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Old 09-15-2012, 07:18 PM   #1
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1971 31' Sovereign
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plenum questions--following Minno's '72

I have really enjoyed following Minno's "Little Girl" thread, (as I have a 71 of the same floorplan)but in trying to follow in his footsteps questions arise. I did not want to clutter up his thread by asking previously covered stuffs, so I started a new one.
Currently, I am attempting the NT40 upgrade. I went with the P40 which is the park model as I am a park dweller, but the only difference is voltage.

It is on page 26 of Minno's thread that he outlines his install.

If Minno happens by this thread, then "Sir, did you happen to save the specifications to your wood box, and if so, might I acquire them?"

To Minno, or any other valued Airstream expert, for my needs/wants it would be beneficial to have three of the four ducts on one side of the box and one duct on the other. As the total inches of ducts is not changing, would this cause overheating/airflow issues?

In case it impacts airflow suggestions, my system will also incorporate a single high temp 170cfm duct fan on the line to the rear bath. The exact location of the fan on the line has yet to be determined.

Thanks to anyone who takes the time,
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Old 09-15-2012, 07:47 PM   #2
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Hi, Living31, and welcome to Airforums.

I recently changed out the furnace in my 31' Sovereign, and I'm wondering why you want a 40? The original in our 31-footer was an NT-32, and when I looked at the difference, and decided that 30 would be plenty. When we got it installed, I knew I was right. It doesn't run for very long, and the heat is abundant.

We also used the original metal plenum that was installed under the furnace when it was new. I had to make some supports to lift it up and inch and a quarter, since the new furnace was lower than the old one, and I did not want to have to cut that same inch and a quarter out of the aluminum exterior skin.

The original plenum give one large output in the lounge area, and runs another large rectangular heating vent all the way to the bathroom in the very back.

It has openings in that vent pipe under the curbside bed, and also under the bathtub. I closed the one under my bed, and most of the one under the bathtub, since I like to have a warm bathroom.

Here is a link to that part of my thread about Henri, our trailer.

http://www.airforums.com/forums/f221...ml#post1059094

It starts at post #129, and I think that link will take you right to it.

Anyway, good luck with your furnace transplant, hope it all works out for you!
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Old 09-15-2012, 08:07 PM   #3
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You might be able to adapt the original plenum with the new furnace with a little tinkering.
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Old 09-15-2012, 08:08 PM   #4
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You might be able to adapt the original plenum with the new furnace with a little tinkering.
That's exactly what I did.
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Old 09-15-2012, 09:44 PM   #5
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reply

Thank you for responding Aage, I have viewed your thread many times and like your work. My rationale for the new plenum is two fold, first my Sovereign has the same vent setup as yours, I have a Wave8 in the front lounge area and do not need the big vent. It is my hope that making a box like Minno's (his setup is pretty clean you have to admit) I could shoot three 4 inch ducts toward the back and one toward the front. The three to the back would go under the bed, beside the bathtub, and the one going to the bathroom (the longest run) getting the inline fan (because I too like a warm bathroom).
The fan would not be constant, only when needed.
I post here because, I keep finding things in the world of Airstreams that are no so cut and dry. Before I started reading here, blocking the lounge vent to cause more heat to go to the back seemed like decent idea.

As far as why I want (actually already own) the P40, the Wave8 and two electric convection heaters is because I do what I believe you have posted not to do many times, that is I live in my airstream in double digit below zero weather. Additionally, or regrettably or sadly, money and time are tight and my airstream is my home. So, while the best plan might be to gut the interior, reseal and replace the insulation, find or have made, double pane windows, btu overkill must suffice for now.

Finally, I guess it means I'm getting long in the tooth when I use phrases like "I remember when" but I do remember when Southern Idaho and Utah would spend a month in double digit below zero, with the added time the cold creeps in every space. Once in the early 80's it hit 50 below for a spell, people living in trailers were dying and staying in sleeping bags in churches. So, I remember, and make sure I have heat and provisions, just in case.
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Old 09-16-2012, 12:17 AM   #6
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Living31,

OK, yes, your quest is more clear to me now. I don't envy you, but I do admire your courage to make an AS a 4-season home. But I am sure you have read all the longer threads on doing it, and the stories of how important ventilation is, the care one has to take with catalytic heaters, the importance of proper skirting, and methods of keeping running water available.

If your budget permits, I would seriously consider one of the small marine wood stoves as a way to get peak heat when you are home without literally burning through your LP gas supplies too quickly.

Best of luck with the project, and please keep us advised on your progress?

Regards,
Aage
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Old 09-16-2012, 01:40 AM   #7
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thank you

Quote:
Originally Posted by Aage View Post
Living31,

OK, yes, your quest is more clear to me now. I don't envy you, but I do admire your courage to make an AS a 4-season home. But I am sure you have read all the longer threads on doing it, and the stories of how important ventilation is, the care one has to take with catalytic heaters, the importance of proper skirting, and methods of keeping running water available.

If your budget permits, I would seriously consider one of the small marine wood stoves as a way to get peak heat when you are home without literally burning through your LP gas supplies too quickly.

Best of luck with the project, and please keep us advised on your progress?

Regards,
Aage
All of the above, I post little but lurk much. Thank you. Those small marine wood stoves I think are the bee's knees but one of my fathers jobs was an fire investigator and he continues to remind me that aluminum burns. When I started to post here last year my goal was to survive a winter, it wasn't a bad winter but check that box none the less. The next goal is to not spend entire paychecks on propane, we'll see how this winter pans out.

For my peace of mind, no red flags on moving a third hole to one side of the plenum? How about the big inline fan? It is a big air mover but claims quiet and handles heat. I thought when I kicked it on it would pretty much shut down all other vents, but then, I am only going to use it for shower/bathroom time.

Finally, I get mixed answers when asking about the importance of turbulence in the ducts. Do you think there would be a benefit of greater heat/efficiency that would justify the added work of using sheet metal duct work over insulated flex duct hose?

Thank you for your time,

PS: One of these days I post some ghetto fabulous tricks in the full timing section. I can now give official results of some ideas that worked and some not so much.
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Old 09-16-2012, 11:03 PM   #8
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Originally Posted by Living31 View Post
All of the above, I post little but lurk much. Thank you. Those small marine wood stoves I think are the bee's knees but one of my fathers jobs was an fire investigator and he continues to remind me that aluminum burns. When I started to post here last year my goal was to survive a winter, it wasn't a bad winter but check that box none the less. The next goal is to not spend entire paychecks on propane, we'll see how this winter pans out.
IIRC, that particular installation (wood stove) was done over stainless steel, but my mind loves to play tricks on me, so I could be wrong. I got it by using the Airforums search engine (Google option in our Search menu) so if you didn't read up on that one, it's worth finding.

Quote:
Originally Posted by Living31 View Post
For my peace of mind, no red flags on moving a third hole to one side of the plenum? How about the big inline fan? It is a big air mover but claims quiet and handles heat. I thought when I kicked it on it would pretty much shut down all other vents, but then, I am only going to use it for shower/bathroom time.
As long as you have enough room above your furnace to u-turn one of the left-side vents, I see no trouble in using all four.

But I am wondering what exactly you are doing in the big picture in your trailer. I ask this because Minno, whose wooden plenum you appear to be ready to copy, did a complete tear-out and re-design rebuild of his interior. He is also lining it in aluminum, to protect the wood, I gather. None of his original cabinets were kept, from what I remember. I don't recall him discussing at all why he decided to forego the large rectangular metal ductwork and steel plenum that his trailer originally had, but I am sure that he had very good reasons for doing it that way.

Minno used round vents, although I don't think he used all four. The manual talks about a minimum of three being necessary, IIRC, so that the internal pressure of the furnace isn't too high. Since I used only the option on my furnace to vent into the plenum, I was comfortable going with the original layout for venting, and if I knew more about your trailer's layout, could comment more on your design.

All that to say, he was completely free as to where he would put his ductwork, and he very logically spread the outlets in the rear between his sleeping quarters and bathroom. On the other hand, I kept everything as original as possible, only to have the simplest, fastest job I could, and also partly because I reasoned that the existing ductwork was better than the metal 'dryer-vent' style ducting that is so popular today. Smooth sides, and wide passages will most certainly give less resistance to the air passing through, so why bother to change what it to me at least superior to what I would probably put in new...?

Also, I looked carefully up and down the length of my TT, and there was no spot where I could put vents without losing tambour door use, and knowing my DW as I do, I never even thought about doing that.

Quote:
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Finally, I get mixed answers when asking about the importance of turbulence in the ducts. Do you think there would be a benefit of greater heat/efficiency that would justify the added work of using sheet metal duct work over insulated flex duct hose?
See my comments above. I would personally use the round hard-wall ductwork and not the soft one with a spring going through it. All those undulations must resist air passage, and if my clothes dryer is any proof, they really hold on to a lot of dust and debris. I don't see any need to insulate the ducts, since they stay inside the trailer, and where they pass can probably use a bit of heat that will radiate from them. I would make sure all the joints and seams were carefully duct-taped, though.

In any event, you have thought it through enough by now, I would say. If you want to stay warm this winter, time to get that furnace installed!
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Old 09-16-2012, 11:10 PM   #9
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Oh, and your idea of a fan: 170 CFM? Do you really feel that is what you need? Sounds like an awful lot of power to me.

I would simply rummage around and find an old computer to take the muffin fan out of and try that. I can't see needing a lot of horsepower in the bathroom... Do it on the back of a vent where you can easily get at it so you can experiment. In my TT, my head is very near that spot, so I would want one that was very quiet.
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Old 09-29-2012, 04:17 AM   #10
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plenum/duct math puzzles

Old furnace out, having a fellow make a heavy gauge sheetmetal box to be used as Minno's lined box. It will be done this week and if it appears flimsy, I will surround it with 1/8 6061.

To any HVAC masters or those with a penchant for math:

The Suburban P40 has a max c.f.m. of 441 and a static pressure of .15"wc. It pushes air from a single bottom vent into a plenum chamber. The plenum chamber is 5.25/12/21(height,width,length)

There will be a single 4inch round duct protruding from one side and three 4inch round ducts protruding from the other.

For reference the bottom vent of the P40 will be the "front", the side with the single duct, the "right" side and the side with three ducts the "left" side.

The left side ducts must be mounted as far as possible toward the back of the plenum.

The right side duct can be mounted anywhere along the right side.

It would be beneficial to have the most c.f.m./pressure exit through the left side duct farthest toward the back. I have several ideas on how to accomplish this task:

*dampers and/or having duct tubes protrude into the plenum chamber at different lengths?

** attaching my monster 170cfm fan (to be mounted on a dimmer switch so it can be cfm up to 170) on the most wanted left side duct?

As I have never designed a ducted system, decided to ask, before further invest.

Thank you for taking the time to consider my post,

post script: I know neither the rationale nor meaning of "static pressure of .15"wc" but, it seemed important to HVAC professionals both here and online. (The same professionals who wanted nothing to do with my project when determined it was a trailer)
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