Installing a Rooftop Exhaust Fan on a Van

A rooftop fan is one of the most important upgrades you can make to a van. An exhaust fan can remove cooking odors, smoke, and heat.  It helps keep the inside of your van close to ambient temperatures with reflective window covers and adequate air flow.

If we were going to build our van again, we would strongly consider two fans, one in front (where we have it now) and one in the back of the van, above the bed.  Two fans can help with air circulation if you have one pulling air in and one pushing air out.  An added benefit of two fans would be increasing stealth by not having to have the slider window T-vent open to get adequate air circulation. Our bed can get hot from time to time as hot air can get trapped above it.  We installed a small 12v fan on the back door above the bed to push the warmer air towards the rooftop fan, which has made it more comfortable in really warm temperatures.

Part List:

First we decided where to place the fan.  Maximizing solar panels on the roof and mounting the panels on a roof rack influenced our decision about fan location.  The Promaster also has an area of the roof in the front which is flat and appears to be designed for a rooftop A/C or fan.  

Building the 2x2 support structure

It was important to create a support system for screwing the fan flange to the roof.  The roof metal is very thin so we decided to build a square out of 2x2s that would sit inside the van, flush against the roof around the flange.  The flange would be attached from above with screws through the roof sheet metal and into the wood.  The wood and flange would form a sandwich around the sheet metal of the roof.

Before we started on the fan installation, we attached our roof rack system to make sure that our rooftop fan would have enough room. It was going to be a very snug fit and we needed make the fan cutout as far back as possible. We measured the internal cutout dimensions of the fan flange (14” x 14”) and marked the dimensions on the roof in pencil at multiple points, checking to make sure they were square and centered. We used a straight edge to connect the tick marks and draw a square on the roof. A good way to make sure you do not dent or scratch the roof while working on it is by sitting on a piece of plywood on top of a towel or painters cloth. The plywood distributes your weight and the towel or cloth keeps the wood from scratching the paint.

Checking the flange fit and placement

The corners of the fan flange, which inserts into the hole in the roof, are curved.  We placed the flange on top of the roof at our square drawing and traced the curvature of the corners.  We checked the fit a few times by lining it up with the pencil lines and confirmed the location of the potential cutout in relation to the roof rack.

We drilled pilot holes with a small drill bit (1/8”) near each corner of the cutout. We made sure that the holes drilled were slightly away from each corner to ensure that widening them would not cut outside of the outline of the flange.  We enlarged the holes with a drill bit to make them large enough to accommodate a jigsaw blade.  A 1/2" drill bit was sufficient. Taping a trash bag to the ceiling inside the van under the section of roof where we cut made clean up easy.

Drilling pilot holes which will be widened in order to fit the jig saw blade

Cutting the hole in the roof for the flange. Painters tape protects the van roof from getting scratched by the jig saw

We used painter’s tape on the roof to prevent damage from the jigsaw around the edge of the cut line. 

We started by inserting the jigsaw into one of the corner holes and began cutting. We made multiple passes for each corner so we didn’t have to twist the jigsaw blade too much.  Once the cut was almost all the way around we carefully cut the last piece and had a nice hole in the roof of our van. It was helpful to have someone inside the van support the metal cutout so it did not fall down and take the trash bag catching metal pieces with it.

We then test fit the fan flange into the hole in the roof. Adjustments were made to widen the hole slightly where it where it did not fit using the jigsaw or a metal file.  Once it fit, we removed the flange, filed down any burrs and sanded to remove sharp edges. 

We used a metal paint/primer over any exposed metal and allowed it to dry to prevent rust. We removed the trash bag to have access to the roof hole from both inside and outside.

Painting the exposed metal after filing and sanding down

Securing the flange to the roof with the 2x2 support structure

We lined up the wood support we built and put the flange in place.  Using multiple clamps we secured the wood support and the flange.  We drilled pilot holes through the sheet metal and into the wood support piece. 

We removed the clamps, flange and wood support. We cleaned any metal or wood shavings and cleaned the area where the flange touches the roof surface with rubbing alcohol.

There are a variety of ways to discourage water from entering, but our method has worked for two years with no leaking and no maintenance needed (yet).  We applied two layers of butyl tape around the edge of the hole in the roof, ensuring that the entire width of the flange would be over butyl tape when we installed it and screwed it down. We overlapped on corners to ensure there wouldn’t be an easy way for water to enter.  An x-acto knife or box cutter can be useful for cutting or trimming the butyl tape.

We then placed the flange in the hole with the wood support and secured it with clamps again. We screwed the flange through the roof and into the wood using the pilot holes and tightened it down.  We then removed the clamps and trimmed any excess butyl tape that squished out from below the flange.

Then we sealed all of the tops of screws and the edges of the flange with RV self-leveling lap sealant.  This type of sealant flows and settles a bit to fill in any voids or gaps in coverage and remains somewhat flexible throughout its life.

Butyl tape and dicor self leveling lap sealant applied

We examined it to be sure that there were no gaps or ways for water to get through cracks.  We let it dry and installed the fan into the flange.  Ours required sliding it in and screwing in two retaining screws per side which hold it down against a gasket.

We finally tested the waterproof seal with a hose and there were no leaks!

Fan wired to the starter battery. Just for testing, not for usage beyond that.

Wiring the fan was fairly simple and just required a fused connection to the house battery bank.  We tested ours on the starter battery, but would not recommend doing this for extended periods of time, due to the risk of draining your starter battery.  We ran ours through a DC distribution panel.

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