Tekmar 521 Programmable Thermostat Specification Sheet


Tekmar 521 Programmable Thermostat


The Thermostat 518 accurately controls the room temperature for a hydronic heating zone using Pulse Width Modulation (PWM) technology. Simple up and down buttons and a display with large type make this thermostat easy to read and use. The 518 automatically detects a single auxiliary sensor to measure either outdoor, floor, or remote room temperature. This easy-to-install thermostat is a direct replacement for tekmar Thermostats 507 and 508.


Tekmar 521 Programmable Thermostat-fig.2


Programmable Thermostat 521 Two Heat or Heat-Cool (Includes Sensor 079)
Literature 521_A, 521_C, 521_D, 521_Q, 521_U
Control Microprocessor control. This is not a safety (limit) control
Packaged weight 0.6 lb. (290 g)
Dimensions 3-11/16″ H x 3″ W x 15/16″ D (94 x 76 x 24 mm)
Enclosure White PVC plastic, NEMA type 1
Approvals Meets Class B: ICES & FCC Part 15, CE
Ambient conditions Indoor use only, 32 to 122°F (0 to 50°C), RH ≤90% non-condensing
Power supply 10 to 30 V (ac/dc), 50/60 Hz, 1.8 VA, Class 2
Relays 30 V (ac/dc) 2 A, Class 2 circuits
Sensor NTC thermistor, 10 kΩ @ 77°F (25°C ±0.2°C) ß=3892
–Included Slab Sensor 079
–Optional tekmar type # 070, 072, 073, 076, 077, 079, 084
Warranty Limited 3 Year (See 521_D for full warranty)
Slab Sensor 079 10’ (3 m) wire
Dimensions 3/16” OD x 1-1/2” (5 mm OD x 38 mm)
Enclosure 316 stainless steel, 10’ (3 m) 24 AWG, 300 volt PVC insulated Zipcord
Operating range -58 to 221°F (-50 to 105°C)
Sensor NTC thermistor, 10 kΩ @ 77°F (25°C ±0.2°C) ß=3892

Energy Saving Features

  • 7 Day Programmable Schedule

Additional Features

  • Optimum Start
  • Permanent Temperature Hold
  • Radiant Floor Heating
  • Two Stage Heating
  • Cooling
  • Fan
  • Backlight
  • Outdoor and Floor Temperature Display
  • Time Clock
  • Four Hour Battery-free Clock Backup

Scan code for quick link to product page on tekmarControls.com

Tekmar 518 Thermostat Specification Sheet-FIG.2

An auxiliary sensor must be used to measure any auxiliary sensor temperatures.

Sample Application Drawing

Below is a sample application drawing for this product. This application may include other tekmar products that are required for installation. More sample applications can be found at tekmarControls.com.

Sample Mechanical diagram


  • P1 = Manifold Pump
  • S1 = Optional Slab Sensor 079
  • T1 = 24 V (ac) Transformer 009
  • Z1 = Zone Valve

Tekmar 521 Programmable Thermostat-fig.1

Sample Electrical diagram

Tekmar 518 Thermostat Specification Sheet-FIG.4

All specifications are subject to change without notice

Tel: (250) 545-7749 • Fax: (250) 984-0815

Other  Manual:

Tekmar 521 Programmable Thermostat Quick Set-up Guide

Tekmar 521 Programmable Thermostat User Manual

Tekmar 521 Programmable Thermostat Installation and Operation Manual


Tekmar 521 Programmable Thermostat Specification Sheet





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