Roof Vent Considerations

rv ventilation

Converting a van often means that you’re working on multiple individual projects at the same time. Currently the Murphy bed with desk has my focus and when that work stagnates, I switch over to a secondary project: the roof vent.

That happens when you run out of materials or just when you only have a few hours to spend. But at the same time I might still be finishing up an already ‘completed’ project and/or preparing or ordering parts for upcoming modifications. Meanwhile, I may spend a few evening hours on the design and changes in design of the remaining project.

Today, it is all about ventilation. A small, enclosed space, like the interior of a converted cargo van, accumulates lots of moisture from breathing, cooking, etc. Opening doors and/or windows would be sufficient, as long as you’re on a one-day or brief multi-day trip. That’s entirely different when you embark on a long trip or when you live in a van. Temperature and humidity control then play a more prominent role, even when windows or doors have to remain closed.

Types of Ventilation

  • Natural ventilation is the process of supplying and removing air through an indoor space by using outdoor air flow caused by pressure differences between the vehicle and its surroundings.
    Generally, air flows between a low entry point and a high exit point, that have a maximum distance between them.
  • Forced ventilation uses a fan or other mechanical system.

Floor ventilation plays an important role by drawing cooler air from the shaded area under the vehicle without the necessity of a fan, if we can induce natural ventilation with the installation of a roof vent at the opposite end of the van’s interior. The floor vent was installed recently in the wall cavity behind the driver’s seat.

Roof Vent Location

  • For improved natural ventilation, at a maximum distance from floor vent.
  • Close to the kitchen area, to remove smells and moisture from cooking.
  • A fully opened vent should avoid obstruction for any of the solar roof panels.
  • Only a few locations in your type of vehicle support the installation of a roof vent.

In my Ford Transit, with a planned rear kitchen, it’s convenient to place the vent between the two rear ceiling cross members. This location is exactly 14 inch long, as needed by most vents.

Vent Types

There are many type of vents that can be installed on RV roofs in any size and form …

… but typically, only two brands are considered by RVers: the Fan-Tastic fan by Atwood Mobile Products and the MaxxFan from Airxcel.

Ford Transit Installation Quirks

The roof is extra thin and even a slight mishap can cause a permanent dent in the roof surface. Like other van manufacturers, Ford implemented roof corrugations, to increase its rigidity. Unfortunately, the central part of the roof, where the vent is to be located, is less than 14 inches wide, making the installation of the vent flange unnecessarily complicated. Spacers are necessary to account for the lower roof corrugations.

  • One option is to install spacers in these ribs, to compensate for the uneven surface.
  • Another is to use a roof adapterroof vent adapter. That seems a nice, yet costly solution, with added uncertainty about long term degradation of the added material. The adapter is available for both exterior and interior of the van, although the interior adapter doesn’t fit between the two rear ceiling cross members.

Either solution creates more opportunities for moisture to enter the vehicle.

I will construct a separate interior ‘roof adapter’ to which the vent can be attached. Separate stainless steel bolts, nuts and screws have to be ordered, before proceeding.

Vent Selection

Both Fan-Tastic and MaxxAir are quality fans, but some significant differences exist. I selected the MaxxAir Deluxe 6200K from Airxcel mostly because of its ability to remain open during rain.

  • It has a low profile and a ‘smoke’ cover to comply with the stealth requirements of my darker, gray-brown vehicle.
  • Capability to take in air & to remove air from the vehicle.
  • Ability to remain open during rain.

This vent in combination with the floor vent should produce enough natural convection, to keep the interior close to the outside ambient temperature, without the use of the built-in fan. This will make it easier on your pet, when you have to leave him alone in the RV.

One thing of this setup still bothers me. The flange and vent body are cream colored and that is also the case for the adhesive materials used during the installation. Most are barely or not at all visible from street level, yet a little effort should make it a bit more stealthy!

I selected darker colors for the following sealants:

  • The sealant between adapter and roof.
    GE Silicone II available in black in your local DIY superstores $6.58 or at Amazon.
  • The butyl tape between flange and adapter.
    Available in dark gray.
  • Sealant over screws and flange.
    Dicor: available in black.

I would like the vent flange and body to be painted black and that seemed a simple idea. I’ve painted plastic window frames before in my old Dodge with a spray paint formulated for plastics. That was on the interior and worked out great, but after consulting with Airxcel, my enthusiasm was a tad less than before. Very prompt in responding to my inquiry, but only supplied me with some basic info.

The issue comes down to the Thermoplastic Poly-Olefin or TPO material, which has a minimal surface adhesion and which properties can be negatively affected by ingredients like Xylene and Toluene, that are commonly found in many paints. Many spray paint manufacturers, such as Valspar, Krylon and Dupli-Color do not have products that work on such surfaces; only Sherwin Williams has a two-product system, but only for industrial applications.

I’m at a stalemate now and unless some of you can come up with a paint solution, I likely have to give up on perfection.

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  1. What does the undercoating spray paint have in it’s formula?Maybe, it doesn’t have the toluene and xylene, it’s great for many surfaces? Flat black.

  2. What about using a heater/ac register for
    The step riser?

    One could close it to prevent exhaust gasses while traveling.

    1. I’ve seen that used in that way before and its forward and low to the ground position is ideal for a floor vent. But it would not replace a roof vent (heat rises).
      The typical home heater/ac register isn’t very good either at closing off the incoming airflow. A vent at this location though, in combination with a roof vent, is a great idea!

      Van Williams

  3. Could you please provide the names and/or links to the three smaller vent fans that you only posted pictures of? Some of us don’t have the space or need for the larger fans. Thanks you!!

    1. Hi Tom,
      These are the specific vents:
      Ventline VP-543 12V Smoke Van Roof Air Vent
      Ventline V2049-03 Colonial White 1-1/2″ Plastic Plumbing Vent
      ECO-WORTHY Solar Powered Attic Fan Solar Venting Stainless Steel Solar roof fan Vent

      One is just a plumbing vent.

      Following up on your comment, if you have the space for a full-size vent or multiple vents and especially if you’re a warm weather camper, my general stance is to maximize venting. In my opinion, venting is much more effective in warm or humid weather than insulation.
      Good luck!

      Van Williams

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