Storing Instruments Safely: Humidity and Temperature Basics

Most instruments, wooden ones above all, are happiest at roughly 40 to 60 percent relative humidity and ordinary room temperature. Stability matters more than the exact number: damage comes mainly from fast, large swings, from dry winter heating, from heat and cold in a parked car, and from condensation after a temperature change. A hygrometer, a sensible spot, a case, and a bit of humidifying or dehumidifying will prevent most problems.

Why climate hurts instruments

Wood is hygroscopic: it takes up moisture from the air and gives it back. It swells as humidity rises and shrinks as it falls, by different amounts along and across the grain. An instrument also combines glued wood parts that run in different directions with metal, felt, leather and finish, which respond to climate in very different ways. That builds stress, and the results are familiar:

• Too dry (below about 40%): Wood shrinks. Guitars and bowed strings can open seams, crack, lose string height and slip at the pegs, and guitars may show sharp fret ends. A piano's soundboard loses tension, tone suffers, and action and tuning become unsettled. Woodwinds can crack, and pads dry out.
• Too damp (above about 60 to 65%): Wood swells, keys and key mechanisms stick, tone turns dull, metal corrodes, and mould growth starts at around 65% relative humidity.
• Rapid changes: Repeated swelling and shrinking stresses glue joints and finish more than a steady value that is slightly off target. A gradual change over days is far gentler than a jump within hours.

Winter heating is the classic culprit: cold outdoor air holds little water, and once it is warmed to room temperature the relative humidity drops sharply, often well below 40%. Most dryness cracks happen in winter.

Target ranges by instrument group

Sources differ slightly, so treat these as guideline values. A room temperature of roughly 68 to 75°F (20 to 24°C) is comfortable for people and instruments alike; many sources give roughly 65 to 77°F (18 to 25°C) as the acceptable span.

Rule of thumb: where there is a lot of wood, aim for 40 to 60% and stay near the middle. Where metal dominates, dryness is less of an issue, but dampness very much is.

Hygrometers: choosing and checking one

Without measuring, you are guessing. A thermo-hygrometer is inexpensive and shows temperature and humidity together. Digital models are easier to read; analog dial models need no battery but are often less accurate. A min/max memory is handy because it shows how much the climate swings while you are not watching.

Where to put it

Place it close to the instrument but not on a radiator, by a window or in a humidifier's airflow. Small units made for cases fit inside. Write down readings at the same times for a week to learn the room's rhythm.

Calibrating with the salt test

Inexpensive hygrometers are often off by several points. To check yours:

1. Put about a teaspoon of table salt in a bottle cap and dampen it with a few drops of water, so it is wet but not swimming in liquid.
2. Place the cap and the hygrometer together in an airtight container or a well-sealing bag with some air left in it.
3. Leave it at least six hours, better overnight, at a steady room temperature, and do not open it in between.
4. Read the value: it should be 75%. The difference is your device's error. If it reads 70%, add about 5 points to future readings.

If the device cannot be adjusted, simply note the offset. Because the error need not be the same across the whole range, the test is a good guide, not a lab value.

Humidifying and dehumidifying

If readings fall outside the target range, there are three levers: the room, the case, or the instrument itself.

Room: humidifiers and dehumidifiers

Room humidifiers come as warm-mist (evaporator) units, evaporative units and ultrasonic mist units. Warm-mist units are effective but use a lot of power. Evaporative units are thriftier and need regular cleaning. Ultrasonic units are inexpensive but need careful upkeep, because otherwise they spread germs. Do not put the humidifier right beside the instrument and never aim its output at it. The hygrometer tells you whether the result is right. In summer or damp rooms, an electric dehumidifier or air conditioning set to dry helps. Adjust in small steps over several days, not all at once.

Case: humidifiers and packs

The closed case is the easiest place to hold a stable climate. Options include sponge humidifiers that you dampen and place in the case, and two-way packs calibrated to a fixed value (commonly around 45 to 50%). Two-way packs release moisture when the air is too dry and absorb it when too damp; they typically last a number of weeks and then need replacing. Larger instruments need more packs than small ones. With sponge units, dampen them only moderately, let them drip dry, never let them drip onto the instrument, and check the sponge for mould regularly. Store them dry after winter.

Inside the instrument: be careful

Humidifiers that go directly into the body (tube or sponge products) are common but carry a risk: if the sponge is too wet, moisture reaches the wood or finish directly, and water marks, mould or loosened glue joints can follow. Wring them out well, never insert them dripping wet, and use them only when the air is truly dry. If that makes you uneasy, use case packs or a room humidifier.

Silica gel as a dehumidifier

Silica gel absorbs moisture until it is saturated, then must be replaced or dried. It suits metal wind instruments and electronics in cases, but it is unsuitable for wooden instruments in dry air because it would pull out even more moisture. For wood, two-way packs are the safer choice.

Avoid homemade fixes involving heaters, hot air or hair dryers: heat speeds up drying and weakens glue and finish. No trick replaces slow, even corrections.

Choosing a spot at home

• Interior wall instead of exterior wall: Exterior walls see bigger swings in temperature and humidity, especially in older houses. A piano sits more calmly against an interior wall in an evenly heated room.
• Radiators and vents: Keep a distance, never directly beside or above them. Rising dry air pulls water out of the wood. The same goes for fireplaces, space heaters, floor heating and air vents; a common guideline is a few feet (about a metre) of clearance.
• Windows and sun: Direct sun heats the wood and ages finish and wood. Curtains or blinds soften it. Windows are also cold surfaces where moisture condenses.
• Basement and attic: Basements tend to be too damp, and attics too hot in summer and too cold in winter. Neither is suitable for long-term storage.
• Air conditioning and drafts: No direct airflow onto the instrument.

More on pianos: humidity and placement for pianos.

Seasons: heating season and summer heat

Heating season

Wherever heating runs from fall into spring, indoor air tends to be dry, and in cold regions it can get very dry. Do not overheat rooms, check the hygrometer more often, and when it drops below 40%, humidify the room or the case. A calm, evenly heated room beats the one with a stove or heating vent close to the instrument. Short dips are fine as long as the average over the year stays in range.

Summer and air conditioning

In humid climates, summer humidity can climb well above 60%, especially in basements and older houses and after rain. Air conditioning dries and cools the air, which helps, but it can also cycle on and off and swing the readings, and a unit that blows directly at an instrument is a problem. Heat strains glue, finish and pads: instruments do not belong in a sun-heated attic room or behind a sunny window.

More on bowed strings in winter: cello humidity, cracks and winter care. For guitars: humidity and storage for acoustic guitars.

Car, transport and acclimatising

A parked car is an extreme climate: in summer the interior heats far above the outside temperature, and in winter it chills deeply. Glue, finish and wood cannot take that for long. If possible, do not leave an instrument in a parked car. If you must for a short time, keep it in its case, in the shade, and never in a sun-baked trunk.

1. Cold to warm: Let the instrument reach room temperature in its closed case before you open it. Depending on the difference, that takes one to several hours. Otherwise condensation forms on the finish, in pads and inside electronics.
2. Warm to cold: Likewise keep it in the case and let it cool slowly, without the shock of a quick trip into freezing air.
3. Protection in the case: On winter drives you can also wrap the instrument in a cloth or blanket and add a desiccant if needed.
4. After a move: For pianos, a common rule of thumb is to give the instrument a few weeks in the new room before it is tuned.
5. Flying: Small instruments are best carried on board. Rules on cabin space and size vary by airline and aircraft, so check the airline's terms in advance. Large instruments in the hold face cold and handling, so a sturdy case matters.

Case or open?

A good case buffers humidity and temperature swings far better than an instrument left out in the room, and it also protects against knocks, dust and sun. For storage it is the first choice, especially for instruments you do not play every day and especially during the heating season. Open storage on stands is convenient but requires a stable room climate. Pianos are protected with a cover and a good room climate instead. For wind instruments, keep mouthpiece and accessories dry.

Long-term storage

• Stringed instruments: For longer storage, many players ease the tension somewhat to relieve neck and top, but do not remove the strings completely; some tension helps keep the neck straight. Pianos are not detuned for storage; have them tuned when they return to use.
• Brass: Remove the mouthpiece, dry the inside completely, care for moving parts, place in the case and store dry.
• Woodwinds: Take apart, dry inside, check keys and pads, case. In dry air, add a two-way pack.
• Piano and grand: Cover but do not wrap airtight, monitor humidity, pick a room without temperature jumps. Have moving and storing done by professionals.
• Drums: Relieve the head tension, keep cymbals dry, store hardware dry.
• Electronic instruments: Store dry, dust-protected and at room temperature, not in a basement.

Check in every few weeks: read the hygrometer and look for mould, discolouration, open glue joints and pests. Care notes for your specific model take priority.

Mould, pests and water damage

Mould

Mould needs moisture, warmth and darkness and shows up from about 65% relative humidity. Typical signs are white or greenish film on finish, case lining and pads, plus a musty smell. For instruments you blow into, it is also a health matter, since spores can reach the mouthpiece and tubing. Dry out the case, replace an affected lining, lower the room humidity, and have a repair shop clean the instrument if the problem is larger. Harsh products on the finish are risky, so do not experiment.

Pests

Moths eat felt and wool, especially in pianos and case linings. Woodworm (small tunnels, fine boring dust) spreads from infested floors or furniture. If you suspect either, check hammer felts, dampers, linings and wood, separate affected instruments from others, and let a specialist decide; poisons and fumigation are not for amateurs.

Water damage

If an instrument gets wet (a leak or burst pipe), do not dry it with heaters or a hair dryer and do not shut it away damp in a case. Let it dry slowly at normal room temperature with good ventilation, and bring in a repair shop. Photograph the damage and ask your insurer; see also instrument insurance and home contents.

Electronics and batteries

Digital pianos, keyboards, synthesizers and amplifiers dislike both moisture and condensation. Let cold equipment sit at room temperature for several hours before switching it on so condensation inside can evaporate. Store it dry and dust-protected. For devices with rechargeable or standard batteries, follow the maker's storage and charging notes; a battery does not belong in heat, deep cold or damp rooms, and swollen or damaged batteries are a job for specialists. Work on the electrics belongs in a shop anyway.

Common mistakes

• Leaving the instrument in the car, in summer or winter.
• Opening the case right after coming in from the cold.
• Keeping it next to a radiator, stove or window.
• Humidifying by feel without a hygrometer, or trusting an uncalibrated reading blindly.
• Using sponge humidifiers too wet, or forgetting them until they go mouldy.
• Raising humidity sharply in winter instead of slowly.
• Putting damp brass in the case without drying it first.
• Putting silica gel in a wooden instrument's case when the air is already dry.
• Tuning a piano immediately after a trip or move, without letting it settle.

Frequently asked questions

What humidity is ideal?

For wooden instruments usually 40 to 60%, best 45 to 55%. Some makers give tighter ranges. Stability counts more than the exact figure.

Do I really need a hygrometer?

For wooden instruments, yes. It is cheap, and you notice problems before cracks appear.

Can I humidify too much?

Yes. Above about 60 to 65% you risk swelling, sticking mechanisms, corrosion and mould.

Should I loosen the strings?

For long storage, relieve them somewhat, but do not remove them completely. Not for pianos.

How long should I acclimatise?

Small instruments a few hours in the closed case; pianos a few weeks after a move before tuning.

What should I check when buying used?

Ask about storage and climate, and look for signs of cracks and discolouration; see the used instrument buying checklist.