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Old 08-14-2015, 02:30 AM   #1
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Question Vent fan confusion

My MaxAir vent fan is bidirectional. A recent RoadTrek poster wanted to install a switch so that the vent fan in their unit could reverse and dry out the shower curtain, for example. The replies included this from "Jim Hammill The reversing switch is not allowed by code. If it was, we would provide it. And the reason is, it's unsafe."

So, what "code" allows the MaxxAir fan to be bidirectional yet whatever fan is installed in RoadTrek's cannot be?
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Old 08-14-2015, 02:45 AM   #2
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It has to do with the proximity of the fan to the sewage vent stack.
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Old 08-14-2015, 02:48 AM   #3
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I don't know of any code that says you cannot draw in air from the outside. It is the same air your fan is drawing through windows when exhausting. However the answer when you don't have a fan with that capability is pretty final and shut up when you put it that way with the unsafe factor trump card.

MaxxAir fans definitely have a reverse and it works.
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Old 08-14-2015, 02:50 AM   #4
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Quote:
Originally Posted by avanti View Post
It has to do with the proximity of the fan to the sewage vent stack.
That's a design issue that can be resolved.
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Old 08-14-2015, 02:52 AM   #5
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So Hammill's statement is misleading in that he implies code prohibits a bidirectional fan when in fact the code merely specifies the distance such a fan must be from the sewage vent stack. Since the RT sewage vent stack is designed to be close to the fan, bidirectionality is prohibited. He's an artful salesman.
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Old 08-14-2015, 03:29 AM   #6
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Quote:
Originally Posted by Davydd View Post
I don't know of any code that says you cannot draw in air from the outside.
NFPA 1192:

5.5.2.1 Flue gas outlets from fuel-burning heating appliances shall be not less than 3 ft (0.9 m) from any motor-driven air intake discharging into habitable areas of the recreational vehicle.

7.6.8.1 Waste holding tank vent openings shall not be less than 3 ft (0.9 m) away from any motor- driven air intake that opens into habitable areas.
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Old 08-14-2015, 12:37 PM   #7
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Yep, as in my followup message, that is a simple design issue and it is not too difficult to move a vent 3 feet away from a fan on a B. So, just saying a reversing switch is not allowed by code is an incorrect statement.

Here is an example of deliberately designing and placing the vent away from the MaxxAir Fan. The bathroom back wall is just adjacent to the sealed skylight and that is the back end of the toilet and black tank. Logic and efficient layout would simply say vent straight up from there but the vent was moved forward and 3 feet away from the MaxxAir fan next to the skylight. mikes77 has the same layout. This explains why the solar panel was penetrated which is something you would think could be avoided. Maybe it could have if they put a gap between the panels but had they done so it would have moved the front panel more forward and more visible so I would rather have what they did.



The first ARV built for a customer did gap a different raised solar panel design to put the vent between.



My former Great West Van Legend did run the vent pipe straight up behind the toilet and toilet wall as I said would be the logical thing to do. The vent is next to the back radio antenna. It looks almost 3 feet away but is very close if it is.

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Old 08-14-2015, 01:17 PM   #8
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Thanks, guys. Blame it on "code" when it is really a question of design convenience - and mass production efficiency. He's an "Artful dodger" might be a more appropriate description.
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Old 08-14-2015, 01:28 PM   #9
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There's nothing to prevent an RV's owner from installing a reversing switch even if the manufacturer can't.
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Old 08-14-2015, 02:02 PM   #10
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We have the reversing fan on our Chevy C190P Roadtrek as it is part of the variable speed upgrade option from Fantastic.

In reality, there is very little chance of much air coming out of the vent stack unless you are running water into a tank, or there is something heating the tanks up rapidly. Wind can't blow through the tanks as there is no inlet for the air, so the fan can't push air into them either.

Hammil will always find a way to push off, or minimize, anything that is questioned. It is his salesman's nature.
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