Ahhhh fall, that time of year when people think about venting their container. It's too hot, too humid, etc. It's the number 1 call I get this time of year for modifications. I blogged about this back in May, 2013. There are a few options to consider.
1. What are your concerns about the inside of your container? Containers are designed to transport goods across the globe in all kinds of weather, from hot, humid locations along the equator to freezing cold places like Alaska, or Minnesota, where we're located. Most everything that you have in your home and office came to the store you bought it by way of a container. They do a good job of keeping stuff the way it should be. I find often that people worry that their container won't maintain a nice indoor atmosphere, but most things are OK in a container as is. But sometimes people are concerned due excessive humidity, heat an cold, or are storing things that produce fumes that need to be vented.
2. Are you worried about humidity? If your main concern is humidity, a vent might not be the best option for you. A container is designed with some small, passive vents that prevent pressure from building up in the container, but do not allow for much airflow. As a result, when you close the doors of your container, it will stay the way you left it. That can be good or bad, depending on what kind of air you trapped in there. If you live in a high humidity area, the answer might be to not add a vent, but rather add dehumidifying products to suck the moisture out of the air. By not adding a vent, you continuously pull and trap moisture out of the air and don't let new, humid air into the container.
There are a few products on the market that you can get at any hardware store that are cheap and easy to use. DampRid is one brand, but there are others out there. The basic idea is the same. (We have used DampRid, only because that is what our local stores carry.) They have pellets that pull moisture out of the air and trap it in a bucket, bag, etc., and depending on how humid your container is, you replace it every few weeks or months. What I like about this option is that it might solve your problem without having to spend a lot of money or hurt your container.
3. Are you worried about heat and cold? If a temperature change is the issue, vents may or may not help. For the cold, vents will only make things colder. But for heat, sometimes some airflow in the container can lower the temperature in a container a bit. It won't take a 100 degree container and make it something you want to cool off in, but the increase in air might help a bit. To do this, louvered vents work well. If you put one vent on one long side of the container by the doors and another one on the other side of the container on the other long side of the container by the other end of it, you will maximize the cross-breeze in the container. This is the same idea as opening windows on opposite ends of your house to cool it down in the summer.
The other option is to add in an HVAC. If you add an HVAC unit, you will probably want to insulate the container. For more information on insulating containers, click here. Containers are made of steel, so any heating and cooling will be lost quickly without insulation.
Conversely, I often get asked about insulating a container, but not putting an HVAC unit in it. It doesn't work very well. It is like buying a cooler, putting your picnic in it without any ice or chillers, leaving it in a hot car all day and hoping for a cool meal.
4. You are storing something that creates fumes. This one is the most dangerous, obviously. The amount of air flow will really depend on what you are storing. For some cases, the pair of louvered vents might work just fine. But if it is something flammable or something where people will be spending a lot of time, you may need to consider a ventilation system. It is best to find out from the manufacturer of the fumes what is the best way to handle that.
In addition to these ideas, there is always the whirlybird/turbine vent. I'll admit it. I just don't like them. You're cutting a hole in the roof and putting a vent that pulls air down into the container. So when it rains, it pulls the rain right down into the container. It snows? Same thing. It just seems like too much of an invitation for trouble. I get some people just love this options, I simply am not one of them.
What are your concerns about venting containers?