Condensation inside shelters
Posted by on 11/29/2018
People will often mention moisture inside shelters and wonder if the
shelter is leaking. The moisture is actually condensation from the cats
themselves! The condensation is likely to be very obvious at
some times and not at others, as the temperature and humidity fluctuate.
But since our shelter helps protect the cat from the cold by creating a zone of warm, moist air where the cat sleeps, condensation
will always be present when the cat is using the shelter.
The cats are spending a lot of time in a small space
and moisture from their fur and even their respiration condenses on the
relatively cooler walls and ceiling. Because our shelters block the
wind, the warm, moist air stays inside the shelter. During very cold
weather the moisture will freeze to exposed cold surfaces but during
warmer weather will thaw and run off the insulation and be absorbed into
the bedding. As long as cats use the shelters it will happen and
there's no way to prevent it, but there are ways to mitigate it.
You can visualize this as a person sitting in a cold car in the winter. Spending just a few minutes in the car will cause the windows to fog/frost as the moisture from the person's breath condenses on the glass. The moisture actually condenses on other surfaces, but it is most visible on the glass. If you open the door, the windows won't fog up any more...because the cold, dry air can freely come in an mix with the warm, moist air and cool it off before it condenses so much on the glass. Many shelters with an opening directly into the living area are designed like a car with a door open...allowing cold air to flow right in...and warm air to flow right out. They don't have much problem with condensation, but the interior of the shelter is pretty much as cold as the exterior...which does little to help the cat.
To illustrate, during testing in our own colony, with an outdoor temperature of 36 degrees F, a shelter housing two cats read an indoor temperature of 56 degrees F, measured at the roof level (it's actually warmer at the bottom, but the sensor unit was too large to locate at the bottom). But more interesting, the interior humidity was a whopping 85%.
It is possible to stop condensation inside the shelter. It can be accomplished by heating the interior of the shelter sufficiently that no interior surface is below the dew point temperature. In practice, though, this requires many hundreds of watts of heating. It's hard to heat it safely with that much heat, and just impractical inside a small shelter. It's like running the engine in the car and running the heater until it gets so warm that you don't see frost on the windows any more.
Practical ways to mitigate it (without degrading the shelter performance) involve absorbing the moisture. Make
sure you have absorbent bedding like straw and some absorbent fabrics
inside the shelter and if possible, change them periodically. Putting
absorbent pads (like puppy pads, diapers, etc.) that will sequester the
moisture into a gel will keep it from pooling on the floor. Put the pads
under the bedding, if using straw. If using fabric, place the absorbent
pads on top of the fabric. Here's an example of such a pad: http://a.co/d/1nkiZ17