Radiator valve numbers: what 1 to 5, ✱ and 0 mean
The numbers on a thermostatic radiator valve head are room-temperature settings: the valve closes as the air around it warms to roughly the temperature for that number. On the three heads in the table that publish a figure per number, 3 is about 20 °C.
Each maker’s own setting temperatures
These are approximate room temperatures that depend on the room — where the valve sits, draughts, sun, furniture in front of it — and the numbering differs by maker, so the same number can mean a different temperature on another head. A dash means the maker’s document gives no figure for that mark.
| Maker, head | 0 | ✱ frost | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|---|---|
| Danfoss RAS-C sensor | — | 8 °C | 12 °C | 16 °C | 20 °C | 24 °C | 28 °C |
| Honeywell Home (Resideo) VT15 / VTL15 | closed | 6 °C | 10 °C | 15 °C | 20 °C | 23 °C | 26 °C |
| IMI Heimeier Thermostatic head K | — | 6 °C | 12 °C | 16 °C | 20 °C | 24 °C | 28 °C |
| Drayton TRV4 | — | below 8 °C | — | — | — | — | — |
- Danfoss: Stated at Xp = 2 K: the valve closes at a sensor temperature 2 °C higher than the scale. Source, checked 2026-09-27.
- Honeywell Home (Resideo): “Values approximate.” Even at 0 the head may open as the room cools. Source, checked 2026-09-27.
- IMI Heimeier: About 4 °C per number, about 1 °C per bar; a moon mark at about 14 °C (night-time reduction) and a sun at 3. Source, checked 2026-09-27.
- Drayton: 1 to 5 then MAX, approx 10 °C to 30 °C across the scale; no figure per number on the information sheet. Source, checked 2026-09-27.
What the manual says to do
Set the number for the room and give it time to settle. Heimeier recommends 3, about 20 °C, for living rooms, and says settings above 4 should be avoided if a lower one is comfortable, because 1 °C more room temperature costs around 6 % more energy. Danfoss says its values are for guidance only.
Turning the head to a number is yours to do. Swapping a valve or head on a filled system, balancing the radiators or draining the system is a job for a qualified heating engineer.
What it does not mean
The numbers are not radiator or water temperatures, and a number is not a promise: Danfoss says the temperatures “are for guidance only as the obtained room temperature will often be influenced by installation conditions”, and Honeywell Home prints “Values approximate”.
- What it looks like
- A ribbed head on the radiator valve with a scale: usually ✱ or a snowflake, then 1 to 5, sometimes 0 for closed, MAX, and small bars or a moon and sun between the numbers.
- Names used
- Thermostatic radiator valve (TRV) setting; TRV head numbers; Setting scale
Where makers differ
Numbering differs by maker. 1 is about 10 °C on the Honeywell Home VT15 but about 12 °C on the Danfoss RAS-C and the Heimeier K; 5 is about 26 °C on the VT15 and about 28 °C on the other two. Drayton’s TRV4 goes 1 to 5 then MAX, about 10 °C to 30 °C, without a figure per number on its information sheet.
Other symbols with the same shapes
Sources
The settings are each valve maker’s own published figures, from the data sheets below, each fetched and read on the date shown:
- Danfoss, RAS-C thermostatic sensor (013G5015, 013G5016): Data sheet Thermostatic sensor RAS-C, VDFNQ302 (05/2015) (PDF) — Setting the temperature: ✱ = frost protection setting; scale ✱ 1 2 3 4 5 = 8, 12, 16, 20, 24, 28 °C (at Xp = 2 K); “The temperature values stated are for guidance only as the obtained room temperature will often be influenced by installation conditions.” Checked 2026-09-27.
- Honeywell Home (Resideo), VT15 / VTL15 thermostatic radiator valve: VT15, VTL15 radiator valves product specification sheet, EN0H-2041GE23 R0121 (PDF) — TRV head settings: 0 closed, frost 6 °C, 1 = 10 °C, 2 = 15 °C, 3 = 20 °C, 4 = 23 °C, 5 = 26 °C; “Note: Values approximate.” Checked 2026-09-27.
- IMI Heimeier, Thermostatic head K: Thermostatic head K data sheet, EN ed.3 10.2017 (PDF) — Recommended room temperatures: snowflake ≈ 6 °C, 1 ≈ 12 °C, moon ≈ 14 °C, 2 ≈ 16 °C, 3 ≈ 20 °C, 4 ≈ 24 °C, 5 ≈ 28 °C; “The difference between each number is approximately 4 °C”; settings above 4 should be avoided if a lower setting is comfortable; 1 °C higher is around 6 % more energy. Checked 2026-09-27.
- Drayton, TRV4 thermostatic radiator valve: TRV4 thermostatic radiator valve information sheet (PDF) — Technical data: setting numbers “Integral sensor 1 to 5 then ‘MAX’”; “* Frost protection … below 8°C”; temperature setting range “1 to MAX = approx 10ºC to 30ºC”. Checked 2026-09-27.
Written in our own words; quotations are the makers’ wording.