Short-Term HVAC Failure: A First-Response Guide for Collections

When the HVAC system goes down, the first hour matters most. In this guide, Christopher Cameron, Conserv’s Director of Conserv Services, sets out what to do in the first fifteen minutes of an HVAC failure, how to stabilise a space, and when to pick up the phone to a conservator.

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This guide covers the first hours of an HVAC failure. If you already know the repair will take longer than 24 to 48 hours, move to the long-term HVAC failure response guide instead.

First 15 minutes

• Confirm the failure. Check your data logger, dashboard, or thermostat readout rather than relying on how the room feels.
• Identify the scope. Is it the whole building, one zone, or a single gallery or storage room?
• Record the current conditions. Note temperature, relative humidity, and how fast conditions are moving.
• Notify your designated emergency contact — facilities lead, collections manager, or on-call conservator.
• Do not make drastic manual adjustments. Sudden swings can shock collections faster than a slow drift.

Stabilise the space

• Close doors, vents, and dampers to the affected area to slow the rate of change.
• If safe and available, use portable dehumidifiers, humidifiers, or fans to hold conditions steady. The goal is to slow the drift, not to “fix” the reading.
• Avoid ad hoc heating measures such as space heaters near collections. These create new hazards.
• As a general guide, try to keep short-term drift under roughly 5% RH and 5°F per hour where possible. Slower is always safer.

Prioritise by collection risk

If you can’t check everything at once, use material sensitivity to decide where to look first. Paper, photographs, textiles, wood, and leather are the most vulnerable to sustained high RH and should be checked before stone, ceramics, and glass, which are generally tolerant over short periods. Metals and mixed-media objects sit in between, with corrosion risk rising the longer high humidity persists.

For a fuller breakdown by material, including when to consider relocating objects, see the long-term HVAC failure response guide.

Document everything

• Log the time the failure was noticed, the starting readings, and every action taken.
• Photograph the affected space and any at-risk objects.
• Take readings every 30 to 60 minutes until conditions are back in range.
• This log supports insurance claims and gives your conservator a clear timeline.

When to call a conservator

• You see condensation, warping, flaking, or tidelines on objects, or you smell mold.
• RH has stayed above roughly 65% for more than 24 hours, or has dropped below roughly 30%.
• Any object shows a visible physical change, however small.

When in doubt, call. Early advice is cheaper than treatment after damage sets in.

After the repair

• Keep monitoring for 48 to 72 hours afterwards. Mold and other effects can appear with a delay.
• Debrief with your team: what worked, what didn’t, and what equipment or contacts were missing.
• Update your emergency plan and confirm backup equipment such as dehumidifiers and generators is in working order.
• If you don’t already have continuous environmental monitoring with alerts, this is a good moment to consider it. It shortens the first step from guesswork to a glance at a dashboard.

If the repair is going to take longer

Once you know that parts, equipment, or labour won’t be available for several days, the priority shifts from containing a sudden swing to managing a sustained event. That’s covered in the long-term HVAC failure response guide.

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This guide is a general reference, not a substitute for your institution’s disaster plan or a conservator’s professional judgement. The printable version, which includes an emergency contacts sheet to fill in and keep posted near your HVAC controls, is available in the Conserv resource library.