CONTACT & SUPPORT
Live Chat: Online Now
0
CART
'/%3E%3C/svg%3E)
Hover image to zoom
Two Stage Heat / Heat - Cool Programmable Thermostat (Includes 079 Sensor)
 --%3E %3Csvg version='1.1' id='Fill' xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' x='0px' y='0px' viewBox='0 0 100 100' enable-background='new 0 0 100 100' xml:space='preserve'%3E %3Cpath fill='%23F15C02' d='M79.44,0.95H20.56C9.78,0.95,0.95,9.78,0.95,20.56v58.87c0,10.79,8.82,19.61,19.61,19.61h58.87 c10.79,0,19.61-8.83,19.61-19.61V20.56C99.05,9.78,90.22,0.95,79.44,0.95z M65.38,58.24l9.38,29.58L49.69,69.78L24.5,87.82 l9.34-29.6L8.8,39.6l30.73-0.17c0,0,6.98-19.61,10-28.93c0.54,1.36,9.88,29.1,9.88,29.1H91.2L65.38,58.24z'/%3E %3C/svg%3E){kind=small}
 --%3E %3Csvg version='1.1' id='Half' xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' x='0px' y='0px' viewBox='0 0 100 100' enable-background='new 0 0 100 100' xml:space='preserve'%3E %3Cg%3E %3Cpath fill='%23F15C02' d='M30.05,70.23l3.79-12.01L8.8,39.6l30.73-0.17c0,0,6.98-19.61,10-28.93c0.54,1.36,9.88,29.1,9.88,29.1h1.58 L93.71,7.18c-3.58-3.82-8.66-6.23-14.28-6.23H20.56C9.78,0.95,0.95,9.78,0.95,20.56v58.87c0,5.41,2.22,10.32,5.79,13.88 L30.05,70.23z'/%3E %3C/g%3E %3Cpath fill='%23FBC8B4' d='M93.71,7.18L60.98,39.6H91.2L65.38,58.24l9.38,29.58L49.69,69.78L24.5,87.82l5.55-17.59L6.75,93.32 c3.55,3.54,8.44,5.73,13.82,5.73h58.87c10.79,0,19.61-8.83,19.61-19.61V20.56C99.05,15.4,97.01,10.69,93.71,7.18z'/%3E %3C/svg%3E){kind=small}
Hover image to zoom
$178.50 each
In Stock
Get 15 Thu, Jun 18
Order by today, receive Thursday
MANUALS (4)
This item replaces: 510, 511, 512
Free Shipping This item ships free
Easy Returns No restocking fee for 90 days
Product Highlights
–
7 Day, Programmable
Low voltage, 24V
1 Heat, 1 Heat/1 Cool, 2 Heat
Horizontal
Hardwired
40°F to 95°F (Heating), 50°F to 100°F (Cooling)
Description
–
The Programmable Thermostat 521 is designed for three different modes of operation: single stage heating, two stages of heating with a fan, or one stage of heating and one stage of cooling with a fan. Two auxiliary sensors may be added to measure the floor, outdoor or room temperature. A Slab Sensor 079 is included to measure floor temperature to protect the floor from overheating and enhance comfort. The programmable schedule supports either a 7 day or 24 hour schedule with 2 or 4 events per day. A permanent temperature hold button overrides the programmable schedule. An optional Adaptor Plate 012 is available to allow the thermostat to mount onto a single gang electrical box.
Features
Features
- 7 Day Programmable Schedule
- Backlight
- Cooling
- Fan
- Four Hour Battery-free Clock Backup
- Optimum Start
- Outdoor and Floor Temperature Display
- Permanent Temperature Hold
- Radiant Floor Heating
- Time Clock
- Two Stage Heating
Specs
–
| Application: | Multi-Stage (Heat/Cool) |
|---|---|
| Stages: | 1 Heat 1 Heat/1 Cool 2 Heat |
| Programmability: | 7 Day Programmable |
| User Interface: | Push Button |
| Mount: | Horizontal |
| Options: | Fan Control Large Display Comes with Sensor |
| Power Method: | Hardwired |
| Temperature Range (F): | 40°F to 95°F (Heating) 50°F to 100°F (Cooling) |
| Enclosure Type: | NEMA-1 |
| Voltage: | Low voltage 24V |
| Color: | White |
| Height: | 3-11/16" |
| Width: | 3" |
| Depth: | 15/16" |
| Weight (lbs): | 0.6 lbs |
| Ambient Conditions: | 32 to 122°F (0 to 50°C), RH ≤ 90% non-condensing |
| Control: | Microprocessor PID control |
| Sensors: | NTC Thermistor, 10 k ohm @ 77°F |
| Floor Sensor Compatible: | Yes |
| Humidity Control: | No |
| Wireless: | No |
Questions?
Speak with a real person who will go out of the way to help!
Call or text 888-757-4774
Monday – Thursday
8am–7:45pm
Friday
9am–7:45pm
Saturday – Sunday
9am–5:45pm
You May Also Need
Product Reviews
4.5 out of 8 reviews
88% would recommend this product
5 star
88%
4 star
0%
3 star
0%
2 star
0%
1 star
13%
Customer Images
Showing 1-8 of 8 reviews
 --%3E %3Csvg version='1.1' id='With-RB' xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' x='0px' y='0px' viewBox='0 0 100 100' enable-background='new 0 0 100 100' xml:space='preserve'%3E %3Cpath fill='%23FBC8B4' d='M79.44,0.95H20.56C9.78,0.95,0.95,9.78,0.95,20.56v58.87c0,10.79,8.82,19.61,19.61,19.61h58.87 c10.79,0,19.61-8.83,19.61-19.61V20.56C99.05,9.78,90.22,0.95,79.44,0.95z M65.38,58.24l9.38,29.58L49.69,69.78L24.5,87.82 l9.34-29.6L8.8,39.6l30.73-0.17c0,0,6.98-19.61,10-28.93c0.54,1.36,9.88,29.1,9.88,29.1H91.2L65.38,58.24z'/%3E %3C/svg%3E){kind=small}
Radiant slab running 20° hotter than thermostat setting
Love the concept but this won't kick off boiler no matter how low I set air or slab temp. Turned boiler down from 120° to 100° (lowest possible setting) so it don't run 24/7 anymore. HELP!!
Miles
NJ
4 years ago
Was this review helpful to you?
Works Great
Easy to set up for radiant slab heat
Bob C
CT
4 years ago
Verified Buyer
Was this review helpful to you?
great features
Easy to wire in. Still trying to get the best settings for my radiant floor with my wood stove nearby. Should save with this unit over a non programmable one.
wrench
Southern New Jersey
6 years ago
Verified Buyer
Was this review helpful to you?
TEKMAR 521 Thermostat
I used it in a multi unit, sensing in two apts., very nice easy to understand operation.
One of the Tekmar room sensors on the other hand, sensed 10 * warmer than it was.
buzz
Mpls. Mn.
7 years ago
Verified Buyer
Was this review helpful to you?
Just what I needed!
I am using this thermostat with two probes to control a water to water heat pump. It works great.
Just Dave
Atkins, VA
8 years ago
Verified Buyer
Was this review helpful to you?
Great thermostat
Great thermostat. Nice looking and perfect working
Pawel
Ny
10 years ago
Verified Buyer
Was this review helpful to you?
Good control
I used for two radiant heat floor installations on a NYC school. It was the right product.
Vinnie, another plumber in NY
Ossining, NY
10 years ago
Verified Buyer
Was this review helpful to you?
Excellent Thermostat
This thermostat replaced three different thermostats that I was using for the in floor radiant heat in my shop.
I had one thermostat to conrol the maximum floor temperature. One thermostat to control the air temperature and one thermostat to control the auxialry electric forced air heat. The Tekmar thermostat controls all three of these with just one unit and does a better job at it.
Russ
Jonestown, PA
11 years ago
Verified Buyer
Was this review helpful to you?
Product Q&A
3 Questions3 Questions
Q: Does the outdoor temperature play a role in how the programming works or it just for information?
Asked by Jim 10 years ago
Add your answer
Verified Reply- SupplyHouse StaffCorrect, the outdoor sensor only provides a monitoring function (displays outdoor temp). The measured valve does not change the thermostat operation in any manner.
Was this review helpful to you?
Q: Does this thermostat have the pulse width modulating like the 518?
Asked by Eric 11 years ago
Add your answer
Verified Reply- SupplyHouse StaffYes, the thermostat uses Pulse Width Modulation (PWM) operation and cycles the heat on and off within +/- 1.5°F (1°C) of the temperature setting
Was this review helpful to you?
Q: Can you program this thermostat using the floor sensor only. It states that it monitors the floor, but doesn't say if it will call for or shut off heat from the floor.
Asked by AJ 11 years ago
Add your answer
Verified Reply- Supplyhouse StaffYes it can, but that needs to setup in one of the back end settings screens
Was this review helpful to you?
Free Shipping
On orders over $99
We offer flexible shipping and scheduling options, up-to-date delivery estimates, and free ground shipping on any order over $99 to make sure your order gets to you on-time, for less.
Shipping PolicyEasy Returns
Returning items is as simple as 1-2-3
Ordered the wrong product? Item damaged in transit? Our 3-step process makes returning products easy – even up to a year after purchase – with no restocking fees on returns made within 90 days.
Return Policy