Re: Installing Fan-Tastic Roof Vent On Cargo Vans
Like I said, I've run mine with the lid open many times. Initially because I forgot that it was open, and later because I needed to. I've confirmed in an e-mail with Fan-tastic tech support that running with the dome open isn't a problem, and I have a friend who has an RV place who also confirmed it. He's taught me a lot about that fan.
When you lower that knob to manually open raise or lower the dome, you disengage that locking pin. When you you push the knob back up, you re-engage the pin. You have to twist the knob ever so slightly to get it to go back up in there. If you are impatient enough times and force it with too much pressure too many times, eventually you'll snap that pin. That's when you find out the support arm is little more than a puppet string to raise and lower the arm and really doesn't provide any support.
I ran my fan for 6 years without a hood cover. I had the 6000RBTA (the one with all the bells and whistles except the remote - the one with the remote wasn't available when I got mine). When I snapped that pin, I could have repaired it, but after 6 years I figured I might as well use the opportunity to upgrade to the one with the remote and the nifty spiffy 14-speed fan.
I used to routinely run the fan with the dome at many various opening levels. When the dome is 1/3 open it reduces the airflow down to 90% efficiency, or by 10%. That's not very much, so the stress on the fan and motor is really minimal even at 1/3 open. When it rained, I could often open the fan just enough so that the fan started, which is about 1/4 open, and the rain wouldn't get in and trigger the rain sensor (or get in and leak all over the place). Sometimes it was just raining too hard for even 1/4 or 1/3 open. But even at 1/4 to 1/3 open, the reduction in airflow is negligible on low and medium speeds. It's on high speed where it's a factor.
I had long considered a hood cover, the Maxxair in particular, just so that I didn't take to tinker with the dome opening when it rained. I know several with roof vent fans who have the cover, and from talking to the RV guy I know, it's not much of a problem with the reduced airflow. The reduction in air flow the hood cover causes is not so much additional stress on the fan or the motor, but the reduced airflow has a tendency for more dust and dirt to collect on the fan and inside the hood (so it need to be cleaned more often).
So really, the bottom line is, a partially opened dome (while parked) is not something to be concerned about. Other than at the highest speeds (3 on the 3-speed fan, 10 and up on the 14-speed fan) there is virtually no added stress on the fan or the motor with a partially opened dome.
When I upgraded my fan to the 6600R with the remote, I decided to go ahead and install a hood cover at the same time. And lo and behold, Fan-Tastic now has one specifically designed for their fans, the Ultra Breeze Vent Cover, with the cover being molded precisely to fit a fully opened dome lid. It's also a little more low-profile and aerodynamic than the others. Installing the Ultra Breeze is the same whether you do it at the time you install the fan or at a later date. You remove 4 of the #8 x 1" screws that are securing the fan to the roof, and replace them with the #10 x 1¼" screws that come with the cover. The reason they are longer is that with those screws you attach 4 metal brackets to the fan with those screws. You then attach the cover to those brackets with cotter pins, making it extremely easy to remove the cover for cleaning or maintenance. The back end opening of the cover has a vent grille screen to prevent birds and other creatures from getting in, although I'm not entirely sure why it's really needed.
But with the hood cover installed, in all but the hardest of rains I can leave the dome lid fully open without the rain sensor going off. And I can often open the dome just enough so that the fan starts running even when it's raining really hard and the wind is blowing the rain right into the vent cover opening. Sometimes all it takes is to ramp up the fan speed enough so that it's bowing out faster than the wind is blowing in.
With my old fan and no cover, I would routinely either stop the dome from fully opening, or, usually, just manually open it to where I wanted it. This was to control rain from getting in, or to better control the airflow speeds. Three speeds on the fan wasn't enough for me, I guess, so manually restricting the airflow was the way to compensate, and it's not a method that the folks at Fan-tastic frown upon. But, manually opening and closing the dome as often as I did, pulling that knob out and pushing it back in, often in a hurry, is what broke it. However, since I upgraded to the new fan with 14 speeds and installed the cover a year and a half ago, I've used the knob to actually open or close the dome exactly once (break that pin once, you learn. Break that pin twice, you're stupid. LOL) I have a handful of times grabbed the knob while it's opening or closing to put the necessary pressure on it to stop the dome where I want it, but that's when it's raining. For controlled airflow speeds the 14 speeds on the remote work great.
The hood cover does restrict the airflow somewhat, simply by virtue of the fact that there's something there to direct the air out the rear of the cover, the same as the vents do on the vehicle's dash air vents or the shroud around your engine's cooling fan does. The Ultra Breeze cover's "exclusive patent pending airfoil technology allows for up to 75% more airflow than competing products." Uhm, OK. I don't think the "competing products" are all that OMG! restrictive in the first place. But there is some, of course. Before I had the cover I needed to clean the screen and the fan blades about every 6 months. Now, with the cover, it seems I have to clean them every 4 or so, so there is a difference. Not objectionable at all, but there is a difference. Certainly not objectionable enough for me to remove the cover and deal with the rain. Others, I'm sure, don't have to clean theirs as often. I smoke so mine is running, at least on the lowest speed, about 95% of the time, even in the winter.
Of course, with a vent cover installed, driving with the dome open or closed is a total non-issue. I still wouldn't drive with the dome partially open, even with the vent cover installed. It needs to be fully open or fully closed, even with vent cover. The reason is, on a windy day, especially a crosswind, with atmospheric pressure and drag being what it is, you can get some turbulence inside the cover that can put undue stress on the partially opened (unlocked with that pin) dome that forces the dome up or down.
Incidentally, my fan is mounted right above the bunk.