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Smart thermostats

Wednesday, 14 Aug

Smart thermostats — Hive vs Nest vs Tado vs Bosch Easy vs Vaillant Senso Home vs Opentherm plus what is Priority Hot Water, Load and Weather Compensation?

Whether you are installing a new boiler or upgrading your thermostat, there are plenty of so-called Smart thermostats on the market to consider. We’ll start with the key facts on each. Below are some common FAQs.

Hive — UK market leader. Competitively priced. A simple retrofit upgrade from an analogue thermostat and programmer where the existing boiler is being kept, or installation cost is a primary factor. Very easy to use with an intuitive app and wall unit. Hive has a UK based customer support centre which can be reached on 0333 202 9614 if any setup or technical issues are ever encountered. The wall unit (thermostat) is battery powered so no need for wires, so the thermostat location can be changed. Hive is a simple but accurate ‘on/off’ control that does not modulate boiler flow temperature, so it is slightly less efficient than a correctly setup and installed* Opentherm or manufacturer control. The Hive system can be expanded with the addition of the optional Hive smart TRVs for individual room zoning but would have a costly initial outlay with each TRV priced at £35-£50 (bundle discounts available) which should be fitted to all radiators. It is compatible with Amazon Alexa voice control. Hive is a British Gas product but don’t let this put you off and don’t read into the haters. This product is simple and does what it does well.

Google Nest — Looks and feels classy/premium. Has a smart nest learning thermostat feature which can be turned on or off that learns when you’re at home and runs the heating accordingly, meaning no need for a typical schedule. Combi boilers can be set up/wired to run the ‘Opentherm’ feature allowing Opentherm compatible combi boilers (not Worcester, Vaillant, Glowworm, or Viessmann) to modulate the boiler flow temperature giving modest efficiency gains. Wiring is awkward thanks to the poorly designed/tiny terminals within the ‘heatlink’ receiver. The wall unit needs to reuse existing thermostat wiring, so location is not easily moved. If no wires are available due to the existing thermostat being wireless, or the location is to be moved without running new wires, an optional Nest Stand can be purchased, but note it requires being plugged into a wall socket. Owned by Google, including the data collected. Can be expanded to run with up to 20 thermostats, so good for very large properties with lots of zones. Compatible with Google Home. Compatible smart TRVs are not currently available.

Tado — Competitively priced. Very similar to Hive except this does allow for Opentherm wiring if being used with a combi boiler so small efficiency gains can be had. Wired or wireless. The Tado system can be expanded with the addition of the optional Tado smart TRVs for individual room zoning but would have a costly initial outlay with each TRV priced at £36 (bundle discounts available) which should be fitted to all radiators. Compatible with Apple HomeKit, Google Home or Alexa Smart Home.

Worcester Bosch EasyControl — Using Worcester’s own ebus protocol, it is designed to work with their boilers. It comes with up to a 12-year guarantee when registered with one of their boilers. This is a neat looking thermostat with many features. Compatible with Alexa and other IFTTT smart home devices. Using local internet weather data, rather than a wired external sensor (optional), the EasyControl automatically responds to changes in temperature and adjusts the heating flow temperature, increasing efficiency and comfort. The EasyControl can also be coupled with Worcester Outdoor sensor kit, providing an additional 2% ErP efficiency increase for their gas boilers. See more on weather compensation below. Similar to Nest, EasyControl has a Home Presence Detection feature. When switched on, it automatically turns the heating down if you’re no longer in the house and detects when you’re returning home, turning the heating up to your desired temperature. Another similarity is the requirement to be hardwired or the use of their optional stand and plugged into a power socket. The app includes free gas consumption graphs with option to include tariff/unit pricing. The app also allows you to book a boiler service with your installer. The system can be expanded with Worcester Easy TRVs for individual room zoning but would have a costly initial outlay with each TRV priced at £50 (bundle discounts available) which should really be fitted to all radiators. If you want a stored hot water system (cylinder) then look at the Worcester 4000 or 8000 system boilers with Worcester’s optional internal diverter valve fitted. This will give you good efficiency gains of Priority Hot Water, more info on this below.

Vaillant senso — Vaillant has several control options, but we will focus on two most recent, the sensoHOME 350 and the senso COMFORT VRC 720. Both are available in wired or wireless versions, allowing for easy location change and simple and tidy installation. The 350 is designed for 1 or 2 zones plus hot water and is load compensating. The 720 can run multiple zones/units and is weather compensating and comes with an outdoor sensor. To connect these thermostats to tablets/phones/PC’s purchase the bundle pack that comes with the My Vaillant Connect Gateway. Without this module, the thermostat won’t connect to smart devices. This module will also allow your installer and Vaillant to monitor your boiler remotely, possibly alerting you of an issue before it occurs. Both systems can also be installed as Priority Hot Water systems with the addition of the Vaillant VR66/2 wiring centre (up to 2 heating zones plus HW) or the VR71 wiring centre if installing multiple zones. A VR10 cylinder sensor is required and possibly additional VR71 wiring centres depending on the amount of zones. Vaillant recently discontinued their ambiSENSE smart TRV.

OpenTherm / Priority Hot Water (PDWH) and Weather Compensation:

We’ll delve into each, but in short they seek maximum efficiency from your boiler. Efficiency gains of 2 — 15% can be achieved over a regular condensing boilers fitted with ‘on/off’ controls, depending on your current condensing boiler setup and whether the boiler is oversized for heat requirement.

Opentherm is an open source protocol/language used by various manufacturers to allow thermostats to speak to a boiler in an intelligent way, rather than traditionally telling the boiler to just turn on or off. For example, as the room gets close to its target temperature the thermostat will run the boiler at a lower flow temperature increasing the efficiency, giving longer run times and reducing inefficient ‘cycling’ (on/off/on/off). As they share a common language, these controls, and boilers can be mixed and matched. Opentherm will work on all compatible combi boilers. Some systems will also use internet data to allow for outdoor temperatures, some will allow for an outdoor weather sensor to be added. Regular boilers with stored hot water (cylinders) where the user wants the benefits of Opentherm or Manufacturer Controls will need to also convert their system to ‘Priority Hot Water’ or PDHW. EPH does a good Opentherm Priority hot water kit. Nest and Tado are also listed as Opentherm but will not allow for Priority Hot Water on their own so best suited for combi boilers, although there are some workarounds we are aware of with Viessmann boilers and their DHW module.

‘Priority Hot Water’ or PDHW. All combi boilers are PDHW by design, and heat pumps are also installed to run this way. When you open a hot tap, the combi boiler will switch from heating your radiators and ramp up its output to give you instant hot water. Regular boilers with stored hot water cylinders can be installed or converted to prioritise the hot water cylinder when it calls for heat. The benefits of doing this is the boiler is now only doing one thing at a time, and if it now knows which, it will set the flow temperature accordingly to maximise efficiency. When it’s doing hot water, it will ramp the flow temperature up to maximum to quickly reheat the cylinder. When it’s running the heating be that underfloor or radiators, the flow temperature will be reduced down low to optimise efficiency, keeping the return temperature below 55 degrees. This will capture as much of the free latent heat that would normally just escape out of the flue. When running in this optimum state, this is when and how your boiler got it’s A rating of 90% + efficiency. Other benefits would be less stress on the boiler, increasing its lifespan and fewer breakdowns. If the heating system is being designed from the ground up, you should ask about a Priority Hot Water System and controls. EPH do a good Opentherm kit here https://mwphs.co.uk/product/eph-priority-hot-water-pdhw-pack-c00p-221981/, but we would always suggest using the boiler manufacturer’s controls where possible.

Weather Compensation:

Whether compensation is suitable for combi boilers or systems running Priority Hot Water. It takes an outdoor temperature via a sensor placed on a north facing wall. In short, on colder days it will run the boiler at a hotter flow temperature, and warmer days a cooler temperature. It uses a heat curve and algorithm to decide these temperatures. This heat curve can usually be adjusted depending on the properties of heat loss/demand. It’s important to understand your radiators will be hotter on cold days and cooler on mild ones. The question needs to change from ‘is my radiator hot?’ to ‘is my room a comfortable temperature?’ The benefit of doing this along with Priority Hot Water is the boiler will run at its optimum efficiency. Helping you energy savings, save money, increasing lifespan and reliability.

Here are a few questions you should ask when considering new heating controls and our guidance:

What is a smart thermostat?
What is the best Smart thermostat for me?
Which is best for your needs?

What is a smart thermostat?

A smart thermostat is one that is more than just a dumb on/off switch. The minimum requirement is that it is digital and can be controlled by a smartphone, tablet, or computer.

What is the best Smart thermostat for me?

This question needs to start with other questions. What’s significant to you, what do you want, how much do you want to spend? If all you want is a more modern looking unit to replace an old analogue thermostat/programmer that you can control by a phone, better accuracy of target temperature (less overshoot) then start by looking at Hive.

If you are looking for optimum efficiency and replacing your boiler as well, then you should consider the manufacturer’s own controls (Worcester Bosch EasyControl or Vaillant sensoHome or sensoComfort).

If you happen to have an Opentherm compatible combi boiler, then controls like ESI or Nest could be worth considering getting your boiler to run at its optimum and help prolong its life.

Hopefully the above article has been of some help. If you live in the Wokingham borough including Woodley, Twyford, Winnersh, Earley, Lower Earley, Reading, or surrounding areas in Berkshire, please don’t hesitate to contact The Boilersmith for all your heating needs, including smart control installation, new boiler installation, boiler servicing and boiler repairs. Our Gas Safe Registered heating engineers are highly experienced with all major manufacturers, including Worcester, Vaillant, Viessmann, Ideal, Potterton, Baxi, and Main Gas boilers. We’re here to ensure your boiler remains in peak condition, extending its lifespan and preserving its warranty.

*Opentherm and Manufacturer controls are often installed as simple ‘on/off’ controls not utilising their Opentherm or Weather compensating features due to the installer or electrician not knowing or understanding the benefits.