In response to Daryles, Montana Fan, asking how I installed the flex duct within the underbelly, I’ll try to describe. Forgive my memory as it’s been 7 years ago I did this.
First let me clarify the flex duct. I used two types of flexible ducts. One was 3 inch plastic flex duct typically used to vent a bathroom exhaust fan, which is indeed very flexible. The other was 4 inch semi-ridged aluminum flex duct typically used for dryer vents. The aluminum duct has flexibility to it but has a certain stiffness to hold its shape or position. This is what allowed me to thread or insert the 4 inch aluminum duct into the underbelly.
This is a Montana Big Sky 3400RL. I installed the bathroom exhaust fan in the ceiling of the basement, immediately next to a white plastic wall, which will be removed for installation of the duct, just behind the service center area, (city water connections and dump valves , etc.).
The water pump is mounted on the floor right behind this wall if that helps.
With the white plastic wall removed, I connected the 3 inch plastic flex directly to the exhaust fan. It was routed down the pump side of the plastic wall among the nest of water lines then towards the area under the gas furnace. In this vicinity, I used a PVC reducer fitting to adapt the 3” to the 4” duct.
Now I have to back up a bit, due to the congestion in this area, the aluminum duct was inserted first with the adapter and 3 inch flex vent assembled and secured with hose clamps. The 4 inch aluminum duct is corrugated and comes collapsed to about 3 feet. Expand the corrugations to its full length, approximately 8 feet. Due to it’s stiffness it can be inserted into the underbelly fairly easy. I do remember encountering a blind obstacle or two, I think a water line and hydraulic line. I was able to determine the duct was not in the path of the kitchen slide movement.
The aluminum duct literally lays within the underbelly loose. It’s extremely light and I did not fore see it doing any harm.
I’ll try to get a photo or two and put in another post.