Condensation in horse trailers is a common problem. To prevent, or more practically, to reduce condensation, you first have to understand how this meteorological process works. Condensation, whether in a trailer or any other enclosed space, occurs when the temperature of the air drops below the air's dew point. The warmer air is, the more moisture it can hold. The colder it is, the less it can hold. That means that 70°F air at 40% humidity is holding more moisture than 50°F air at 40% humidity. And believe it or not, that 70°F air is holding twice as much moisture as the 50°F air with the same relative humidity. Or looked at another way, 100% humidity at 50°F is the same exact amount of moisture as 50% at 70°F. And this is why we call it "relative humidity" when using percentages to quantify that humidity — it's "relative" to the temperature.

Meteorologist also measure "absolute humidity", but using percentages would make no sense. Instead, they quantify it as grams of water per cubic meter. So, you can expect condensation whenever the air in an enclosed space is cooled. If you close up your trailer in the afternoon, you can expect condensation to occur if the air overnight cools down enough.

In reality, there really is no way to stop all condensation unless you're willing to spend more time and money. For example, you could put a dehumidifier inside your trailer. Of course, it would require electricity and periodic emptying of the condensate pan. Or, you could buy large desiccants that you place inside the trailer before closing it up. Then, as the temperature drops and the relative humidity rises, the desiccants will absorb it. You've seen desiccants before: those are the packets you find inside items wrapped in plastic bags that manufacturers use when shipping expensive electronic products. You would need big ones for a trailer and would likely find it too expensive for the long run.

So, let's talk about what realistic options you do have to reduce condensation. One thing to think about at the beginning is getting an aluminum trailer. While the frame will likely still be steel, at least you reduce the materials susceptible to rusting.

Another option is to insulate your trailer. Placing insulation on the metal walls will reduce the contact of humid air with those walls. Therefore, the air will not quickly cool and cause the water vapor in the air to condense out. There are various insulating materials you can use from Styrofoam to more rugged urethane foam panels enclosed in fabric or some synthetic material. The hardier the material covering the foam, the better — horses are generally tough on their surroundings, so you need something that will hold up over time.

Practically speaking, providing for adequate airflow by cracking a vent and a window or so is likely the most common sense approach. Providing adequate ventilation to allow an exchange of air as it cools into the night will greatly reduce the amount of moisture available to condense. Even then, you'll still have occasional moisture in there when the air is saturated, such as on a foggy evening. But at least you'll have reduced the frequency of occurrence.

Besides being an avid trail rider, Jerry Tardif is a technology consultant and a horse and nature photographer in SE Connecticut — see his work at: www.jerrytardif.com. He is also co-founder and President of QueryHorse.