Optimum start controls vary the times that heating systems come on, depending on the weather, occupancy, and the current heat in the building. Using optimum start instead of fixed time control can save up to 10 % in energy costs. 

An optimum start controller costs between € 90 (£ 80) and € 340 (£ 300), which means investment costs could be recuperated in less than five years.

Optimum start controls should take no longer than a day to install. Once in place, the user can programme in the times when the building is occupied and the desired inside temperature to maintain. The controller, based on records of outside air temperature and residual temperature in the building, then automatically starts the heating to meet the required temperature by the time people start to arrive (i.e. the 'optimum start'). By removing pre-heat times, and heating when spaces are not used, optimum start controls help to achieve significant savings.