Library heating and humidity control is a question of stability, not warmth. A boiler does not control humidity at all: it heats water, and what happens to the air depends on the controls, emitters and any separate humidification plant downstream. Get that chain wrong and paper, bindings and archive material can suffer even in a building that feels comfortable to staff.
For facility managers in the North East, the pattern is familiar: cold, damp coastal air through autumn and winter, then heating that swings the indoor climate. This article explains what damages collections, which published guidance to follow, how a commercial boiler system shapes conditions, how to spot problems, and what to ask before changing anything.
Relative humidity (RH) is the amount of moisture in the air expressed as a percentage of the most it could hold at that temperature. Warm air can hold more moisture than cold air. So when you heat a room, RH falls even though no moisture has been removed, and when the room cools, RH rises again. This is why a hotter building is not a safer one for books: warming a space without managing moisture dries it out.
The damage falls into three broad categories:
Different materials in a single volume respond at different rates, which is why a book with a leather spine, paper text block and wooden boards is particularly vulnerable to swings.
Consider a typical illustration. After a cold winter night, with the heating off or set back, a stack room is cold and the air near the walls is damp. At six in the morning the boiler fires hard to bring the building up to temperature. Within a few hours the air warms, RH drops sharply, and the books on the shelves lose moisture faster than they would in a gradual change. Repeat that every working day through a North East winter and the cumulative stress is considerable. Similar environmental stability challenges are covered in our guide to museum climate control heating requirements.
The same applies in reverse in spring and autumn, when mild, humid spells arrive after dry, heated weeks. The aim is not to freeze the building in a fixed state, but to avoid fast, repeated change.
Published standards exist for exactly this question, and you should work from them rather than from a remembered figure. The key documents to look at are:
Recommended ranges and the status of these documents can change. Confirm the current versions and figures as of 2026 with the British Standards Institution and The National Archives before setting targets, and take advice from a conservator or archivist on how they apply to your collection.
A public reading room serves people first. It needs to be comfortable for readers and staff, with reasonable temperature and ventilation, while still avoiding extremes. A closed store or archive serves the collection, and conditions there are usually cooler and drier than people would choose for themselves, with minimal variation. Treating both with a single thermostat setting tends to fail one or the other. The same principle of separate controls for different space types is explored in heating zone control strategies.
Items may also move between the two. Moving material from a cool store to a warm reading room changes its immediate environment quickly, so many institutions allow time for acclimatisation.
Most guidance describes an acceptable band and a limit on how quickly conditions may change within it. The practical target is a band you can hold consistently with the building and plant you actually have. A listed or historic building may not support the ideal: thick stone walls, single glazing and limited space for plant all constrain what is achievable. In those buildings, a slightly wider but steady band is generally a better outcome than an ambitious target that the system cannot hold.
A commercial boiler heats water. That water then circulates to radiators, fan coil units or air handling units, and those emitters warm the space. The boiler itself neither adds nor removes moisture from the air. Its influence on humidity is indirect: it comes through how steadily and evenly the heat is delivered.
Some of the following may suit your building and some may not. A Gas Safe registered engineer can advise on what is realistic for your system:
Where the building needs added or removed moisture, that job belongs to humidifiers or dehumidifiers, or to air handling plant with those functions built in. They are not part of the boiler. They need to be specified, commissioned and maintained alongside the heating so the two do not work against each other. Boiler work and any gas-related elements must be done by a Gas Safe registered engineer, and you can check registration on the Gas Safe Register.
Some signs show up in the building and its contents. Others show up in the heating plant. Both matter, and they often point to the same cause.
Any of these deserves an engineer's attention rather than a workaround from staff. Report suspected boiler faults promptly, and do not attempt to adjust, repair or reset gas appliances or flues yourselves. If the building is slow to warm, our guide to fixing a heating system that takes too long to heat up covers the usual causes.
Complaints about the building feeling stuffy or cold are useful, but they are not evidence. Data loggers, small devices that record temperature and RH at set intervals, give you a record you can act on. Place them in the main reading room, in each store and in at least one problem area, and leave them in place for a full year so you capture the seasonal pattern, including a North East winter and the damp shoulder months.
Check the calibration of any logger you use. Sensors drift, and an uncalibrated device can give you confident but wrong readings. Ask the supplier for calibration details and how often recalibration is advised.
If you smell gas at any point, leave the building immediately and call the National Gas Emergency Service on 0800 111 999. Do not switch electrical items on or off on your way out.
Stability depends on components doing the same job every day. A failing motorised valve, a drifting temperature sensor or a tired pump can quietly undermine zone control without triggering an obvious fault. Annual servicing by a Gas Safe registered engineer checks the combustion side and the controls, so small problems are caught before they show up on the shelves. For a structured approach, see our guide to commercial heating maintenance contracts.
The Gas Safety (Installation and Use) Regulations 1998 require gas appliances, pipework and flues to be maintained in a safe condition, and the Health and Safety at Work Act 1974 places wider duties on employers and those in control of premises. All gas work must be carried out by a Gas Safe registered engineer. You can verify any engineer or business on the Gas Safe Register before they start. Keeping the right records is part of this, as outlined in our article on commercial heating system documentation requirements.
Libraries and archives are often draught-proofed to protect collections and hold conditions steady. That makes ventilation and flue safety more important, not less. Boilers need an adequate supply of combustion air and a flue that discharges safely. Staff, builders and non-registered contractors must never block, alter or cover vents or flues, including during refurbishment or when adding insulation and shelving.
A maintenance contract can formalise servicing and response arrangements, which is worth considering for buildings where an unplanned shutdown carries more than an inconvenience.
Upgrades work best when they answer a defined problem. Before committing to new controls, zoning or plant, work through these questions:
Involve a conservator or archivist early so the targets reflect the collection's needs, and a Gas Safe registered heating engineer so the proposals can actually be delivered safely. Decisions should rest on your logged data, not on guesswork or generic claims that a particular product will transform conditions or cut bills. If an upgrade is likely, our step-by-step guide to planning a business premises heating system upgrade is a useful starting point.
Costs, grants and energy-efficiency requirements change, and as of 2026 you should check current funding schemes and regulations rather than relying on older figures. Be wary of any quoted saving that is not based on a survey of your own building.
The most useful rule for protecting a collection is to hold conditions within an agreed, achievable band and to prove it with data. A boiler cannot manage humidity on its own, but well-controlled, well-maintained heating removes many of the swings that do the damage.
Commercial Boiler Solutions is Gas Safe registered and carries a 5-star customer rating, serving commercial properties across Newcastle, Sunderland, Middlesbrough, Tyneside, Wearside, Teesside, Northumberland and North Yorkshire. We can help with annual inspections, maintenance contracts and emergency callouts. Our FAQ covers common questions, and you can Learn more about our services.