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How to use an analogue thermometer

Updated: October 2026

An analogue thermometer shows temperature without a battery. On a dial, a needle moves across a scale. On a column, a thread of coloured spirit rises in a glass tube. Either kind can check a living room, a bedroom, a greenhouse or an outdoor spot, as long as you site it fairly, give it time, and read it straight on. This page is the method once you already own one. The product table stays on the [analogue thermometer comparison](/hub/climate-measuring/analogue-thermometer). The sensing part reports the air or the surface right beside it. It does not average the house, and it does not repeat the number on the hall thermostat.

An analogue thermometer shows temperature without a battery. On a dial, a needle moves across a scale. On a column, a thread of coloured spirit rises in a glass tube.

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On this page
  1. 1.Site it in ordinary air
  2. 2.Wait, then read square to the scale
  3. 3.Check a doubtful reading
  4. 4.Let the figure guide the room
  5. 5.Care, and the jobs it will not do

Site it in ordinary air

For a room, hang or stand the thermometer at about chest or head height, roughly 1.2 to 1.5 metres from the floor. Warm air rises, so a dial on a picture rail reads high. Keep the case off radiators, ovens, tumble dryers and bright lamps, and out of direct sun. Avoid a draught and the window glass. In a greenhouse, shed or conservatory, use shade and keep the instrument off the glazing. Outdoors, use a north-facing wall. On a south or west wall, put it under deep eaves.

Wait, then read square to the scale

Nothing analogue jumps to the new temperature the moment you carry it indoors. Wait at least 15 minutes after a move. Half an hour is safer if it came from a cold car or a January porch. Read only when the needle has stopped creeping, or when the spirit has stopped climbing. After unpacking, leave it overnight before you treat the first look as a baseline. Put your eye square to the scale. From the side, a needle appears to sit on the wrong mark. On a small domestic dial that shift is about half a degree. On a column, read the top of the spirit. If the indicator lies between 19 and 20, just under 20°C is fair.
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Check a doubtful reading

Melting ice is the home reference when the scale includes 0°C. Fill a glass with ice and a little cold water, stir for a minute, and the mixture sits at 0°C. Do not dunk a cased dial or a wall column unless the maker says it is waterproof. Press the back of the case against a thin plastic bag in the ice water. More than a couple of degrees is an offset to remember, or a reason to replace the thermometer. Wrong in the sun and right in the shade: move it. Wrong in the shade as well: the movement or the column is the problem.

Let the figure guide the room

Many households in Britain find occupied rooms comfortable around 18°C to 21°C. The NHS advises keeping those rooms at 18°C or above in cold weather if you can. A hall stat can call for heat while a back bedroom on an outside wall stays several degrees colder. Read that bedroom in the early morning if you use a setback. A fridge dial sits on a middle shelf in the air, not in the door rack and not hard against the back wall. The household cold band is on the fridge thermometer dial page. Outside, cold air pools at the foot of a slope, so hang the thermometer among the plants, in shade, at foliage height.

Care, and the jobs it will not do

Wipe the glass with a dry cloth. A light tap may free a needle that is brushing the face. If it sticks again, replace the dial. An analogue thermometer will not log a fortnight or alert your phone. About one degree is the practical step for home heating and garden frost. When you need a stored trace, or a probe for food, that choice is on the analogue vs digital thermometer page.

Common questions

Should I read Celsius or Fahrenheit?
In Britain, use the Celsius scale. Some faces print Fahrenheit as well. Match the scale to the place. A room instrument often runs from about 0°C to 40°C or 50°C. An outdoor one should show temperatures below freezing, or a night near 0°C will sit off the end of the face.
How can I tell sun-error from a faulty movement?
Move the thermometer into shade and wait. If the needle or the spirit falls back over the next half hour, the earlier figure was the case heating up. A fault sticks, jumps when you tap the glass, or stays several degrees out in stable shade. A spirit column split into blobs will not track the room until it is reunited or the thermometer is replaced.
Why can two thermometers in one room disagree?
The sensing part answers a local question. Two working instruments can disagree if one sits over a radiator and the other is on a cold outside wall. Neither is averaging the house, and neither has to match the hall thermostat. Compare them only after both have stood in the air you actually want to judge.
What if the spirit column has split?
A column that has separated into blobs, or a thread parked at the top of the tube after a hot spell, will not track the room until the liquid is reunited or the thermometer is replaced. A bent needle will not straighten itself either. If a light tap frees the needle once and it sticks again, replacement is the usual remedy.
What should I do with minimum and maximum markers?
If the thermometer has minimum and maximum markers, reset them at the start of the period you care about. The control is usually a button or a small magnet. Read the high and low at the same time each day. Reset again only if you want the next 24 hours on their own. A plain dial with no markers cannot store the night’s low.

Related pages

Analogue thermometer buying guide

Analogue thermometer

Best analogue thermometer: room, fridge or humidity

Fridge thermometer dial: check the UK air at 0–5°C

Analogue vs digital thermometer: dial, memory, probe

Sources

Public UK sources listed in the research digest. Listing prices, stars, and review counts are from amazon.co.uk on 19 October 2026.

  1. GOV.UK — controls on mercury (retrieved 19 October 2026)
  2. Food Safety (Temperature Control) Regulations 1995, regulation 4 (retrieved 19 October 2026)
  3. GOV.UK — chilling and freezing for food businesses (retrieved 19 October 2026)
  4. GOV.UK — how to chill, freeze and defrost food safely (retrieved 19 October 2026)
  5. Food Standards Agency — Safer Food, Better Business, chilled storage (retrieved 19 October 2026)
  6. The Lullaby Trust — room temperature (retrieved 19 October 2026)
  7. Centre for Sustainable Energy — temperature and humidity at home (retrieved 19 October 2026)
  8. Royal Meteorological Society — measuring temperature and humidity (retrieved 19 October 2026)