Honeywell RC840T-240/U Electro...
IN STOCK (leaves warehouse same day if ordered before 3pm ET)
$182.27
$140.76
Honeywell RC840T-240/U Electromechanical heating relay with a 24V - 208/240V transformer

Honeywell RC840T-240/U Electromechanical Heating Relay with Built-in 24V-208/240V Transformer

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Model: RC840T-240/U
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In Stock (leaves warehouse same day if ordered before 3pm ET)

$182.27
$140.76
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Honeywell RC840T-240/U Electromechanical Heating Relay with Built-in 24V-208/240V Transformer

Professional HVAC Control with Integrated Transformer

The Honeywell RC840T-240/U electromechanical heating relay delivers reliable line voltage load control from low voltage thermostats with an integrated 24V-208/240V transformer. This professional-grade relay features epoxy-soundproofed construction for quiet operation, terminal board connections for easy installation, and compatibility with both 2-wire (R,W) and 3-wire (R,W,C) thermostat connections. Designed for direct replacement of any brand name relay, it provides immediate activation for improved temperature control and comfort.

Professional Features & Benefits

  • Built-in 24V Transformer: Eliminates need for separate transformer installation, simplifying wiring and reducing installation time
  • Low Current Consumption (40 mA/1.2 VA): Allows multiple relays to be controlled by a single thermostat for zone control applications
  • Epoxy-Soundproofed Relay: Ensures quiet operation in residential and commercial environments
  • Terminal Board Connections: Enables easy installation and secure wire termination up to 12 AWG
  • High Electrical Ratings: Handles up to 1.5 HP @ 240 Vac and 13 A @ 208 Vac for demanding heating loads
  • UL and CUL Approved: Meets North American safety standards for professional HVAC installations
  • Universal Compatibility: Direct replacement for any brand name relay with 2-wire or 3-wire thermostat connections

Technical Specifications

  • Application: Control a line voltage resistive load from a low voltage thermostat
  • Approvals Canadian Underwriters Laboratories Inc : Approved
  • Approvals Underwriters Laboratories Inc : Approved
  • Comments: Compatible with 24 V thermostats with 2-wire connections (R, W) or 3-wire connections (R, W, C)
  • Control Signal: 24V/40 mA/1.2 VA
  • Dimensions In : 3-7/32 in. wide x 2-9/32 in. high x 1-13/32 in. deep
  • Dimensions Mm : 82 mm wide x 68 mm high x 36 mm deep
  • Electrical Ratings: Inductive Load-- 1.0 HP @ 208 Vac, 1.5 HP @ 240 Vac, At full load-- 13 A @ 208 Vac, 12 A @ 240 Vac,
  • Frequency: 60 Hz
  • Includes: Lock-nut
  • Input Voltage: 208 Vac; 240 Vac
  • Item Type: Product
  • Operating Humidity Range Rh : 0 to 95% RH, non-condensing
  • Shipping And Storage Temperature Range C : -40 C to 80 C
  • Shipping And Storage Temperature Range F : -40 F to 175 F
  • Switching: On/Off switching
  • Temperature Ratings C : -20 C to 60 C
  • Temperature Ratings F : -4 F to 140 F
  • Terminal Wire Size: 12 AWG
  • Transformer: 22 A @ 208/240 Vac
  • Used With: TH140-28-01-B; TH135-01-B; TH114-A-024T; TH115-A-024T
  • Weight G : 326 g
  • Weight Oz : 11.5 oz

Professional Applications

  • Residential heating system control
  • Commercial HVAC installations
  • Multi-zone heating control systems
  • Retrofit and replacement applications
  • Electric baseboard and unit heater control
  • Professional service and maintenance

Why Choose Honeywell Quality?

Honeywell heating relays deliver proven reliability with UL and CUL approvals for professional HVAC applications. The robust construction withstands operating temperatures from -4�F to 140�F and humidity up to 95% RH non-condensing, ensuring dependable performance in demanding environments. Backed by Honeywell's commitment to quality and compatible with leading thermostat models for versatile installation flexibility.

Manufacturer Resources

Product Specs

Application:
Control a line voltage resistive load from a low voltage thermostat
Approvals Canadian Underwriters Laboratories Inc :
Approved
Approvals Underwriters Laboratories Inc :
Approved
Control Signal:
24V/40 mA/1.2 VA
Dimensions In :
3-7/32 in. wide x 2-9/32 in. high x 1-13/32 in. deep
Dimensions Mm :
82 mm wide x 68 mm high x 36 mm deep
Electrical Ratings:
Inductive Load-- 1.0 HP @ 208 Vac, 1.5 HP @ 240 Vac, At full load-- 13 A @ 208 Vac, 12 A @ 240 Vac,
Frequency:
60 Hz
Includes:
Lock-nut
Input Voltage:
208 Vac; 240 Vac
Item Type:
Product
Operating Humidity Range Rh :
0 to 95% RH, non-condensing
Shipping And Storage Temperature Range C :
-40 C to 80 C
Shipping And Storage Temperature Range F :
-40 F to 175 F
Switching:
On/Off switching
Temperature Ratings C :
-20 C to 60 C
Temperature Ratings F :
-4 F to 140 F
Terminal Wire Size:
12 AWG
Transformer:
22 A @ 208/240 Vac
Used With:
TH140-28-01-B; TH135-01-B; TH114-A-024T; TH115-A-024T
Weight G :
326 g
Weight Oz :
11.5 oz

Honeywell RC840T-240/U – Frequently Asked Questions

1) Will the Honeywell RC840T-240/U work on a 208V circuit, or is it 240V only?
Both. The RC840T-240/U heating relay takes 208 Vac or 240 Vac line input at 60 Hz. Load capacity changes with the voltage: 13 A at 208 Vac and 12 A at 240 Vac at full load, or 1.0 HP at 208 Vac and 1.5 HP at 240 Vac on an inductive load. Size the heater to the voltage you actually have at the panel, not to the higher of the two numbers.
2) Do I need a separate 24V transformer with the Honeywell RC840T-240/U?
No. The transformer is built into the RC840T-240/U, rated 22 A at 208/240 Vac, so it powers the thermostat off the same line feed running the relay. That is one less component in the can and no separate 24V supply to mount, fuse, or find room for.
3) Can I run this Honeywell heating relay from a 2-wire thermostat, or does it need a C wire?
Either works. The RC840T-240/U accepts 24 V thermostats wired 2-wire (R, W) or 3-wire (R, W, C). If you are replacing an old mechanical stat on two wires you can leave the wiring as-is; if you are putting in an electronic stat that wants a common, the C terminal is there.
4) Will this relay fit in my existing heater junction box?
The RC840T-240/U measures 3-7/32 in. wide x 2-9/32 in. high x 1-13/32 in. deep (82 x 68 x 36 mm), and it ships with a lock-nut for mounting. Check the depth against the box you are putting it in before you pull the old one out. It weighs 11.5 oz (326 g).
5) Can I use this relay to run a heat pump compressor or a condensing unit?
No. The RC840T-240/U is built to control a line voltage resistive load from a low voltage thermostat, on/off switching only, which means electric baseboard, unit heaters, and similar straight resistance heat. It has no staging, no time delay, and no compressor protection. For a compressor or a multi-stage system you want a proper contactor or a control board, not this relay.
6) Will the RC840T-240/U replace another brand of heating relay in an existing install?
It is built as a direct replacement for any brand name relay running 2-wire or 3-wire 24 V thermostat connections, and the terminal board makes rewiring straightforward. The two things to verify on a swap are that the old relay was on 208 or 240 Vac and that the existing load is inside 13 A at 208 Vac or 12 A at 240 Vac.
7) How many RC840T relays can one thermostat drive for multi-zone electric heat?
The control signal draw is low, 24V at 40 mA / 1.2 VA per relay, which is what lets several RC840T-240/U relays sit on one 24 V thermostat for zoning a run of baseboard or unit heaters. Add up the VA of every relay on the stat and keep it inside the thermostat's switching rating.
8) Which Honeywell thermostats are matched to the RC840T-240/U relay?
Honeywell lists the RC840T-240/U as used with the TH140-28-01-B, TH135-01-B, TH114-A-024T and TH115-A-024T. Any of those pairs directly. It is not limited to them, since the relay takes any 24 V stat on R/W or R/W/C, but those are the confirmed matches.
9) What size wire will the terminals on the Honeywell RC840T-240/U take?
Terminals on the RC840T-240/U are rated to 12 AWG. That covers a 20 A branch circuit landing directly on the relay board. If your heater feed is larger than 12 AWG, you will need to transition it in the box rather than land it on the relay.
10) Is the Honeywell RC840T-240/U UL listed for commercial work?
Approved by both Underwriters Laboratories and Canadian Underwriters Laboratories, so it clears inspection on either side of the border for commercial HVAC installs.
11) Can the RC840T-240/U be mounted in an unheated space like an attic or garage?
Operating range on the RC840T-240/U is -4 F to 140 F (-20 C to 60 C) with humidity 0 to 95% RH non-condensing, so an unconditioned attic, crawlspace, or garage is within spec as long as it stays inside that band and does not condense. Storage and shipping tolerate more, -40 F to 175 F.
12) Is this heating relay quiet enough to mount near an occupied room?
The relay in the RC840T-240/U is epoxy-soundproofed specifically to cut the click and hum, which is why it turns up in apartments and hotel rooms where the relay ends up on the other side of a wall from a bed. Standard open-frame relays are noticeably louder in that spot.
13) What is the exact part number to order for the Honeywell 24V to 208/240V heating relay with transformer?
Honeywell RC840T-240/U is the full designation, and it is the model as well as the MPN, so there are no suffixes or options to pick. Standardizing a building on one number matters here because the 208 and 240 versions of these relays look alike on the shelf.
How fast can I get the Honeywell RC840T-240/U delivered?
Most orders ship the same day from our distribution partners, with quick delivery throughout the continental U.S. Need it urgently? Contact Us for expedited shipping options.
Can I return it if it doesn’t work for me?
Yes—ZenSupply offers a hassle-free return policy. If the product isn’t the right fit, reach out to our support team for a return authorization or setup a return by following our return instructions.
Does the Honeywell RC840T-240/U come with a warranty?
Absolutely. The Honeywell RC840T-240/U is backed by a manufacturer’s warranty. For full warranty terms, check the product documentation or Contact Us.
How do I get technical support or installation help for the Honeywell RC840T-240/U?
You can call, text, or email our expert support team for fast answers. We’re here to help with product selection, installation tips, and troubleshooting. Contact Us
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