How Temperature and Humidity Affect Clock Accuracy

Mechanical clocks are finely tuned instruments, and even small changes in the environment can influence how well they keep time. Temperature shifts, humidity swings, and seasonal climate changes affect pendulum length, lubrication behavior, wooden clock cases, and metal components inside the movement. These factors can cause a clock to run fast, slow, or drift inconsistently throughout the year. This guide explains why clocks react to environmental conditions and how to improve accuracy in homes with variable climate control.

Temperature Effects on Mechanical Clocks

Temperature changes impact almost every part of a clock’s movement, but the pendulum is the component most sensitive to heat and cold.

Pendulum Expansion and Contraction

The length of the pendulum determines a clock’s rate. Temperature changes directly affect that length:

• Heat makes the pendulum rod expand → the clock runs slow

• Cold makes the rod contract → the clock runs fast

Even small temperature variations—5–10 degrees—can create noticeable drift over the course of a day or week. Metal rods, especially brass or steel, show measurable movement with temperature swings. This is why older clocks may include temperature-compensated pendulums such as gridiron rods or mercury pendulums.

Metal Plate Expansion

Clock plates expand in warm conditions and contract in cooler ones. This can cause:

• Slight changes in pivot hole clearance

• Increased or uneven friction on arbors

• Minor alignment shifts between gears and pivots

If friction increases due to expansion, the clock may slow down or stop during hot weather.

Mainspring Behavior

Temperature affects the torque a mainspring produces:

• Warmer temperatures may make the spring slightly more flexible, reducing torque.

• Cooler temperatures can stiffen the spring, changing recoil behavior.

These changes are subtle but can contribute to seasonal rate variations, especially in older or partially worn springs.

Humidity Effects on Clocks

Humidity often affects clocks more dramatically than temperature, especially those housed in wooden cases.

Wooden Case Movement

Wood reacts to moisture in the air:

• High humidity → swelling

• Low humidity → shrinking

Because clock movements are mounted to wooden cases or seatboards, this movement can:

• Tilt the clock slightly

• Shift the movement out of alignment

• Change the beat (uneven tick–tock rhythm)

• Cause the pendulum to swing off-center or lightly brush the case

Even a small tilt can cause a pendulum clock to run poorly or stop altogether.

Oil Breakdown

Humidity accelerates:

• Oxidation

• Thickening of oils

• Evaporation of lighter oil components

Old or degraded oil becomes sticky, slowing pivots and causing inconsistent timekeeping. Moisture also encourages contaminants to cling to pivot holes, forming a sludge-like residue.

Rust Formation

Moisture is the enemy of steel components. High humidity can cause rust on:

• Pivots

• Arbors

• Steel pinions

• Suspension springs

Even light rust increases friction dramatically. Severe rust may cause permanent damage that requires replacement components.

Clocks Most Affected by Temperature

Some clock types are especially sensitive to environmental changes:

• Regulator clocks — designed for precision; even small temperature changes affect their long pendulums

• Longcase (grandfather) clocks — large wooden cases respond heavily to humidity

• Antique pendulum clocks — older materials and worn pivots react more to climate variations

Quartz clocks are far more stable but still experience crystal oscillator drift in extreme temperatures, especially below 50°F or above 90°F.

How to Improve Accuracy in Changing Environments

Environmental control can stabilize a clock’s rate and reduce seasonal drift. Here are the most effective strategies:

• Keep clocks away from vents, fireplaces, windows, and exterior walls
  These areas experience large temperature swings and drafts.

• Maintain consistent indoor temperatures
  Ideally between 65–75°F for older clocks.

• Use a humidifier or dehumidifier as needed
  Most clocks perform best between 35–55% relative humidity.

• Re-level clocks seasonally
  Wood movement can tilt the case, affecting beat and pendulum alignment.

• Make small pendulum adjustments
  Raise or lower the bob in tiny increments (½ to 1 turn) and allow 24 hours to evaluate.

• Keep movements clean and properly oiled
  Fresh lubrication helps a clock tolerate environmental changes more smoothly.

If you live in the southeast US, where the humid climate can fluctuate dramatically between seasons, clocks may require more frequent beat adjustments, leveling checks, and routine maintenance to stay accurate year-round. Visit us in Calhoun, GA for all of your timekeeping maintenance needs.