Smart Thermostat Installation

The honest answer on whether it will save you money

Most companies selling smart thermostats lead with a percentage. We are not going to, because when Which? looked at how those percentages were calculated they did not hold up well.

Which? examined the savings calculators the manufacturers publish. Hive’s was built on a household using 16,489 kWh of gas a year, which is around 37% more than the Ofgem average of roughly 12,000 kWh. Google Nest’s assumed heating running at least 17 hours a day, more than double the 7.5 to 8 hour daily average in the government’s own figures. Which? described the assumptions as not representative of the average UK consumer. tado’s headline figure had no accessible working behind it.

The Energy Saving Trust is more useful because it is more modest. It says a full set of heating controls could save around £100 a year in Great Britain, and it is explicit that whether smart controls save you anything will depend on how you currently control your heating. If you already have a working programmer, a room thermostat and radiator valves, and you use them competently, a smart thermostat is not going to transform your bills.

The single biggest lever is duller than any app. The Energy Saving Trust puts turning the thermostat down by one degree, from 22 to 21, at around £120 a year. A smart thermostat helps with that only if it actually changes what you do.

So here is the position we will give you on the phone. Buy a smart thermostat for control, not for a guaranteed saving. Genuine control means heating that follows an irregular working week, the ability to turn the heating off from a train when plans change, room by room temperatures in a house where one bedroom is always cold, and hot water on a schedule that matches when people actually shower. Which? found seven in ten of its members reported their heating was easier to control after fitting one. That, we can stand behind.

Where there is a real efficiency gain, it comes from a different mechanism entirely, and that is worth understanding.

Boiler Plus: if you are replacing a combi in England, this is a legal requirement

This is the part of the page that matters most, and most homeowners have never heard of it.

Boiler Plus came into force in April 2018 and sits under the Building Regulations through the Domestic Building Services Compliance Guide. It applies in England, which covers our whole working area. Every gas boiler installation has to meet a minimum 92% ErP efficiency, and must have time and temperature control and a boiler interlock.

On top of that, a gas combination boiler installation must include at least one of four additional measures:

• Flue gas heat recovery
• Weather compensation
• Load compensation
• A smart control with automation and optimisation

System and regular boilers are exempt from this additional requirement. If you have a cylinder, Boiler Plus does not force the choice on you.

Two things are commonly got wrong here, and both matter if anyone ever inspects the work.

First, TPI control does not count as load compensation. The Heating and Hotwater Industry Council states this directly. A control carrying an ErP Class IV designation is a TPI control, and fitting one does not satisfy the combi requirement on its own. It is a legitimate control and it can sit alongside a qualifying measure, but it is not one.

Second, an ordinary programmable thermostat with an app is not automatically a smart control for these purposes. To qualify it has to do all of the following: provide time and room temperature control, adjust settings automatically based on occupancy detection or on stored data from your own adjustments over time, start the boiler at the optimum time so the room is at temperature when you want it rather than when the timer says, and allow settings to be changed remotely. Automation and optimisation are both mandatory. Plenty of connected thermostats have one and not the other.

There is no official government list of approved products. We confirm compliance with the control manufacturer for the specific model and keep that confirmation on file with your Benchmark commissioning record, so if you sell the house or building control ever asks, the evidence exists.

The commercially honest framing, which you will not get from a company selling thermostats: a smart control is one of four routes to compliance, not the route. If your new boiler achieves load compensation through the manufacturer’s own OpenTherm control, that is equally valid and often cheaper. We will tell you which route is right for your installation.

What the installation actually involves

On a combi with a straightforward two wire thermostat connection, this is a short job. Most of the complications are in older systems, and they are worth knowing about because they are what turns a quoted price into a different one.

What it costs

We quote before we start, not after. The variables are the system you have rather than the thermostat you choose, so a price given over the phone without knowing whether you have a cylinder, a neutral at the thermostat position and an OpenTherm capable boiler is a guess.

As a guide, a straightforward single thermostat swap on a combi, supplied and fitted, typically lands somewhere in the region of £180 to £300 depending on the unit. Multi zone systems, radiator valves across a house, an S-plan conversion or any rewiring at the thermostat position are quoted separately once we have seen the property.

Fitted as part of a boiler replacement, the labour largely disappears into the install, which is the cheapest moment to do it. Our boiler swaps start at £2,850 including installation, flush, warranty registration and VAT.

On grants, so nobody wastes their time: no current UK scheme funds a smart thermostat on its own. The Boiler Upgrade Scheme funds heat pumps and biomass, not controls and not gas boilers. ECO4 funds controls only as part of a qualifying whole system upgrade for eligible low income households, and it runs to the end of December 2026. Anyone telling you there is a grant for a smart thermostat is wrong.