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Old 04-26-2016, 10:32 AM   #1
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8KW vs. 10KW Onan Question

Hello,

I'm looking into ordering a new RV currently, and have the choice between 2 or 3 AC units on the coach (FWIW it's a 40' Newmar Dutch Star). The base option is 2 13.5k BTU units, but I'm selecting between either 2 15k BTU or 3 15k BTU units. My current 34' coach has 2 units, but I think they're only 13.5k BTU and can struggle a bit to keep up on the hottest of hot days. The new coach obviously will have more air space, but also better insulation.

If the only difference was the AC units themselves, I think it'd be a no-brainer for me. However, selecting 3 ACs brings the Onan 10Kw genny, vs. the standard 8Kw.

A few of my friends with 45' coaches swear by 3 ACs. They have the 10Kw genny with them though and hate it. Apparently it doesn't idle down when the loads are lower and uses a lot more fuel vs. friends that have the 8Kw version that does idle down off load.

Does anybody know if the newest Onan 10Kw units will idle down?

FWIW I'm not trying to be cheap when it comes to the fuel, it's just that we often do 10+ days in Glamis where it can be 90-100 outside all day long and don't want to need to be taking the rig to town for fuel.

Thanks,
TJ
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Old 04-26-2016, 03:30 PM   #2
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If it were me, I'd opt for the three A/C units. If $ is not an issue, I'd rather have them and not need them than need them and not have them. We have three and rarely run all three at once, but we can.
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Old 04-26-2016, 03:59 PM   #3
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There is not a doubt in my mind one of the best things we did was get the 3 AC units. 2 would not have kept our coach at the temps we want......having 3 does!!

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Old 04-26-2016, 04:36 PM   #4
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I'd also go with the three. We have two on a 40 ft. Knight and they are not adequate for the heat. Also, per the current Onan brochure, there is a QD 10000 which is 68 dBA at half load versus 66 dBa for the QD 8000. That is noticeable, but hardly severe. The noise of the 3 A/C versus 2 A/C is probably more.

The QD is their alternator/inverter design which is what allows it to throttle down under light loads. Fuel consumption at full load for the QD 10000 is actually less than the QD 8000 (1.0 gal/hr versus 1.02 gal/hr).

Seems the only penalty is to your wallet.
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Old 04-26-2016, 04:43 PM   #5
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We had two 13.5 heat pumps on our '02 40' triple slide DSDP and the (at that time) optional roof insulation package and dual pane windows. In 90 weather in Yuma we did just fine with running only one unit.
If I was in the middle of summer in Quartzsite then you might need 3 heat pumps and you could make the rig into a meat locker!
You will find the Newmar's are very well insulated compared to a most other units out there.
The 10,000 is a constant speed gen set like our 12,500 is and our last PowerTec 8,000 was. The Onan 8,000 is a variable speed which I don't like.
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Old 04-26-2016, 04:48 PM   #6
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3 15kBTU A/C units and a 12.5kw generator. Might as well go big.
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Old 04-26-2016, 04:57 PM   #7
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3 15kBTU A/C units and a 12.5kw generator. Might as well go big.
OP doesn't have a choice of a 12.5, 8.0 or 10.0.
The 8.0 will idle down, the 10 and 12.5's won't as they run at 1800 rpm all the time. The 8.0 will go up to 3,600 as I remember.
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Old 04-26-2016, 05:30 PM   #8
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OP doesn't have a choice of a 12.5, 8.0 or 10.0.
The 8.0 will idle down, the 10 and 12.5's won't as they run at 1800 rpm all the time. The 8.0 will go up to 3,600 as I remember.
It was a bit of a "go big or go home" tongue in cheek statement. Either way, I don't see why, if 10kw is on the table that 12.5kw can't be, unless Newmar simply won't do it. The enclosure size is the same and the weight isn't that much different. The big difference I see between the two (other than power output) is the extra half gallon an hour the 12.5kw uses at full load.
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Old 04-26-2016, 05:39 PM   #9
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Last motorhome had 7500 watt and this one has 10,000 watt. The little one vibrated more and was noisier inside than this one.
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Old 04-26-2016, 05:43 PM   #10
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Quote:
Originally Posted by tjZ06 View Post
Hello,



I'm looking into ordering a new RV



A few of my friends with 45' coaches swear by 3 ACs. They have the 10Kw genny with them though and hate it. Apparently it doesn't idle down when the loads are lower and uses a lot more fuel vs. friends that have the 8Kw version that does idle down off load.







Thanks,

TJ

I would bet that the actual problem with their coaches is that their power consumption does not drop below the threshold.



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Old 04-26-2016, 08:08 PM   #11
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I have a 40 ft with a 10KW QD. A 15K AC in front and a 13.5 in the back. Cools just fine in Central Florida.
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Old 04-26-2016, 09:09 PM   #12
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The 10000 is also 240 volt so one can add a cloths dryer that really works. If buying new I would go over kill on the AC, nothing worse than sweating all night trying to sleep. Plus in most coaches you can run the air in more moderate temps away from either the bedroom or the living room for a quieter time.

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Old 04-26-2016, 09:26 PM   #13
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Quote:
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The 10000 is also 240 volt so one can add a cloths dryer that really works. If buying new I would go over kill on the AC, nothing worse than sweating all night trying to sleep. Plus in most coaches you can run the air in more moderate temps away from either the bedroom or the living room for a quieter time.

LEN
Both the 10 and 12.5 are 240 volt output, we also have a 240 volt dryer. Not sureI like that as we can't run the dryer if in a 30 amp spot and not all parks are setup with 50 amp yet.
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Old 04-26-2016, 09:49 PM   #14
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We had a 40' bus with two 15K A/C units and a 7500K generator. We moved to a 43' bus with three 15K A/C units and a 10000K generator. The 7500K generator was a load sensitive unit that would change rpm's with the load. You could always hear it running. The 10000K generator ran at 1800 rpm's regardless of load and you don't hear it running after a short time. In Oklahoma in the 100 degree heat the three A/C units sure make a big difference.
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