More about thermostats
Thermostats are controls designed to engage or disengage various types of heating, cooling or ventilation (humidification/dehumidification/Indoor Air Quality) equipment based on the ambient (indoor) or floor (radiant heat applications) temperature and, depending on model, programmed temperature & schedule, occupancy and others.
Types of thermostats
Thermostats mostly differ from one another by application and programmability and other options:
Thermostat applications can be divided into 2 major groups -
conventional thermostats (also referred to as 24V - used with boilers, furnaces, heat pumps, air conditioners, etc.) and
line voltage thermostats (used on 120/208/240/277V heating equipment such as electric baseboards, electric unit heaters, convectors, etc.). Some 24V thermostats may have a 750mV millivolt option (for applications such as gas fireplaces), however millivolt-only thermostats are very rare.
Programmability determines whether a thermostat can be programmed to turn the equipment on or off at pre-set times of selected days of the week.
Non-programmable thermostats, as the name implies, cannot be programmed and are either on or off depending on current temperature set by user.
Programmable thermostats allow user to set temperature as described above and may come in various options, including 5+2 days (separate program for 5 weekdays and a separate program for 2 weekend days), 5+1+1 days (5 weekdays + program for Saturday + a separate program for Sunday), 7-day (a separate program for every day of the week) or 1-day (same program for every day). Some models (w/ commercial mode) may offer scheduling for holidays for added energy savings. Practically all such models offer 4 time periods to program - Wake (morning), Leave (morning through end of day or evening), Back (return to sleep) and Sleep (from evening/night until morning).
Additional thermostat options
Automatic or manual changeover - determines whether the transition from heat to cool and back is done by the thermostat itself (auto) or selected by the user (manual). If a thermostat has an auto/manual changeover, it offers user a choice between two modes. In a manual-only changeover thermostat, the change from heating to cooling (and back) must be done by hand, commonly using a slide switch on the thermostat body.
Power method - determines whether the thermostat is powered by an external AC source (C-wire is common for most applications), battery only (generally 2 or 3 AA or AAA batteries) or is hardwired but has battery backup (for power outages, etc.).
Wireless internet connectivity - wi-fi thermostats allow user to control thermostat settings via a phone, tablet or PC and usually require installation of an application indicated by the thermostat manufacturer. This functionality is very useful for vacation homes, rental units and instances where occupants leave and return at irregular times.
Geofencing links the thermostat to the smart phone and automatically transfers the system to Away mode when user leaves the home/office (radius of the premises is selected via the app); when user returns, the system goes back to its' normal schedule - no interaction with thermostat is needed.
Keypad lockout is an option provided on some of the more advanced thermostats, allowing user to lock out the screen to prevent unauthorized access. Lockout options are generally Full (complete lockout), Partial (allows to change temperature but not system settings) or None (thermostat unlocked). This option is great for homes with curious children, rental units (think Airbnb and similar) and commercial settings (offices/warehouses, etc.).
Temperature override feature allows user to override scheduled program either temporarily (thermostat returns back to schedule settings in the next time period) or permanent (override will stay in place until user cancels it, after which the thermostat returns back to schedule).
Vacation mode is useful for frequent travelers and allows for quick transfer of the thermostat to the Away mode, where (adjustable) temperature can be kept at minimum for energy savings.
