TechReport (UK)

Product Reviews:

Honeywell evohome ‘Smart’ Central Heating Control System

Main Components

evohome Controller:

The central control / programming interface for the evohome system, the controller combines the functionality of a programmer, thermostat, WiFi connected internet gateway and main display.

The inclusion of the internet gateway in this unit is a neat touch – many other systems use a separate box connected to the router (I have three of these in my house already!)

The unit is powered by a rechargeable battery and rests on a mains charging base, but can also be wall mounted.

Wireless Relay Box:

Wired directly into either the central heating boiler or a zone valve, a minimum of one of these units (two if separate hot water control is required as well – see picture) is required to switch the boiler / flow of hot water from the boiler on and off according to wireless communication from the controller unit (above).

Radiator Controller:

 Replaces the normal radiator control / thermostatic valve and communicates wirelessly with the controller, sending room temperature, on/off confirmation and receiving switching instructions. The radiator controllers are supplied with various adaptors to fit the majority of radiators, although the standard fitting will work with most anyway.

A rather neat touch is the control knob on top which allows the user to manually adjust the temperature in that zone (it will return to the pre-set temperature at the next pre-programmed switching point).

The Radiator Controllers have a small display on the front which can be temporarily back-lit (above) and indicates the room name (set-up on the main controller) and temperature. A range of functions can be programmed via the control knob and the back-light switch such as window-open sensor, displayed temperature (‘Set’ temperature or ‘Actual’ temperature), temperature offset (if the sensor is in a position where it is not representing the real room temperature) etc.

Optional Components

If Hot Water control is also desired (as it invariably is in the UK), a separate Hot Water kit can be purchased (~ £80). This includes another Wireless Relay box, a Wireless Cylinder Thermostat and a Temperature Sensor (actually two – one suitable for ‘Vented’ and one for ‘Unvented’ hot water cylinders):

This allows the same kind of timing control over the Hot Water as a completely separate circuit (so that you can use this in the summer when you would have no need for central heating) with an option to set the required hot water temperature in the ‘Settings’ menu on the evohome Controller.

Honeywell also offers several evohome compatible wall-mounted Wireless Thermostats:

So why would this be necessary when you already have a Radiator Controller? In some cases, the Radiator Controllers may not be ideally located to measure a realistic room temperature (behind a curtain, in a corner), or may just be inconvenient to reach to check / adjust the temperature manually, so a freely-locatable wall-mounted Wireless Thermostat can get around these problems.

evohome also caters for underfloor heating (hot water based systems only – not electric), although it would appear that this can get quite expensive, with a separate Controller for this costing about £260, plus the cost of the thermal actuators.

To help with system design / creating a list of the required components there is a design tool available on the evohome website: evohome System Builder

Once all the components have been purchased, the installation can begin.

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