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 Line Voltage Thermostats for Heating & Cooling
Where to buy, how to install, wire, troubleshoot, repair or replace a 120V or 240V thermostat used for heating or cooling
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Guide to line voltage thermostats 120V or 240V room thermostats for electric heat, fan heaters, radiant floor heat, convector heaters. This article describes types of line voltage wall or floor thermostats used to control heating or heating & cooling equipment where switching of 120V or 240V devices is required.
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Line Voltage Thermostats: choices, wiring, repair, replacement
 I have a two wire honey well thermostat T451A - I want to replace this thermostat with a programmable. Presently
there is a two wire ( black and White ) 120 volt line;
Any suggestions ?
Thank you -
M.S. 3/15/2013
Reply:
The Honeywell T451A room thermostat (illustration at left) is a line-voltage (120V) wall thermostat, a member of the product family including the T651 and T694 light duty line voltage wall thermostats.
These controls are widely used to directly control 120-V equipment such as valves, fans, motors, contactors, and electric heat systems as well as fan coil units in heating/cooling systems. Illustration at left of the Honeywell T415A and T651A from product literature. [4]
The T451 is a heat-only controller - I'm guessing yours may be controlling electric heat. I understand why you asked for help. Honeywell's own website includes a "thermostat finder" feature but is unable to give even one suggestion for a programmable line-voltage room wall thermostat. Happily the news is better than that.
Honeywell gives a succinct description of this class of wall thermostats:
Line voltage thermostats control the electricity directly, thus the name "line voltage." If you have a baseboard heater, electric wall heater, or resistive electric heater, you may require a line voltage thermostat. These thermostats are generally made for either 2 wires (SPST) or 4 wires (DPST - more common). ... These are NOT to be used with gas heating systems (gas heaters are generally single stage systems). Most line voltage systems are mechanical rather than digital programmable, and are almost always either 2 or 4 wires.... [however there are indeed some programmable line-voltage thermostats available as we list below ] [5]
Honeywell's newer replacement for the T451 includes the Honeywell TH114 which is also non-programmable and NOT what you want.
Programmable Line Voltage Heat-Only Hemostats
 Other Honeywell line voltage thermostats and line voltage thermostats from other manufacturers, however should work fine where you want to add thermostat programmability, automatic setbacks, etc.
Examples of modern line-voltage programmable room thermostats include:
Honeywell TL8130A1005 - for electric baseboards and fan-forced heaters. (This is a single-function or "heat only" single-pole-single-throw (SPST) thermostat. Approximate Price: $50. U.S. designed to control 240V heating equipment.
Honeywell YTL9160AR1000 - line voltage, heat only, for electric baseboard or fan convector or fan-forced heaters, is an interesting development in wireless thermostats.
The kit includes a Wireless EConnect programmable wall thermostat and one Electric Heating Equipment Interface Module (EHEIM). Each EHEIM can support a maximum load of 3000W at 240V - figure $150. U.S.
The Honeywell EConnect™ TL9160AR is shown at above-left.
Honeywell's EConnect™ wireless thermostats can accept up to 8 EIMs on a single thermostat - sketch below right. [click any InspectApedia image to see an enlarged detailed version] [6] Honeywell EConnect™ wireless thermostats can control multiple electric heating baseboard units but only up to a total amperage load specified by the manufacturer, e.g. 12.5A - sketch, below left.[6]
Honeywell
Line Voltage Thermostat, Heating Only Digital Programmable, Switch Type DPST, Switch Action Open on Rise, Number of Switches 1, Sensor Type Thermistor, Digital 7 Day Programmable, 15 Amps Max; 3600 Watts at 240 VAC, 3120 Watts at 208 VAC, For Use With Electric baseboards, convectors and fan forced heaters (resistive rated loads), Color White, Application Heating, 7 Programs per Week, Digital LCD Display, 208-240, 208-240, -, -, 15, 15, 15, 2, UL, CSA
 Lux PSPLV512 - 120V or 240V programmable wall thermostat intended for electric baseboard or radiant type electric heat, about $50. U.S.
Lux Luxpro Programmable Line Voltage Thermostat -( $70. U.S.) 120/240V SPST 1,900W at 120VAC (noninductive). 3,800W at 240VAC (noninductive).
[illustration at left]
Radimo Radistat-Pro, line voltage 120/240V thermostat intended for electric radiant floor heating ($120) available through Sears
This thermostat, or its double, appears under a range of name brands, so we suspect they're all the same product sold with re-branding as Radimo. Laticrete, etc |
Dayton's line voltage room thermostat shown at left is the Dayton 1UHG4 heating-only digital, programmable room thermostat suitable for electric heat control. About $57. U.S.
Specifications from granger.com include:
Line Voltage Thermostat, 5+1+1 Programmable, Switch Type SPST, Switch Action Open / Close on Rise, Number Of Switches 1, Control Range 41-95 F, Differential +/- 1 Deg F, Height 4 1/4 In, Width 3 5/8 In, Depth 1 1/4 In, Temp Sensitivity +/- 1 Deg F, Sensor Type NTC Thermistor, For Use With Heat Only, Color White, Application Programming 5+1+1, LCD Display, Enclosure Type PVC, Includes Screws and Mounting Plate |
Trane also produces a range of line voltage thermostats (Trane Line Voltage Thermostat M TC126 004 NIB, Trane TX 126 004, Trane T4039M1095, Trane THT0567) and programmable thermostats (ComfortLink™II, Trane XL900-XL200 compatible with 24-V systems when a 24-V relay accessory panel is added), with more information from from Trane.
Trane's wide array of electric unit heaters (wall mounted, ceiling suspended & others) include some models that can be operated from a room thermostat (24V WD1 or WD2 controlling 240V heaters or WD3/WD4 120V control operating 240V heaters with additional line voltage and 600-volt controllers available). [7]
Line Voltage Thermostats for both heating & cooling
Honeywell T6052A1015 - heating or cooling, but not programmable, SPDT thermostat. About $140. U.S. Supports 2-stage heat and 2-stage cooling.
Instructions for Wiring of Line Voltage 120V Wall Thermostats
 The typical wiring connections for older, non-programmable line voltage thermostats is described ain Honeywell's T451A, T651A, T694A,B,D,F Light Duty Line Voltage Thermostats from which we excerpt and adapt some advice from Honeywell:
Watch out: disconnect all electrical power before making any electrical connections, tests, or even touching wiring on line voltage thermostat systems. While some old timers figure out wiring by shorting thermostat wires together, that is imaginable only for low-voltage thermostat systems. Touching live line voltage wires risks death by electrocution as well as fire, shock, and equipment damage.
- Use copper wire only with line voltage thermostats. All wiring must comply with the applicable electrical codes for your area.
- Check specifications: Make sure that the line voltage thermostat electrical rating is sufficient for the current requirements of the equipment it will control. Check voltage, amperage, and wattage. For example,
Watch out: be sure to check the total wattage of heating equipment that you are going to be switching against the capacity limits of the programmable (or non-programmable) line voltage wall thermostat you plan to purchase and install. For example the Lux PLSPLV512 we recommended above is rated to control 1900 to 3800 watts.
- Use a proper electrical box for mounting: because line voltage thermostats are using 120V or 240V wiring connections, don't just run wires through a wall into the thermostat. Line voltage thermostats usually include a suitable faceplate to cover the junction box mounted in the wall. Illustration above left, showing typical mounting of a line voltage room thermostat onto an electrical box, courtesy Honeywell Corporation [5].
- Connect the equipment wiring (the 120V 240V wires) to the proper terminals at the rear of the thermostat before trying to mount the thermostat to the wall.
For a heat-only application the wiring will be simple as there are just two wires, the L1-hot wire and the L2 heat or load wire. For a heating + cooling application there will be a heat load wire and a cool load wire (see illustration above left) one of which will be fed by the thermostat depending on whether it is in heating or cooling mode.
See this 1949 Honeywell Control Handbook for an explanation of older line voltage (120-Volt) and 24-Volt thermostats and other controls such as the T40 series 4-wire 120V T44 Thermostat
The installation manual for your particular line voltage room thermostat will include connections for additional wires that may be necessary when the thermostat is being use in more complex installations such as connections to a winter-summer changeover switch, connections to control a separate blower fan motor, etc.
Thermostat wiring instructions for all types of room thermostats, including color coding of wires and terminal connections are found at
...
Frequently Asked Questions (FAQs) about line voltage thermostats & Electric heat
 Question: can I hook up a wall plug on my electric heat circuit?
I want to add a 120V electrical outlet and noticed that we already have wiring for electric baseboard heat. Is there a way to use that circuit to add a wall plug?
Reply: no but you can install a wall electrical receptacle to control a portable electric heater
Interestingly when first asked about this I said I didn't think so, out of concern that there may be no neutral wire or ground wire suitable for wiring an electrical receptacle or "wall plug" up to an electric baseboard heat circuit.
Watch out: and indeed, normally you would not be able to safely wire a 120V wall receptacle into the 240V circuit that controls electric baseboard heat since that circuit may be missing a suitable neutral and ground wire. See ELECTRICAL OUTLET, HOW TO ADD & WIRE.
But in researching wall thermostats we came across the combination line voltage wall thermostat for electric heat and wall receptacle combination shown in our photo (left).
This device is sold by Dayton, Model 1UHG6 and is intended to control electric heat as well as to provide an electrical outlet plug. Sold by grainger.com who includes these specifications:
Line Voltage Control, Outlet Plug Thermostat, Switch Type SPST, Switch Action Open On Rise, Number Of Switches 1, Control Range 40-95 F, Differential +/- 1 Deg F, Height 5 1/2 In, Width 2 7/8 In, Depth 2 5/8 In, Temp Sensitivity +/- 1 Deg F, Sensor Type NTC Thermistor, For Use With Portable Heaters [italics ours], Color White, Application Heating Only, LCD Display, Enclosure Type PVC - about $60. U.S.
So let's get clear just what this is: this is not an electrical outlet that you add to one leg of the 120V or 240V circuit that controls built-in electric baseboard heat. This is a device that is installed in the wall where a conventional electrical receptacle would have been installed. Dayton's 1UHG6 is, however a neat device. It is a wall thermostat that is intended to control a portable electric heater that is plugged into the wall where this device is installed.
You might note that the wall thermostat may be a bit low on the wall and you won't want it too close to the heater itself or it'll be dominated by heat local to the heater. Nevertheless it's a nice way to make your portable electric heater thermostatically controlled.
...
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
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Phone: +1.978.692.3375
Toll Free (U.S.): 866-IP-LIVING (866.475.4846)
Fax: +1.978.692.3378 - Sales: sales@proliphix.com Marketing: marketing@proliphix.com Customer support: support@proliphix.com http://www.proliphix.com/ - quoting from the company's website:
All Proliphix Network Thermostats come with our free Uniphy Remote Management Service. This unique offering lets you monitor and control your HVAC systems by simply pointing your Browser to our secure Proliphix Web Site. Enjoy the convenience of programming a thermostat from any location, using a simple graphical interface. No computer equipment or software is required. And since Proliphix takes care of the network configuration for you, you’ll be up and running in no time. We’ll even proactively monitor your thermostats and send you an immediate email or SMS message when an HVAC problem is detected.
- [2] "The Nest Learning Thermostat", Nest Thermostat, 900 Hansen Way
Palo Alto, CA 94304, Tel: 855-4MY-NEST, Email: info@nest.com, website http://www.nest.com/, retrieved 1/24/2013.
- [3] Honeywell Controls, the company wants you to use their contact form at this web page: http://www51.honeywell.com/honeywell/contact-support/contact-us.html
Honeywell Consumer Products,
39 Old Ridgebury Road Danbury, CT 06810-5110 - (203) 830-7800
World Headquarters, Honeywell International Inc.,
101 Columbia Road,
Morristown, NJ 07962,
Phone: (973) 455-2000,
Fax: (973) 455-4807 1-800-328-5111
- [4] Honeywell Corporation, Honeywell T451A, T651A, T694A,B,D,F Light Duty Line Voltage Thermostats, [installation, troubleshooting manual], 1992, Honeywell Consumer Products,
39 Old Ridgebury Road Danbury, CT 06810-5110 - (203) 830-7800 copy on file as Honeywell_Line_Voltage_T651A.pdf
World Headquarters, Honeywell International Inc.,
101 Columbia Road,
Morristown, NJ 07962,
Phone: (973) 455-2000,
Fax: (973) 455-4807 1-800-328-5111 copy on file as Honeywell_Line_Voltage_T651A.pdf
"T451, T651, T694 Thermostats provide on-off control of valves, fans, motors, contactors, electric heat elements, duct furnaces and fan coil units in heating/cooling systems. Switching sub-bases provide manual control of heating, cooling and fan."
- [5] Honeywell Corporation, "Honeywell Thermostats", website http://www.honeywell-thermostat.com/line-voltage.html retrieved 3/16/13
- [6] Honeywell EConnect™ Wireless Thermostat Kit TL9160AR System Installation Guide, retrieved 3/15/13, copy on file as Honeywell_EConnect69-2474EFS.pdf
- [7] Trane, Ingersoll Rasnd Residential Solutions, Trane PO Box 9010, Tyler TX 75711, Website www.trane.com
- [8-10 pending]
- [11] White Rodgers Thermostats and HVAC controls,
Homeowner information: http://www.emersonclimate.com/en-US/brands/white_rodgers/Pages/wr-homeowner-info.aspx
Contractor information: http://www.emersonclimate.com/en-US/brands/white_rodgers/wr_contractor_info/Pages/white-rodgers-contractor-info.aspx
White Rodgers Product Catalog (don't misspell the company's name as White Rogers Thermostats) -
http://www.emersonclimate.com/Documents/thermostats.pdf - Thermostat Catalog
- [12] Domestic Central Heating Wiring Systems and Controls, 2d Ed., Raymond Ward, Newnes, ISBN-10: 0750664363, ISBN-13: 978-0750664363, Quoting from Amazon.com:
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- [13] "Automatic Oil Burner Controls - Thermostats", Domestic and Commercial Oil Burners, 3rd Ed., Charles H. Burkhardt, McGraw Hill, 1969 (and later editions), ASIN B0000EG4Y8
- [14] Hunter Fan
2500 Frisco Ave.
Memphis, TN 38114
888-830-1326
www.hunterfan.com
- [15] Trane TCONT800 Series Touch Screen Programmable Comfort Control Ownes Guide, American Standard, Inc., Troup Highway, Tyler TX 75711, January 2005, Telephone: Customer Service: 1-877-3381, website: www.trane.com
- [16] Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
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