Thermostats, also known as thermal switches or thermostatic switches, mainly work as on and off switches in industrial, commercial and domestic HVAC applications. However, besides HVAC, there are select types of equipment that also turn on and off based on temperature. For instance, rocket motors and overheat protection systems contain thermal switches.

The most common temperature-sensing element in a thermostat is a strip comprised of two metals, one of which expands due to heat at a higher rate than the other. The result is that the strip coils and uncoils depending on temperature levels. The thermostat opens or closes a circuit either by means of a mercury tube or an electronic thermostat switch.

Along with the common types mentioned above, there are several types of thermostats to choose from:

1. Reed or magnetic reed switch thermostats;

2. Mercury switch thermostats;

3. Bi-metal disc thermostats (also called snap action);

4. Rod and tube thermostats that come with a variety of temp coefficients;

5. Vapor-tension thermostats (also called gas actuated).

Action Steps
The best contacts and resources to help you get it done

Buy thermostats with adequate ratings to fit your application

Most thermostats perform at a range of levels. It's important to match your applications with your industrial heater thermostat or other thermostats that have the right maximum current and max AC or DC voltage. If you can find information on the lifespan of a thermostat as well, this will help you choose the best value.

I recommend: Mor Electric Heating Association, Inc. distributes residential, commercial and industrial thermostats. They clearly publish specifications along with pictures, so you can match a thermostat with your application. Grainger categorizes its huge selection of thermostats by function and type.

Choose thermostats with the right pole-and-throw

Single pole/single throw (SPST) thermostats open and close one conductor in one circuit. However, single pole/double throw (SPDT) operate as three-way switches. SPDT thermostats open or close two conductors in one circuit. Also, the double pole/double throw (DPDT) opens or closes two conductors in a pair of circuits.

I recommend: You'll notice that good thermostat distributors and industrial thermostat manufacturers clearly indicate the pole-and-throw of their products. AmericanHVACparts.com, for instance, adds "Double Pole Single Throw, 3 or 4-wires 45 F to 80 F Temperature" to the title of one of their products. Glo-Quartz includes a column for pole-and-throw in their product spec table.

Save money and take it easy with a programmable thermostat or a wireless thermostat

Because the wireless thermostat is mobile, you can take it with you throughout the building; it's not stuck in a hallway or far from where you do most of your living or business. Programmable thermostats have domestic purposes but are absolutely great for businesses, because they can take the temperature down after hours and bring it back to warm just in time for the start of the next business day.

I recommend: ThermostatsUSA distributes both commercial and domestic wireless thermostats, as well as Venstar programmable thermostats. You can program each digital thermostat to an optimal weekly temperature schedule. Before you buy, though, do a little price comparing at other places, such as SmartHome, which carries wireless programmable heater thermostats.

Tips & Tactics

Helpful advice for making the most of this Guide

• •  If you need to control the temperature of a battery, use a snap action thermal switch for your thermostats.