the two controls fight each other.
• Not rebalancing the system when a new radiator or loop is added.
• Not recording the balancing settings, so valve positions later get changed by accident.

Zaferoğlu İnşaat handles building services work as part of the overall renovation plan for apartments and private houses. Keep a week's note of which radiators run hot and which stay cool; balancing is far easier to start from that list.