Thermostat

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Radiator thermostat

Older radiators may have just taps - on, off, and some smallish range of limited flow.

When they have markings they are likely to be thermostatic radiator valves, meaning they will close when the air around them reaches a temperature.

These are both nice to avoid continuous adjustments, and can save energy when you want to keep some rooms at somwhat constant temperature, particularly for lower temperatures.

There's often:

• off, regularly marked zero or with some symbol

• frost protection, often marked with a snowflake. Means the temperature won't get close to 8°C (46°F) so you don't have to worry about water freezing in radiators. You may find your house is never cold enough for this to be necessary, but it's a good setting for a radiator you'll set and forget.

• A range of numbers, e.g. 1..3, 1..4, or 1..5. Typically with the idea that this is for different kinds of rooms, such as:
  • bedroom - good enough when you're typically not staying there, or likely under your covers, something like 16°C (61°F)
  • active working rooms - that you do active work in. Too cold when you sit still, and/or for some people's tastes.
  • sitting rooms - warm enough for people who type or read or otherwise don't heat themselves up much.
  • "I'm always cold, still not warm enough for me" setting, on the order of 24°C (75°F)

• continuous - won't cut off at any temperature, no matter how hot the radiator water or room temperature become.

Rarely what you want. Marked by some symbol, C, or sometimes just the highest number.

While they do relate to real temperatures, the knobs are not marked with temperatures because they are approximate-and-relative at best, and may estimate a little high if, say, there isn't much airflow because of a curtain.

As such, adjust for comfort.