Fan 101

[TheFreedomMobile]

Forgive me if this is a dumb question, but I'm sitting here wondering what is the standard operating procedure regarding the fans - in particular with regard to temperature control.

I have noticed that, when it's very hot in the rig, turning on the ceiling fan will make a good, and immediate improvement in the temperature. Is this the primary purpose of the fans?

Also, what happens when the A/C kicks in? Is it better to then shut the fan off? Do I leave the fan cowling lid up?

 

[Molaker]

When the temps are allowed to get very high, that means the temp of everything in the MH is high, as well.  So, to cool things down takes time because more than just the air has to be cooled.  Turning on the fan can start the process by rapidly expelling the hot air, especially at ceiling level.  Of course, turning on the A/C means you are more serious about cooling things down.  Just keep in mind, the hotter the air, the harder (and longer) the A/C has to work.  So, it is a good thing to run an exhaust fan for a while to help the A/C bring temps down.  However, the location of the fan can make a difference in how effective this is.  If the vent is located very close to the A/C output, it can draw off valuable cool air, actually slowing the cool down process.  So you have to make your own judgement based on A/C and fan locations.

We had a Fantastic fan in the cabover bunk area in our old class C and our A/C was ducted.  If the MH was very hot, I would turn on the fan and A/C and set the A/C to dump directly below rather than using the ducts.  This would move the hot air fairly quickly.  In addition, the Fantastic fan has a thermostat which would shut off the fan when the temps (at the fan) reached the set level.  I set the fan to roughly 85 degrees.  When the fan shut off was my cue to close the fan vent and switch the A/C back to ducted.  If very hot outside, sometimes the fan would not shut off on its own, so I had to monitor that condition and close it later to keep from losing what cooler air there was.

 

[Gary RV_Wizard]

We use the fans as an alternative to a/c., leaving windows open and fans on (exhaust) as long as we are comfortable, then turn a/c on, fans off and windows closed when it gets too hot. I try to anticipate "too hot", so that the a/c doesn't have to play catch-up with an already overheated coach.

Note that the fan can't exhaust air unless there is some opening for air to come into the RV, so you are bringing warm outside air in as you exhaust the hot interior air. You may feel a gain at head level, but there is no benefit after the first bit of super-hot interior air is expelled. If you leave a window open a bit to replace the air the fan is trying to blowout, you just gain heat right back again. If you don't leave a window open, one of two things happens: (1) the fan blades spins but no air actually moves, or (2) air finds its own way in via various gaps around the RV,e.g. the slide seals.

 

[TheFreedomMobile]

Great. Thanks for the answers.
I have been doing exactly what you describe, Gary. Thanks for the confirmation.