Untangling the Heat Ducts

[geo]

While installing the rear tank heaters for the Fresh Water and Gray2 tanks on my Alpine, I took the opportunity to correct the mess and tangle of the living area duct work. Once I had cut and removed a 4' (1.2m) section of coroplast (See UltraHeat Tank Heater Installation, Part 3), I had access to the duct work passage from the upper utility basement to the lower, the ducts as they passed the Fresh Water and Gray2 tanks, and the area immediately behind the Fresh Water tank.

The two heating ducts feeding the rear living vents (passing along the starboard side of the belly) were entwined with the aluminum duct that directed heat on the Gray2 dump valve and the valve control wire. I removed the support for the valve heat duct and pulled it out of the tangled mess. I removed the clamp from one of the heat ducts to free it and untangled the whole mess. I laid the rear heating duct parallel to its neighbor and reattached it. These ducts now curved a parallel path to the starboard side of the trailer to squeeze past the end of the Fresh Water tank and onward to the rear area. (Forward.jpg) These passed over the Gray2 valve control wire. The Gray2 valve heat duct was fed over the parallel rear heating ducts and reattached to direct warmed air on the Gray2 dump valve. (Gray2_heat.jpg)

I noticed the heating duct that fed the kitchen heat vent (down the port side of the tanks) had a large horseshoe bend both forward in the area near the forward tanks and aft past a cross-member between the two I-beams. (Rear_duct.jpg) The Gray2 tank is quite shallow, so there is about 6+ inches (15+ cm) of space beneath it. This kitchen heat duct passed within this space. I pulled enough duct from the front to smooth out the turn and remove the horseshoe bend. Then I did the same for the rear bend of this duct (carefully pulling the duct from within the cross-member's bracing). I removed about 8 feet (2.4m) of duct such that my splice would occur beneath the Gray2 tank. (Rear_fixed.jpg) I used a short piece of 4" (10cm) aluminum duct and clamps to join these two segments together. The outside insulated covering was taped with high/low temperature furnace tape.

As I was adding insulation to the underbelly area also, I used unfaced fiberglass R-13 and R-19 insulation to separate the Fresh Water fill line and the Fresh Water feed line from the tank to the pump away from the I-beam. Where before, these lines were in direct contact with the I-beam and subject to freezing from heat dissipating from the water lines by conduction, these lines were now resting on a bed of insulation with an open space above. It should be noted that this open space was also separated from the I-beam by insulation. A previously mentioned "Warm Air Circulation System" provides warmed air from the upper utility basement to the port side of the Fresh Water tank. This open area above the mentioned lines allows this heated air to return to the upper utility basement and to warm the mentioned lines. On the starboard side, I lined the inside of the I-beam with unfaced fiberglass insulation. Part of this area was adjacent to the Fresh Water tank and above the area where the rear living heat ducts were to pass. Other parts of this area were adjacent to "empty" space which I filled with unfaced fiberglass insulation.

I laid the kitchen heat vent duct along the port outside area of the Fresh Water tank, to the outside of the Fresh Water tank drain. This area is offset from the port I-beam and affords a non-restricted space for this duct. Though there is a minimal of insulation inside the outer covering of this duct, it should provide additional heat to the Fresh Water fill and withdrawal area on the port side of the tank. (FW_side.jpg)

I also worked the rear living ducts along the starboard side of the Fresh Water tank so they would be minimally crushed when the coroplast was reattached. This was quite a feat as these two ducts are relatively large diameter and the area at the starboard side of the Fresh Water tank is minimal. When the coroplast was reattached, there was a definite sag in the area of these ducts. I added aluminum support cross-bracing beneath the coroplast to support it. In the area of where the heat ducts passed the Fresh Water tank, I bent the aluminum such that it was pre-formed beneath this bulge and allowed the bulge to remain. I have yet to test this, but I trust that the warmed air will not be too restricted in this area. If the warmed air is too restricted, I am considering reopening the coroplast and installing a larger single heat duct that will have a smaller diameter than these two ducts. This would involve putting a "Y" at each end of this larger diameter to join the two ducts' airflow and to separate it behind the Fresh Water tank. I will post what my final decision and arrangement is on this duct work after a test.

In all, what did I learn about this duct work? It appears that Keystone utilizes standard lengths of duct work to attach the furnace distribution to the living area duct vents. It this length is too long, the duct is curled and fed into curves to compensate for the extra length. It is probably more efficient to use too much ducting material than it is to use the labor-hours to cut the ducts to the correct length. However, these loops and curves can relocate during transportation and become restricted against other basement items and utilities, such as power cables. I would also guess that the person(s) who are laying out this duct work attaches one end of all ductwork at one time. This would result in a "pile of ducts" that would have one end grabbed and fed through a cross-member bracing, then another, etc. In this way, it would be easy to crisscross the ducts and result in the "French braid" of ductwork I saw forward of my Gray2 tank. This "mess of duct work" could also result in restricted duct areas which would reduce the flow of heated air. Finally, the area on the starboard side where two large ducts pass between the Fresh Water tank, the starboard I-beam, and the coroplast is a very tight fit!

It is this last area, located on my Alpine slightly rear of the door on the starboard side, that I now believe is probably the cause of many complaints concerning lack of heat to the rear living area heating vents. I spent quite a bit of time arranging the heat duct work in this area to attempt to assure that the inner ducts would not be crushed and minimally restricted. In a mass-production operation, there is not time to check, double-check, and arrange in the manner which I utilized. It would be very easy to gloss over the problem that the ducts were actually trapped beneath the Fresh Water tank and crushed to near closed restriction. I would suggest that if your Alpine and maybe Avalanche, Montana, or Big Sky is experiencing low heat from the rear living area vents, this might be the first place to loosen the coroplast and have a peek.

Ron

[allentx1]

I'm not sure I have enough detail, perhaps you can come to my house and I'll video you doing my Avalanche. You know, for the good of the forum.

I look forward to your next project. I will be dropping all the coroplast on mine to correct the heating and some of the insulation deficiency.

[geo]

Originally Posted by allentx1

I'm not sure I have enough detail, perhaps you can come to my house and I'll video you doing my Avalanche. You know, for the good of the forum.

I look forward to your next project. I will be dropping all the coroplast on mine to correct the heating and some of the insulation deficiency.

Allentx1 -

My DW would love to spend some more time at Pecan Grove RV Park and the surrounding area, but I don't think "helping with someone else's underbelly" would meet with much approval. Besides, there's already rumors circulating on the Forum that my underbelly obsession is "worrisome".

On a serious note, and before I post about finishing the tank heater installation, if you are going to cut the coroplast, order the underbelly tape at least a week in advance. I also triple taped / overlapped my cut seams. I'll try to get that all posted in the next day or two.

Ron
"Grand Poobah of The Royal Order of Underbelly Crawlers" (self-appointed).

[f6bits]

When I was pretending to be geo, I stopped by Home Depot and picked up some Gorilla Tape, just in case I had to do some cutting. I didn’t do any cutting, but don’t you think Gorilla Tape is as good as underbelly tape?

[66ken]

I used Gorilla tape on the coroplast and it works great.

[SteveC7010]

Originally Posted by 66ken

I used Gorilla tape on the coroplast and it works great.

Ditto, and maybe even better. My Cougar came with a bunch of that shiny HVAC tape holding the flaps in place. Half of it was already peeling away. I replaced it with Gorilla tape and so far, no problems.

I've used Gorilla tape to patch cheap plastic tarps, and it seems to stand up to the weather pretty well. As always, making sure the surfaces are clean and dry before applying the tape is necessary.

I am getting the beast out of storage this week and that will be one of the first things I check on.

[geo]

Originally Posted by sdayman

When I was pretending to be geo, I stopped by Home Depot and picked up some Gorilla Tape, just in case I had to do some cutting. I didn’t do any cutting, but don’t you think Gorilla Tape is as good as underbelly tape?

Scott -

I have not used Gorilla Tape on coroplast. I have used it on Solitaire mobile home "underbelly covering" with limited success. Now, admittedly, the Solitaire mobile home had more of a tar fabric (like tar paper but definitely fabric, not paper) material rather than a plastic based cardboard. So I am just not in a position to praise or condemn Gorilla Tape on coroplast. I see Ken66 and Steve have had success with Gorilla Tape, so I would have to say it is good for coroplast.

As will be mentioned in an upcoming post, I did use the low/high temp HVAC tape to hold and seal the reflective bubble wrap located beneath the coroplast. This was not the cheap HVAC tape.

As Steve mentions, though, getting a clean surface is key for any surface to be tape sealed. I first cleaned the area with OxyPower Fantastic. That was followed by another cleaning with 91% Isopropyl Alcohol soaked shop towel. There was no moisture, grease, dirt, or oil on the surface to be taped when the cleaning was complete. I would say this is necessary whether one uses Gorilla Tape or RV Underbelly Tape.

The trouble I did have was self-caused. My DW was wanting to help, but she doesn't like to crawl under the RV. (Yes, I am alone in my Realm of the Underbelly! ) However, I had allowed the underbelly tape to fold over on itself and now had a sticky mess! So I simply cut the sticky tape mess off the end and promptly got three fingers entangled in the very sticky adhesive. She asked, "Can I help?" So I stuck my hand out from beneath the Alpine and asked, "Yes, could you get this off my fingers?" Well . . . have you ever been wrapping Christmas presents and the cat walk by? You know, you grab the cat, take short pieces of tape and apply it to one front paw and one back paw and release it? Now don't call the ASPCA, it's been over 7 years ago! That's what basically happened! Now my DW had tape stuck to her fingers, no the fingers on the other hand, no back to that hand now. After about 5 minutes she did get a paper shop towel and embedded the tape in it - and left without a word! Yup, knew I was in trouble at that point in time!

So, I would say Gorilla Tape, from Forum members recommendations, seems to be acceptable. I do like the RV underbelly tape because of its high adhesive quality, it is very thin plastic with embedded fiberglass, and the 4" width. But I would dare say it is the RV owner's choice!

Ron

[Propilot11]

Gentlemen. I am going to have to access the middle to the rear of my 2011 Cougar 325srx underbelly. Any pointers about what to cut with, where to cut in relation to the frame screws, how big an opening is possible etc

[JRTJH]

What are you trying to access under your trailer? If you're looking to tighten or align a slide motor, a simple 3 sided "flap" type of opening would be the least intrusive, but if you're trying to access a holding tank or plumbing runs, then removing the entire coroplast, possibly from the front or from the rear would be the best way to access a larger area.

So, what are you trying to do and what are you trying to access?

[Propilot11]

Planning to add a washer dryer in the garage. I need to run electric, water and drain lines.

[chuckster57]

If your coroplast is held on with screws, just remove as many as you have to to get it to lay on the ground. When your done start at the end that's still attached and work your way backwards, the original screws should line up.

If your coroplast is "riveted" in a place just remove the rivets as needed and then use self tapping screws when you put it back up.