After a fun and adventurous hike, you hunker down to sleep. ZZzzzz….Only to find that you wake to a dewy mess in the middle of the night. Overnight, water crept into your tent and your sleeping bag is soggy, and your back, after rubbing up against the tent, is wet and cold. Been there, done that! How did this happen? And how do I go about eliminating tent condensation? Let’s take a look.
Why does my tent get wet inside? Condensation and humidity. Condensation forms when the temperature drops at night causing a large temperature difference in the inside and outside of the tent. This difference causes dew or water droplets to form resulting in condensation just like when you have a glass of iced tea sitting in the sun.
Besides, the relative humidity adds to the issue in the air, from breathing, our clothes, and that tired dog at your feet causing a damp tent environment.
Most hikers don’t want to wake up to this scene after a long night of tossing and turning. So, what can be done about it? Is there more you need to know? This is what we cover going forward. Let’s take a closer peek at the mystery of tent condensation.
What Does Science Have To Say About Tent Condensation?
Let’s take a deeper dive into condensation and what has to happen for condensation to appear. So, let’s define our terms.
According to Sciencing.com “condensation is a change in state from a gas or vapor into liquid form.” This change happens when the warmer air vapor hits a cooler surface. Like when you breathe warm humid air into the air in your tent. This air floats to the cooler surface of the tent at night and changes from vapor to liquid.
But How Does Water Change From Vapor To Liquid?
The answer is in the molecules. Vapor molecules are fast-moving and carry energy. When the molecules near or contact a cooler surface, they tend to slow down and collect in the form of dew. This newly formed water sits on your tent just waiting for you to rub your hand across or bump your head into the tent walls.
According to the National Weather Service, “the dew point is the temperature that the air needs to be cooled to achieve a relative humidity of 100%.” Meaning, when the temperature drops down and reaches a relative humidity of 100% the vapor needs to turn into a liquid.
When you are sleeping or sitting in your tent you are breathing warm, moist air increasing the humidity of the air. Couple this with cooling temperatures outside of your tent. When the two meet condensation forms.
Hydrostatic head tells us just how water-resistant our tents are. Meaning, how much water can form before it starts to leak into our living area. Anecdotally, the average hydrostatic head for a backpacking tent is around 3,000 mm. And for a tent to be considered waterproof, a hydrostatic head is set at 1,000mm of pressure. This tends to provide durability and appropriate condensation prevention.
Here are some examples of hydrostatic head ratings:
The North Face Stormbreak 2
The North Face Stormbreak 2 is a lightweight 2-person tent that has a rating of 1,200 mm – while in the range of waterproof this appears low at first glance. However, The North Face claims to have a new technology that pushes the limits of water-resistance, breathability, and lightweight material. Meaning, if you are looking for a lightweight 2-person tent this should be in the running.
The North Face Wanona 4
The North Face Wanona 4 tent has a hydrostatic head of 1,500mm and is said to withstand the most extreme conditions. If you remember back to condensation and temperatures. When you have a low hydrostatic head it would appear to lose the ability to repel water.
However, The North Face Wanona 4 is designed for colder temps so the difference between outside and inside temperatures is similar to summer temp differences and the colder temps would lead to less humidity and water in the air. Those combined would lead to less chance of condensation in the tent.
But what does all this mean? I live in…(fill in the blank)
What Should I Expect In My Area Of The Country?
For Example Diurnal Temperature Range – Comparing Arizona and New Hampshire
When it comes to day/ night temperature differences, regions of the US vary. The diurnal temperature range (difference in the maximum and minimum temperatures in one day) varies by region and what are called diurnal zones. Here are two opposite examples: Arizona and New Hampshire.
According to the University of Arizona CLIMAS “the daily range between maximum and minimum temperatures sometimes runs as much as 50 to 60 degrees F during drier periods of the year. During winter months, daytime temperatures may average 70 degrees F, with night temperatures often falling to freezing (32 deg F) or slightly below in the lower desert valleys. Therefore, you might expect a large amount of condensation. However, you need to couple this with humidity which is very low in the Southwest at this time.
Where I live in New Hampshire, according to RSSweather.com the average diurnal range during the summer is about 20 to 23 degrees. So, with less temperature range you might assume less condensation. However, the increased humidity in the Northeast causes a good deal of condensation on your tent.
Relative Humidity Comparison Between Arizona and New Hampshire
Therefore, condensation is worse with large diurnal temperature ranges and higher humidity. The Western states win with the temperature changes but the Northeast win with humidity (and bugs!).
Also, the Northeast has such high humidity that the tent tends to get very ‘stuffy’ during a summer hike lending to the ‘uncomfortableness’ of getting a good night’s sleep. So, find out what your diurnal temperature range is and your relative humidity in your area. This will help you plan for your next trip.
The image below shows the high temperature but low humidity in Phoenix Arizona. Compare this with the next image showing Manchester, New Hampshire. By the way, this was a comfortable day in New Hampshire – Humidity can get up to 85 or 90 % in the summer months.
Weather conditions will play a role in tent condensation. Typically, you think of the precipitation: rain/ snow. These conditions will have similar effects on whether you get condensation.
First, the rain will cause an increase in humidity and a drop in temperature. If you are sitting in your tent you will feel the tent getting stuffy inside. Condensation will occur when the temperature drops enough to cause a disparity between the inside and outside of the tent as noted previously.
Second, snowy conditions may drop the temperature outside causing the temp difference needed but won’t necessarily cause the inside of the tent to gain humidity. Oftentimes, the result is a dryer tent.
How Much Water Vapor Is In The Air?
To prevent tent condensation from forming, you need to look at what causes it. Water vapor at the walls of the tent gets changed from liquid to gas when the temperature drops outside. So, what are the biggest culprits producing water vapor?
It turns out that humans will breathe out an average of 40 grams of water vapor per hour when laying down. Say that you are in your tent for seven hours that is a total of 280 grams of water vapor (or 9.8 ounces of vapor). This additional vapor adds to the humidity and eventually leads to condensation.
Wet Clothes, Socks, and Boots
After a long day of hiking your clothes and boots get soggy from perspiration, rain, fog, etc. So, placing them in your tent for the night adds to the humidity level. So, common sense dictates that this will add to the condensation as the temperature drops outside and your clothes attempt to “evaporate” the moisture.
Dogs (or any mammal in your tent)
Because dogs don’t perspire, they reduce their body heat through panting. A long day on the trail and you could have a panting dog much of the night. When a dog pants it expels the heat and causes moisture to evaporate thus cooling the tongue and reducing body heat slowly over time. This additional moisture in the air adds to the humidity. Depending on the time of the year, most dogs can sleep outside of the tent – something that should be practiced before your trip. Nobody wants to hear a howling dog all night long.
Backpacks, Sleeping Bags and Pads
These items do not inherently carry moisture, however, if you do not dry your gear from the night before, bags, pads, and backpacks can bring water back into the tent after a long day. Also, if you get rained on during the day it is unlikely that the backpack is completely dry when you set up camp for the night. Besides, if your tent is not properly ventilated the humidity and sweat rate can increase thereby sticking to the sleeping bag and pad.
So, now that we know our major causes of humidity and water vapor inside the tent, let’s take a look outside.
What Causes Increased Condensation Outside Of The Tent?
While we can’t control the weather, we can make adjustments to reduce the chance of condensation on the tent. Here is what we found to be the biggest contributors.
Tent placement can make a huge difference in regards to condensation. Rivers and streams by nature have increased humidity surrounding them. So, it makes sense that setting up the tent near a river will increase condensation.
In Open Fields Verse Under Trees
If you set up your tent out in the open field, the temperature will drop greater than setting up under a tree or at the edge of the woods. Setting up your tent under a tree is advised to keep it warm throughout the night.
Be aware of deadfalls and widow makers to limit the chance of a branch falling on your tent while you sleep!
Rain, Rain, go away…rainy days will produce much greater humidity and water vapor leading to a higher level of condensation.
Setting up your tent facing the wind is a good way to provide ventilation on your tent and increase evaporative cooling.
How Do You Prevent Water From Leaking Into Your Tent?
After reading all of the above, it seems futile keeping your tent from becoming a big water droplet. What are some ways to reduce the main culprits, get a comfortable night’s sleep, and eliminating tent condensation for good?
- Remove and declutter the tent of your backpack, wet clothes especially socks, and boots.
- Properly ventilate your tent. If you do not have good ventilation it is probably a good idea to purchase a better tent.
- Do not cook or boil water in your tent (for many reasons) as this adds water vapor and therefore humidity into the air.
- Open window and rainfly to balance temperature and proper ventilation.
- Set up your tent facing into the wind.
- DO NOT light a candle inside your tent! While this seems like it would help reduce humidity and increase temperature, it also is very risky. You really don’t want to sleep under the stars using your backpack for a pillow!
- Don’t touch the tent which eliminates hydrostatic head properties and causes a leak in the tent.
- Dry the tent in the sun even if that means taking it out midday while you are having lunch on the trail.
- Dry all the items by the fire or in the sun after a long hike. Or as above during your lunch break on the trail.
- Remove and dry all sleeping items before putting them into a backpack for the day.
- TIP: bring a ‘shammy’ with you to dry wet areas on your tent. These work great at eliminating really wet areas of the tent before packing up for the day.
- Use a small battery-operated fan to gain ventilation and circulate the air in the tent.
- Stake the tent taut. This allows the hydrostatic head properties to work effectively and reduce the chance of leaking.
What About Tent Dehumidifiers?
In recent years, tent dehumidifiers have gained popularity. As the name implies, they reduce the humidity in your tent. As we discussed at length, reducing the humidity will reduce the chance of condensation when the temperature drops at night. Thereby causing cold outside air to meet warm inside air at your tent surface.
There are two types of dehumidifiers on the market today: chemical and rechargeable. Both help with eliminating tent condensation.
Chemical dehumidifiers use non-toxic calcium chloride salts (desiccants) to draw water from the air. They work well in a small space like a tent but are not reusable. When hiking, place them inside the tent, hanging them from the tent supports. Here is the Zarpax 9 ounce bag pack found on Amazon.
Rechargeable dehumidifiers like the VERITAS Small, Portable, Rechargeable, and Renewable Dehumidifier can remove up to 150 ml of water vapor per day. Which should be enough to get through the night comfortably and help by eliminating tent condensation. This is good for short humid backpacking trips or car camping as it only weighs 8.1 ounces.
Where Can I Buy A Good Backpacking Tent?
I would suggest that it isn’t so much where to buy your tent but what type of tent do I need. Learn more about tents in our post: How heavy are backpacking tents?. Oh, and to answer the question, backpacking tents can be purchased online at outdoor retailers, Walmart, and outdoor gear shops.
Why Are Backpacking Tents So Expensive?
So, why are backpacking tents so expensive? To begin with – the fabric and pole material is rugged, durable, and meant to be repeatedly broken down and handled. Backpacking tents feature simple, straightforward setup designs so you can have access to a quick shelter should the moment call for it. Additionally, you will find that their diminutive size provides advantages that you would not get out of your traditional camping tent. To learn more go to our blog post: Why are backpacking tents so expensive?
How Do I Sleep Better When Backpacking?
How do I sleep better when backpacking? Once you are comfortable in your tent, cognitive and behavioral therapy techniques help you get to sleep easier: they include cognitive behavioral therapy, stimulus control, and relaxation techniques. Practice before your trip to reduce tension and anxiety at the campsite. To learn more go to our blog post: How do I sleep better when backpacking?