Mercury is an excellent conductor of electrical current. This toxic element was used extensively in the electrical control mechanism of thermostats. Approximately three ounces of elemental mercury sealed in a glass ampoule with metal electrical conductors serves as the active control device in thermostat mechanisms. The ampoule is attached to a wound bi-metallic strip that contracts and elongates in proportion to temperature variations. The mercury containing thermostat serves as a primary control for contactors that in turn provide power to HVAC and/or industrial process equipment. Improvements in electronic control system technology have rendered mercury containing thermostats no longer adequate for state-of-the-art mechanical equipment control. Many of these antiquated mercury thermostats are still in use and are being replaced as systems become too costly to operate and maintain.

Mercury contained in old thermostats is very likely to be released into the environment if the glass ampoule is mishandled. Any mercury spill can involve serious liability issues since proper clean-up procedures are expensive. Disposal of mercury containing devices in municipal solid waste collection is forbidden by state and federal law. Mercury containing thermostats are regulated as universal waste and are the responsibility of the generator at the time the device is considered a waste material.

Mercury Thermostat Recycling

Full Title: Thermostat Recycling Corporation
Full Work Author: National Electrical Manufacturers Association
Abstract: This Web site explains how a not-for-profit organization, now expanded to 48 states,  facilitates the collection and recycling of mercury-containing thermostats. 

Full Title: Earth 911
Full Work Author: Earth 911.com
Abstract: This website specializes in providing consumers with accessible and actionable recycling information across the country. The recycling directory contains information for recycling over 240 different products.

Regulations Affecting Thermostats

Full Title: Universal Waste Rule
Full Work Author: U.S. EPA Office of Solid Waste
Abstract: As part of the U.S. Environmental Protection Agency’s commitment to reinvent environmental regulations, the agency recently issued the “Universal Waste Rule.” This rule is designed to reduce the amount of hazardous waste items in the municipal solid waste stream, encourage recycling and proper disposal of certain common hazardous wastes, and reduce the regulatory burden on businesses that generate these wastes.

Full Title: Removal and Recycling of Mercury-Containing Products from Structures to be Demolished
Full Work Author: General Assembly of North Carolina
Abstract: Session Law 2010-180, House Bill 1766 requires the removal of mercury containing thermostats prior to structural demolition and further bans disposal of mercury containing products in unlined landfills.

General Information on Thermostats

EPA Waste Reduction Resource Center Mercury Thermostat Topic Hub: This primer is intended as a quick guide to the essential P2 information on mercury-thermostats, as well as a compilation of pertinent on-line resources.

Information Sheets/Links

Full Title: General Information on the Universal Waste Rule
Full Work Author: N.C. Division of Waste Management
Abstract: This fact sheet addresses common questions and answers about the rule.

N.C. Division of Waste Management Hazardous Waste Services

Thermostat Replacement

Full Title: Specifying and Sourcing Mercury-Free HVAC and Building Equipment
Full Work Author: INFORM Inc.
Abstract: While manufacturers of building equipment have made substantial progress in reducing or eliminating mercury in building system control devices, some HVAC and building equipment on the market today still contains mercury components. By asking manufacturers a few simple questions, specifiers can avoid including mercury in new building systems.