How do you decide what to open, close depending on the weather?

I have drop downs with bus windows on the head side (and jail bar option) and slats on the butt side with plexiglas inserts.  I also have roof vents and a bus window in the rear door.  While it is easy to know what to do in the summer (open everything!!) I was wondering what everyone does when the weather gets colder? Rainy? How do you decide how much to open?

For example, yesterday it was around 50F and I had only one window completely open (jail bars up) and took out one of the plexiglas inserts.  Everything else was closed.  It was only a 15 minute ride, so I could not tell if he was getting too warm or not.  BTW - my trailer is a 2H GN slant if that makes a difference. 

What do you do for different types of weather and why?

Thank you farmboy and Gard for your quick responses.  I agree that it will be my preference and that traveling in the trailer will help me to see what it is like back there - but that is not what I am asking.  I want to know what others do and why so that I can make a more informed choice myself.  For example Gard - when you traveled in the back of the trailer, what did you look for?  What did you find out that changed what you were doing?  Farmboy -  do you open up more vents/windows when you are traveling down the highway or do you open different ones?

I am looking for what others do so that I can understand the thinking behind decisions and use that in deciding what I want to do.  You have lots more experience in hauling than I do and I am just looking for that type of information.

When you go out and load the horses what factors do you use to decide what to open/close etc?

Thanks

Gard - when you traveled in the back of the trailer, what did you look for?  What did you find out that changed what you were doing?

When I was a first time father with my daughter, I asked the Dr. how much to dress her for different temperatures. His reply was, "she feels the same as you do, so use similar clothing." My goals when hauling, are to have the horses as comfortable as I can be without artifical means.

You have been given a lengthy reply, on how one trailer owner achieves that goal while travelling. It instructs the many variables that are available to achieve the horses' comfort. It does not address the fact, that many trailers will differ in the final results. The sizing of the windows, their placement and number will change the affects. Having slats at the butt side, will produce different results than buss or drop windows. The ceiling height,  stall sizes and number will effect the interior's space. More horses produce more body heat. Are your trailer's walls and roof insulated or single skin? Is your roof painted a light or dark colour? There are many variables. Another owners experiences may be just a guide for you to get started.

A rear door window pulls air into the box. The front of a side window sucks air out of the stalls, while the rear area of the same window allows air inside. The top vents can direct ambient, outside impact air into the interior; the same vent can suck warm, stale inside air out. Cold days, hot days, the number of trailered horses, the highway speeds and length of your travels, will all effect your decision on how best to heat or cool the interior stall space.

We have more cool and moderate days than oppressive hot days. On hot days, all the windows are open and the top vents are directing air to the inside. Parking a loaded trailer in the sun, will quickly raise the inside temps to endangering levels. This is similar to warnings about pets or babies left in automobiles. If the horses are sweating, they need to be cooled. Optional cooling fans may be necessary.

If you're cool in the back, consider sheets or blankets. You can feel underneath them against the skin to determine if it's enough insulation or too much. During cold trips, we blanket the horses and use rear most vent to suck out the inside air. All the windows are closed. Horses, like humans, are subject to air chill factors. If the cold air is hurting your face, the horses will similarly suffer.

I can't offer you a perfect example of what to do under a given condition. Your experiences, horses, rig and environment differ from mine. Again, by riding in the stall area, whilst opening and closing various windows, vents and slats, you can more accurately guage what your horses are experiencing. You can then accurately determine what works best for your circumstances.

Well said, Gard.

It's going to be completely subjective. For example, we rode this past weekend. It was ~37-38 degrees outside. The trailer we use for day trips is an all steel 3h slant. It is black in color and the horse area is not insulated. In the sun, it was a good 20-30 degrees warmer in the trailer than outside. I partially opened the slide windows on each drop down and partially opened the rear bus windows leaving the back window and roof vents closed. It maintained temperature very well and was very warm when we got to the park to ride and when we got home. I wanted enough ventilation and airflow for them to cool down, but not get chilled after a wet and sloppy ride. Both horses I had with me that day grow winter coats to the likeness of a grizzly bear. They just don't get cold. They enjoy standing in the snow and ice. I have seen them with an inch or more of snow & ice on their backs and not give it a second thought.

You just have to determine what is best for you and your circumstances.