Vent fan confusion

[mikes47]

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?

[avanti]

It has to do with the proximity of the fan to the sewage vent stack.

[Davydd]

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.

[Davydd]

Originally Posted by avanti

It has to do with the proximity of the fan to the sewage vent stack.

That's a design issue that can be resolved.

[mikes47]

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.

[avanti]

Originally Posted by Davydd

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.

[Davydd]

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.

[mikes47]

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.

[eric1514]

There's nothing to prevent an RV's owner from installing a reversing switch even if the manufacturer can't.

[booster]

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.

[mkguitar]

another consideration could be CO poisoning-

on my model when using the gas burners, it is advised to open the vent and the window by the burners.

in practical use, this moves the hot air/ byproducts of combustion up and away...and out of the enclosed space


we don;t use the shower, and have removed the curtain. we have used the outside shower. we figure if we are in a campground, we use that shower- if we are in the boonies, then we use the outdoor shower and keep the interior of the van dry from vapor- and also preserve the capacity of teh grey water tank


owners can do what they want to their van- manufacturers do not have that latitude- they cannot contravene codes or do anything which would make them liable for any harm to the occupants of the van.
or they'd spent more time in court than building vans.

mike

[gerrym51]

maybe it's a canadian code

[Davydd]

Drying shower curtains was not the first time I had heard a use for drawing air in. In another thread I had read a discussion on drawing air in there were examples given. I don't remember now what they were but at the time I dismissed them as not important to me to ever do it same as drying curtains. So, I have the capability but highly doubt I'll ever use it...as he dashes out to the B to experiment.

[avanti]

The two reasons I've ever had to reverse the airflow are (a) sometimes the air is fresher up there--e.g., genset exhaust; and (b) ground-hugging insects are getting sucked onto the window screens.

[eric1514]

Originally Posted by avanti

The two reasons I've ever had to reverse the airflow are (a) sometimes the air is fresher up there--e.g., genset exhaust; and (b) ground-hugging insects are getting sucked onto the window screens.

Exactly. It's easy to make one very effective no-see-um screen for the roof top vent and then blow air out of all the lousy window vents.

Eric

[mumkin]

I had this issue in my Libero too. The Canadian code is because it is too close to the cooking facilities... which is certainly also true in the 170/190/210... can't say about the Sprinter/Promaster. With the RT rigs, the kitchen tends to be right across from the toilet... and thus the vent issues... which the average buyer is likely to find more of a problem.

But if you want it to reverse, you just do as I did and call Fantastic Fan company and they will send you the switch. Easy to install...

[mlts22]

One use for the reversing fan would be useful when a "B" is not in use in hot weather. Place a box with filters (assuming it has proper airflow) over the vent fan hood, turn the fan on in reverse, and open windows slightly. The result is positive air pressure in the cab, and no dust (due to the filter on top taking care of that. Rain can be a factor, but that wouldn't be impossible to engineer around.

[mkguitar]

Originally Posted by mlts22

One use for the reversing fan would be useful when a "B" is not in use in hot weather.

Hot air rises by convention, since it is now about 110º and rising I can state with certainty that drawing air in the windows and venting it out the rooftop vent is most effective- fann off or on

yesterday I working inside the van, unshaded.
temp inside was 122º ambient temp was at 114º
fan speed set at 1

while a user may want to add a capability - manufacturers do not have the same latitude with codes and regs.
you can sit on the rear bench while going down the road...but you may see stickers warning you not to

mike

[mlts22]

Very true. The reason why I mentioned doing it the opposite way is because even though hot air rises, having incoming air get filtered would mean less dust and insects getting in.

[obgraham]

I don't understand what you lot are on about. The Fantastic on my 2015 CS reverses just fine via the remote. It defaults to "exhaust", but we use it on "intake" probably 75% of the time. No mods needed -- it came that way.