Honeywell Thermostat T4398A1021 110V, In-Line, Tradeline High Performance Electric Heat Thermostats provide precise line voltage control of resistive-rated electric heating equipment. For control of resistance-rated baseboard electric heaters. Vapor-filled dual-diaphragm sensing element provides accurate temperature sensitivity. Extremely sensitive to temperature changes. Replace virtually all standard wall-mounted line voltage thermostats. Color-coded leads allow easy installation. Include long-lasting Micro Switch mechanism. Rugged, plastic mounting base. Well suited for upgrades and high-end new construction.