It’s not the heat, it’s the humidity!  It may be a cliché, but it is a pretty accurate statement.  Damp, humid air does maintain heat more than dry air. That is why, during the air conditioning process, your AC removes humidity from the air.

As hot air is blown over the evaporator coils in your air conditioning system, moisture is removed from the air as it condenses. The condensate is then collected in a pan and drained from the system. It is important to keep in mind, though, that this dehumidification is required during the cooling process: it is not a primary function of most air conditioning systems.

Humidity is a critical, yet often overlooked feature in wine cellar design. A relative humidity (RH) of 50% to 70% is recognized as adequate, with 60% the ideal. Without ideal humidity, wine quality may be affected in a number of ways.

Wine corks are a natural product and will deteriorate with time.  The cork will still dry out even when the bottle is placed on its side.  Although the bottom of the cork is in contact with the wine, the top of the cork is exposed to the air and influenced entirely by the conditions of the air around it.  

  • When the humidity is higher than 70%, it will likely cause mold and degradation of the labels and glue and damage your storage area.
  • When the humidity is below 50%, corks will begin to dry out resulting in loss of liquid in the bottles and possible degradation of the wine.  Even if the seal remains intact, opening a bottle with a crumbly cork will cause lots of swearing and cork crumbling into your wine. The problem is made worse if low humidity is accompanied by temperature fluctuations.

Problems resulting from humidity issues can be solved or avoided with the right planning.

  • The first step should be the installation of a vapor barrier around the entire room. A minimum of 4 mil. plastic is recommended, with seams overlapped and taped. The vapor barrier is installed on the outside (or warm side) of the cellar insulation. This is to prevent condensation forming on the vapor barrier, potentially causing mold.
  • A cooling unit alone cannot add moisture or humidify cellar air. It needs a humidifier to do so.  The best option is a humidifier integrated into a cooling unit so it operates and distributes the moisture evenly in the re-circulating air. However, a freestanding humidifier can also be installed in conjunction with a cooling unit as long as this is controlled by a high-quality, wall-mounted thermostat.


Summit Cool Cellars ( and Summit Wine Cellars ( offers one-stop expertise as a complete wine cellar contractor guiding both residential and commercial clients from concept and consultation through wine cellar design, fabrication and installation. Owner/designer Fred Tregaskis creates dramatic custom wine cellars for fine homes, restaurants, hotels and wineries throughout the world.

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