Central air vs roof air

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Tom

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We were looking at the Newmar Essex today (nice coach and the second time we've looked at the Essex this trip). They have central air and make a big deal of it their literature. A couple of weeks ago we looked at Marathon Prevost conversions and noted that they have changed from central air to roof air effective 2006 models.

I'm trying to figure out if there are any advantages of central vs roof air or vice versa. Also, is there a reason that Marathon went out of their way to ruin the clean look of the roof of their coaches by adding roof air?
 

rhmahoney

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"I'm trying to figure out if there are any advantages of central vs roof air or vice versa. Also, is there a reason that Marathon went out of their way to ruin the clean look of the roof of their coaches by adding roof air?"

To gain basement storage cubic? 
 

Tom

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rhmahoney said:
To gain basement storage cubic?

Maybe Russ, but that coach has so much basement storage it's not funny.
 

John From Detroit

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I would think the considerations are as follows

ROOF AIR: takes up no basement storage, however it "Raises the roof" and is vunerable to tree limbs and the like, NOTE: thisis not often a problem, but it could be in theory (I know of no case where it has been a problem) in addition it is a hole in the roof which has the potential to leak (And this is a common problem)  Service requires climging up on the roof.

Centeral (Basement) air is easier to service, and you can build the RV a bit higher (Since the roof air is not up there) thus gaining back the lost space.  You may well be able to make it larger (MORE BTUs  too) but there I don't know.  It is standard on busses and train cars

But I'd say the major advantage is the ability to service it with a stool to sit on instead of a ladder to climb

Oh yes, no hole in roof to leak either,s,, Just a hole in your floor and you have a lot of those too, they almost never leak
 

Tom

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If I spent $1.5M on a Marathon I don't think I'd be servicing the a/c myself.
 

Gary RV_Wizard

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And some of the basement a/c's I've seen are really buried - not accessible through a bay door or anything convenient like that.

None of the arguments I've read, here and elsewhere, for or against basement a/c, have been convincing.  They all seem like very minor tradeoffs of space, noise,  and appearance with some marketing gee-whiz and even personal preference  thrown in.  It may be that it is the sum total of all those things and, at the bottom line, pretty much a toss-up.

Some of the other arguments I've heard:
  • Need to run insulated ducting to and from (cold out, warm return) a basement a/c - takes space in sidewall or rear cap as well as basement
  • More noise or less noise - guess it depends on where the basement unit is located and where you are standing/sitting/lying
  • Less top heavy - keeps weight low rather than on the roof
  • Let's them make the coach lower
  • Lets them make the coach taller
  • Gives the rig better karma  ;D
 

Tom

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LOL Gary, I doubt that basement air would be any noisier than our roof air units. They're much noisier than the ones in our friend's Monaco. OTOH ours have the ability to dump a lot more air into the coach (aka cool/heat faster).
 

John From Detroit

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Tom said:
If I spent $1.5M on a Marathon I don't think I'd be servicing the a/c myself.

While this is true, If you pay to have it serviced you will pay for every trip the tecnician makes up/down the ladder at close to $100/hour  You put it where it's easier for him to get to and a hand's reach from his truck load of supplies and you are going to save money

Of course if they burry it so deep it takes him an hour to get to it,  that kind of negates the savings
 

Tom

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John In Detroit said:
you will pay for every trip the tecnician makes up/down the ladder at close to $100/hour

The way that service tech rates are charged and rounded off to the next higher hour, I don't think I'd notice the few minutes it takes to make a couple of trips up and down the ladder.

When the CAT tech comes to work on the boat I'm charged much more than $100/hour and they add a per hour "truck charge". I live between where some of the techs live and their shop; They drive to work and I pay travel time for them to drive back to me. When I've called a tech before he leaves the shop and told him to pick up a couple of bolts from their inventory (so he doesn't have to make another trip), I'm charged an hour of "shop time" for him to pick the bolts out of a bin.

There are two big CATs in the boat, so double the charges except travel.

The CAT dealer charges $1,200 for an oil change and the boat dealer charges $2,100 for the same thing. I do my own oil and filter changes on the boat and the coach, but I call for help when a/c units fail. I don't do heights and I'll gladly pay for someone to go on the roof of the coach.
 

Tom

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caltex said:
basement air dribbles directly on the ground, not down the side of the coach.

Good point and I see them all the time, although some coaches have a gutter to channel the dribbles.
 

Gary RV_Wizard

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They're much noisier than the ones in our friend's Monaco. OTOH ours have the ability to dump a lot more air into the coach (aka cool/heat faster).

Nearly all the noise we hear *inside* the RV is air rushing through the ducts, rather than compressor noise (which is mostly a background hum). The design of the ducting system has a lot more to do with noise levels than the location of the compressor and heat exchanger.  However, I heard from one lady (on another website) who complained that she could not sleep with the compressor cycling underneath her bed (the typical location on a gas rig with basement air).

Most RVs have poor ducting - they just fit it in wherever they can, the sizes are often inadequate for the efficient (and quiet) movement of air  and there may be several right angles and poorly fitted connections as well. 
 
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