Change to smart thermostat

Discussion in 'Plumbers' Talk' started by exenobby, Mar 1, 2020.

  1. exenobby

    exenobby New Member

    Hi,
    We have move home and the combi boiler has one of those pin timers that you push the pins in for the time you want the heating to come on. There is also a Honeywell thermostat and receiver. It's the kind where you turn the wheel to adjust the temp.
    Because my wife and I work at different times (she does shift work) I thought a change to a honeywell smart meter would be a good idea.
    I would get the wireless version, so no worries about wiring it in, but I wondered if I need to change the current receiver or could the smart thermostat be paired to the current one?
    Your thoughts are gratefully received.
     
  2. MGW

    MGW Screwfix Select

    Seem to remember reading there was a change of frequency used, so although a new one of each type may use same base, likely new onto old will not work. There are so many so called "smart" thermostat it's hard to say what is best, for wall thermostats there a two basic types, digital (on/off) or analogue (up/down) or modulating is another name. Which you can yes depends on boiler. Then we have programmable and non programmable with the programmable it moves target temperature through the day, and so a eco and comfort temperature is set, so on a really cold day the house is pre-warmed. The we have occupancy detection this auto turns up temperature when it detects some one walking past the thermostat, and there is geofencing this connects to phone so when phone is x miles from home it turns the heating on.

    Then we have the anti-hysteresis software, this can be simply turning heat on/off as the target is approached, or it can remember how fast everything heated up last time and turn off/down the heating at just the right point so it does not over shoot.

    Also window open detection software so it detects a rapid temperature drop and assumes window has been opened (in real terms the door) and turns off heating for a set time.

    Thermostats can be wall mounted or on the radiator the thermostatic radiators valve (TRV) and the TRV and wall thermostat can be independent or linked together.

    So fit some thing like EvoHome, Wiser or Tado and your reasonable sure it will work, but looking at around £150 to £200 for wall thermostat and £45 to £80 each for the TRV heads, and may be a hub, and maybe an annual fee. So in the main people try doing it on the cheap.

    So first thing is boiler type, with oil boilers in the main on/off, with gas most are modulating that is they turn up/down, some can connect to a modulating thermostat. The general idea is in winter the boiler never turns off, it just goes up/down in output, switching it off means any heat in boiler is lost through the flue, and when turned on again it starts off flat out which is not normally economical. In Summer clearly switched off, but Autumn and Spring causes a problem as the boiler can only know using return water if heat is required if it runs, so it tends to cycle on/off to test if required, best cure is a modulating thermostat, but not all boilers are equip to use them.

    So the idea is an on/off thermostat in a room normally kept cool, on the entrance floor, with no outside doors, and no alternative heating, and that thermostat turns off boiler on warm days. Problem is often the room does not exist, so we compromise, and that is the operative word, compromise. So we want to turn off the boiler on a warm day. So if the TRV is set to 18°C and the wall thermostat is set to 19°C in the hall, then in winter the wall thermostat will not turn off, but in Spring it will. Not quite that cut an dried as the TRV is lower than the wall thermostat, so it could be TRV set at 17°C to compensate. This leaves a problem if you want to have a comfort and eco temperature set, as standard TRV is one temperature, however programmable TRV heads start at around £10 so easy enough to set both TRV and wall thermostat to change together.

    However I have found in real terms no need to worry about the TRV, switch off or down the wall thermostat and it turns off boiler while away and turning back one as you approach home works even if the TRV is not altered. Do tend to get the temperature over shooting because it takes so long for heat from hall radiator to reach wall thermostat, but without touching the TRV settings the geofencing and occupancy detection on my Nest thermostat works well.

    The Energenie MiHome TRV heads can also be set for geofencing, so I could set both to change, theory the TRV head can be set to follow the Nest thermostat, in practice it does not work.

    This theory v practice is a big problem, the theory behind Hive it should work well, in practice reports say it does not work as it should, in theory the Wiser TRV heads learn how long it takes to warm a room, so should reheat rooms faster than those that don't, as to which works best, how many times do you hear some on praising how good a car is, then you get one, and it does not do as your mate said it did, no one will admit they go something that does not work as it should.

    So theory if the cheap TRV heads are set to turn down heating at 7 am and up at 5 pm what should happen is the boiler will detect heat not required and start to cycle off/on because the boiler has started the cycle it should turn back on at low output, so the home will slowly cool over the day, then at 5 pm the valves all open but nothing happens until the boiler cycling turns it back on, it will then realise there is a demand for heat, and it will turn up output so possibly 5:30 pm before boiler switches on, and 6 pm before heating flat out, so 6:30 pm before house is at comfort setting. However using a wall thermostat as well with a set seclude you could delay temperature change to 5:45 pm and get same result. But as to energy saving likely very small difference between the two.

    However fitting programmable TRV heads is a lot easier than changing a room thermostat.

    It all depends on life style and house which is best, last house open plan with central heating and a 4.5 kW gas fire in living room, from getting home to house warm 15 to 20 minutes so geofencing was not required, this house switch on to full temperature over an hour, so geofencing is a good idea.
     

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