Setting the temperature

My air-con can have a temperature set and aim for it.

  • It has a wide range of ± a few degrees which I don't like.
  • It is not setting temperature by me, it is basing it on some sensor it has.

To fix this I have used an environmental sensor - on my desk, and for my bedroom, on my bed head. I then control the air-con - telling it I want it higher or lower than it thinks things are, so as to aim for the right temperature by me. It works well most of the time and keeps the temperature very close.

That is my bedroom, last night (cooling), units in ℃, so maybe ±0.2 ℃ at most. Good.

I also have radiators for the winter, and they have the same fun, driving the valve on the radiator with some prediction.

Which to use for heating? air-con (heat pump) or radiator... Bearing in mind some of the house does not have air-con, so has radiators anyway. I don't actually know which is most cost effective / efficient. But I can choose. Have systems in place to make sure they are never fighting each other :-)

Per room radiator control

One of the key things is per-room controls - this means a temperature sensor in the room, and a radiator control, and some way to tell the boiler that one of the rooms needs heat. We have two heating loops (up and down), my daughter has two (left and right!). But for each radiator there is one boiler control that is needed.

The hard way

So, the hard way, I have my fancy environmental monitors with a display. They have a config for temp targets throughout the day. I have systems to override for empty rooms. Using the light switch marks a room in use for the day :-)

They talk MQTT to a Shelly running Tasmota that controls the radiator. So needs an MQTT broker.

The Shelly talks MQTT to a FireBrick to say radiator is on/off.

The FireBrick has a set of profiles, and any one in each loop will cause a message to another Shelly running Tasmota to operate the heating loop valve.

This triggers the boiler as needed.

It works.

It is not cheap or simple - the env sensors cost, the FireBrick costs a lot.

The easy way - maybe

So I am working on an easy way - my daughter happens to have a FireBrick, but even so I am trying to make a really easy way to do this. Not all of my kids have one (?!).

The first step is the reference temperature. A sensor that can be placed sensibly, e.g. by a bed.

I had found some nice industrial (BlueCoinT) ones at €31, but now have found, thanks to a recommendation, some stupidly cheap ones on Amazon. They are only £9, and even cheaper on AliExpress. They can be refreshed with sensible code.

The next step is controlling the radiator, and something like a Shelly Plus Mini would be ideal. Not sure of price yet, but the normal Shelly Plus 1 is £16.49. Whoa, they used to be less than that! Interesting. The Mini may be less. We'll see. But up to under £26. The radiator control itself is something like this, £19.63

So yes, we are up to £45 per room. A few more £s for back box and fused spur box for the Shelly mini by the radiator. And one Shelly at the boiler.

The comms can all be BLE. Sensor to Shelly, and Shelly to boiler control Shelly. Just needs a bit of software.

Not ideal, but £50 per room for exact per room heating control is probably quickly worth it. Simple web interface (or maybe even HomeKit) for unoccupied rooms, and controls for times of day and target temperatures via a web page. This can quickly save on heating costs and make things more comfortable.

It always amazed me people ran their house with one thermostat on the wall in the hall.


  1. I've been using Tado for per room radiator control since they launched the TRVs (& hot water control), we don't have AC. The first gen TRVs are a little annoying as they don't like rechargeable batteries (they work, but complain about being low on charge, the newer ones have this sorted), makes total sense to heat the home this way, Tado is reasonably good for integration, I have mine hooked into home assistant.

    1. Sounds interesting - power is what is stopping me from doing something like this. How frequently do you need to recharge the batteries?

    2. Indeed, hence my env sensors being USB. The BLE probably manage a year, but they do report battery level so easy to know in advance if I make the a/w tell you.

    3. I'd say about every 4 months using low self discharge AAs, not a huge chore & home assistant tells me when they drop off, not perfect but more than good enough.

  2. If you only have radiators to control you can get remote thermostats that don't need power at all. They use a "capilliary", which I think means a heat pipe. Eg this one https://www.screwfix.com/p/pegler-white-remote-adjustment-trv-head/8255v

    1. That won't allow time profiles and the like will it? Or link to the boiler so that it only runs if one of the radiators needs to be on?

    2. Yes, it's just an unusually shaped TRV. You can do more with electronics.

  3. There are good reasons with regards boiler efficiency no to go overboard with zoning your heating system.

    Heat Geek on Youtube has a couple videos on the hydronics involved.


    1. Whilst the science in those videos is valid, it's applicability depends heavily on the amount of heat loss to adjacent rooms vs the amount of heat loss to outside. It also depends on how oversized the radiators are for the rooms.

      In a modern well insulated house with radiatirs sized for minimum cost, what they say is likely to be valid. In something built in the 1800s with radiators sized by a pessimist who doesnt want to be cold it may be entirely wrong.

    2. You really need a buffer tank between your boiler and your radiators to make that work. Say there is just one radiator calling for heat and its power output is below the minimum rating of the boiler, then the boiler will respond by short cycling. This is less efficient than just letting it run continuously supplying more heat. With a buffer tank you can modulate your heat delivery down to zero and, with the boiler running at the same time, up to well over 100% of the boiler output (until the buffer runs out). Downside is you need the space for a very large tank and the heat losses that go with the tank. My home system is like this and its not uncommon for just my study to be calling for heat during the day. I can also combine heat sources in the buffer tank, wood burner plus gas boiler, and send the heat wherever it is needed.

  4. "It always amazed me people ran their house with one thermostat on the wall in the hall."

    Yes but then again plumbers used to balance radiators so that the heating system worked properly rather than open all the valves to maximum and hope for the best with TRVs, which never ends well.

  5. I feel your pain with AC. We have a Daikin 5kW unit and if you set it to "23C auto" it seems to feel anything between about 19C and 27C is acceptable. We end up setting it to cool in summer and heat in winter which is stupid because we should just be able to leave it on auto all year round.

    Unfortunately, I don't think I am equipped to set up the systems you have to manage it :D

  6. Any reason not to use Zigbee or mesh sensors ?

  7. These seem to just work, and I have not (yet) done any zigbee processor work yet.


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