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Old 08-02-2022, 01:12 PM   #1
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Are Two 15K Roof ACs enough for a 40' Coach

Howdy. Currently working on a deal for a 2011 Phaeton 40QTH. It only has two ACs (15k each). Is that enough?. My 2006 Winnebago Tour had the basement AC (30k) in it. It barely held its own in the AZ summer heat.
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Old 08-02-2022, 01:20 PM   #2
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We have three ACs and one went out when we were in Spokane Washington. Not exactly hot… the front area at the windshield would get warm; about 3 degrees over our set point. The rear would be able to maintain temps. If it was really hot, I don’t think we could have managed with just two airs. I recommend having the three ac units if for no other reason for safety if one goes out.
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Old 08-02-2022, 01:36 PM   #3
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My old 2012 36QSH had two. They did the job, but barely when it was really hot and humid. The third AC on my 2019 37BH was a must have, especially considering the reliability of the current Mach8 units.
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Old 08-02-2022, 01:54 PM   #4
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My coach is almost 40' and came with two 13.5K BTU units, when they were newer they did OK but not great in real hot weather.
I just changed both of those out for 15K BTU high capacity units. Last year I was in TX and during the day temps were bumping up in the high 80'sF. I was able to run 1 AC and it easily cooled the coach.

But I did do quite a bit of work on my duct work to make sure they were all sealed and tight. I actually found a joint in the ducts that had not tape on it. I used a remote camera to check the entire length. To fix the gap I installed a new register/vent so I could access and tape. Also found some mouse holes that I had to fix.
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Old 08-02-2022, 02:17 PM   #5
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For comparison, our coach is similar in length to your prospective Tiffin, and we are based in (and currently in) Florida along the Space Coast...low 90's and medium/high humidity on the "hot" days. Nothing like AZ summers however.

Our experiences follow for reference. Your experiences will likely vary as much of this is dependent on coach insulation, use of window shades/blinds and just how cool you want your coach to get. We are also full timers, and I work remotely out the coach most of the time. We have a small dog so we never let the coach get warm even if we are away for the day.

We have 3 A/C units (all 15K, one is a heat pump as well) which we typically keep on all the time regardless of outside weather...they just cycle much less than two units would. During the day we keep all three A/C units (rear, mid, front) set between 75-77F...rear, mid, and front units cycle more/less than one another depending on time of day and sun position.

Our coach seems to be well insulated. When we run an exhaust fan it "bogs down" unless a window is opened, so the coach is pretty tight. We like to keep our shades up during the day unless the sun is directly in a window, and we lower both the shades and blinds at night.

When we were in Texas a few summers ago it was over 100F and very humid most days, and if I pulled down the day shades (but not the blinds) I could run with two A/C units, running much of the time during the day (and it was cool versus cold). Turning on the third A/C helped immensely (cold versus cool), but was not required.

I think you could get by with two A/C units, but a third A/C would provide margin if one unit failed. I would not be in AZ in the summer with a 40' coach without that extra "reserve" capacity.

Hope this's just what we have experienced.
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Old 08-02-2022, 02:53 PM   #6
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Originally Posted by Old Grape View Post
Howdy. Currently working on a deal for a 2011 Phaeton 40QTH. It only has two ACs (15k each). Is that enough?. My 2006 Winnebago Tour had the basement AC (30k) in it. It barely held its own in the AZ summer heat.
Do you intend to ride out another summer in AZ?

A number of factors will determine if two A/Cs are enough. Here are a few that may help you decide.
Outside temperatures. Expect the RV to hold a temperature that is 20-30F below the outside temperature. Dont expect an inside temp of 70F if its 115F outside.
Parking in sun or partial to full shade.
Windshield facing south or north.
Exterior window covers, window tint, color of RV.
RV insulation and number of slides.
As mentioned, modifying ductwork may improve A/C output.

It really depends on where and when you intend to park the RV, as well as the inside temperature youd like to achieve.
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Old 08-02-2022, 03:04 PM   #7
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We have a 43 foot Haulmark Super C with 2 15K air conditioners. They work well most of the time. Our coach was built for the Canadian market and has extra insulation. A couple years ago we spent a week in St. George, Utah and saw temps in the low 100's.
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Old 08-02-2022, 03:38 PM   #8
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The simple answer is no. Two A/C units are good for up to 30 feet. after that you should consider 3 A/C units . Two may be adequate in most cases , but there will always be days when it's just to hot. With 3 units, it will also drop the temperature a lot quicker if they have not been running.
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Old 08-02-2022, 04:03 PM   #9
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Had a Tiffin Phaeton 36 QSH with a NASA paint scheme, two AC units. No, two are not enough if you are in a hot sunny environment. Try southern Utah in the summertime. We did and could never get the coach below 82-85 during the daytime. Newmar has two AC units on their 40 foot and sub units but they are built with more insulation and far less air intrusions points than my Tiffin 36 QSH. A light colored paint job also helps a lot with cooling during the summer. Most 40 day motorhomes need three AC units unless you buy from a quality manufacturer with a focus on insulation and cooling.
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Old 08-02-2022, 07:52 PM   #10
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We have a Tiffin Allegro Bus 37AP, which has three 15k heat pumps, in North Texas, We've camped in 100+ heat. We like our MH a little warmer, 78, than some.

On days when you aren't starting out in a deficit, e.g., driving without running the generator and 1 or more ACs running, two ACs can just keep it comfortable. That is assuming you have windows shaded, outside windshield shade, etc.

I agree three really are needed, just in case one fails. We went with only two last summer because no one had a replacement in stock.

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Old 08-02-2022, 08:00 PM   #11
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IMHO, a major problem cooling a Tiffin coach is the lack of insulation above the windshield. I can stop much of the heat coming in through the windshield with a sheet of double/quilted aluminum that I roll out. The heat will continue to roll in behind the overhead cabinets. There is a world of difference in a Newmar Mountain Air. In the sun and 90 degrees, my front never shuts off and is noticeably warmer by the captain chairs. My sons 2015 MA maintained the same temp and the front AC cycled off when the set temp was reached. We love our Bus, but I never understood why Tiffin ignored that area.
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Old 08-03-2022, 09:55 AM   #12
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We owned a 2014 Phaeton QBH and I was glad we ordered the 3 ACs. In my opinion, 2 will not make you happy.
If you decide to go with that coach, do as suggested. Insulate the front cabinets above the dash and invest in a Magnashade for the windshield.
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Old 08-09-2022, 03:51 PM   #13
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We seldom use all three AC’s even in AZ BUT when one went out was glad we still had two working ones. It is also nice to just use the AC in the bedroom to cool that area down and still hear the TV upfront.
An advantage for us is in having three is to be able to use the heat pump on the middle unit without it connecting to one of the furnaces on a cool morning.
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Old 08-09-2022, 04:36 PM   #14
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Is 2 ac's enough - I would say not if you travel in the Southeast with heat and humidity. Most with only 2 are saying it is tolerable not comfortable. However there are things you can do to help. I have 3 and I did extra work to help mine.

The first thing is to remove the tv in the front cabinet and stuff insulation into the front cap over the windshield. Be sure to avoid pushing on the wiring up there. I used a whole roll of R19 faced insulation up there. The front ac now cycles and doesn't run constantly.

Add a small fan to blow air from the rear to the front of the unit. The front has all the glass and will struggle while the rear ac has a small area and very few windows.

Add Reflectix or similar insulation to the back and top of all cabinets and every place you can reach an outside wall. Leave a small air gap so that it is effective. That cooled the cabinets in mine by 15 degrees so food isn't compromised, chocolate does not melt.

Put those vent pillows in the ceiling fantastic fans when you aren't using them. Cuts out a lot of heat.

The skylight in the bathroom is a heat producer. Stuff it with a large piece of foam or cover it on the outside with truck bed liner spray or even Krylon black paint for plastics. I had mine covered when I had the RV FlexArmor Roof coating put on mine.

All of these things made a big difference in the temps inside of our coach. Our power bill for hookups at the house dropped by 21% on the coach power bill. We can run the ac's set on 73 and be very comfortable and they don't run constantly.

Some have added a 3rd ac (not ducted) where the fantastic vent is in the kitchen area and said it made all the difference for them. So you could add that 3rd ac after the fact if you love that coach enough.
Mel (Melanie) and Harry
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