Air conditioning systems require regular filter replacement, so many factories and commercial buildings keep spare filters in stock. From primary-efficiency cardboard-frame filters and medium-efficiency metal-frame filters to high-efficiency fine-pleated HEPA filters, each type has a different construction and therefore requires different storage considerations. Simply remembering to “keep them indoors and unused” is not enough. If factors such as humidity, stacking, and handling records are overlooked, problems with the filter frame or media may only be discovered when the filters are taken out of storage for installation.

How Should Industrial Air Filters Be Stored?

Unused filters should be kept in their original packaging and stored indoors in a clean, dry environment free from water leakage and condensation. They should also be protected from excessive weight, direct sunlight, and repeated handling. If cardboard-frame filters and other types of filters are stored in the same warehouse, 20–25°C and 45–55% RH can be used as general environmental management targets. However, attention should be paid to whether humidity remains elevated for extended periods. These values should not be treated as universal storage specifications for all filter media or models. When specific supplier documentation or project requirements are available, the more specific product instructions should take precedence.

Why Shouldn’t You Set a Single “Filter Storage Life”?

Filters are not made from a single type of material. Hencolin’s high-dust-loading primary-efficiency cardboard-frame filters use moisture-resistant, heavy-duty paperboard frames. The paperboard is part of the product structure, so checking only whether the outer carton is dry is not sufficient.

Medium-efficiency synthetic-fiber pleated filters may use metal frames, but the pleated filter media and support structure still need to be protected. High-efficiency fine-pleated HEPA filters require even greater care to avoid contact with the fine filter media and damage to sealing components.

The approximately one-year recommendation provided by Hencolin to customers is better described as a stock-rotation and pre-installation inspection guideline for unused filters, rather than a guarantee that all filters will remain undamaged for one year or that they must be discarded after one year.

Whether a filter can actually be installed should still be determined based on the specific model, storage records, packaging condition, and physical condition of the filter.

Warehouse Temperature and Humidity: Can Cardboard Frames and Fiberglass Media Use the Same Values?

A common warehouse management target can be established, but it should not be presented as a common product storage specification.

The 20–25°C and 45–55% RH range recommended in this article is primarily intended to support the overall stability of cardboard frames, packaging, and warehouse conditions. Information on paper preservation from the National Archives of Australia emphasizes stable temperature and humidity and avoiding prolonged exposure to high humidity. This can serve as a reference when planning storage conditions for cardboard-frame components. However, archival paper and industrial air filters are different products, and such information does not establish the storage life of Hencolin filters.

Fiberglass filter-media raw materials, assembled fiberglass filters, and HEPA filters from different manufacturers may also have different storage requirements. For example, a technical document for an assembled HEPA filter from another manufacturer specifies stricter controlled storage conditions for that particular product. Those requirements apply to that specific product and should not be directly applied to Hencolin products.

When purchasing fiberglass filter media or specialty filters, obtain the applicable storage and packaging documentation from the supplier. The maximum operating temperature or humidity stated on a product page should also not automatically be treated as the long-term storage condition.

What Should Be Checked Before Release from Storage?

Primary-Efficiency Cardboard-Frame Filters: Check Whether the Frame Can Remain Flat and Seal Properly

Inspect all four sides of the cardboard frame, including the corners and joints, for water stains, softening, warping, delamination, or damage. Also confirm that the blue pleated filter media and the original support structure for the model remain intact.

If the cardboard frame has become deformed, it may affect installation and sealing even if the filter media itself appears clean and dry. Hencolin’s cardboard-frame filter installation instructions also note that an improper fit between the frame and mounting slot can result in air bypass.

Medium-Efficiency Metal-Frame Filters: Check the Frame, Pleats, and Support Structure

Confirm that the metal frame has no significant deformation and that the pleats have not been compressed, torn, or displaced. The support mesh and fixing components should also remain intact.

During handling, support the filter by its frame rather than gripping the filter media with your fingers. For stacking, follow the original packaging instructions or supplier recommendations and avoid placing excessive weight on the filter surface.

High-Efficiency Fine-Pleated HEPA Filters: Check the Filter Media and Sealing Areas

While waiting for installation, HEPA filters should remain in their original packaging as much as possible to minimize unpacking, contact, and repeated movement.

Before release from storage, verify the model and relevant documentation, then inspect the frame, fine filter media, and sealing areas for visible damage. Visual inspection does not replace any post-installation testing required by the project.

If the filter has been impacted, the packaging is damaged, or the filter media appears to have been compromised, isolate the product and consult the supplier before installation. Do not install a filter simply because it has “never been used.”

What Simple Records Can Warehouse Staff Keep?

At receiving, record the model, quantity, arrival date, batch or order information, and condition of the outer packaging.

During storage, retain temperature and humidity records as well as records of abnormalities such as water leakage or condensation.

When filters are issued, verify the product again and perform a visual inspection.

Filters should be kept away from floors that may become damp, leaking pipes, and wet-cleaning areas. They should be positioned and stacked according to the packaging instructions. If packages are opened for inventory checks, the filters should be properly protected again afterward, and identifiable product markings should be retained.

A brief period outside the warehouse management target does not automatically mean that an entire batch of filters has become unusable. First determine how long the conditions deviated, whether condensation or water intrusion occurred, and whether the products show any abnormalities. If a problem is found, label and isolate the affected products, document the condition with photographs, and consult the supplier before deciding whether they can be released for use.

Frequently Asked Questions

Can Filters No Longer Be Used After Being Stored for One Year?

Not necessarily. Approximately one year is Hencolin’s practical recommendation for stock rotation and reinspection; it is not a guaranteed shelf life for every product.

Whether a filter can be installed should still be determined based on the individual product, storage records, and inspection results.

Can a Cardboard-Frame Filter Be Used After It Gets Damp if It Is Dried Out?

Do not judge the filter solely by whether its surface appears dry.

If the frame has softened, warped, delaminated, or can no longer fit the equipment properly, installation should be suspended and the supplier consulted.

Can Fiberglass HEPA Filters Simply Be Stored at 20–25°C and 45–55% RH?

These values can be used as a provisional general warehouse management target, but they do not replace the storage documentation for fiberglass filter media or a specific HEPA model.

If the supplier specifies stricter conditions, those requirements should be followed.

If the Outer Packaging Is Intact, Is It Unnecessary to Inspect the Filter?

The filter should still be checked before installation and the model verified.

Intact outer packaging provides useful protection, but it alone cannot confirm that the frame, filter media, and sealing components are free from abnormalities.

Planning to Purchase Multiple Types of Filters or Store Them for an Extended Period?

Provide information such as the equipment being used, filter models, planned inventory quantity, expected storage period, and warehouse conditions to Hencolin. This will help determine suitable primary-, medium-, and high-efficiency filters and the applicable storage precautions for each product.