Balancing Loops

Your living room is 18°C and the thermostat is set to 21°C. The thermostat compares the two, finds a gap of 3°C and switches the boiler on. The radiators warm the room, the gap shrinks, and at 21°C the thermostat switches the heat off. Heat leaks out through the walls and windows, the room cools, a gap opens again, and round it goes.

That is a balancing loop: a change comes back round opposing itself, so the loop keeps pulling something towards a goal. Engineers call it negative feedback, where “negative” means opposing, not bad. A reinforcing loop amplifies a change; a balancing loop resists it.

This is a simplified model of the idea, not instructions for adjusting your own heating system; real controls have timers, limits and delays. Central Heating explains how they work in its lesson on controls and TRVs. And a balancing loop doesn’t always settle neatly: give it a delay and it can overshoot, which is the subject of Delays.