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Author Topic: How many btu's for a basement a/c?  (Read 3418 times)
ilyafish
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« on: December 25, 2008, 11:42:52 AM »

Online guides are saying 9,000-10,000 should be fine.  I will only be using this when not in motion and will be using my OTR a/c while underway.

Thanks guys!  Time to go rip up my floor
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« Reply #1 on: December 25, 2008, 01:46:43 PM »

Ilya,

Are you sure that you want basement air? What about roof air? I am just curious because if your basement unit goes out (I know you guys with basement units...it never happens Grin Grin Grin) you don't have air. If you have four or five 15,000 btu Due therm Dometic low profile units, and one breaks, no big deal. The band is happy because they can sleep, you are happy because all you have to do is take it down and get it fixed.

Just some food for thought.

Merry Christmas,

God bless,

John
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« Reply #2 on: December 25, 2008, 02:04:31 PM »

My 40 x 102 bus has three 13,500btu Coleman roof airs.  I do not have any other a/c, but with 2.25" sprayed foam insulation, usually two do the job fine and one will keep everything cool once the sun is down.  If you use basement air, one 27,000btu (double 13,500btu unit in one) would be my choice.  Remember during the day lots of heat can come in just sitting still.  Good Luck, TomC
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« Reply #3 on: December 25, 2008, 02:09:16 PM »

Right on Tom!!!

Merry Christmas,

God bless,

John
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« Reply #4 on: December 25, 2008, 02:19:43 PM »

Ilya,

I am sure with John and Tom.  You need redundancy....especially in a system that will make the bus not habitable.  

The roof airs/heat pumps are the easiest to install and replace and many advocate for them for that reason.  If you duct them they are quiet enuf but less efficient.  Does not take up any basement space.  You will need two so three seems prudent.

The home stuff is more efficient but some say that they won't stand up to RV use.  There isn't much in those units that can flop around so I am a little skeptical that they won't last.  The only home units that have been used are the "Mini Split".  I think that is the way to go and I suggest you install two of the 27KBTU units and put one heat exchanger in front and one amidships.  Lots of choices so be careful for the best deal and quietest operation.  Uses no ducts.  read up on these.

Basement air is popular but it needs ducts and uses a bay.  Nick has two in his bay and I think they are heat pumps.  He has all the info and sells the basement airs.  No reason not to buy from him especially considering the support.

You can't size these things using "HOME" formulas.  Beside simply need more BTU you have the added consideration of needing to col the bus down FAST ater a heat soak.

HTH

John
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« Reply #5 on: December 25, 2008, 02:48:16 PM »

I have 3 basement heat pump units. I love them. My only drawback is heat. My coach is total electric and I have toe kick heaters. I would love to have one of the diesel fired units for heat as well as to help start this beast in the winter.
--
BILL
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Nick Badame Refrig/ACC
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« Reply #6 on: December 25, 2008, 04:22:53 PM »

Hi Ilya,

Merry Christmas!

The average basement A/C or HP system is 15,000 btu's for the single and 27,000 btu's for thr twin system.

With that said, the avarage car A/C system is around 5 tons [50 to 60,000 btu's] tonnage is very important for moving vehicles.

The heat gain in the sun, the traveling speeds in the wind, and the ability to cool off a 100 deg. + temp when parked in the sun

is calculated inti every vehicle on the road. If you notice that it usually takes 5 min's to cool off your very hot car and it could take

as much as 4-6 hours to cool off your home in the same temps should tell you something.

Good Luck
Nick-
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« Reply #7 on: December 25, 2008, 05:38:01 PM »

I have had both and presently have two roof units.  I will never have another coach with roof units.  The noise, the vibration and the dripping water have turned me off forever.
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« Reply #8 on: December 25, 2008, 08:37:23 PM »

10,000 BTUs won't even make a dent, particulary on a hot day if you have large windows (like my bus).

I only have a single 15,000 BTU unit in the front area of my bus and I might add another one because one doesn't do much on a hot day.  I have spray foam in ceiling and walls, but I also have four 3' by 4' windows.
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« Reply #9 on: December 26, 2008, 05:24:38 AM »

I have had both and presently have two roof units.  I will never have another coach with roof units.  The noise, the vibration and the dripping water have turned me off forever.


Len, that is interesting. We haven't had any problems with ours. What model do you have? What brand? I am just curious, because we will want to steer clear of those in the future. We have five 15,000 btu penguin Dometic Low profile roof airs (my dad always said go for redundancy Grin Grin Grin), and we love them. I just wondered why you didn't like yours.

Ilya,

Also, get a roof sealant, like Dicor  http://www.rvupgradestore.com/browseproducts/Dicor-EPDM-Rubber-Roof-System-Lap-Sealant.HTML roof sealant. That link is from a quick Google search. We sealed every single rivet on the roof of our coach. Otherwise you might have a little leak somewhere, and you don't want to fix that later, once it has ruined everything.

JAT

God bless,

John
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Len Silva
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« Reply #10 on: December 26, 2008, 06:38:57 AM »

John,

Admittedly, they are 1994 models, both Dometic.  Perhaps just replacing them would make a difference, I don't know.

I had basement air in my 4104 and it was whisper quiet just like at home.
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« Reply #11 on: December 26, 2008, 06:53:22 AM »

Len, Thanks the explanation. Basement units probably would be quieter.

God bless,

John
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« Reply #12 on: December 26, 2008, 11:34:49 AM »

Ducting the roof airs will quiet them down a lot.  In your design make way to allow the opening of the duct right under the unit....much more efficient that way if you get in a bind somehow.

John
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« Reply #13 on: December 26, 2008, 01:37:15 PM »

If you use "basement" units just make sure they're rated for Marine or RV use - HTH
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« Reply #14 on: December 26, 2008, 04:22:06 PM »

We've had both and I couldn't agree more with Len. Rooftops were noisy, water running off the roof, vibrating the whole coach. The latest experience was with 2000 Coleman Mach's. The others were on an older SS. We currently have three basement air and their effecient, quiet, couldn't ask for better. But we're planning on removing the front one to make room for a hide-a-way TV. Just my 2cents worth.
Good luck, Will
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« Reply #15 on: December 26, 2008, 04:55:55 PM »

Excellent posts everyone.  Thank you.  If we ever do the Crown Super Coach Bus Conversion, (ex-schoolie with NO real luggage bays per say) we will really look hard at finding some place/space to mount the two (2) basement airs.

However, all the prior planning came to the same conclusions---there is just no room anywhere under the floor for all the stuff needed, plus finding space for the actual duct work.  Sosss, that leaves just the rooftop warts.  HB of CJ Smiley Smiley Smiley
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« Reply #16 on: December 28, 2008, 08:41:04 AM »

I've got a Duo-Therm by Dometic dual compressor basement ac; 27,000 btu total.  It has been unreliable and a pain in the patootie to pull for repair (it's broken at this moment).  If I really needed air conditioning I would look closely at replacing it with a pair of garden variety household window units mounted in the space now occupied by the Dometic.
-RickBrown in Reno, NV

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« Reply #17 on: December 28, 2008, 11:03:30 AM »

Something to consider:  the roof tops mount sitting on top of a foam cushion.  I thought at first that it was a vibration/sound insulation AS WELL as a waterproof seal.  There is no sound absorbing quality to the install due to the fastening screws going through the roof and attaching directly to the AC unit.  Any body have any ideas on how to isolate the AC unit from the noise amplifying METAL ROOF?

Thanks,

John
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The price of apathy towards public affairs is to be ruled by evil men." Plato
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« Reply #18 on: December 30, 2008, 07:56:44 AM »

John-I have three Coleman 13,500 roof tops and with the 2.25" of sprayed foam insulation, you don't even know when the compressors kick in, except for a quick dip in the generator.  The noisiest part of Colemans is the interior fan since it is only two speeds-like medium and high.  Ducted roof tops will be quieter.  I bought my Colemans in 1994 and have had zero problems with them, except to replace one of the outside shrouds.  Good Luck, TomC
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« Reply #19 on: December 30, 2008, 09:57:49 AM »

TomC,

Thanks for that.  I guess that that is just one more reason to go with foam.  I read a post long ago by a Knut that had just had his interior foamed.  He was overjoyed at his QUIET bus.  He said he could not even hear the engine run anymore and had to look at his tach.  An overstatement, no doubt, but a point well made.  If it also has the effect of quieting the roof tops.....great bonus and another option for AC.  My RTs are set on that sponge seal and my roof is as follows: 3/8 plywood, 3 1/2 foam board, aluminum sheet, 1/4 ply, 1 1/2 foam board, 1/4 ply.  I can hear the compressor a little due to the mounting bolts connecting the interior most layer of my roof directly to the AC unit frame as they all do.  The real noise is coming from the air flow through that restrictive interior shroud/defuser and that is considerable, to me anyway.  I suspect that all these AC units are not created equal and some must be quieter than others.  I agree with you about ducts as I have been in a few bus type coaches with that feature and I couldn't hear the rush of air or the compressor either one. Really nice but I have been told that ducting eats up a lot of the BTU ability of the RT units.  I have never heard a number associated with that inefficiency, however.

Thanks for your comment,

John
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"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
“We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light.”
—Pla
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