Smart Replacement for Central Heating Thermostat

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johno1234

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#312682 8-May-2024 09:54

Hi all, our home central heating is switched on/off by this:

It works but it's not very good - it's in a hallway that has no vents, is that the right place to measure the temperature? It can't be remotely operated or scheduled. I wouldn't mind replacing it with something smart that can be remotely controlled and scheduled preferably with Homekit (or HomeBridge + Homekit).

There are lots of options but not sure which is a direct replacement - any suggestions?

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#3227742 8-May-2024 10:47

You can replace the thermostat with a homebridge/homekit compatible one. Or remove it and set a smart relay to control the central heating unit power (a shelly or zwave equivalent).

The relay woudl then give you the ability to turn on your central heating via app.

Next you would add 1 or more temperature sensors, they can then be used to control the relay. I pull 3 sensors myself into one average reading. And use that reading to drive a thermostat in home assistant. I think you could do similar in homebridge - maybe not the average bit, but I believe there was s thermostat that could take a reading from x sensor, and user specified target temp to switch on/off a switch (the relay).

Obviously it's easier in home assistant, and you have access to more hardware and more rules. I used a mqtt thermostat which I could set the current temp to a topic and the switch to a different topic. I had a quick look and couldn't immediately find a thermostat as I described above that wasn't mqtt. But it might exist.

Easiest consumer option, is to buy a ready made one.

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johno1234

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#3227812 8-May-2024 11:56

Yes, a Shelly1 could switch this thing on and off in conjunction with a Shelly H/T sensor, but I would still need a wall mounted user interface on it so it can be operated by the technically challenged in the household.

So far I haven't found a NZ supplied/certified Homekit/Homebridge option though. Possibly a NEST 3? Although they are very expensive and not sure what sort of wiring they support.

davidcole

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#3227813 8-May-2024 11:57

johno1234:

Yes, a Shelly1 could switch this thing on and off in conjunction with a Shelly H/T sensor, but I would still need a wall mounted user interface on it so it can be operated by the technically challenged in the household.

So far I haven't found a NZ supplied/certified Homekit/Homebridge option though. Possibly a NEST 3? Although they are very expensive and not sure what sort of wiring they support.

If you went shelly + shelly ht, you'd go mounted-less.

Gets too hard to try and display as well- is possible though (wall mounted ipads/tablets etc)

bigreddog

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#3227815 8-May-2024 12:03

Shelly now have their own wall display: Shelly Wall Display - Shelly Wall Display - All products - Shop - Shelly

Size wise looks very similar to Sonoff branded tablet, if so, the performance isn't amazing but your use case probably not that intensive either?

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johno1234

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#3227900 8-May-2024 14:38

bigreddog:

Shelly now have their own wall display: Shelly Wall Display - Shelly Wall Display - All products - Shop - Shelly

Size wise looks very similar to Sonoff branded tablet, if so, the performance isn't amazing but your use case probably not that intensive either?

That display looks ideal in terms of size, mounting etc but looks to me that it works with the Shelly home ecosystem - I don't think it would work with Homekit. However as dscole mentioned, could do something with a permanently allocated iPad, surplus old iPhone etc.

davidcole

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#3227901 8-May-2024 14:41

You can get shellys into homebridge. I think it has a plugin....or can use mqtt. So I woudn't let that stop you.

The driver should be a working thermostat...the secondary should be homekit compatibility - IMO. the only influence technology should have is - do I want local or cloud based.

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johno1234

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#3227904 8-May-2024 14:51

I have the "Homebridge Shelly" plugin installed - doesn't currently list the wall-display. There are a bunch of other Shelly plugins, will have a trawl through them and see if they have it.

davidcole

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#3227905 8-May-2024 14:54

johno1234:

I have the "Homebridge Shelly" plugin installed - doesn't currently list the wall-display. There are a bunch of other Shelly plugins, will have a trawl through them and see if they have it.

Wouldn't the wall display just display via native shelly protocols the state of a relay/temp sensor. Or are you hoping to use the wall display as display, sensor and relay?

johno1234

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#3227909 8-May-2024 15:10

The Shelly Wall display does have a relay included (max 5A). What is obscure and not explained on Shelly's website is how you configure its UI, actions and so on. According to the website, you can control up to 6 devices with it but no detail on automation/scenes etc.

Shelly Wall Display

Handle9

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#3227916 8-May-2024 15:38

If you want to replace the thermostat the first thing you need to determine is how the furnace is controlled. Does it require clean contacts or is it switching 24VA or mains? Once you know that you can determine what to control the unit with.

The next step is to determine what cores you have in your proposed thermostat location. For a bellows thermostat like you want to replace it could be only 2 cores run to the localtion or there may be more. If you can't get power to the thermostat location your options become more limited. There are plenty of battery operated thermostats available which you can load schedules etc but they won't usually connect to wifi or have an app.

Once you know what you are working with you can determine the best solution. Most smart thermostats are 24VAC so if you have to switch mains you'll probably need to design some form of interposing relay arrangement.

Nest or Ecobee are the bigger of the global players. I'm runnning Ecobee on my ACs as they are homekit certified which means fully local control. You can add remote sensors as well.

tweake

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#3227964 8-May-2024 16:24

first thing is what is it running and how does it interact with the house. if its a proper hvac system do you even need scheduling or remote operation? is the thermostat even in the right location?

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johno1234

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#3227987 8-May-2024 17:20

Hi, good questions. The furnace is a diesel fed unit in the basement that heats air and blows it through ducts and out through floor registers with dampers in all rooms. There are no floor registers in the hallway where the thermostat is located. It does a very quick job of heating up the living areas and is a bit slower in the bedrooms. I find my office on the south side of the house warms up the slowest despite being the smallest room in the house.

The thermostat itself has a what looks like a single TPS cable running into it that is carrying live power according to the non contact voltage detector. Probably just 2 cores and a single pole switch?

tweake

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#3228020 8-May-2024 17:51

where is the return?

johno1234

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#3228048 8-May-2024 18:12

There isn't one with a 2 wire thermostat - one in one out, single pole switch.

Handle9

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#3228051 8-May-2024 18:31

johno1234:

Hi, good questions. The furnace is a diesel fed unit in the basement that heats air and blows it through ducts and out through floor registers with dampers in all rooms. There are no floor registers in the hallway where the thermostat is located. It does a very quick job of heating up the living areas and is a bit slower in the bedrooms. I find my office on the south side of the house warms up the slowest despite being the smallest room in the house.

The thermostat itself has a what looks like a single TPS cable running into it that is carrying live power according to the non contact voltage detector. Probably just 2 cores and a single pole switch?

It's a conventional thermostat then. They generally work with a bimetallic strip or gas bellows which make or break based on the temperature. They are mechanical devices and pretty simple.

If you don't want to rewire and just want to replicate the functionality you should look at a battery powered thermostat. If there are three cores you could use interposing relays for a smart thermostat but it's a bit of a faf around.

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