Heating

9 Low-Voltage Thermostats

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are smaller and cheaper to install and maintain, and the wiring does not need to have as high a voltage and power rating as their line-voltage counterparts. This is why are favoured for central heating units. Low voltage thermostats are also more sensitive to changes in heat than line-voltage thermostats, and so can provide more precise control.

When controlling a single large heating unit, such as a or , there is no zone control as with baseboard heaters; either the whole house is getting heated, or none of it is. A low-voltage thermostat installed in a central location, and powered by a , can senses the ambient temperature and be used to control a to deliver power to the heating load.

By using an source for the control circuit we get the benefit of lower cost and easier installation along with increased safety, allowing a simple two-wire low-voltage cable to be installed in an ideal location in the house. Because it is only meant to handle the control current and not the load current, low-voltage thermostats are highly responsive and can provide more accurate control than line-line voltage thermostats.

Some models of low-voltage thermostats used to control central gas furnace or electric furnace loads incorporating heat exchanges and blowers, will have a small, series connected, resistive device called an . The purpose of this device is to fine tune the sensitivity of the thermostat and prevent overshoot of the desired room temperature.

Low-voltage thermostats, fall into two general categories, some are simple temperature activated switches while others are more modern incorporating solid-state circuitry and allowing for programmable behaviours such as 24-hour cycles, and weekday vs weekend scheduling.

Electronic thermostats use semiconductor components for both temperature sensing and control-circuit switching. If installed to replace an existing analogue thermostat, the electronic thermostat must have a separate power source, which is usually a battery.

An electronic thermostat with a touch screen attached to the wall.
An example of a programmable thermostat.

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Basic HVAC by Aaron Lee is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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