Ans: No, programmable thermostats are not compatible with all HVAC systems. The compatibility of a programmable thermostat with your HVAC system depends on several factors, including the type and complexity of your HVAC system and the thermostat's features and capabilities. Some specialized HVAC systems, such as line voltage systems or proprietary systems used in commercial setups, may not be compatible with standard programmable thermostats. With that said the programmable thermostats are usually compatible with domestic HVAC systems without any problem.