Honeywell Home THR99C3013 evohome Review: room-by-room heating control that’s smart but a bit fussy

I’ve been using the Honeywell Home THR99C3013 evohome kit with the boiler relay and three smart radiator heads for a while now, and it’s one of those products that’s both clever and slightly annoying at the same time. On paper, it ticks a lot of boxes: Wi‑Fi, app control, works with Alexa and Google, and you can split your house into multiple zones. In practice, it does give you real control over which rooms are heated and when, but you have to be willing to tinker a bit.

Before this, I just had standard TRVs and a basic programmer: whole house on or off, maybe two time slots per day. With evohome, I can have the bedroom cooler, the living room warmer in the evening, and the spare room almost off most of the time. That part is genuinely useful, especially with energy prices going up. You stop wasting heat in rooms you barely use.

Where things get less perfect is the setup and the accuracy of the radiator heads. The marketing makes it sound plug‑and‑play, but depending on your existing valves and how picky you are about temperature, you might end up fiddling with adapters, offsets, and schedules. If you expect it to nail the exact temperature in every room all the time, you’ll probably be a bit disappointed. It’s good, but not magic.

Overall, my first impression is: this is a pretty solid smart heating system for people who like to tweak settings and don’t mind a bit of DIY. If you want something ultra simple where you never touch it again, or your valves are old and weird, you might run into some frustration. It does the job and can save money, but it’s not a perfect out‑of‑the‑box experience.

In terms of value, this kit isn’t cheap, especially once you start adding extra radiator heads to cover a whole house. You’re paying for the hub, the boiler relay, and the three smart valves, plus all the software and app stuff. Compared to a basic programmable thermostat and manual TRVs, it’s a clear step up in price. The question is whether the savings and convenience justify that cost over a few winters.

If you live in a house where you only really use a few rooms and you’re disciplined about setting up proper schedules, it can pay off. One of the Amazon reviewers mentioned cutting their bill roughly in half over several years with this system, which sounds optimistic but not totally crazy if they were previously heating everything all the time. Being able to drop little‑used rooms to, say, 15–16°C and only warm them when needed does add up. In my case, I noticed the boiler cycling less and the overall gas usage dropping a bit, especially in shoulder seasons.

On the other hand, if your home is small, quite open‑plan, or you’re not going to bother with fine‑tuning schedules and offsets, then you’re paying a premium for features you won’t fully use. There are simpler smart thermostats that just control the whole house and cost less. Also, the slightly clunky setup and the temperature quirks mean this isn’t the most user‑friendly kit on the market. So for someone wanting absolute simplicity, the value is weaker.

Overall, I’d rate the value as decent but not outstanding. It makes sense for a medium to large house with radiators in lots of separate rooms, where you’re actually going to create multiple zones and tweak them. If you’re in a small flat or you hate messing with settings, you’re better off saving your money and going for a simpler system.

Design‑wise, the evohome controller is fine but nothing special. It’s a white, slightly chunky rectangular unit with a full‑colour touchscreen. The screen is bright enough, the backlight is handy, and the size (about 21.5 cm across) makes it easy to read from a distance. It doesn’t scream “premium gadget”, but it doesn’t look cheap either. It’s more like a decent router or an older tablet stuck on the wall. In a modern living room it blends in ok, but it’s not going to impress anyone visually.

The interface is where you feel its age a bit. The touchscreen works, but it’s not as smooth as a phone. The menus are fairly logical once you’ve poked around, but there are some hidden moves, like holding the MENU button for several seconds to get into advanced settings. That’s not obvious at all, and it’s the kind of thing you only find by reading forums or the manual carefully. Once you know it, you can get to the important stuff, but it’s not exactly intuitive for a casual user.

The radiator heads themselves are bulky compared to standard manual TRVs. They’re white plastic with a small screen that shows the set temperature and some icons. The finish is shiny plastic, which is ok, but on some radiators they do stand out. On the plus side, having a screen on each head is genuinely useful, because you can see the setpoint and binding status without going back to the main controller. On the downside, if you like very clean, minimal radiators, these will look like little gadgets bolted on.

In terms of physical controls, you’ve got buttons on the heads and the touchscreen on the hub. That’s it. No fancy rotary dials or touch sliders. Personally, I don’t mind: they’re simple and they get the job done. But overall, the design and UI feel one or two generations behind the slickest smart thermostats. It’s functional and robust enough, just not stylish or super modern.

The system is mostly battery‑powered on the radiator side, and that’s both convenient and a small ongoing chore. Each smart radiator head runs on batteries (typically AA or similar, depending on version). In my experience and from what others report, you’re looking at roughly a year or so of life if your heating is active for a good part of the year. If you have a big house with a lot of heads, that’s a fair amount of batteries to replace over time. With just three heads like in this kit, it’s manageable, but still something to remember.

The main controller itself is powered from the mains via a base station, so you don’t worry about that day to day. Once it’s on the wall or on its stand, you just leave it there. The boiler relay is also wired, so no battery issues there either. The battery hassle is really just the radiator valves. They do at least give you warnings when power is running low, so you don’t usually wake up to a dead valve and a cold room out of nowhere, but you still have to keep a stash of fresh batteries around.

One thing to keep in mind: when a battery is low and you replace it, the head has to recalibrate its travel on the valve. That’s usually automatic, but it takes a minute and you’ll hear it whirr back and forth. It’s not a big deal, just slightly noisy if you do it late at night in a bedroom. I’d suggest changing them in the daytime and doing them all at once at the start of the heating season if you want to avoid surprises.

Overall, the battery situation is what you’d expect from wireless TRVs: it’s not disastrous, but it’s extra maintenance compared to dumb valves. If you hate changing batteries in gadgets, this will annoy you a bit over the years. If you’re used to smart devices already, it’s just another thing on the list, but not a deal‑breaker.

On the performance side, the concept works: you really can heat just the rooms you care about. For example, I keep my bedroom at 17–18°C at night, the living room at 20–21°C in the evening, and the office warm during the day but cooler later. The system handles these different schedules without drama. When a room calls for heat, the boiler kicks in and the relevant radiator valve opens. When it’s satisfied, it shuts again. You feel the difference on days when you’d normally have the whole house roasting just because one room was cold.

The weak spot is temperature accuracy and response speed. The radiator heads measure temperature right next to the radiator, which is usually the warmest spot in the room. So they can easily think the room is hot enough while the far side is still cool. Honeywell lets you tweak an offset (for example, telling it that 22°C at the valve is really 20°C in the room), but it’s not perfect. One Amazon reviewer mentioned seeing differences of up to 3°C compared to what they wanted, and that lines up with my experience in tricky rooms. Sometimes it tracks nicely, other times it overshoots or undershoots for a while.

The control logic also feels a bit slow. It’s clearly optimised for steady systems like underfloor heating, where you want gentle changes, not rapid swings. With radiators, which can heat quickly, it can feel like the system is reacting late. You might be sitting in a room that feels chilly while the valve still thinks it’s close enough to the target, then it finally wakes up and you get a burst of heat later. It’s not terrible, but if you’re picky about a rock‑steady temperature, it’ll probably bother you.

In practice, performance is decent once you accept its quirks. You get clear benefits in terms of not overheating unused rooms and having different schedules per zone. But if you’re expecting precise, thermostat‑grade control in every room without any calibration or extra sensors, that’s not what this gives you. It’s more “good enough for comfort and savings” than “lab‑grade temperature control”.

Installing this system is where you realise it’s a bit more involved than a simple smart thermostat. If you’re comfortable turning off power to the boiler and dealing with a couple of wires, the boiler relay isn’t too bad. It usually replaces your old thermostat or programmer wiring. Honeywell’s instructions are okay, but they assume a reasonably standard setup. If your system is older or was bodged in the past, you might want an electrician or heating engineer to handle that part. Once wired, you bind the relay to the controller during the guided setup, which worked first time for me.

The radiator heads are where some people hit problems. They come with a set of adapters meant to fit common valve types, but not all valves are equal. One Amazon reviewer mentioned having to Frankenstein adapters and even use a bit of BIC pen tube to extend the pin so the valve would fully close. That sounds ridiculous, but I’ve seen similar issues: sometimes the motor doesn’t push far enough to shut the valve, so the radiator keeps getting warm when it should be off. In my case, two radiators were fine, one needed a different adapter and some fiddling to stop it leaking heat.

The software setup on the controller is guided but not idiot‑proof. You go through adding zones, pairing each radiator head, naming rooms, and setting initial schedules. It works, but there are moments where you’re not totally sure if something actually registered until you see it on the screen. Binding confirmation on each head helps, but if you’re not patient you can easily skip a step and then wonder why a room isn’t heating. Expect to spend a good couple of hours the first day if you want everything named nicely and basic schedules in place.

Overall, I’d say installation is “manageable DIY” for someone moderately handy, but not what I’d call plug‑and‑play for everyone. If you have unusual valves or a messy boiler wiring, prepare for some swearing or budget for a pro to do the hard bits. Once it’s in, you mostly forget about the hardware, but getting there can be a bit of a project, not a quick Sunday afternoon toy.

This kit is basically the “starter pack” for evohome zoning. In the box you get the main evohome Wi‑Fi touchscreen thermostat (the hub/controller), the boiler relay module, and three wireless electronic TRVs (radiator heads). So out of the box, you can properly control three radiators as separate zones, and you can expand to up to 12 zones later by buying more heads. The controller connects to your Wi‑Fi and to Honeywell’s Total Connect Comfort app, so you can change temperatures and schedules from your phone or using Alexa/Google.

The idea is simple: instead of one thermostat for the whole house, each radiator head becomes a mini thermostat for its room. The hub is the “brain” that talks to them and tells the boiler when to fire. So if only one room needs heat, it’ll call the boiler just for that, instead of heating the entire house. In theory, that means lower bills and better comfort, especially if your usage is uneven (like working from home in one room all day).

The system is advertised as easy to install without touching pipework, and that’s mostly true if your existing radiator valves are compatible and in decent shape. The boiler relay is just a box that replaces or sits alongside your old thermostat wiring. The radiator heads screw onto your valves using the supplied adapters. There’s a guided configuration on the controller and the heads show binding/connection status on their small screens, which helps, but it’s still a bit of a learning curve if you’re not used to this kind of thing.

Overall, the presentation is: a modular, Wi‑Fi connected heating system that lets you split your home into multiple zones, with per‑room scheduling and app control. It’s not just a thermostat, it’s more like a basic building management system for a normal house. It’s powerful, but with that comes some complexity that Honeywell doesn’t always make totally clear in the marketing blurbs.