Air quality in 36 Danish storage buildings was investigated, ranging from naturally ventilated historical buildings to modern purpose-built storage facilities, some with full HVAC climate control systems. Most were able to maintain a humidity level within 40–60% RH. The main deviations were for older heated buildings without humidity control, resulting in dry winter periods. Many modern stores were un-heated, which resulted in an annual average temperature about 12–13°C, and a high (>80) time-weighted preservation index (TWPI). The older buildings often struggled to maintain a moderate temperature, but experienced summer levels of 20–30°C. This lowered the TWPI considerably, typically to index 40–80. Concentration of organic acids in air was below 50 ppb for 22 sites, and only high (>100 ppb) for a few sites due to off-gassing from heritage materials. The outdoor pollutants ozone and nitrogen dioxide were mainly found in low concentrations indoors (<5 ppb) except for a few locations with forced but unfiltered air intake. Low-energy storage had the lowest energy consumption of <3 kWh/m³ annually, while repositories with traditional climate control systems were in the range of 10–30 kWh/m³. Information on energy consumption in storage buildings is sparse, and the authors call for more research. The most optimal solutions were offered by the modern low-energy buildings, where the best conservation conditions as defined by TWPI (high), pollution levels (low), and energy consumption (low) were observed, and where sustainable operation such as sharing space between several institutions was often practiced.