There is a reason why the Honeywell round heat only manual thermostat is considered one of the most popular thermostats in the world. Installed in well over 70 million homes and buildings, the Round heat only manual thermostat is an easily accessible and reliable option to adjusting your surrounding's temperature. This model has been designed to be especially user friendly and features a simple and precise round that's been celebrated for its ease of use and precision. Mercury free and featuring a decorative covering ring to cover surrounding wall marks, the round heat only manual thermostat is a modern classic that has earned its distinction as a top end thermostat. The CT87K Honeywell thermostat is compatible with heating only systems including: forced air (gas, oil and electric), hot water and steam, heat pumps without backup.