HoneywellYTHX9421R5101WW/U Prestige IAQ Kit with Redlink technology

For the past few years I've been looking for a full-featured Wi-Fi thermostat. I've purchased other Honeywell variations as well as the 3M-50 by 3M. These other thermostats were OK but some feature was always missing. I had avoided the Honeywell Prestige & RedLink products in the past due to cost and the extra Internet Gateway you had to purchase, but now I see extra benefits of the RedLink System and it is worth every penny. The Wireless Outdoor Sensor is a great feature and is beneficial of you have multiple stages, a heat pump, HRV, or humidifier. The system I installed this on is a single state heat/cool system with an HRV.The Good: - Nice looking display with very easy-to-use menu layout. Not quite a "Retina" display, but very good. - Advanced Setup has controls, options, and lockouts for almost every HVAC scenario you can think of. - Equipment Interface Module (EIM) installs in your utility room and can control all of your "Indoor Air Quality" devices, thus reducing the amount of wires to the thermostat and eliminates the need for other control modules on your wall. This was a must for me since I needed to control an HRV. This thermostat gives me an option to run the furnace blower when the HRV is on, which I need since my HRV is installed to my return-air ducting. - Works with Honeywell's Total Connect Comfort system, which is accessible via the web or an app on your smartphone. This system allows you to setup alerts to email you if your equipment isn't working and the temp is too high/low. - Fully Compatible with Honeywell's RedLink Product Line. - Outdoor Sensors even comes with Lithium Batteries. - Has a "Circulate" feature for the fan, which runs the fan 35% of the time. - Has the ability to switch from heat pump to emergency heat remotely.The Bad: - Is smaller than the thermostat I replaced, so I need to do some repair and painting to the wall where this unit doesn't cover. - Would be nice if there were settings to activate the HRV to control high indoor humidity in the winter. This setting is only available if you also have a humidifier in your system that is being controlled by this thermostat. - Would be nice to have a lockout for the A/C based on outdoor temperature. There is a lockout for this if you have a heat pump, but not regular A/C.I've seen other reviews claiming the difficulty of installation and setup of the Honeywell Prestige products. If you can wire a light switch or operate your smart-phone, you can handle this thermostat, just make sure you take your time and read the installation instructions. You will need some of that multi-conductor thermostat wire in order to connect the EIM to your HVAC equipment, and it helps to have a small screwdriver for those little wire terminals. It took me a couple of hours to install this thermostat, most of the time was spent mounting and wiring the EIM.

i have a 2 story house where the first floor would always be colder and the upstairs always hotter during the summer when the AC is running. this completely fixed that.I am using nearly all of the features this unit allows1.) return and supply air temperature sensors. This is awesome as it allows monitoring of the temperature rise of the furnace and the temperature drop of the AC coil. alarms levels can be set for each mode allowing the stat to inform me if there are issues of perhaps low air flow causing issues that could otherwise actually damage the HVAC system2.) controlling my whole house humidifier with window frost protection using the external outside air temp sensor. I used to have a separate humidity controller from Honeywell that allowed me to have the window frost protection and it worked perfectly. the issue was that i now had a Tstat and a Hstat next to one another which looked more unprofessional. now i have one controller.3.) controlling my new whole house dehumidifier for the fall and spring. i would have had to install a third controller to control the dehumidifier but again this Tstat can control it without issues. it can control both the humidifier and dehumidifier at the same time with a dead band in the middle so the house is always at the right level.4.) connects to two different float switches on my condensate lines. one lower on the line set is programmed to give a warning but still allow the system to run. if the condensate lines fill too much the second float switch right at the AC coil will actually disable all calls for heat, cooling, humidification, and de-humidification. that is exactly what i want as the AC, humidifier, and dehumidifier all use the same condensate lines. as i have no basement and my HVAC system is on a finished floor, this will prevent possible damage to the house in the event of a clog.5.) using the averaging feature of having two indoor air sensors to get the second floor to cool better. previously my first floor would cool to 73^f when commanded without issue, but the 2nd floor would be around 77^f. now with the averaging the first floor cools to around 72.5 and the second floor to around 73.5 which is amazing.6.) using the remote control base station. i have the remote control base station next to the couch so i can easily set the temperature, see the temp and humidity, and set temp holds etc. very nice since my main living room is on the second floor and the Tstat is otherwise installed on the 1st floor.7.) data logging. the stat records the following paramters-min/max indoor air temp-min/max indoor air humidity-min/max outdoor air temp-min/max outdoor air humidity-min/max return temp-min/max supply temp- min/max return/supply temperature differential- run times for heat and AC broken down by stageyou can see all of these things on a daily basis, weekly basis, and monthly basis. this is cool as it gives you a good idea of system performance, and to see if a multistage system is running mostly on stage 1 (which is preferred)8.) scheduling. the great thing is all 7 days can be independently set from one another. all other stats i have seen only let you net M-F as one setting and Sat-Sun as another.programming is actually very straight forward. the on screen menu literally guide you through the process and it is rather easy to understand how to answer them. yes there are a TON of settings which is great but it is easy to configure.

As many people find, our 20 year old homes are/were wired with only 5 wire thermostat wire. When replacing my HVAC system I decided on a dual stage AC and furnace. 5 wires were not enough to connect the thermostat to the furnace and AC and operate all the stages. The contractor installing the system jury rigged the 5 wires to run the two stage system (not). He did something tricky and deceptive which I won't get into here. Thankfully my father was a builder and I have a pretty good understanding of HVAC. So the issue. You have only 5 wires and need 7. This system is the answer. The ECM is awesome. I now could correctly wire both stages of the furnace and compressor. I love the return and output temp sensor. It handles drain switch without having to wire the switch in the middle of the red (hot) power supply. This really is capable of light commercial applications very feature rich.Installation- I would agree with Honeywell should normally be left to a professional if you don't have electrical experience. The installation of the ECM, airflow sensor requires you be a bit handy.After installing both the ECM, thermostat, air flow sensors, preparing the remote devices, outside temp/humidity sensor, Wan link, I power up the thermostat and EIM. The thermostat immediately went into setup and ask to press the button on the EIM to sync to it. The it ask about the outdoor sensor which was in hand and it discover it and finally ask about the Redlink WAN device, push the synch button on it and they linked up perfectly. It will take you though question of which terminals you connected the airflow sensors to. It walks you through everything. The key is to read everything up front and have all sensor ready for discovery before you power up the system. You can of course go back and configure things later, but it's so much easier with the guided setup.I have had zero problems with connections issues the Redlink protocol. Very solid.I would highly recommend this document Honeywell THX9321 & THX9421 Product Data.pdf as the definitive installation and configuration guide. I found it while researching this system before I purchased and was sooo glad, as it contains information not included with the docs shipped with the system. Without this it would have been a struggle to configure the airflow sensors properly, run diagnostics testing the sensor and the system in general.Now for what I don't like as muchseparate remote module needed for WiFi connection - Honeywell - Money grab.. so easy and cheap to include on the thermostat. A $5 chipset these days.Utilization report on the web interface.Performance and diagnostic statistics on the web interface. This is a semi-commercial thermostat after all.Integration into the same web application used by the WiFi enable thermostats. I have two Honeywell thermostats and have to use two separate application to manage them.

Product is fantastic but getting it installed was a nightmare. Our HVAC dealer wanted to charge us 5 times more for the item with installation. We tried Amazon Home installation twice one installer just said no way and left. The other quoted us a minimum of 2.4 times more for installation but said he had no maximum. He would have to go get parts one item was as simple as wire and would charge us a trip charge and hours to pick any needed parts up. I am not an electrician or an HVAC person but following the instructions and watching a couple you-tube videos I was able to install in about 20 minutes. Works perfectly, with wireless outdoor temperature and humidity, 2 duct sensors (constantly monitoring efficiency of HVAC system, and best of all the optional wireless remote so we can take it in our bedroom at night and control the temperature in the bedroom all night. We love it.

This is a great thermostat with tons of features at a killer price. Five stars for the system, one star removed due to lack of clear directions. While it is not difficult to install, the directions and schematics left a lot to be desired. There is a good bit of information online that is available, but takes some sifting through to find what you need.