Honeywell Home RTH221B1039 RTH221B Programmable Thermostat, White

Why I tried this thermostat

I wanted a straightforward, battery-powered thermostat for a single-stage gas furnace and central AC in a small rental. My wish list was modest: reliable temperature control, a simple weekly schedule, and no smart-home complexity or need for a C-wire. The Honeywell programmable thermostat (RTH221B) looked like the right fit: one identical program for all seven days, four daily periods (wake/leave/return/sleep), a basic LCD, and two AAA batteries. After several weeks of use, here’s how it fared.

Installation and setup

Installation is genuinely DIY-friendly if your system is compatible. I cut power to the furnace at the breaker, removed the old stat, and labeled the wires. The backplate on this unit is compact and mounts with two screws; wall anchors are included, though I used existing holes. Wiring is a simple terminal block with clear labels (R, W, Y, G, etc.). For a two-wire heat-only system, it’s usually just R and W. For typical forced-air heat/cool, I landed R (with the factory jumper to Rc), Y for cooling, G for the fan, and W for heat.

A few practical tips:
- Take a photo of the old wiring before you disconnect anything.
- If you have more than one stage of heat/cool, or a heat pump with auxiliary/emergency heat, this thermostat isn’t the right match.
- This unit is battery-powered and doesn’t need a C-wire, which is particularly helpful in older homes.

Initial setup took less than 20 minutes, including mounting and entering the clock settings. After powering up with two AAA batteries, I set Fahrenheit, 12-hour time, and programmed the four daily periods.

Everyday use and temperature control

For day-to-day operation, it’s about as simple as it gets. The screen shows the current temperature and setpoint, and the up/down buttons change the setpoint quickly. The system switch (Heat/Cool/Off) and fan switch (Auto/On) behave as expected. Temperature control has been stable and predictable. In my tests, room temperature stayed within about a degree of target, which lines up with the spec of ±1°F.

One limitation worth noting is that there’s no user-adjustable “swing” or cycle rate. In well-matched systems, you won’t notice. In oversized furnaces or homes with poor airflow, you could see slightly wider swings or longer run times because the thermostat can’t tune the differential. In my install, cycling felt normal—no short cycling, no obvious overshoot.

Programming and overrides

Programming is intentionally basic. You get one schedule for the entire week, with four periods per day:
- Wake
- Leave
- Return
- Sleep

For a consistent household routine, that’s often enough. For example, I set a morning warm-up, a daytime setback, a late-afternoon return temperature, and a sleep setback. If your weekday and weekend schedules differ, you’ll either compromise on a single plan or use the override features.

It supports:
- Temporary override: bump the temperature up or down and it holds until the next scheduled period.
- Permanent hold: lock the setpoint indefinitely until you turn hold off.

Those two options are all I typically need. There’s no learning algorithm, geofencing, occupancy detection, or app control—just set it and forget it. That simplicity was the point for this installation.

Display and usability trade-offs

Daytime readability is good: clear digits, sensible icons, and an uncluttered layout. The major trade-off is the lack of a backlight. In dim hallways or at night, you’ll need ambient light or a quick phone flashlight to read the screen. If that’s a deal-breaker, you’ll want to look at a model with a lit display.

Button feel is positive, and the interface is logical—system and fan switches are labeled plainly; “Set” walks you through programming in a predictable sequence. There’s no fancy UI, but that also means less to mis-tap or misconfigure.

Compatibility: what it works with and what it doesn’t

This thermostat is made for:
- Single-stage heating (e.g., conventional gas furnace)
- Single-stage cooling (central AC)
- Single-stage heat pumps without auxiliary or emergency heat

It is not for:
- Electric baseboard or line-voltage systems (120–240 V)
- Multi-stage heat or cool
- Heat pumps with auxiliary/emergency heat
- Systems requiring a common wire for power (this unit is battery-powered instead)

If you’re unsure, check your existing thermostat terminals. Labels like W2, Aux, or E usually indicate auxiliary/emergency heat (not supported here). Multiple Y or W stages (Y2, W2) indicate multi-stage equipment (also not supported). When in doubt, consult your equipment manual or a pro—this saves time and avoids returns.

Power, batteries, and outages

Two AAA batteries power the thermostat. There’s a low-battery reminder, and replacing them is quick. Because it’s battery-driven, it doesn’t rely on a C-wire and it retains your schedule and setpoints during a power outage. To be clear: if your furnace or air handler loses power, the HVAC won’t run until power is restored, but you won’t lose your programming. In my case, batteries have been stable and the unit draws very little power.

Where it fits and where it doesn’t

This is a practical choice for:
- Homes with a single-stage furnace/AC where occupants prefer a simple, reliable controller.
- Rentals and secondary properties where ease of use matters more than remote access.
- Older systems missing a C-wire.
- Users who keep a consistent daily routine and can benefit from a one-week schedule.

It’s not ideal if you want:
- Separate weekday/weekend schedules or day-by-day customization.
- A backlit screen for nighttime readability.
- Wi‑Fi, app control, or voice assistant integration.
- Fine-grained control over cycle rate or temperature differential.
- Compatibility with multi-stage equipment or heat pumps with auxiliary heat.

Performance notes and small quirks

• Temperature stability has been solid in a modest-sized home with decent ductwork. If your system is oversized, you might see a bit more swing due to the lack of adjustable differential.
• The interface avoids hidden menus. That’s a plus for simplicity, but it also means there’s no advanced tuning. What you see is what you get.
• The “one week” program is both its biggest limitation and its charm. For households with unpredictable schedules, frequent manual overrides are likely. For steady routines, it just works.

Alternatives to consider

If you like the overall simplicity but need a backlight or separate weekday/weekend schedules, consider stepping up within Honeywell’s non-connected lineup or comparable models from other brands that add a 5-2 day schedule and a lit display. If remote control and energy reports appeal to you, a basic smart thermostat with Wi‑Fi may be a better long-term fit—just confirm you have a C-wire or a compatible power adapter. For line-voltage baseboard heat, you’ll need a dedicated line-voltage thermostat; this model won’t apply.

Final recommendation

I recommend this Honeywell programmable thermostat (RTH221B) for basic, single-stage systems where simplicity, reliability, and low cost matter more than advanced features. It installs easily, keeps temperature on target, and offers just enough scheduling to save energy in homes with consistent routines. The lack of a backlight and the single weekly program are the main drawbacks; if either is a priority, look at a step-up model. For the right system and user, though, this is a dependable, hassle-free controller that does its job without drama.