FAQs on line voltage thermostats 120V or 240V room thermostats for electric heat, fan heaters, radiant floor heat, convector heaters.

This article series 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.

Line Voltage Thermostat Q&A

These questions & answers about line voltage room thermostats (120VAC or 240VAC thermostats) were posted originally

at LINE VOLTAGE THERMOSTATS - you'll want to read the thermostat selection, wiring guides, and free manual downloads found in that article.

How do I turn on my electric baseboard heat?

How do you turn the heater on - On 2016-10-23 by Clarice Nathaniel

Reply by (mod) -

Clarice:

1. confirm that electrical power has been turned on to the electric heating circuit(s) - at the electrical panel

2. Turn the heater thermostat to a setting above room temperature or until you hear the thermostat's relay click

My electric baseboard heat is off and I'm freezing; how do I turn it back on?

Please I'm freezing

How do I turn it on - On 2017-11-21 by David González

Answer by (mod) -

IF your electric heating baseboards are "OFF",

First check that the power is on in the electrical panel.

If it is and you set the thermostat above room temperature and the heat does not go on then you need to leave that circuit off and ask for repair help from an electrician since most likely there is an open connection or bad relay or switch.

Watch out: don't force or keep switching a tripped circuit breaker back "on" or you risk an electrical fire.

Why is there no "OFF" position on this electric baseboard heater thermostat?

I have a single pole wall-mounted thermostat for an electric baseboard heater 240 V the thermostat shows high and low but does not show off does this mean that voltage is always going to the baseboard

On 2020-12-27 by Roy

Answer by (mod) -

Roy

Typically the way that thermostat is wired, voltage is brought from the circuit breaker in the electrical panel directly to the electric baseboard heater;

There in the heater the incoming "hot" wires are interrupted or "switched" by the thermostat connections.

So in a sense, there is voltage at the connections at one end of your electric baseboard heater, but the actual heating element is not being sent voltage unless the thermostat decides that there is a call for heat.

When the thermostat is set to LO, the thermostat will not call for heat until the room temperature falls below a certain number, for example, 60 degF; the actual "LO" cut-on temperature varies depending on the specific thermostat brand and model.

That information may be found in the owners or installation manual for your specific thermostat brand and model.

Is the inability to turn "off" electric heat at a Stelpro Z-Wave thermostat a code violation?

Looking at a Z-Wave line voltage thermostat Stelpro STZW402+ (It's the only Z-Wave line voltage model I have found).

The only thing that bothers me is that it has a low setting of like 40 degrees F and no actual 'OFF' mode.

I would think that the inability to turn heat off at the thermostat would be some kind of code violation.

I understand the idea of freeze guard, but it just doesn't sit well that a 240v thermostat can't be fully turned off without turning it off at the circuit breaker. Any thoughts? On 2016-09-08 by Leo F

Answer by (mod) -

For other readers, the Stelpro is a line-voltage 120/240V thermostat handling 16Amp loads, suitable for electric baseboard heaters or convectors and specifically not suited for central heating nor forced air heating systems.

The user's manual discusses set point temperatures:
Temperature set points
The set point may be edited by the user using the UP and DOWN buttons located on the thermostat.
The set point may also be modified through the Z-Wave network.
The minimum set point is 5°C (41°F) and the maximum set point is 30°C (86°F).
NOTE: if the set point is set at 7°C (45°F) or below, the frost-free warning icon will be displayed to warn the user that water pipes might be subject to freezing.
...
This product can be included and operated in any Z-Wave network with other Z-Wave certified devices from other manufacturers and/or other applications.

Reading through the product user's manual I agree that it looks as if the heat is always ON at low temperatures, and specifically at temperatures below freezing the thermostat is always "ON". If, for example, this thermostat were installed to control electric heat in a building that was to be "shut down" with heat "off" in a winterized condition, you cannot turn off the heat compeltely at the thermostat.

However you can turn off your heat at the circuit breaker - just as you proposed. I imagine that this would be the company's response to a direct question about the absence of an "off" position on the thermostat itself.

Functionally this is probably fine, but technically, since circuit breakers in an electrical panel are not designed nor intended to function as a standard, frequently-operated "ON/OFF" switch, it may be a questionable design.

Unless a circuit breaker is labelled as "SWD"-rated, it is NOT intended for regular use as an on-off switch. (SWD-labelled circuit breakers are in fact designed and rated for use as control switches.) Even SWD-rated switches are not intended for very frequent on-off cycling (thousands of times vs. tens of times).

MIke Holt's Electrical Forum discusses the NEC and provides this helpful description of circuit breakers and SWD ratings:

Brittian, L.W., "Circuit Breakers", [web article], L. W. Brittian, Mechanical-Electrical Instructor, lwbrittian@hot1.net retrieved 2016/09/08, original source: https://www.mikeholt.com/mojonewsarchive/NEC-HTML/HTML/ElectricalCircuitBreakers~20020419.htm

Stelpro can be contacted at
E-mail: contact@stelpro.com
Website: www.stelpro.com

 

What size electric wire do I use to wire a line voltage thermostat? Is it single pole?

What size wire do I need to wire a wall thermostat to replace an on heater control thermostat It`s a single pole line ? On 2020-04-03 by Ken Killam

Answer by (mod) - match the heater's wires

Ken

If your wall thermostat is directly switching a 120VAC or 240VAC Electric baseboard heater you'd use the same gauge wire as powers the heater - e.g. #12 wire for a 20A circuit (check your heater circuit and breaker or fuse and specs) or a #10 copper wire on a 30A circuit.

 

Line voltage thermostats set the baseboard to half-power?

Does a line voltage thermostat ever turn on the baseboard to half power? On 2022-01-16 by Anonymous -

Reply by Inspectapedia Com Moderator - No, line voltage thermostat turns electric heat on or off

@Anonymous,

I'm not sure if I understand the question but a line voltage thermostat will basically turn the electric heat on or off.

I wouldn't expect it to change the voltage or power level.

Electric Heat / A/C Line Voltage Thermostat Identification, Selection & Wiring FAQs

How do I wire up a Val6 MPX diesel fueled heater?

I have a Val6 MPX diesel heater. It has a connection on it for a thermostat. The connection has 4 pins.

I have the connector to hook up to a thermostat that has the four pins to connect to. I want to use an inline 120v thermostat with this heater. I won't have it hooked up to 120volt line, just to the connector that connects to the Val6 MPX heater.

It says the inline 120v thermostat can be used with 24vac systems, as the heater is a 24vac thermostat system according to my dealer. I only have two wires coming out of the thermostat, and don't know what wires go where on the connector, as I don't know what the four pins functions are. Can anyone help me out with this?

I am totally green upon what is happening. I saw online that you could by the connector with the inline thermostat already connected to it, but since I have a half dozen of these thermostats, I thought I could do it myself. I am lost.

val6parts dot com/externalthermostatepx dot aspx is the link to the thermostat that is hooked up to the connector.

val6parts dot com/externalthermostatplug dot aspx this is the connector I purchased to hook up to my thermostat which is similar to the one they sell. Can anyone explain this to me? Totally lost! Thanks for your help! On 2022-01-11 by Jason Day

by Danjoefriedman (mod) - Contact info and technical support from VAL6 Heaters Parts & Customer Service

@Jason Day,

Apologies Jason but these parts are totally outside our expertise; I don't want to steer you wrong by guessing.

I'd start by getting a copy of the IO Manual for your Val6 MPX diesel heater as that will certainly include wiring diagrams of its control needs.

Here's the contact information

VAL6 PARTS: CUSTOMER SERVICE - Questions or help with your order
PHONE: 631-325-5555
EMAIL: orders@val6parts.com
MAIL: A1 Infrared Technologies, Inc.
PO Box 8
Eastport, NY, 11941

VAL6 HEATERS: Website
www.val6heat.com

How do I identify the type of line voltage thermostat I've got?

Hello:

is this White-Rodgers old LV thermostat dual pole? What is the model number? Thanks.

On 2021-11-10 by Gio

Is there a quick way to know the manufacturer of this LV Thermostat? Is it a dual pole thermostat? It controls a radiant heater.

Thanks

by Inspectapedia Com Moderator

@Gio,

There are several White-Rodgers line voltage thermostats that look identical but vary in support for 120V or 240V;

Try pulling the cover to see, photograph, and post a photo of any labels or stickers inside the device or on the inside of the cover, and post an additional photo of the wiring - that will tell you if it's a 2-pole thermostat.

For your second photo, that's a bit unusual: an electric heat thermostat whose numbers are on the dial rather than on the thermostat body;

Pull the cover and post a photo for us of any labels you find inside (one photo per comment) - even a patent number may be sufficient.

 

What's an updated line voltage thermostat to replace White Rogers 1A10-651 with S29-21 subbase.

Anyone know of an updated thermostat to replace White Rogers 1A10-651 with S29-21 subbase.

I have cool and heat switched manually on thermostat.

One cold water valve one hot water valve and fan all 120 volt.

3 speed fan control on the fan unit itself. On 2021-10-15 by Steve

Reply by inspectapedia.com.moderator

@Steve,

Did you look at the White Rodgers 1A10-1A16 or did you consider buying a new WR 1A10-651 - still listed by some suppliers like Supplyhouse.com ?

For other readers: we've added the IO or installation instructions for popular White Rodgers line voltage heating and cooling thermostats to LINE VOLTAGE THERMOSTATS.

 

 

 

 

Find a digital repalcement for this old Trane line voltage thermostat

I have this old TRAN heating/ cooling system with line voltage thermostat. I can’t figure out if there is a replacement for one with digital display. Do you have a suggestion? Most of Honeywell line voltage is heating only. Thanks On 2021-09-10 by Eddie

Reply by inspectapedia.com.moderator - convert line to low voltage thermostat - PECO Fan Coil Thermostat # TA180-001

@Eddie,

Peco is a source of line voltage thermostats that can control both heating and cooling equipment, like the PECO Fan Coil Thermostat # TA180-001

But let's be sure we understand accurately what's really needed. Do both your heating and cooling systems really require a line voltage thermostat?

We usually see line voltage TT where controlling electric baseboard heat but an A/C unit is usually switched by a low voltage control.

So what are we controlling here? If it's a commercial type fan coil unit then often one line voltage thermostat switches the FCU between heating and cooling.

Is your Tran [Trane?] thermostat using line voltage to control both heat and air conditioning? Or is it switching a relay that ultimately goest to 24VAC at the A/C unit?

Line Voltage Thermostats that can control heating and cooling:

The Dayton 6GVX8C or the Dayton 2NNT2 line voltage thermostats are designed to control cooling systems.

The Honeywell TL8230A1003 line voltage thermostat can control electric baseboard and fan-forced heaters in residential and light commercial settings. I'm unclear why it'd also be switching a cooling system using line voltage.

Possible alternative control scheme?

We discuss replacements for line voltage thermostats by converting to a low-voltage thermostat, e.g. using the Nest, at https://inspectapedia.com/heat/Replace-Line-Voltage-Thermostat.php CONVERT LINE to LOW VOLTAGE THERMOSTAT

It would help us research further if you'd look into your existing Trane thermostat and post a photo of its labels or ID tags, specifically its model number.

What is a compatible replacement for Honeywell TA42 thermostat

I'm looking for a compatible replacement for an old thermostat (Honeywell TA42). The thermostat controls an electric forced heat/cool connector unit - an individual thermostat for each heat/cool unit in every room.

120V, line voltage, forced air, 3-wire.

Low voltage DC rating 2 amps, 24V; 1.5 amps, 32V.

It's impossible to find someone knowledgeable that can help. Recommending a specific unit, preferably a more up-to-date one (basic, non-programmable is fine), will be much appreciated. On 2021-07-20 by PT

by mod

@PT,

There are a number of options for line voltage thermostats given in LINE VOLTAGE THERMOSTATS as well as a discussion about how to choose among them. Please take a look.

What's a replacement for a Honeywell T651-A2028 line voltage thermostat?

I have a Honeywell T651-A2028 and I want to replace it. I think it has a unique wiring setup that I cannot understand. There are 3 wires connected to it, 1 has 120v (COM) and the others have no volts (HEAT & COOL). My apartment complex has very old radiators that have constant supply of hot water in the winter and cold water in the summer.

The thermostat only controls the power to the fan at each radiator. When the apartment complex switches from hot to cold or vice versa they somehow change the wiring so the thermostat can cool or heat appropriately.

What are my options for replacements? On 2019-11-02 by DustMan

Reply by (mod) - Replacement options for a Honeywell T651-A2028 line voltage thermostat

DustMan

Thank you for a helpful question.

Please find your question repeated along with our detailed reply at LINE VOLTAGE THERMOSTATS in the section titled

Honeywell T451A, T651A, T694A,B,D,F Light Duty Line Voltage Thermostat Wiring Instructions

as those can replace your T651- series thermostat.

It would be helpful as well to see a photo of the front of your thermostat, showing its controls. I suspect from your note that the model you want is the Honeywell T694A2002

 

What thermostat can control both line voltage heat and 24VAC A/C unit switching?

i have a line voltage thermostat for my heat and 24v thermostat for my a/c unit do they make a thermostat to control both ? On 2018-04-29 by carmen

Answer by (mod) -

There is a way to use a low voltage thermostat to control both. Basically the low voltage heating system will have to talk to a separate switching relay that turns your heat on and off. We've written about this solution at LINE VOLTAGE THERMOSTATS

How do I wire the TB6575A1000/U replacement for an old line voltage thermostat ?

Trying to replace a old line voltage tstat with a TB6575A1000/U

Existing stat has to wires hot and neutral. New tstat has 7 wires and I am unsure how to wire

On 2020-11-19 by Reece

Answer by (mod) - replace a old line voltage tstat with a TB6575A1000/U

Reece

The Honeywell TB6575A thermostat comes with an instruction pamphlet that gives a table (on page 5) of wire connections to use.

If you don't have a copy of those instructions you can download it from Honeywell or from InspectApedia.com at

HONEYWELL TB6575-THERMOSTAT INSTRUCTIONS [PDF]

I agree that the table could be more clear - but if your original thermostat had just two wires, AND if it was controlling a fan coil unit (which is the purpose of this thermostat)
and if your two wires are truly

black - hot (confirm it has line voltage or 120VA )

and

white - neutral (confirm it's neutral, and not line voltage)

then according to the table on p. 5 you have a heat only (or cooling only) system and you would connect in any case

Black (line voltage) to the L (for line) terminal

White (neutral) to the N (for neutral) terminal

in the thermostat.

That table is shown above - [Click to enlarge any image]

Watch out: if you are not familiar with proper and safe electrical wiring you need to know that you're connecting line voltage 120VAC or 240VAC wires and you could be shocked or killed.

CLICK on any image to see an enlarged version on any InspectApedia.com page, including the line voltage wiring connection table I posted above.

For other readers, here is a what this Honeywell TB6575A thermostat looks like - as sold by supplyhouse.com

 

Building manager says line voltage thermostat is unique and can't be replaced with a programmable model

I want to replace my current line voltage theromostat but our building is unique and the manager says they arent exactly replaceable with new programmable models. We have radiant heating/cooling where our boiler and chiller feed into the same loop system where fans force air accross the radiators.

There is a sensor on the piping leading to the main unit of the condo that feeds the thermostat to tell it what mode to be in, heating or cooling. Apparently it is this summer/winter changeover that makes finding a replacement tough. The thermostat also controls 3 seperate fan units off 1 thermo pipe sensor. My email is blueduck3285@gmail.com 8/21/2014 Duckly

Reply:

Duckly

I don't know details about the specific installation you describe but it's a fair guess that it's not a unique design and that among the huge number of thermostats for sale (Grainger lists more than 100) there is either a suitable model or a pair of models that would suffice.

Honeywell lists at least 6 line voltage thermostats that are in the right "ballpark" for your application.

The Honeywell T4159A is for electric inductive/resistive heating.

Possibly more appropriate for your application:

The Honeywell T4051 and the Honeywell T6051 "Heavy Duty Line Voltage Thermostats are used to control fan coils, fans, motor starters, valves, contactors, and circulator motors in heating and/or cooling systems."

The Honeywell T4051 line voltage wall thermostat is shown at left.

The company also provides a Honeywell Q651 used for manual switching between two T6051 units.

It may help to point out that basically a wall thermostat is an "on-off" switch that calls for heat or calls for cooling based on room temperature.

Question: plug in themostat for a 220V AC unit

I am looking for a plug in thermostat for a 220VAC wall A/C unit. do you have any or can recommend a location to get one?

e-mail info@kevlau.com (June 13, 2014) Ray

Reply:

Ray

Take a look at room thermostats used to control electric baseboard heaters for 220/240V rated models listed at LINE VOLTAGE THERMOSTATS.

They are available at your heating supplier as well as at most building supply stores such as Home Depot. Several models are described in the article above including the plug in thermostat you asked about.

...

Continue reading at LINE VOLTAGE THERMOSTATS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see

Or see these

Recommended Articles

• CONVERT LINE to LOW VOLTAGE THERMOSTAT
• ELECTRIC BASEBOARD HEAT INSTALL
• ELECTRIC HEAT
• LINE VOLTAGE THERMOSTATS
• MANUALS & PARTS GUIDES - HVAC - home
• THERMOSTAT POWER & VOLTAGE

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LINE VOLTAGE THERMOSTAT FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HVAC THERMOSTATS

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