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Old 02-19-2009, 02:04 PM   #1
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need help with package unit ductwork


Hi,

I have an old furnace in a lake house (~30 years old single wide mobile home) that I frequently use about once a month. The existing furnace is too old and has to go. Window AC are used during summer.

I purchased a used Package unit (Carrier 48SS-042 -LP furnace and 3.5 tons AC.) I plan to install it myself to save $$$money. My neighbor is a plumber and will be taking care of the propane part. Luckily for me, a dedicated circuit was already allocated to the Window AC, so all I have to do is rewire to the unit.

The toughest part for me is the ductwork from the unit to the trailer. I have never done ductwork before (except the minor sealand or insulation) so I really need your help in determinning what type and size of ductwork and how to use it, if all possible.

btw.. I plan to reuse the existing furnace closet area for the air-return and also to connect to the main ductwork. any concerns!?

Thank you in advance.

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Old 02-19-2009, 04:48 PM   #2
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need help with package unit ductwork


All kinds.

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Old 02-19-2009, 04:49 PM   #3
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need help with package unit ductwork


First. Doubtful the electric line for the window A/C is big enough for that package unit.

Without pics of the furnace alcove, we can't say much about how to run the duct work.

Your current duct system may be too small for that package unit.


What is the rest of the model number.
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Old 02-19-2009, 04:56 PM   #4
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Mobil home duct are notoriously undersized and always employ a high static blower. That is one problem that will disallow you taping existing duct.

The other:

You try hooking ducts from the Pkg unit to the existing duct the airflow will back feed thru the furnace and out the existing cold air return.
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Old 02-19-2009, 08:00 PM   #5
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The mobile home is 1100 sqft. the floor plan is shown in the pics below.

The Package Unit model number is 48ss-042100331; a lot of information is found in the this document.

I am now beginning to understand to the importance of careful ductwork design. I'm an electrical engineer -by education only- and strong believer in the design approach, but HVAC is not one my fortes. Please keep in mind that the mobile home is maybe worth $10k at most.

If the current ductwork is not suitable for this unit, then, would you recommend a whole new ductwork? what type? size?
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Old 02-19-2009, 08:11 PM   #6
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Run a central return off Pkg unit to mobile home. You will have to cut a new opening in the home(be careful. Flimsy mobile home construction).


Run a large size plenum under home from Pkg unit. Run new branches to existing registers using six round 26ga pipe or insulated flex.
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Old 02-20-2009, 06:17 AM   #7
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100,000BTU input 80,000BTU heat output.
Just a bite on the over sized side.
3.5 tons of cooling, your probably over sized on that also.

Gonna be hard pressed to get enough air flow for it.
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Old 02-20-2009, 09:03 AM   #8
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The insulation value in a mobile home of that age is negligibly. He's got what he needs. Current production homes of 750 sq ft with better insulation are calling for 2.5 tons.

It's like trying to cool a home with all screened windows and doors.
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Old 02-20-2009, 01:23 PM   #9
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You are both correct. the unit is over sized because the insulation is very poor. I also agree that maybe it is best to build new ductwork instead.

I spent few hours on the internet researching and learning from others and come up with two options:

1 - Keep the existing trunk line, and use two helpers at each end. This option seems fairly easy to do and cost less.
2- Build new duct work and add new registers. I like this option best but I'm a little nervous in attempting this size of diy.

Someone may not of good website resources out there on how to build ductwork?
Also, Please see the pic below showing the two options and feel free to make any suggestion or comments. Thanks.

If the pics is too small, please use this <<link>> for a larger one.
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Last edited by bekind42; 02-20-2009 at 01:30 PM. Reason: pic is too small
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Old 02-20-2009, 01:59 PM   #10
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Quote:
Originally Posted by bekind42 View Post
You are both correct. the unit is over sized because the insulation is very poor. I also agree that maybe it is best to build new ductwork instead.

I spent few hours on the internet researching and learning from others and come up with two options:

1 - Keep the existing trunk line, and use two helpers at each end. This option seems fairly easy to do and cost less.
2- Build new duct work and add new registers. I like this option best but I'm a little nervous in attempting this size of diy.

Someone may not of good website resources out there on how to build ductwork?
Also, Please see the pic below showing the two options and feel free to make any suggestion or comments. Thanks.

If the pics is too small, please use this <<link>> for a larger one.

I like your second proposed set up. Butt up grade to 14" or 16" flex for trunk and add a second low loss three way tee for your secondary trunk. . I would place the return in the living area along an inside wall.
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Last edited by hvaclover; 02-20-2009 at 02:11 PM.
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Old 02-20-2009, 03:19 PM   #11
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Use your second design.

But, on the master bedroom side. Shorten the helper up. So that it taps into the supply duct between the first supply for the master, and the last supply for the dining room.
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Old 04-27-2009, 09:33 AM   #12
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need help with package unit ductwork


Hi,

I'm about ready to lay out the concrete slap for the Package unit. The plenum has been ordered as well as the flex ducts.

As I have mentioned before, there is an existing 220 V AWG 10 wiring, with the disconnect box (un-fused, but I plan to replace with fused one.)

Please see the Package unit electrical information and the exiting wire info and let me know if it is possible to use the same wire and save me some money.

a side note: The unit will be installed in a summer-weekend place with a little use.




Package unit info:



Volatage: 187-253


Power Supply: MCA 30.9; MOCP 50

Existing Wire info:
E18679 (UL) AWG10 CU 2 CDR with AWG10 Ground. type NM-B 600V.

I have attached the package unit documentation in a previous posting within this thread. please see page 24 for more information. The model is 48ss-042100331.

Your feedback is greatly appreciated. Thanks.

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Old 04-27-2009, 10:02 AM   #13
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can't say for certain but between 400.00 and 600.00.

The existing electric box is full.. Electricians normally inflate the rate because they don't like to work on mobile homes in the area where I'm at.
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Old 04-27-2009, 10:07 AM   #14
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Nope.

Need min of 8 guage.
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Old 11-04-2011, 03:04 AM   #15
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Early 90s we had a 55' X 28' in Salem, ny also the last fifteen feet was addition, with cobbed 4" circles cut into the floor for heat. Went to a tin knocker in Glens falls, custom made us 4" X 10" straight line duct, with 90s and 45s. Added that to the two end runs, dampered down other house registers evened out temperature across the home. But what I didn't tell you was dealing with the underside of a doublewide or single mobile is completely a royal pain. Cut out all black insulation under house, trying to find dead animal in between floor and insulation that was mistake, anyway. You'll notice mobile home ductwork is junk at best, odd size and flimsy. Tied the two trunks in, they work fine, then installed all in one ac unit, made by Heatcontroler, from Sawyers in Glens falls ny. Installed large 12" round duct and 10"straight return round duct. Mobile homes have uninsulated ductwork the ac causes the ductwork to sweat perfusely, which in turn keeps underside of floors damp in summer.
My daughter, husband, and four kids are living there now, but if I could do one thing different, I would have insulation contractor come in the spray the whole underside, including ductwork with the blue expandable insulation, also while I had insulation out from the underside exposing ductwork, sealed every nook and cranny with aluminium duct tape, what a difference that made....
This year 2011, we bought parents in laws home in Greenwich, sticking with 25,000 btu window unit instead. New windows, doors, sub floors, electrical service, riping out every peice of Sheetrock, to run complete new wiring. The only thing we don't plan on changing is the roof and structure. Well, if the roof starts, steel roof time.... we didn't intend all of this, but once we got in here, what a mess, and cigarette smoke all throughout with yellow on walls, yuck.


Last edited by gregieOops; 11-04-2011 at 03:10 AM. Reason: spelling and typos
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