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Your cart is empty.Compatible with 2- and 3-wire thermostat, this all-in-one relay includes a built-in 24 V transformer.
Big Ben
Reviewed in Canada on March 8, 2025
Commandé 4 unité pour un projet spécifique relié aux thermostat intelligent . Exellent produits je le recommande
Golden Charcoal
Reviewed in Canada on February 19, 2025
The Honeywell RC840T-120 Electromechanical Relay is a high-quality solution for controlling electric baseboard heaters, convectors, and fan-forced heaters. Featuring a built-in transformer, it seamlessly connects low-voltage thermostats to high-voltage heating systems, ensuring efficient and consistent operation. Designed for 120V applications, this relay provides quiet switching and reliable performance, reducing electrical noise and wear. Its compact and durable construction makes installation easy in residential and commercial settings. Users appreciate its efficiency, ease of wiring, and compatibility with various heating systems, making it a trusted choice for temperature control solutions.
Colorado Jim
Reviewed in the United States on December 28, 2024
I used this on a Dayton tube heater that needed a line voltage thermostat. I don’t like line voltage thermostats so I use this instead.This takes the place of your 24VAC transformer and a (120VAC) contactor to turn the heating unit on and off. I used a simple two wire thermostat with this product.Highly recommend
Antonino Mazzurco
Reviewed in the United States on November 9, 2024
Use it to convert my high voltage thermostat to low voltage to install Amazon thermostat works perfect
Spectra Research/ bp Design
Reviewed in the United States on October 24, 2024
This product enable you to update older, high voltage, cooling system, and heating system to modern low voltage controllers
Customer
Reviewed in Canada on January 25, 2024
I used this device to connect a Google thermostat to an electric resistance heater.
Daniel J MacArthur
Reviewed in the United States on June 18, 2023
EDIT: this RC840T-120 works well, no overheating. Have tested with 15A 120V heater with 1400W showing at the kill-a-watt.Using a multimeter, there is 5.6VAC at red LOAD wire, even when thermostat is OFF.Apparently this might be normal OFF voltage, as the other model RC850 manual indicates that the OFF voltage should be So if 5.6V is above the breakdown resistance of the resistor (I think yes for most heaters as it's just a very simple wire?), you will consume 3.6W all the time, even when heater off. Which is 31kWh per year about 50c. I can't tell with the kill-a-watt as the kill-a-watt does not turn on.I use a switch in line, so I can turn off the whole system during the summer. Use gray for that switch and the outlet so it's clear that it's not a normal outlet.It DOES work very easily. Just add black (C common) white (W) & red (R) small wires (I used 14Ga stranded) and join the white and red for the heater to be on.My opinion: DON'T buy a return. Get a NEW one. The "very good" return I was sent did NOT work. The NEW one works great.NO excess heat when running a 15A 120V heater. I have seen more excess heat from a GE extension cord when running 15A than from this. A+++ on the excess heat issue, which is an important issue for me.The other kind of in-line thermostats seem to suffer a lot from excess heat issues (unless people are just wiring the 240V versions wrong, which might be the case. I saw one video where a guy was referring to one of the wires as "neutral")I use another 4 square metal box for it. I don't just hang it off the side of a 4 square box. So I have a 2 gang box with a light switch on the left and a blank on the right and then I have another 2 gang box above that with a blank plate over it, just for this thing and a couple of connections. Although I partly did that because I was anticipating excess heat because you can't even buy an extension cord these days that is rated for 15A that doesn't have excess heat. But there was no excess heat so maybe the hanging it off the side of 4 square box method is OK.Power is proportional to V squared at constant R, so if I was running a pure resistive load, it would consume 0.24% of full power all the time. So 1.5kW resistive heater would consume 3.6W all the time. "if my calculations are correct"For scale, you lose 0.76W in a 2A resistive fuse. So this power loss is like the power loss in 5 fuses.22A rating is good
LowJack
Reviewed in the United States on December 27, 2023
I had a simple 120v contractor controlling my 240v heating units on the main floor. I wanted to add a smart Google thermostat to control the system. I needed a 24v thermostat interface to a 120V switch that could control the contractor. This unit was made to order for my application. Know your system or talk to someone who knows electrical wiring before you order and save the lost time returning items....j
John Duval
Reviewed in the United States on February 16, 2022
This is 220v only. It allows using any smart thermostat with a 220v system. You must have 3 wires so that you have 220v available whether the circuit is actuated or not. My install was a retrofit to replace an old 220v Honeywell mechanical thermostat with a T9. I had 2 wires that read 220v across when open. I found an adjacent light switch where I measured 220v between one of the heating legs and the hot leg of the switch, and connected the blue wire to that. My only complaints are that the locknut attaching it to the box loosened if I even breathed on it, and even mounted outside the box it still made things a bit tight inside the box.
Mike McLean
Reviewed in Canada on November 26, 2022
I will be using this to turn on the pump for a single zone radiant floor manifold.
Mike Carver
Reviewed in Canada on April 11, 2022
I purchased this relay to operate an electric fireplace using an old programmable thermostat I had laying around. Works like a charm. The selenoid in the relay is audible but not intrusive.
William Davidson
Reviewed in the United States on September 20, 2019
This has been working very well for me and was easy to install with the instructions. You should have electrical building experience to install it though. It is installed to a 1900 junction box in my attic and the thermostat wire is ran from the relay down to the Nest thermostat in the bathroom. The Nest thermostat gets the right low voltage to operate and will request the 120 volt circuit to complete through the relay when it calls for heat. The heater is 700 watts. You can schedule the Nest when to call for heat, along with all the Nest options. I'm very happy to have found this relay it was the perfect match and cost for my project. P.S. This is a real review from a real home owner... I will check this review for any questions..
Jeff M
Reviewed in the United States on October 16, 2017
I used this to connect two that were previously connected to a traditional line voltage wall thermostat (in a 1 gang switch box) to a .For installation, I broke out the legacy plastic box which contained the feeder wire and the wire going to the two heaters. Once the legacy single-gang plastic electrical box was removed, I replaced it with a with the RC840T-120 installed thru the 1/2 inch knock out. I connected the thermostat wire prior to inserting it into the hole in the wall, and ran the thermostat wire out of the wall for easy access later. I placed a blank metal face plate over the single-gang metal handy box, after making all my high voltage connections inside the box per the instructions provided. I connected the thermostat wire to the Nest E, configured it, and now I'm able to control my electric baseboards using the Nest app. The nest came with a wall plate that covered everything over nicely.NOTE: If you aren't comfortable with installation of this device, you should definitely contact a licensed electrician. You will be working with both high and low voltage.
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