Suggestions for smart thermostats for central heating?

We're going through a similar exercise at the moment. None of the units I've looked at so far (regardless of how "smart" or otherwise they're marketed) have more than one genuine thermostat.

Radiators seem more straightforward. You have a central thermostat that will turn the water heater/flow of water around the radiators off and on. This represents the "maximum" temperature of the house. You can then control each radiator/room by means of the on-radiator valve which essentially throttles the flow of water into the radiator from 0 to 100%. You can therefore have an individual radiator/room less than the central maximum, but it will never be more than the central max. In theory, 100% on an in-room radiator = the room at the central maximum temperature.

Central ducted heated air doesn't have the room by room granular control, but you can have "zones". Again, you set a single central maximum on the thermostat which controls whether heated air is flowing or not. Each zone has a "damper" which (like the on-radiator valve) seems to throttle the flow of air to a particular zone. Again, you can have a room less than the central max, but not more than the central max.

I have yet to find a system/thermostat that will properly control either the on-radiator valve or the zone damper on any system in New Zealand. Ideally I want the central heating equivalent of a Heatermate that will automatically flick on or off the flow of water/air in order to keep a room constant at an actual temperature. This is for comfort rather than cost control.

So for both radiators and ducted air, setting the temperature of each room/zone seems to largely be a matter of trial and error. And the setting isn't dynamic - i.e. you can set it to 50%, but you can't automatically get it to throttle up or down in response to the actual temperature in the room. While "off" seems to work well (no heating), whether 30%, 50%, 90% etc. is the right temperature for any given room is trial and error.

The reason I have put inverted commas and "in theories" around "maximum" temperature is that if the central thermostat isn't located right (e.g. it's somewhere very drafty/chilly), you may find yourself with rooms that are hotter than the maximum as the central heating unit tries to warm up the central point where the thermostat is located.

I would be also be very interested if someone did know of a system with multiple actual in-room/in-zone thermostats.

FWIW for anyone else evaluating the options, this is what I have been able to glean so far. This is what I've been told/researched. No first-hand experience as yet.

Radiators:

- More expensive upfront costs
- Better granular room-by-room control
- "Nicer" heat (common consensus)
- Heat only, no DVS/HRV/home ventilation capability
- Difficult/more expensive to retrofit to existing homes unless renovating anyway or very good under floor access (the water pipes have to be run somewhere). But actually quite easy to install if there is good underfloor access (note that easy does not = cheap)
- Longer time to heat house from cold (suggested to me that you leave it on, just at a lower temperature, at all times)
- Need to be installed at the "right" time in a house's life/renovations - while it's possible, it's inconvenient to remove a radiator just to paint behind it
- Typically more expensive to run

Central air

- Cheaper upfront costs
- Zone-by-zone (not room-by-room) control only
- Some models have home ventilation capability
- Some models have "bypass" capability (i.e. circulate unheated air when necessary - in summer for quasi-cooling, in winter for DVS/HRV-like dehumidifying)
- Difficult to install unless good under floor access (preferred) or in-roof access (not quite as good)
- Some people don't like the airflow/find to too drying
- Typically lower cost to run

For the installation, for both, I was told the first best option was to install the radiators/vents at the outside walls (for big rooms, you will need multiple radiators spread out, which might include interior walls) to ensure best distribution of heat. Unfortunately for us, it would have been really easy to install radiators on the inside walls, but really hard to get to some of the outside walls, so something else to bear in mind.

Deralikt

mdf