For gas boilers, there are really four types of stats. Also note lower flow temp improves efficiency, more condensing and less heat out of the exhaust:
| No modulation | Modulating |
| Dumb | Conventional programmable stat. The boiler will still modulate down the power output once the set flow temp is reached, however you would need to manually adjust flow temp to get the best efficiency. | Once the home gets to to the set temp the stat will communicate with the boiler to lower the flow temp, this will improve efficiency. More efficent than a non modulating 'smart' stat. Plus no reliance on internet connection.
Example: ideal halo lite |
| Smart | Only advantage over the conventional type is the ability to turn on and off via a phone. Can still do this manually with a conventional stat, but not before you get home. No real efficiency bonus.
Example: hive | Efficiency of modulation with smart control, best of all worlds as long as your internet is reliable.
Example: google nest |
System design is important, most boilers, especially combis, are oversized and therefore cycle on and off when the home is up to temp, which increases wear and reduces efficiency. This affects whatever type of stat you have.
Heat pumps are different again, require a different system design with much lower flow temps and higher flow rates than gas boilers (lower dT), and also require an always on regime in winter, otherwise you will be always cold.
