Polar Cub AC in a Bigfoot? - Fiberglass RV


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Old 02-14-2007, 11:14 AM   #1
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Name: David
Trailer: Bigfoot 25 ft (25B25RQ)
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My new-to-me 21.5' Bigfoot came without air conditioning. It is pre-wired for AC at the existing 14 inch ceiling vent. I'm researching which roof-top A/C to buy. The Bigfoot factory A/C's are Duotherm 11000 BTU models. However, I am reluctant to buy one that I cannot comfortably operate with my Honda 2000 generator. Recommended generator for the 11000 is 2500 watts. I recently sold my Casita 17' that had a Coleman Polar Cub A/C at 9200 BTU. This unit cooled beautifully in temps well over a hundred, and the generator handled it just fine. Against conventional wisdom, I am thinking of putting a Polar Cub on the Bigfoot. Polar Cubs are factory-installed in lots of Truck Campers and Casita trailers, but not in larger trailers. I have researched this topic on several RV forums and found a few people who installed them on 18-22 foot trailers who claimed they did the job. I found some interesting discussions about how an A/C with too much capacity causes condensation issues because the compressor cycles too much. They claimed that a slightly undersized unit is better than oversized. My Bigfoot has the winter insulation package which should be an asset for cooling as well. I have already been advised by some to buy a larger A/C and then a larger generator. Or buy a second Honda 2000 to run them in tandem. That is money I am reluctant to spend unnecessarily. Besides, I like my little generator and prefer to live within its capacity if possible. Interestingly, Bigfoot uses the same 11000 BTU A/C on its 17', 21.5" and 25' models. If 11000 BTU's will cool a 25' trailer, wouldn't 9200 cool a 21'? I could sure use some educated opinions from the excellent minds on this forum.
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Old 02-14-2007, 11:51 AM   #2
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David, you'll be cooling an additional (approx) 256 cu. ft. of area than you did with the Casita, however I can't fault your logic for inquiring about the reserve capacity of the 11,000 from the 17' to the 25' trailers.

I haven't yet used out 25' in the summer heat, so I can't tell you how well the 11,000 does in a 25', but I can tell you that a 13,000 couldn't cool a 34' Airstream, and the new 15,000s they're using on the 34's are questionable. We had TWO 13,000 BTU units on our 32' Airstream moho and they were just able to keep it comfortable when it was really hot out. I recognize that there is a difference in heat absorption and transmission between an Airstream aluminum hull and a FGRV.

I don't see a problem with the Polar Cub per se be frankly though, my gut instinct is that I think I'd probably install the 11,000 and go with the dual 2000s when necessary. Just an opinion.

Roger
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Old 02-14-2007, 12:05 PM   #3
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Dave,

Is your Bigfoot a 2500 series with double glazed windows? Your logic seems reasonable. I suppose the risk is not being cool enough under some conditions and possibly the smaller AC unit might not last as long. Give it a try!
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Old 02-14-2007, 01:44 PM   #4
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Dave, I think you would be just fine with the smaller Coleman. RV ac's are really very efficient as they sit on the roof and cold air settles toward the floor and ideal situation when cooling. I have an auxillary AC of 8500 btu output in my garage which is insulated but has a lot of air leaks. Except on the hottest days - over 90 deg it will hold the set temp of 78 deg and the area cooled is over 425 sq ft. The only downside I see in your 21 Bigfoot is the time required to cool the unit if it has been sitting in the sun, with a high rise in ambient temp., will be somewhat longer than a higher btu unit would require. Martin
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Old 02-14-2007, 04:01 PM   #5
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Roger, Bob, and Martin:

All three of you hit on things I am considering. Roger, my worst fear is that I won't get cool enough no matter how long it runs. Of course you are right that I SHOULD use the 11000 BTU like the factory installs to be on the safe side. But how to break it to my wife that I now need another $1000 generator and a $200 tandem connector? Do Airstreams reflect heat or absorb it with that aluminum skin? I am trying to cling to my theory that the white fiberglass and great Bigfoot insulation will save the day.

Bob, yes this Bigfoot is a 2500 model with the thermal pane windows. That is one reason I thought I might get away with installing the smaller A/C unit. I hadn't really thought about the A/C unit not lasting as long if I work it harder. Will have to factor that in.

Martin, your experience in your garage is encouraging. You mentioned that the amount of time to cool the trailer will likely increase. This is one consequence I think I can live with. I just did some math on this. 9200 BTU's is 83% of 11000. In my logic, the smaller unit should take 17% longer to cool the same amount of space. So if the bigger one takes thirty minutes, the smaller one will take thirty five. Not bad if the logic actually works in real life.

Thanks guys for your opinions. It isn't hot here yet, so I am still thinking it over.
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Old 02-14-2007, 05:19 PM   #6
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Roger, Bob, and Martin:

All three of you hit on things I am considering. Roger, my worst fear is that I won't get cool enough no matter how long it runs. Of course you are right that I SHOULD use the 11000 BTU like the factory installs to be on the safe side. But how to break it to my wife that I now need another $1000 generator and a $200 tandem connector? Do Airstreams reflect heat or absorb it with that aluminum skin? I am trying to cling to my theory that the white fiberglass and great Bigfoot insulation will save the day.
Airstreams tend to absorb more heat than the white FG trailers, there is no doubt. Further, with the aluminum ribs directly attaching the outer and inner skins without a thermal barrier, they transmit more heat/cold into the trailer than the Bigfoot. That's why it's sort of an apples/oranges comparison in some ways; but it's really the only experience I can pass on. The biggest thermal item IMHO on the Bigfoot are the reflective dual thermopane windows. The tinted windows on the Airstream used to get HOT in the direct sun. The Bigfoot windows just reflect the heat.

All that said, I CAN tell you that a HOT Bigfoot trailer interior does take a while to cool down with the AC running full tilt until all of the furnishings drop in temp and stop radiating heat.

I guess the question I'd ask you is how often do you run the A/C on the genset? I know that my 11,000 BTU Penquin will run on a 15 amp circuit and my 13,000s in the Airstreams NEEDED a 30 amp feed to run. I say this out of ignorance, but are you sure that the 11,000 BTU Penguin won't fire up on a 2k genset? How 'bout if you JUST run the A/C on the genset and run the refrigerator on LP?

Just curious... and it helps to consider the options.

Roger
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Old 02-14-2007, 07:28 PM   #7
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David, Roger is correct about Airstream. I speak from being a former owner of a wide body 25. The standard Dometic heat pump was working very hard to cool that unit and they used the same heat pump in the larger units. Our Airstream also had the white roof panel used by Airstream since the mid eighty's. The remainder of that aluminum body asborbed heat like a tin can on a hot coal stove. I still believe the 8500 btu AC unit you are considering will more than do the job on a Bigfoot 21. The same unit in my Casita 17 is oversized for practical purposes. The few extra cubic feet to cool in a Bigfoot should be of little consequence. Martin
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Old 02-14-2007, 08:37 PM   #8
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Roger -
Actually, I have gotten mixed info regarding the ability of the Honda 2000 to run the Duotherm 11000. I read a post by a Bigfoot owner that claimed he did run his A/C with a Honda 2000. The Bigfoot dealership in Colorado Springs strongly advised me NOT to do that. They said running on marginal power could damage the A/C or maybe even the generator. They also said it would definitely not work at high altitude. They also advised that I buy a second generator. Duotherm data sheets recommended a minimum of 2500 watts to power the 11000 with a generator. So I have info that the Honda 2000 will fire up that A/C, but advice to the contrary from the manufacturer and a Bigfoot dealership. Who to believe? As to how often do I need to run A/C on the genset? Having recently moved to Arkansas from Alaska I am not boondocking as much as I used to. But I did spend a week last summer in Oklahoma running my Casita A/C with my Honda. We had to be there for an annual event. The daytime temps were running from 95 to 100+. We also camped near Moab, Utah in temps up to 107. It was even in the high 80's at 8000 feet in Colorado on that trip. The Honda 2000 and the Polar Cub A/C were very useful. Thank you for your input, it definitely makes me wonder if the Cub will do the job in a 21.

Martin-
Between your words of encouragement and Roger's cautions I am still left wondering. But I still agree with you that the Polar Cub puts out a tremendous amount of cold air in a Casita and should adequately cool something larger. I wish there was a financially risk-free way to find out for sure. Thanks again.
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Old 02-15-2007, 06:14 AM   #9
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I don't have A/C in my trailer, but I use a large window-style A/C to cool my entire home. I put an occilating fan on the floor, in the doorway (where the cool air pools). It pushes the cool air down the hallway and down the stairs to the lower level of my home. I know the few times without that fan, the bedroom is freezing and the rest of the house is quite warm. The fan makes a world of difference to even out the temperature.

Wonder if using a small fan to push the air around the trailer would be of benefit to you?
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Old 02-15-2007, 06:23 AM   #10
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David, you need to make the choice best for you but you may want to consider a few other items. Dometic may have a contract with Bigfoot to supply all their appliance needs. I may be mistaken but I don't believe Dometic supplies a 8500 btu AC. Regardless, the published retail prices of competing AC units in the 11000 btu range are almost identical to a Coleman 8500 btu unit. Even with the same manf. the wholesale cost is probably a minimal difference between larger btu and smaller capacity btu units On a wholesale basis there may be no difference to Bigfoot between a larger Dometic and smaller 8500 btu unit by Coleman if Dometic has an exclusive supplier contract. The fact that Bigfoot uses a somewhat larger AC unit may have nothing to do with cooling requirements - in their estimation a little to much capacity at the same cost - well I think you see the point. Martin
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Old 02-15-2007, 07:18 AM   #11
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Between your words of encouragement and Roger's cautions I am still left wondering.
David, I'm not even sure I'm issuing cautions here... just stuff to consider. The Cub may very well be able to do the job. Another angle to research might be to see what other similar sized trailer manufacturers install and use the Cub in a larger trailer application.

Roger
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Old 02-15-2007, 07:36 AM   #12
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Hi: Bigger is not always better!!! when A/C is concerened a slightly smaller unit will work more efficiently to draw out the moisture in the air. If your comp. cycles too little you will feel clamy... What do I know??? I am still trying to figure out which Vent Fan to buy/install.
Alf S. North shore of Lake Erie
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Old 02-15-2007, 12:59 PM   #13
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Hi Donna- Good idea about the fan. I have a little desktop size fan that would be perfect for this experiment. Moving the air around a little more is usually a good thing, whether heating or cooling. Thanks!

Roger, Martin - I have been to some websites for other trailer brands, but they don't reveal what A/C's they are using. The small stick built trailers I have seen at dealers around here are using various brands, usually 13500 BTU's. I expect these are readily available in bulk and probably cheaper than a Coleman Polar Cub. I kind of figured that Bigfoot uses the same A/C in three different models because that is their contract supplier. They don't seem overly concerned with matching size of trailer with A/C BTU's. When I have researched the retail prices of various units, I won't save any money if I buy the Coleman Polar Cub. It costs as much or more than many of the 13500 to 15000 BTU models. I found some sale prices on some 13500's that were way under the lowest price for a Polar Cub, in fact.

Alf - I found a discussion on another forum that completely agrees with your statement. In a humid climate, too much humidity is left in the air if the compressor cycles off too quickly. Makes sense, I hope the theory is correct. By the way, it probably doesn't matter which vent fan you buy. But you should get one - they are wonderful. Mine is a Fantastic Fan, but I suppose other brands are just fine. Fans are not very complicated. Just make sure it has a forward and reverse, and several incremental speed settings./

Thanks again for everyone's insight. This forum remains the best for fine minds.
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Old 02-15-2007, 08:45 PM   #14
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Its been a long time but I probably could do a BTU load calculation for your camper. I would need a drawing of your camper r value of the insulation window sizes door sizes and the worst case summer place you plan to take your camper. Let me know if yoiu want me to doit I will dig out my old hvac j manuals

Don
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