Besides the obvious of one being ducted or non ducted I am trying to decide where to buy a Ducted A/C unit if I end up having to replace mine. When I call Camping World or someone like that to get prices for a new roof A/C unit when I tell them mine is ducted they always tell me that's a special order. What is the difference between the units? I realize one just blows straight down and one blows down and around the ducts but what makes them special order? I would think any RV built in the last 10 years will have a ducted system so why would they not stock a Ducted A/C? I am looking at replacing my Dometic Duo Therm Model 57915.541 out of my 2007 Georgetown 351DS if I cannot figure out what's wrong with it in the next few days. Also wondering if this may be a heat pump also as the wall thermostat for this unit runs the Heat in the Motorhome also. When I am looking for a replacement unit what specifically do I need to ask for? Can I just go off this model number? I would assume it has been upgraded over the years. Plus I would like to probably go to a 15000 unit instead of another 13.5.Also as far as installation goes is this going to be a lot harder of an install because of the heat and ducting compared to a non ducted unit? And can I still use my current thermostat or do I need to upgrade that also. Here is what my current thermostat look like..

Get a 15k unit ducted...it's the only way to go. You'll never be sorry you bought it. We replaced the 13.5 with the 15K model.Now the 5th wheel gets uncomfortably cold if we turn the thermostat all the way down. With the 13.5 it was tough to get it cold enough to be comfortable.

Not a heat pump. Heat pump, cool, heat, off, furnace. The ideal unit is ducted with dump grill.

If you have ever had an RV with a non-ducted AC you would know the difference in sound. Not all MHs have ducted AC. It does cost a little more to do ducted so you won't find it in entry level MHs.

I think the OP wants to know what is physically different in the units. I have wondered if you could just put any unit on top. I don't know the answer.

If you go to the Dometic web site and look at their different AC and Heat Pump units, some say they are suitable for ducted and non-ducted installation. I would call their Customer Support Center (1 800 544-4881) and verify your requirements.

Difference between Ducted and Non Ducted when buying AC?

the_bear_II
Explorer
Jun 05, 2014
Get a 15k unit ducted...it's the only way to go. You'll never be sorry you bought it.

We replaced the 13.5 with the 15K model.

Now the 5th wheel gets uncomfortably cold if we turn the thermostat all the way down. With the 13.5 it was tough to get it cold enough to be comfortable.
J_R2
Explorer
Jun 05, 2014
Not a heat pump. Heat pump, cool, heat, off, furnace. The ideal unit is ducted with dump grill.
bsinmich
Explorer
Jun 05, 2014
If you have ever had an RV with a non-ducted AC you would know the difference in sound. Not all MHs have ducted AC. It does cost a little more to do ducted so you won't find it in entry level MHs.
USARMYCW
Explorer
Jun 05, 2014
I think the OP wants to know what is physically different in the units.

I have wondered if you could just put any unit on top. I don't know the answer.
justlou
Explorer
Jun 05, 2014
If you go to the Dometic web site and look at their different AC and Heat Pump units, some say they are suitable for ducted and non-ducted installation. I would call their Customer Support Center (1 800 544-4881) and verify your requirements.
jtel
Explorer
Jun 05, 2014
There is no diffrence between in the upper units. Just the lower.
cjoseph
Explorer
Jun 05, 2014
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cjoseph
Explorer
Jun 05, 2014
Our 15K unit has a heat pump. The thermostat has Electric Heat/Gas Heat and AC settings.

If you get a new unit with a heat pump you will need a new thermostat. I've seen them for $35 on line.

The furnace will still run on propane and 12V. The heat pump must have 110V AC. Just like the AC.
wa8yxm
Explorer III
Jun 05, 2014
Roof air conditioners are divided into 3 parts
There is the part you see on the ceiling, this is different for ducted and non-ducted units

There is the part on the roof, Same for all takers.

There is the part in between and that too is different for ducted and non-ducted.

NOW: if you have ducted.. Tell us.. What make/model do you have? There may be a lower cost option though CW is not the best source here.

For example: I have a Carrier Air V in the front, and 1/2 of a Carrier in the rear (The bottom 2 pieces) the top part is an Advent Air, with an ADAPT-A-KIT CONNECTING THEM.. sOUNDS A Whole lot harder than it is.. I will describe the procedure.

Remove inner cover, Unplug upper unit from lower unit, Remove 4 bolts, Remove upper unit,

Position new upper unit (Replace gasket if necessary) re-install 4 new bolts (included in kit) Open control box and remove one of the MOLEX connecters (Easy for me, there is a trick, which I know, to it however) and install new connecter in the kit.

Plug in "Y" cable (there is only one way to plug it in ) and plug upper unit into the remaining connector on the "Y".. Re-install inner cover, power on.

That easy. You do not disturb the ceiling unit at all (Save the control box is part of it) it remains in place throughout.

The reason they need to be custom ordered for ducted is to make sure the ducts line up. Non Ducted do not have that issue.

But it may be possible to just replace the problem part and leave the ceiling parts alone.
cjd10
Explorer
Jun 06, 2014
I don't think the GT 351's have a heat pump. On my old Georgetown I had that same thermostat and it controlled the propane heat as well as the AC.