Smart thermostat guide
Honeywell Home X2P Programmable Thermostat RTH20B (White)
Single-stage 1 heat/1 cool systems where Wi-Fi is not needed
A programmable thermostat that runs on two AA batteries, not included. It handles 1 heat/1 cool systems, hot water and forced air, not line voltage baseboards. The guide limits the RTH20B to a 5-2 schedule while Honeywell's spec table lists more options, and the warranty is one year limited.
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Published specifications
- Maker: 1 heat/1 cool conventional or heat pump; 750 mV; hot water; forced air
- Maker and guide: powered by 2 AA alkaline batteries (not included)
- Guide: RTH20B schedule 5-2 only, 4 periods a day, or off
- Guide: heat pumps 1 compressor stage; electric backup only where backup is used
- Maker: 3.44 x 5.13 x 1.188 in; UWP wall plate; backlit LCD
- Guide and maker: 1-year limited warranty
Fit and limits
Strengths
- Runs on AA batteries, so no C wire is described for this model
- Extended 32°F minimum heat setpoint, per guide and maker page
- Guide and maker page agree on single-stage 1 heat/1 cool compatibility
Caveats
- Schedule conflict: guide says 5-2 only; maker spec table lists 7-day too
- No Wi-Fi or remote control described for this model
- 750 mV claim appears on the maker page but not in the guide pages we read
What the X2P RTH20B is, and what it is not
The X2P RTH20B is a Honeywell Home programmable thermostat for one-heat, one-cool systems. The guide shows Mode, Menu and Fan controls, and Honeywell lists a backlit display. Neither Honeywell's product page nor the guide pages we read describe Wi-Fi or app control for this model. Honeywell's page shows SKU RTH20B/U; the listing's model and part number is RTH20B.
The guide covers three X2P versions: RTH20B and RTH21B, both for 1 heat/1 cool, and RTH22B, rated up to 2 heat/2 cool conventional or 2 heat/1 cool heat pump. This page is about the RTH20B only. The guide lists a replacement accent piece in the package for the RTH21B and RTH22B, not the RTH20B.
Power: two AA batteries, not included
Honeywell's page says the X2P runs on 2 AA batteries that are not included, and the listing repeats that. The guide's installation section calls for two AA alkaline batteries. A text search of the English guide pages we read found no mention of a C wire for this model.
The guide covers battery changes. It lists alert 405 for low batteries and 407 for critically low batteries, and its troubleshooting section says a blank display means you should check for fresh AA batteries. Battery replacement, as the guide describes it, involves pulling the thermostat off its mount.
Compatible systems, and the 750 mV claim
Honeywell's product page lists compatibility as 1 heat/1 cool, 750 mV, hot water heat and forced air, and says it does not work with electric baseboard heat at 120-240 V. The guide says it will not work with a line voltage system, and describes the signs of one: thick black wires with wire nuts, or an old thermostat rated 120 V or more.
The 750 mV compatibility appears on Honeywell's page and in the listing, but a search of the English guide pages we read found no mention of millivolt systems. If you are replacing a millivolt control, confirm with Honeywell before relying on it. We do not give wiring steps here; follow the guide or a qualified installer.
Heat pumps: limited support on this version
Honeywell's specifications list 1 heat/1 cool heat pump systems alongside conventional ones. The guide's installer settings say only one compressor stage is available on the RTH20B and RTH21B, and that heat pumps support only one stage. It lists backup heat stages only for the RTH21B and RTH22B, not the RTH20B.
Where backup heat is used, the guide says this thermostat only supports electric backup heat, and should not be used if your heat pump has a gas or oil backup heat source. Honeywell's page lists heat, off, cool and auto modes for this SKU; the guide's mode list adds emergency heat and says the available modes vary by model.
The schedule: two maker statements that disagree
The guide says the RTH20B only has the 5-2 day setting, with four periods a day, or scheduling switched off. Honeywell's features text and the listing also describe 5-2 or no schedule. Honeywell's specification table for the same SKU lists 7-day, 5-1-1, 5-2 and 1-week programming. The two statements conflict, so confirm with Honeywell if you need anything other than 5-2.
Other settings in the guide include a minimum heat setpoint from 32°F to 50°F with a 40°F default and a frozen-pipe warning, filter reminders by run time or calendar time, fan Auto, On or Circulate (about 33 percent of the time), and Smart Response.
Warranty and remaining figures
The guide states a 1-year limited warranty and points to resideo.info/US-Warranty-THERMOSTAT for the terms; it also says Resideo Customer Care at 1-800-633-3991 will mail a printed copy free of charge. Honeywell's product page lists the warranty as 1 year limited, and the listing bullet also says 1-year warranty.
We did not read the full written warranty, so check it before relying on details such as coverage of batteries or reinstallation. The guide's setpoint ranges are 32°F to 90°F for heat and 50°F to 99°F for cool, and Honeywell lists the thermostat at 3.44 x 5.13 x 1.188 inches.
Check the current listing
Confirm the model, included parts and availability before ordering.
Primary sources
- Honeywell Home X2P Programmable Thermostat product page and specifications (SKU RTH20B/U)
- X2P Programmable Thermostat Installation and User Guide 33-00688ES-01 (listing-supplied PDF)
Primary sources checked .
Compare with
- Sensi Smart Thermostat ST55
Conventional or heat pump systems up to two stages, on a 2.4GHz network, in the old thermostat's footprint
- Google Nest Thermostat (Charcoal)
Single-stage 24V systems that need a schedule and app control, not multi-stage equipment
- Mysa Smart Thermostat V2 for Electric Baseboard Heaters (BB.2.0.01.NA-US)
120V or 240V electric baseboard, fan-forced convector and radiant ceiling heat in a standard gang box
- ecobee Smart Thermostat Premium with SmartSensor
24 VAC forced-air, heat pump, boiler or PTAC systems, checked first with ecobee's compatibility tool
- Google Nest Learning Thermostat (4th gen) with Nest Temperature Sensor (2nd gen)
Multi-stage 24V systems run through the Google Home app, in homes with or without a C wire
- ecobee Smart Thermostat Essential (EB-STATE7-01)
Simple single-transformer systems with one stage of cooling, on a 2.4GHz network
Side-by-side pages, this model next to: Honeywell Home X2S Smart Wi-Fi Thermostat RTH2SMC/N (White), Honeywell Home X8S Smart Thermostat X8VMC8B (Black, no sensor).