Flexible Heat Ducting Poorly Routed

[itat]

While working at mouse-proofing my new 5er in the pass through area I discovered why we don’t get nearly as much warm air towards the rear of the trailer. The furnace is installed immediately behind the pass through on the drivers side. One of the 4” flexible ducts feeding the rear comes out of the rear side of the furnace (side opposite the pass through), turns 90 deg towards the centre of the trailer, turns 90 deg again towards front and then turns 180 deg towards the rear. At the 180 deg turn, they tee’d in a smaller flexible duct that sends warm air the the pass through. The duct at the 180 deg turn is wedged fairly tightly between the furnace and the water pump.

I’d like to redo the routing to eliminate the 180 deg turn and the second 90 deg turn. Does anyone know how they would have tee’d in the smaller duct and what size is the smaller duct?

[Witch Doctor]

Don't know how they did it, most likely with a 4x4x2 Wye. The two sizes in all the RVs I have seen are either 4" or 2" . May I suggest to you if your going to do all that work that at the 90 your talking about, that you install a 4" 90 degree hard elbow. Your probably loseing close to 30 to 40 % of air flow at that point. The flex duct will close up by itself when you make a hard 90 degree turn. When you take a piece out bend it 90 and look inside you will know what I'm talking about. You will be surprised at the difference in airflow.

[5picker]

In mine they simply cut a hole in the 4" duct and stuffed the 2" duct into it and gobbed some silver duct tape on it.

2nd graders could have come up with a better plan.

[itat]

Well, it’s definitely not a wye connection. A hard 4x4x2 wye would have been a much better way to do it. I’ll have to search the local big box stores to see if they have one. It may be as 5picker said. There is a lot of aluminum tape around the connection. They taped all the connections at the furnace, too. They are leaking air but it’s severely restricted the air flow.

[itat]

Edited post:

I can't see a wye doing an internet search but I did find a 4” x 3” reducer. I’ll have to measure the smaller duct.

[Comanchecreek]

Mine were kinked at the 90's off of the heater. I rerouted them to help unkink the turns. Helped some, although I can't get to the ducting under the floor without removing the underside of the trailer. I had the same thought about getting rigid elbows. Let us know what you find.

[TimVWulp]

I had the same problem with the two registers in the living room at the far end of the TT V-lite. No air flow to 2 registers and furnace was overheating and tripping the high limit. Found that flex duct takeoff was on door side of the furnace plenum and made a 180 deg turn with flex duct around the plenum then an other 90 deg turn toward the rear of the TT. I cut open the Coraplast bottom cover to expose the furnace ductwork and plenum in a U shape. I could not cut in a takeoff on the opposite side of the plenum as there was no room. So I cut a 4" hole in the bottom of the plenum with a hole saw. Bought 3 four inch 90 deg aluminum elbows and a 2' length of 4'' duct. installed the new duct work which eliminated 6' of flex duct and patched the old 4" hole in the plenum. Taped and screwed the new duct work. Cleaned the coraplast and taped back together with gorilla tape which is holding up very good (about 18,000 miles last 1.75 years). the new duct work pushed the coralast down a little more than 1"and has not caused any problems. Now the furnace dose not trip the high limit and gives two times more air out the 2 register in the back of the trailer heating it much better.

Hope This Helps Tim

[itat]

I've found 2" flexible duct on Amazon since reworking the ducts will mean I need a longer length of 2" to feed the vent in the pass through area, but I can't find any heating duct metal fittings to reduce to 2". Just a shop dust collector plastic reducer. Anybody know where I can find a metal HVAC duct 4" to 2" reducer or wye? Maybe I have to go to a local HVAC supply house?

[itat]

If I can’t find a proper 4”x2” reducer I’ll probably get the longer 2” flexible ducting and splice it somehow to the exist 2” flexible duct and realign the 4” duct to eliminate the U-shaped bend the factory installer put in it.

[itat]

Well, with the cooler weather approaching I decided it was time to get off my butt and get the ducting re-routed to eliminate the 180 degree bend that the factory installer created. There is a 2” flexible duct teed off the 4” duct at the 180 degree bend to feed the heat vent for the pass through area.

The factory installed the water pump about 10” from the rear of the furnace and put the 180 degree bend and the tee in the space between the water pump and the furnace. The only reason I can think of that they did that would be that they were short on the 2” duct and had to locate the tee closer to the back wall of the pass through. The aluminum framing for the rear wall of the pass through and the shorter height of the pass through (I can’t sit up straight) made it a difficult job to access and work in there. I’m in shape but unfortunately that shape is round! Thankfully, my skinny DS was home from university for the weekend so I enlisted his help.

After deciding how I was going to re-route the ducts I had to secure a flexible 1/2” hose (that feeds the black tank flush) to a nearby aluminum stud to keep it out of the way and away from the re-routed heat ducts.

Before taking things apart I was able to confirm that the factory used a hard manufactured 4”x4”x2” tee (I’ve never seen one in local hardware stores) so I decided to re-use it. On the upstream side of the tee I left the existing 4” flexible duct connected and cut it off at the furnace. On the downstream side i cut off the exist flexible duct so I could shorten that duct.

To improve air flow, I took Witch Doctor’s advice and used a 90 degree hard adjustable elbow off the furnace. Thanks for that advice Witch Doctor!

I reconfigured the duct routing so there would be a straight line between the furnace and where the duct goes down into the underbelly, eliminating the 180 degree bend that the factory installer created. I cut back the 4” duct to the lengths i needed for the straight run and reconnected to the tee and the furnace. Then I connected the new 2” flexible duct to the tee. I screwed and taped the flexible ducts to all the hard fittings. I re-used a vinyl strap that the factory had used to keep the flexible duct bent at 180 degrees and used it to secure the tee away from the water pump and route the 2” duct on the floor between the water pump and the furnace.

We’re heading to Algonquin Provincial Park tomorrow so we’ll see if my work pays off in better warm air supply to the rear of the trailer.

I was going to build a platform to mount the water pump on to better separate the water lines from the heat ducts but I discovered that the factory stripped the Robertson screw head so I need to get a screw extractor first. That’s a project for another day.