Introduction

Smart heating controls have become central to modern retrofit programmes across the UK. However, their specification, installation and commissioning must align with PAS2035:2019 – the professional standard for energy-efficient retrofit of buildings. This guidance clarifies what the standard requires and how it affects retrofit delivery.

What PAS2035 Says About Controls

PAS2035 emphasises that heating controls are integral to retrofit performance. The standard does not mandate specific brands or technologies, but it does require that:

• Controls must be fit for purpose and suitable for the building's heating system
• They must be commissioned and verified to operate as designed
• Their performance must be demonstrated through Post-Retrofit Verification (PRV)
• Occupants must receive clear guidance on operation

The standard treats controls as a critical component of the retrofit package, not an optional upgrade. This reflects evidence that poorly specified or installed controls can undermine the entire retrofit investment.

Control Specifications Under PAS2035

Types of Control Required

PAS2035 aligns with Building Regulations and CIBSE guidance, which require:

• Thermostatic radiator valves (TRVs) on all radiators except those in rooms with the main room thermostat
• A room thermostat capable of controlling temperature to within ±2°C
• Time and temperature control – the ability to adjust heating by time of day or occupancy patterns
• Hot water control – separate from space heating where feasible

For properties with heat pumps or other renewable technologies, controls become even more critical. Smart thermostats with weather compensation or demand-led operation can substantially improve seasonal efficiency.

Installation and Commissioning

PAS2035 requires that commissioning is not a tick-box exercise. Installers must:

• Set controls correctly for the building fabric and occupancy profile
• Test operation across a range of conditions
• Document all settings and adjustments
• Verify that heating ramps up and down smoothly without over-heating
• Confirm wireless or networked controls communicate reliably

This is particularly important where existing heating systems are being retained or refurbished. Legacy boilers often perform unpredictably with modern smart controls; proper commissioning identifies these issues before handover.

Smart Controls and Performance Verification

The Role of Post-Retrofit Verification

PAS2035 requires Post-Retrofit Verification to confirm that predicted energy savings are being realised. Smart controls directly affect this outcome:

• Controls must be monitored for at least three months post-handover
• Data from smart meters and control systems provides evidence of actual vs. predicted performance
• If performance falls short, the retrofit team must investigate and correct the issue

This creates accountability. If a property is not delivering expected savings, poorly optimised controls are often the cause. Retrofit coordinators should ensure control settings are reviewed alongside building fabric performance.

Data Access and Privacy

PAS2035 acknowledges that smart controls generate heating data. The standard advises that:

• Occupants must consent to data collection and understand how it is used
• Data protocols should align with GDPR requirements
• Housing associations should have clear policies on data retention and access

This is increasingly important as smart controls become more networked and connected to cloud-based platforms.

Practical Challenges

Older Buildings and Control Compatibility

Many retrofit projects involve properties built before modern heating standards. Common challenges include:

• Boilers without OpenTherm or modulating capability – limiting the effectiveness of smart controls
• Poor insulation making it difficult for controls to maintain stable temperatures
• Oversized heating systems that cycle on and off erratically

PAS2035 requires that controls be matched to the heating plant. In some cases, this means upgrading the boiler or heat emitters alongside the controls to achieve real benefit.

User Engagement

Smart controls only deliver savings if occupants understand and use them. PAS2035 requires clear, practical user guidance covering:

• How to adjust temperature and heating schedule
• How to access performance data or alerts
• Troubleshooting common issues
• Contact points for technical support

Housing associations should plan post-installation training and ongoing support to maximise control effectiveness.

Conclusion

PAS2035 treats smart heating controls as fundamental to retrofit success, not a peripheral technology. Proper specification, meticulous commissioning and occupant engagement are all required. When these elements are in place, controls can deliver substantial energy savings and improved comfort. Retrofit teams should view controls as an integral part of the retrofit design, not an afterthought.