Optimum Start and Stop is one of the most effective energy-saving strategies available in a Building Management System, yet it is often misunderstood or under-used. When applied correctly, it allows a building to reach comfort conditions exactly when occupants arrive, without wasting energy by starting heating too early or running it too late.

This article focuses specifically on optimum start/stop for heating, how it interacts with occupancy profiles, and how building fabric and heat losses influence the calculations behind it.

Occupancy profile - the anchor point
Every optimum start/stop strategy begins with an occupancy period. This defines when the building is actually in use - for example:

  • Occupied: 08:00–18:00
  • Unoccupied: All other times

The aim is simple:

The space should reach its occupied temperature at the start of occupation - not before, not after.
Rather than switching heating on at a fixed early time (e.g. 05:00 every morning), optimum start dynamically calculates how long the building needs to warm up, based on real conditions.

Warm-up, occupation, and cool-down

A typical heating profile consists of three phases:

1. Warm-up period (Optimum Start)
This is the variable section. The BMS calculates how early it needs to start heating so that the building reaches setpoint by the occupied start time.

The warm-up duration changes daily depending on:

  • Internal temperature
  • External temperature
  • Recent heating performance
  • Building thermal behaviour


2. Occupation period
Normal occupied setpoints apply. Comfort takes priority, with temperature control maintaining conditions efficiently.

3. Cool-down period (Optimum Stop)
Heating is switched off before the end of occupation, allowing the building’s thermal mass to carry conditions through to closing time without noticeable comfort loss.

 
Building fabric - why no two buildings behave the same
The effectiveness of optimum start relies heavily on understanding the thermal characteristics of the building.

Key fabric factors include:

  • Insulation levels
  • Glazing type and area
  • Air tightness
  • Thermal mass (concrete vs lightweight construction)

A heavyweight, well-insulated building may only need a short warm-up period, while a lightweight or poorly insulated building may need significantly longer.

Modern BMS algorithms do not rely on static assumptions. Instead, they learn the building by comparing:

  • Start temperature
  • Time to reach setpoint
  • Resulting performance

Over time, the system refines its calculations automatically.

 
Heat losses and gains during warm-up
During the warm-up phase, the heating system must overcome:

  • Fabric heat losses to outside air
  • Ventilation and infiltration losses
  • Any cold soak from overnight conditions

At the same time, it may benefit from:

  • Solar gains (especially in perimeter zones)
  • Residual heat stored in the building mass
  • Internal gains from early occupancy or equipment

The optimum start algorithm balances all of these factors to determine when heating must begin.

 
Boost strategies during warm-up
A well-designed optimum start strategy does more than just “turn the heating on”.

During warm-up, the BMS can temporarily:

  • Raise space heating setpoints (controlled boost)
  • Drive heating valves fully open
  • Increase flow temperatures where appropriate


Air handling and ventilation optimisation
To accelerate warm-up efficiently, air systems can be forced into:

  • Recirculation mode (where permitted)
  • Maximum heat recovery
  • Reduced fresh air volumes until occupancy

This ensures that heat is retained within the building rather than immediately exhausted to atmosphere.

Once occupied conditions are reached, systems revert smoothly to normal operation.

 
Optimum stop - finishing efficiently
Optimum stop applies the same logic in reverse. Rather than heating right up to the end of occupation, the system predicts how long the building will remain within acceptable comfort limits after heat input is removed.

This avoids:

  • Late-day overheating
  • Unnecessary boiler runtime
  • Wasted pump and fan energy

In many buildings, optimum stop alone can deliver measurable energy savings.

 
Getting it right in practice
For optimum start/stop to work well:

  • Occupancy schedules must be accurate
  • Temperature sensors must be reliable
  • Heating plant must be capable of responding quickly
  • Control strategies must be coordinated across heating and ventilation

When these elements align, optimum start/stop becomes largely invisible to occupants - which is exactly the point.

 
In summary
Optimum start and stop is not just a time schedule - it is a predictive control strategy that adapts to the building, the weather, and real performance.

By combining:

  • Occupancy awareness
  • Building fabric understanding
  • Intelligent warm-up and boost strategies

a BMS can deliver comfort only when it is needed, and nowhere else.

This is one of the clearest examples of how good control design saves energy without compromising the user experience.