High power roof fan rain hoods- Crash course - Fiberglass RV


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Old 03-29-2012, 12:25 AM   #1
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Name: Russ
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High power roof fan rain hoods- Crash course

I was thinking I need a hood over my Fantastic fan since I have sliding windows that would let in rain when open. My bathroom window is a transom, which hinges on top and could be open in a rain storm. The Fantastic fan is over the rear dinette in the opposite end. So all I need is to open the bath window and fire up the fan, as long as it has a hood.
I did a little reading and discovered that most of the older designed hoods were too restrictive and could damage high volume fans or void their warranties. I went to Camping World to check out their offerings, and was told only a few were suitable for use with a high volume fan. The two big players are Maxxair and Fantastic Fan. I liked the look of the Maxxair ll which is compact and the package said had more area than "any other hood". I purchased it and took it home. First I set it down over the Fantastic fan, cranked open the vent, and turned it on "high blower". I then took a sheet of Kleenex held at two corners and lifted it closer and closer to the running fan. At about 8" below the fan the Kleenex would lift and lie out flat. I then went up on the roof and removed the Maxxair ll and went back and did the same test. The Tissue would lift at 12" below the fan. It looked to be a 33% loss with the cover on. The test was repeated with the same result. I then called Maxxair and they said their Maxxmate would have a very slight flow advantage over the Maxxair ll. I went back to Camping World to get one of those to test, but was persuaded by the salesman to give the Fantastic Fan company's new high volume Ultra Breeze hood a try.
I purchased one and hauled it home to test. I laid it over the fan and re-ran the test. The tissue would lift at 12” below the fan. That hood had virtually no effect on flow. This hood has no bug screen included, where the Maxxair used window screen on theirs to keep insects from nesting under the hood. I re tested the Maxxair ll without the screen to see how it would affect the test. It made only a slight difference. The tissue lifted around 9” below the fan. The Fantastic Fan Ultra Breeze was the clear winner in the flow category. The still untested Maxxair Maxxmate has a long rear overhang, costs close to double, has a shorter warranty period, but may be more competitive in the CFM race. I ruled it out for me due to the size and cost. The two tested units cost about the same at around $50.00. I then un-packaged the installation hardware and read the instructions. The Maxxair people came up with a more elegant installation solution. They include angle clips that simply butt up against the side of your fan. You drill through the curb of your fan and install sheet metal screws or through bolts to fasten the clips. They include 2 ss bolts and nuts to fasten one side of the hood to the clips. The other side gets ss wire pins that can easily removed without tools. The clips act as hinges and with the pins pulled the hood can be rotated aside. I will order 2 more pins and eliminate the bolts so it will pivot either way. Very simple. The Fantastic Ultra Breeze hardware was also fairly simple, but not thought out as well. Their clips were flat and required removing 4 rivets from the original fan install and fastening the clips to the fan flange. This means you have a waterproofing issue to reseal the screws. Also if the mounting clips were disturbed after the caulking was dry it could leak. The fan cover will buffet in the wind and could bread the seal. Another thing that was not thought out well was the instructions said to remove the two screws, but the dimension between those screws was not correct for their hood! The hood had 4 slotted holes which allowed for lots of differing hole dimensions, but none would fit their fan holes. Woops… I just wasn’t going to use that hardware to install the hood. I liked the hood, but the installation needs refining. I could have spent the time to fabricate new ss angle clips and re-engineered the fastening method, but I decided to go with the more restrictive Maxxair ll. I installed it in 15 minutes without any need to caulk anything. The angle clips actually do not sit down tightly to the trailer top. As it turns out that 3/8”-1/2” gap added enough gap to increase the CFM of the unit!
After installation I did the Kleenex test and got within 10” , and the bug screen was in place. Still not on par with the better performing Fantastic Ultra breeze, but close. Just to be safe I did some current draw tests to see if the restriction would cause the fan motor to run hot. I tested the fan with no hood and the cover wide open. 1.8 amps. I put the maxxair hood over the fan with the screen installed and the bottom edge of the cover lying right on the roof of the trailer. 1.8 amps. No difference. I then cranked the fan cover down to the shut off switch limit, about 2” open. 1.8 amps. I concluded that the Maxxair hood is not going to hurt my fan. It just won’t produce as much CFM per watt as an un-hooded fan.
Now we can camp in the rain. Too bad it doesn't rain here...
Russ
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Old 03-29-2012, 07:24 AM   #2
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Thanks for the comprehensive report.
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Old 03-29-2012, 07:50 PM   #3
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Thanks for the comprehensive report.
Absolutely great post. It's really going to help for people in the decision stage.
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Old 03-29-2012, 11:18 PM   #4
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Nice report Russ!
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Old 03-30-2012, 10:55 AM   #5
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Nice report and good to know - all I need is a place to park my trailer that allows for the added height of a fan cover.

I used the Window Maxx on my Scamp to solve the problem of keeping windows open while its raining. Works well.
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Old 03-30-2012, 07:56 PM   #6
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Nice report and good to know - all I need is a place to park my trailer that allows for the added height of a fan cover.

I used the Window Maxx on my Scamp to solve the problem of keeping windows open while its raining. Works well.

Carol,
The Window Maxx looks like it would work well with the Fantastic Fan pulling air through. I'll pick one up.
Russ
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Old 03-30-2012, 08:47 PM   #7
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Be careful of the window max vents, they screws on mine allowed water to leak inside.
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Old 03-30-2012, 10:52 PM   #8
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Carol,
The Window Maxx looks like it would work well with the Fantastic Fan pulling air through. I'll pick one up.
Russ
We have WindowMaxx vents on both sides of our Scamp and they have worked well for us and look great. As for leaks...Not a drop in eight years.
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Old 03-30-2012, 11:28 PM   #9
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Be careful of the window max vents, they screws on mine allowed water to leak inside.
I'll install em with those new aluminum magnets


Seriously, I will investigate the fastening and then make the call.
Russ
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