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Old 05-07-2014, 08:32 PM   #1
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Upgrade from Dinosaur to Heat Pump


I am in desperate need of advice. We live in a 1983 Wicks 28 X 65' Doublewide near Auburn, AL on a permanent concrete block foundation. Our original Carrier ac/gas furnace unit has a cracked heat chamber and I am having the unit replaced with a heat pump. I will not attempt this myself, and will be hiring a professional to do the installation. I am not sure what unit is needed, although I am leaning toward a Trane. The original unit has one recirculation vent located directly on the unit itself, with no recirculation tubes anywhere else in the house.

My questions are these: 1. We have two runs of floor vent, 4" X 12" in size, with 4 x 10" vents, connected by an insulated crossover. Do all of the vents in the house need to be upgraded to 4 x 12" to improve airflow, and are recirculation tubes of some sort needed to pull air from the hottest rooms at the other end of the house?

2. The main vent run under the ac/heat unit has no insulation around it, only the insulation that came with the house, which has fallen out in places. Condensation drips constantly from only this vent run during the summer. There is no insulation remaining at all below the ac evaporator housing. I need to have this vent run insulated. It was suggested by a contractor to insulate it by wrapping plastic around it and injecting spray foam between the plastic and the vent. Is this a viable option? A contractor said running ceiling vents would be impossible because the living room ceiling, in the middle of the house, follows the contour of the roof pitch.

And, 3. Our current Ducane ac unit has a SEER rating of 8 (our power bill has run upwards of $300-400 a month during the summer) and I am thinking we need a unit with a rating of around 17. Last summer when it got 100 degrees here, the inside temperature was around 80 degrees with the ac running full blast constantly. Our walls are well-insulated, and we have energy-efficient double-pane glass windows.

We are going to have to spend several thousand dollars here, and I want this installation to fix our current listed problems. I also have to remove the double-wall pipe from our roof and patch the hole. Any advice will be honored and appreciated. Thanks!

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Old 05-07-2014, 08:33 PM   #2
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Sorry for such a long letter; I'm also a part-time horror writer.

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Old 05-07-2014, 09:28 PM   #3
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Not sure what you want to hear or are asking.

- Mobile homes/trailers don't have return air ducts due to the nature of their construction so you will still take the return from the one spot you have. The return comes in the one grill because there is no practical way to run a return duct to the top of the airhandler/furnace and then back down thru the floor and under the trailer as it is usually jammed in a closet.

- Definitely the ductwork needs insulating so it does not sweat or lose cooling or absorb heat. Try get quotes from 3 or more reputable contractors and ask them what they recommend. You want a well sealed Professional job not just some slapped on DIY business.
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Last edited by yuri; 05-07-2014 at 09:58 PM.
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Old 05-08-2014, 03:53 AM   #4
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Go to your thermostat and turn the fan switch to "on". If your current system isn't wired to run the fan by that thermostat setting, then turn the A/C on. Go to the furtherest register and see how little air it is blowing, then go to one closer the the furnace, and see how much more it is blowing. Your problem with the rooms that don't cool right in the summer is because your duct system is too small. Its standard size for MH, and they all come under sized. This may cause a problem for a heat pump to heat your house.
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Old 05-08-2014, 06:52 AM   #5
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I tested the ducts like you recommended. The vents at the far end of the house furthest from the AC/Furnace do not blow as much air as the ones nearest the AC/Furnace, which, as you say, causes this room to be hot in the summer. I know the vents are built into the floor of the mobile home because I've been under there inspecting them. Is there any way to run larger ducts beneath the house, am I stuck with the existing vent runs, or do I just need to get an opinion from a professional?

I thought the house was not cooling on the far end because of no return/recirculation ducts. I see by your reply that the problem is the size of the ducts, which was one of my questions. Thanks for the reply!
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Old 05-08-2014, 06:54 AM   #6
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What I meant by the ducts being built into the floor is that it looks like it would be impossible to remove them.
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Old 05-08-2014, 07:19 AM   #7
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Not sure if it has ever been done or is possible but if you never plan to move the home on wheels again I would see if the ducts can be ripped out and larger ones installed below the level they are now. They are tucked up in the frame for transportation reasons. If the home is permanent and you find a contractor with some imagination then new ducts may be able to be hung lower. Going to be at least another $1000 to do it due to the labor time involved. I would do it if it was mine.
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Old 05-08-2014, 08:01 AM   #8
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Not sure how long you plan to stay in the home or how serious you are but where I am people add another piece/room to the trailer by the front or rear entrance door. They make a storage room there. If you really want comfort and add a extra room/space and can find a contractor with some imagination it is possible to relocate the furnace/airhandler there and possibly add some return ducting to it. That would GREATLY increase your comfort and make the heat pump work a lot better. I have 4x10 return grills in my floor ( not walls ) and as long as the supply vent is on the opposite wall of the room it works well. Some of mine are 4 feet away in smaller rooms and it works well.
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Old 05-08-2014, 03:23 PM   #9
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Quote:
Originally Posted by eric woodall View Post
I tested the ducts like you recommended. The vents at the far end of the house furthest from the AC/Furnace do not blow as much air as the ones nearest the AC/Furnace, which, as you say, causes this room to be hot in the summer. I know the vents are built into the floor of the mobile home because I've been under there inspecting them. Is there any way to run larger ducts beneath the house, am I stuck with the existing vent runs, or do I just need to get an opinion from a professional?

I thought the house was not cooling on the far end because of no return/recirculation ducts. I see by your reply that the problem is the size of the ducts, which was one of my questions. Thanks for the reply!
A plenum can be installed under the home where the heat pump sits. And a larger duct then the cross over ran to the other side. but before reaching the other side, install a wye, and then run those ducts to mid point between the end of the duct, and where the old cross over use to tie in.

Same can be doe for the duct on the air handler side. A helper duct can be ran under it, and then tied in 3/4 of the way down.
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Old 05-08-2014, 04:25 PM   #10
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This message is for Old Tradesman: You were the one helping me last winter when I was discussing this same problem on here. If I understand you correctly, you are saying a plenum can be installed beneath the new heat pump as it is being installed, then a new larger air handler installed to replace the existing vent run on the side of the house the heat pump is on. Install a larger air handler over toward the existing 4" X 12" vent run on the other side, but make a wye in it and attach one end of the wye to where the old crossover hose connected. Go halfway down the vent run, cut a new hole in it, and attach the other end of the wye there. Correct? This would mean installing only one new larger vent run on one side and using the existing vent run on the other. This sounds like the most efficient and time-saving option. Thank you for this valuable information. The one contractor I had look at it said nothing about replacing one side of the run, actually said it couldn't be replaced.
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Old 05-08-2014, 04:27 PM   #11
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I will suggest this setup to the contractor I have come out this time.
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Old 05-08-2014, 04:35 PM   #12
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Did I understand you correctly? The new heat pump unit will sit directly atop where the vent run joined the old furnace/ac unit. You were talking about trashing the entire vent run on one side and replacing it with a larger duct, weren't you?
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Old 05-08-2014, 06:03 PM   #13
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Quote:
Originally Posted by eric woodall View Post
Did I understand you correctly? The new heat pump unit will sit directly atop where the vent run joined the old furnace/ac unit. You were talking about trashing the entire vent run on one side and replacing it with a larger duct, weren't you?

New air handler will sit where the current furnace does. Plenum installed directly below it. New cross over duct installed, but goes to a wye. The wye branches then get ran 3/4 of the way down the current duct on then tap into it. This will increase air flow to the far rooms on that side.

2 helper ducts get installed on the side the furnace is on, and ran 3/4 of the way down each side, and then tie into the duct. it will increase air flow to those far rooms. Don't need to replace all the duct.
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Old 05-08-2014, 06:12 PM   #14
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I either get a negative response, or no response when I suggest this but why not put a packaged unit outside on a slab, add a floor or wall return and be done with the noisy indoor furnace which plagues so many mobile homes?

I've seen quite a few mobile homes converted and even did one myself and the results are great and you can add a nice little pantry or closet where the old furnace came out of.
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Old 05-08-2014, 08:30 PM   #15
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Quote:
Originally Posted by beenthere View Post
New air handler will sit where the current furnace does. Plenum installed directly below it. New cross over duct installed, but goes to a wye. The wye branches then get ran 3/4 of the way down the current duct on then tap into it. This will increase air flow to the far rooms on that side.

2 helper ducts get installed on the side the furnace is on, and ran 3/4 of the way down each side, and then tie into the duct. it will increase air flow to those far rooms. Don't need to replace all the duct.
The advantage I see also for a package unit is, you can have a plenum centralized between both haves of the house and branch off 4 ways, 2 for one side of the house and two for the other.

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