There’s a specific, unwelcome shock that can ruin a perfectly good morning: the first step out of a warm bed onto an ice-cold bathroom floor. For years, this was my reality. We invested in a beautiful radiant floor heating system during a renovation, envisioning a spa-like experience of consistent, gentle warmth underfoot. The reality, however, was a clunky, unreliable thermostat that either turned the floor into a lukewarm slab or a surface hot enough to cook on. It lacked precision, it lacked scheduling, and it robbed us of the very luxury we had paid for. The problem isn’t just about comfort; it’s about efficiency and control. Without a dedicated, intelligent controller, a radiant heat system is like a sports car stuck in first gear—full of potential but ultimately frustrating. This quest for the perfect balance of comfort, safety, and control is what led us to rigorously test the Honeywell TH115-AF-GA/U Programmable Thermostat with Floor Sensor.
- Brand: Honeywell
- Product number: TH115-AF-GA
What to Consider Before Buying a Programmable Thermostat for Radiant Heating
A programmable thermostat for radiant floors is more than just an item; it’s the key solution for unlocking the full potential of your underfloor heating. It acts as the brain of the operation, ensuring you get targeted warmth precisely when you need it, which translates directly into lower energy bills and a higher level of personal comfort. Unlike standard thermostats that only read the air temperature, these specialized units use a floor sensor to measure the actual surface temperature, providing a far more accurate and pleasant heating experience. They solve the problem of energy waste by allowing you to program lower temperatures during times you’re asleep or away from home, and automatically ramping up the heat just before you wake up or return.
The ideal customer for this type of product is a homeowner who has installed or is planning to install an electric radiant floor heating system, typically in a bathroom, kitchen, or basement. They are looking for granular control over their comfort and are conscious of energy consumption. It’s perfect for DIY renovators who understand line-voltage wiring or those working with a contractor on a new build. However, this thermostat is not suitable for everyone. If you have a standard forced-air furnace, a hydronic (hot water) system, or a heat pump, this line-voltage unit is incompatible. For those systems, you would need a low-voltage programmable thermostat, like the LUX LTX9100U.
Before investing, consider these crucial points in detail:
- Voltage & Wattage Compatibility: This is non-negotiable. The Honeywell TH115-AF-GA/U is designed for line-voltage systems (120/240V) and can handle up to 3600 watts. You must confirm that your heating system’s electrical requirements match these specifications precisely. Mismatching voltage is a serious fire hazard and will destroy the thermostat and potentially the heating system itself.
- Control Modes & Sensor Type: A key feature of a quality radiant heat thermostat is its ability to use different control modes. This unit offers ambient air sensing, direct floor temperature sensing, and a combination mode that targets an air temperature with a floor temperature limit. This third mode is often the most desirable, preventing overheating while ensuring the room is comfortable. Ensure the thermostat includes a floor sensor, as this is critical for proper operation.
- Safety Features (GFCI): Because radiant floor heating is often installed in bathrooms and kitchens, a Ground Fault Circuit Interrupter (GFCI) is an essential safety feature. The TH115-AF-GA/U has one built-in, which protects against electric shock hazards. While this is a huge plus, you should also be aware of the component’s potential lifespan and reliability, which we will discuss in depth.
- Programmability & Ease of Use: Look for a 7-day programmable schedule if your weekday and weekend routines differ. This allows for maximum efficiency. The interface should also be intuitive. A clear, backlit screen and straightforward buttons are far more important than a suite of confusing smart features you may never use.
Keeping these factors in mind, the Honeywell TH115-AF-GA/U Programmable Thermostat with Floor Sensor stands out in several areas. You can explore its detailed specifications here.
While the Honeywell TH115-AF-GA/U Programmable Thermostat with Floor Sensor is an excellent choice for its specific application, it’s always wise to see how it fits within the larger world of programmable technology. For a broader look at how programming brings intelligence to everyday devices, we highly recommend checking out our complete, in-depth guide:
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First Impressions: A Purpose-Built Controller
Unboxing the Honeywell TH115-AF-GA/U Programmable Thermostat with Floor Sensor reveals a device that is functional and purpose-built. There are no flashy design elements here; it’s a clean, white rectangular unit made of hard plastic that feels sturdy enough for its job. The packaging is straightforward, containing the thermostat itself, a coiled 15-foot floor sensor wire, wire nuts, and a detailed instruction manual. The main unit separates into two pieces: the programming interface and the power base with the GFCI components and wiring pigtails. The wires are clearly labeled (L1/L2 for Line and Load), which is a crucial detail for ensuring a correct and safe installation. The 1.5-inch digital display is recessed, and while not large, it’s clear and the backlight is bright and effective. The buttons for programming have a satisfying, tactile click. Compared to more modern, sleek smart thermostats, it looks a bit dated, but for a utility device designed to do one job well, its design is logical and unintimidating.
Key Benefits
- Flexible 7-day programmability for custom heating schedules.
- Three distinct control modes (Ambient, Floor, Ambient with Floor Limit) offer precision comfort.
- Integrated GFCI provides essential electrical safety for wet areas.
- Dual voltage (120/240V) compatibility makes it versatile for different heating systems.
- Clear backlit display is easy to read in low light.
Potential Drawbacks
- Numerous user reports suggest potential long-term reliability issues with the GFCI unit.
- Audible click from the internal relay can be noticeable in quiet environments.
- Lacks modern smart home integration features.
A Deep Dive into the Honeywell TH115-AF-GA/U’s Performance
A thermostat’s true worth is only revealed after it’s been wired in, programmed, and lived with through chilly mornings and cold nights. We put the Honeywell TH115-AF-GA/U Programmable Thermostat with Floor Sensor through its paces, focusing on the entire user experience from installation to daily life. Our in-depth evaluation focused on the critical aspects that determine whether this device is a reliable partner in home comfort or a source of frustration.
Installation and Wiring: A Straightforward Process for the Confident DIYer
Installing a line-voltage device requires care and a healthy respect for electricity. That said, we found the installation process for the Honeywell TH115-AF-GA/U to be remarkably straightforward, assuming a basic understanding of home wiring. The instruction manual is clear, with diagrams that are easy to follow. The unit features a four-wire, dual-pole (DPST) setup, and the wires are pre-stripped and clearly labeled, which significantly reduces the chance of error. One of the most common uses for this thermostat is as a replacement for an older, failed unit. We found this to be a simple swap in most cases. As one user noted when replacing an 8-year-old Warmly Yours thermostat, it was an “exact fit” even though the wire positions had changed slightly. This is a common occurrence as models evolve, but the clear labeling on the new unit made it a “non-issue.”
Another user, replacing an older model with the part number PB112B-120GB, found this new PB112D-GA model to be a compatible successor. They were concerned about needing to add a resistor for their existing floor probe but found it worked perfectly out of the box, showing the correct temperature immediately. This backward compatibility is a huge advantage for those not wanting to rip up tile to replace a floor sensor. The process involves turning off the power at the breaker, connecting the line wires from the panel to the thermostat’s ‘LINE’ leads, and the heating system wires to the ‘LOAD’ leads. The floor sensor connects to two dedicated, low-voltage screw terminals. The power base mounts securely to a standard electrical box, and the main display unit then snaps firmly into place. While the process is manageable for an experienced DIYer, we always recommend hiring a licensed electrician, as one user wisely did, to ensure everything is done safely and to code.
Programming and Daily Use: Precision Control at Your Fingertips
Once installed, programming the thermostat is where its value truly shines. The 7-day scheduling capability allows you to set four distinct periods for each day of the week (Wake, Leave, Return, Sleep), tailoring the heating cycle perfectly to your household’s rhythm. We found the button-based interface intuitive; setting the time and then moving through each day to program the schedule took less than ten minutes. The true game-changer, however, is the choice of temperature control modes. In “F” (Floor) mode, the thermostat works to maintain a precise floor temperature, which is ideal for areas where underfoot warmth is the primary goal. In “A” (Ambient) mode, it functions like a traditional thermostat, using only the air temperature sensor. But the “A/F” (Ambient with Floor Limit) mode is the most sophisticated and useful. We set our test bathroom to a comfortable 70°F ambient temperature with a floor limit of 82°F. The system efficiently heated the room while ensuring the tile floor never became uncomfortably hot, achieving that perfect, luxurious warmth. This level of control is something simpler thermostats simply cannot offer.
During operation, the unit is mostly silent, but there is one notable exception. As confirmed by a user who called Honeywell support, the thermostat emits an audible “click” when the relay engages or disengages to turn the heating system on or off. This is the sound of a mechanical switch handling a high-amperage load, and it is technically normal for this type of device. In a bustling kitchen, it’s unnoticeable. However, in the dead of night in a quiet bedroom or ensuite bathroom, this click can be distracting for light sleepers. While not a defect, it is a characteristic worth being aware of. The fantastic programmability and control options offered by the Honeywell TH115-AF-GA/U make it a powerful tool for managing home comfort.
The Built-in GFCI: Safety Feature or Achilles’ Heel?
The inclusion of a Class A, 5mA GFCI is a critical safety feature. In environments where water and electricity are in close proximity, such as a bathroom, this is not just a nice-to-have; it’s a necessity for preventing severe electrical shock. The test and reset buttons are located on the side of the unit, and our tests showed the GFCI tripped instantly when simulated, cutting power to the floor heating system as designed. On this front, the thermostat performs its safety duty perfectly. However, the story from the field paints a more complex picture. A significant number of user reviews point to the GFCI component as the primary point of failure for the entire unit. We saw multiple reports of thermostats working flawlessly for a period—ranging from one year to several—only to fail suddenly. The common symptom described is a GFCI that trips (often after a minor power surge or brief outage) and then refuses to reset, rendering the thermostat useless. One user lamented purchasing three such units over time, all of which failed in the exact same manner. This recurring issue suggests a potential weakness in the GFCI’s electronics, perhaps a sensitivity to power fluctuations. This transforms the thermostat’s most important safety feature into its most significant reliability concern, creating a frustrating paradox for owners who are left with a non-functional heating system.
Longevity and Reliability: The 6-Year Question
Beyond the specific GFCI issue, the overall lifespan of the Honeywell TH115-AF-GA/U Programmable Thermostat with Floor Sensor is a topic of debate. One user provided a balanced perspective, noting their original unit lasted “less than 6 years.” While this is more than double the typical warranty period for such an electronic device, their feeling that “an item such as this should last longer” resonates deeply. A thermostat is a semi-permanent fixture in a home, not a disposable gadget. The expectation is that it should last for a decade or more, similar to other electrical components. The recurring theme of failures, often linked to the GFCI, suggests a potential design or component quality issue that may limit its long-term durability.
Adding another layer to this is the branding. As one user correctly pointed out, this thermostat is manufactured by Resideo Technologies, Inc., under license from Honeywell. While this is a common practice, it can sometimes lead to confusion about support and quality control. The same user also raised a valid point about UL testing versus being tested *to* UL specifications, a nuance that can be important for those with stringent safety standards. When you combine these longevity concerns with the GFCI failure reports, a pattern emerges. While the thermostat offers excellent functionality when it’s working, prospective buyers must weigh this against the risk that they may need to replace the unit sooner than anticipated. It performs its job admirably, but its endurance is a significant question mark.
What Other Users Are Saying
Synthesizing feedback from numerous owners provides a clear and balanced picture of the Honeywell TH115-AF-GA/U Programmable Thermostat with Floor Sensor. The positive sentiment consistently revolves around its functionality and its role as a perfect OEM replacement. One user who replaced a failed 8-year-old Warmly Yours thermostat called it an “exact fit” and praised the well-labeled wires. Another successfully replaced a 10-year-old Danfloss model, highlighting its value in updating older systems. When the unit works, users find it “easy to use” with a “nice set of programming options.”
However, the negative feedback is just as consistent and focuses almost entirely on a single, critical issue: GFCI failure and poor longevity. One frustrated user stated they had three units fail “after the first GFI trip from power surges,” calling the component “defective.” Another reported their unit, purchased in July 2023, failed by November of the following year when the GFCI tripped and would not reset. This short lifespan is a recurring theme, with another user noting their original unit lasted under six years. This feedback is crucial, as it suggests that while the thermostat’s features are excellent, its long-term reliability is a significant gamble.
How Does the Honeywell TH115-AF-GA/U Compare to the Alternatives?
The Honeywell TH115-AF-GA/U Programmable Thermostat with Floor Sensor is a specialized tool for a specific job. To understand its place in the market, it’s helpful to compare it to other types of thermostats, even those designed for different systems. This highlights who the Honeywell is for—and who should look elsewhere.
1. Cadet Built-In Thermostat Kit
- RANGE: This thermostat has a temperature range: 45º - 80ºF (7ºC to 27ºC) with an easy to use large, adjusting twist dial
- COMPATIBLE: This thermostat has been made for Cadet F series electric baseboard heaters only (sold separately)
The Cadet Built-In Thermostat Kit is a different beast entirely. It is a simple, mechanical, single-pole thermostat designed specifically to be installed within a Cadet electric baseboard heater. It offers no programmability, no digital display, and no floor sensor. Its function is to turn the baseboard heater on or off to maintain a general room temperature set by a simple dial. Someone might prefer this alternative if they own a Cadet baseboard heater and want the most basic, integrated, and low-cost control solution possible. It is not an alternative for radiant floor heating and lacks any of the precision, efficiency, or safety features of the Honeywell model.
2. LUX LTX9100U Programmable Thermostat
- Lux Pro Thermostat: A versatile solution for precise climate control
- House Thermostat: Designed to efficiently regulate indoor temperature for comfort
The LUX LTX9100U is a direct competitor in the programmable thermostat space, but for a completely different type of system. This is a low-voltage thermostat designed for conventional central HVAC systems, controlling both heating (up to 2 stages) and cooling (up to 2 stages). Like the Honeywell, it offers 7-day programmability, giving users flexible scheduling. However, it operates on 24V power supplied by the furnace and cannot handle the high-voltage/high-wattage load of an electric radiant floor. A homeowner would choose the LUX thermostat if they have a standard furnace and air conditioner and are looking for an affordable, programmable upgrade from a basic manual thermostat. It is completely incompatible with the Honeywell’s application.
3. White-Rodgers 1F78-151 Programmable Thermostat
- Easy-to-read display with backlight
- 5-2 day programmable - set different schedules for weekdays and weekends
Similar to the LUX model, the White-Rodgers 1F78-151 (now Emerson) is a low-voltage digital thermostat for single-stage central heating and cooling systems. Its key differentiator from the Honeywell is its application and its programming style. It offers a 5-2 day schedule, meaning you can set one program for weekdays and another for the weekend, which is slightly less flexible than the Honeywell’s full 7-day schedule. This is a solid, reliable choice for someone with a basic furnace/AC system who wants to add simple programmability for energy savings. It is not suitable for line-voltage applications like radiant floor heat and lacks a floor sensor or GFCI.
Our Final Verdict: A Capable Controller with a Critical Caveat
After extensive testing and analysis, our verdict on the Honeywell TH115-AF-GA/U Programmable Thermostat with Floor Sensor is that it is a highly capable and feature-rich controller that is unfortunately marred by a significant reliability concern. On the one hand, its 7-day programmability, versatile control modes (especially the Ambient with Floor Limit setting), and clear interface provide an outstanding level of comfort and efficiency for electric radiant floor systems. It does its primary job exceptionally well, transforming a simple heated floor into a truly luxurious and intelligent home feature.
On the other hand, the persistent and widely reported issue of GFCI failure cannot be ignored. The thermostat’s key safety feature appears to be its Achilles’ heel, leading to premature failure that leaves users in the cold. We would recommend this thermostat primarily to two groups: individuals who are replacing an identical failed model and want a simple, direct swap, and users who are willing to accept the potential risk of a shorter lifespan in exchange for the excellent features and precise control it offers while it works. For those prioritizing long-term, set-it-and-forget-it reliability above all else, the known issues may be a deal-breaker.
If you’ve decided the feature set of the Honeywell TH115-AF-GA/U Programmable Thermostat with Floor Sensor is the right fit for your project and you understand the potential trade-offs, you can check its current price and purchase it here.
Last update on 2025-10-13 / Affiliate links / Images from Amazon Product Advertising API