What Humidity Should a Gun Safe Be?

For a stable mixed collection at normal indoor temperatures, aim for 40–50% relative humidity (RH). Follow different storage conditions when specified for your firearm.

Why 40–50%?

The Canadian Conservation Institute recommends 35–55% RH for stable metal objects stored in mixed collections. Our 40–50% working target falls within that guidance. Extremely dry conditions can affect wooden components, which matters when choosing conditions for a mixed collection. [1, 2]

Some firearm manufacturers give a more specific target. SIG Sauer’s P365 manual recommends no greater than 40% RH at 80°F. For a P365, follow SIG’s storage guidance rather than using 50% as the target. [3]

How to check the humidity

An inexpensive digital thermometer-hygrometer measures temperature and RH. Search Amazon for a monitor with the features you need. For a quick overnight check, choose one with minimum/maximum memory. Let its readings settle inside the safe before resetting that memory, then check the highest RH reading the next morning.

For a clearer picture, choose a temperature-and-humidity monitor with data logging. Look for saved readings and a history graph in the app. The graph shows whether humidity briefly rose after you opened the safe or stayed high for most of the night.

Place the monitor near the stored firearms, away from direct heat from a heating rod. Keep the sensor openings exposed to the surrounding air. A heating rod warms the air and lowers its RH, so a reading taken directly beside it may be lower than the reading near the guns. [4]

Start with a week of recording and look at the graph each day. If you can adjust the recording interval, use 10–15 minutes. Note when the door was opened so you can recognize those changes in the record. Repeat the check during wetter weather to see how well your storage equipment keeps up.

For the 40–50% target, a reading around 45% is comfortably within range. If the monitor supports alerts, set a high-humidity alert at 50% to prompt a check of the history. A brief rise after opening the door needs a different response from humidity that stays high while the safe is closed.

What to do when humidity stays high

If the safe repeatedly stays above your target for hours, check the room’s humidity too. A second inexpensive monitor outside the safe makes that comparison easy.

When both readings are high, a room dehumidifier can address the larger moisture source. Humid room air enters the safe whenever the door opens; drying that air reduces the moisture introduced during use. It also reduces the work the desiccant inside the safe has to do. [5]

For help deciding whether to add equipment, see Do You Need a Gun Safe Dehumidifier?. Check the safe’s readings after any change to see whether it helped.

If the room is already within target but the safe remains damp, look for moisture in its contents. Case padding can remain wet after the firearm looks dry. Check the desiccant’s service indicator and dry or replace the material according to its instructions. Compare the following days’ readings to see whether servicing helped. [6]

What a humidity card can tell you

A humidity indicator card offers a visual check without a battery. The Desco 13853, for example, has marked RH spots that move from brown toward yellow as conditions become more humid. Read the spots against the card’s printed color reference. [7]

The card reports local humidity and its colors are reversible, so use a logger to retain the history of an overnight peak. [7] Our guide to desiccant service timing explains the card’s response time and when it needs replacement.

Where XeroMag fits

Once you’ve established a humidity target and addressed persistent dampness, XeroMag offers a passive addition to your firearm-storage routine. It’s designed to take the place of a compatible firearm’s magazine during unloaded storage. It contains activated alumina desiccant to take up water vapor, alongside a separate Cortec VpCI-170 element for corrosion inhibition. It works without electricity or batteries, so you can use it where routing power into the storage enclosure would be inconvenient.

The separate Desco indicator card gives you a quick visual humidity check. The removable baseplate lets you replace the desiccant and inhibitor element while keeping the insert, making regular servicing straightforward. Choose the listed configuration for your exact firearm.

Sources

1. Canadian Conservation Institute: Storage of Metals, CCI Notes 9/2, stable mixed collections.

2. Canadian Conservation Institute: Caring for metal objects, relative humidity and composite objects.

3. SIG Sauer P365 operator’s manual, revision 05, section 10.1.

4. Canadian Conservation Institute: Incorrect relative humidity, temperature differences within enclosures.

5. Canadian Conservation Institute: Airtightness Measurement of Display Cases and Other Enclosures, enclosure exchange and moisture-control demand.

6. Canadian Conservation Institute: Preparing silica gel for contained storage of metal objects, monitoring and servicing.

7. Desco: Humidity Indicator Cards, TB-3087, application and response instructions.