13.5K BTU AC versus 15K BTU AC

[4advtr]

So we were not forward thinking enough when we purchased our TT back in December and opted for the smaller 13.5K AC in lieu of the 15K BTU option. My thinking at the time was that the smaller unit had a better chance of running off of a generator.

Well... Jump forward to now. We sold our house and now Full-time in our trailer. For the next 3-4 weeks we're staying in Mesa, AZ where its a tad hot! We're insulating the windows and everything the best we can but our AC runs full speed all day and can only keep the trailer at around 85*. I'm wondering if a 15K unit would do much better? If I knew it would help keep things about 5*+ cooler I'd have no problem spending the money on the upgrade and just get one of the new Coleman Mach 8 units.

Hopefully somebody has some first hand experience with this and can let me know if this is a good idea or not? Also, not interested in portable or window units as we will be travelling a bit and would just like to do it once (twice in this case...) and do it right.

[DiskDoctr]

4advtr wrote:
One other thing, we have two slides and I've noticed when the sun is on the side of the trailer with slides the slides act as radiant heaters. The insulation in the slide is nowhere near the roof of the trailer. The roof is several inches of foam and with the infrared thermometer on it in the heat of the day (108*) it'll read about the same as the interior temps, high 80's.

Do you have slide toppers over your slides?

If so, you may have some relief by adding something like PUGs to your toppers. They work wonders for PUPs and HTTs.

If not, you may be able to rig something up in a similar way- especially if you are not moving very often.

Another idea some have found helpful is to add a self-adhesive foil to the inside of the AC shroud to help reflect the sun's rays and reduce the heat load on the AC unit.

[pianotuna]

Hi,

Thanks for the adhesive idea.

[4advtr]

pianotuna wrote:
Hi,

Is the foil on the outside or on the inside? How did you fasten it?

We put it on the inside. This seems to be the way others have done it in this park. We fastened them with the tiny "Command" strips you can get at Wal-Mart. Super easy to use and remove and won't leave a permanent stain.

As for cleaning the unit, I'll give it a once over but the trailer is literally about 6 months old and spent the better part of 4 of those months in my shop. The filter is another question, I'll give that a look tomorrow as I'm sure it's getting dirty. I also do have an infrared gun that I use constantly on the trailer.

One other thing, we have two slides and I've noticed when the sun is on the side of the trailer with slides the slides act as radiant heaters. The insulation in the slide is nowhere near the roof of the trailer. The roof is several inches of foam and with the infrared thermometer on it in the heat of the day (108*) it'll read about the same as the interior temps, high 80's.

[peirek]

A couple of points. The portable unit requires an exhaust vent (the hot air has to go somewhere). Not sure how you would manage that in a trailer. Secondly, when is the last time the condenser coil was cleaned on your unit? Inside filters also. These can have a huge impact on performance. But 100 w/ sun beating down is a tall order for a 1 ton+ unit. If you had a portable thermal gun you could verify the intake and output air temp and post back. Should see at least a 20 degree delta.

We have a 15K unit and it performs great in the Texas sun. Never regret the upgrade.

[pianotuna]

Hi,

Is the foil on the outside or on the inside? How did you fasten it?

[4advtr]

Definitely not planning on spending more than a month in the AZ heat. However we'll likely see high 90's in our trips throughout the rest of the summer. If we continue full-timing by next summer we might just upgrade to a bigger trailer/5th wheel so really only worried about this summer.

I'll give it a couple of days and see if our changes help. We added the foil bubble wrap to all windows late yesterday and it seemed to help instantly. Last night we cooled the unit down to the low 60's before the AC finally shut off. Today we have the advantage of having the foil on the windows from the get go so we'll see.

[jrichard]

It's tough to compare since no one here has had each size a/c on the same trailer.

FWIW, my last trailer had a 13.5 and my current one has a 15. Same size trailers but I don't know if the insulation R value is significantly different. In any event, the new one can definitely hold a larger temperature differential by 3-5 degrees and the a/c cycles less than the prior unit. No way of knowing how much of that difference is attributable to the a/c. Probably some, but 15k is not that much bigger than 13.5k.

For me, it was a no brainer to upgrade for $150 at the time of purchase. But I don't think the difference enough to justify a significant sum...I think you'd get much more bang for the buck adding a second 13.5 unit.

[dadmomh]

Interesting question. We just made the leap from our HTT with a 13.5 to a TT with a 15. We never had a problem with the 13.5 until a trip to Vicksburg, MS with 99/99%. Could not get the HTT cooler than 85 during the day even with the PUGS on. Made a Walmart run and got some small personal-size fans thinking that would help in the bunkends, but wrong. All it did was help move the hot air around. After sundown, it cooled off nicely.....until the next day. UGH! The dealer we bought the TT from orders 13.5 A/C routinely, but for whatever reason, this one has the 15. In what I'd consider "normal" summer weather, does anyone notice any difference in performance/efficiency/operating costs in the 13.5 vs the 15. We're not headed to AZ for sure, but TN has some pretty darned hot/humid weather. We keep our TT under cover 24/7 at home, but also keep the A/C set at about 80 since we're in and out all the time. Am I going to drop over when I see the electric bill with the 15 now?? I never noticed any appreciable difference when we started keeping the HTT plugged in over not.

FWIW, if this AZ visit is not going to be a routine thing and the 13.5 is normally effective, I'd look into that portable unit that was linked....at least for the short haul. It may do all you need for a bunch less $$$.

[pianotuna]

Hi,

Add a second 13500 btu unit and give up one roof vent. Use an auxiliary shore power cord to power it.

[Goldstalker]

I would add another unit rather than replace the one you have. Many TT's have two A/C's shouldn't be an issue.

[B_O__Plenty]

The difference in capacity is slightly less than 10% more..I don't think that would make much difference. I'd go with downtheroad's answer also..

B.O.

[4advtr]

the bear II wrote:
We have a 15000 BTU DuoTherm in our 38ft 5th wheel. In up to 100 degree temps it will keep most of the 5th wheel at 78 or below during the heat of the day when the sun is overhead.

We had a 13.5 unit before and it would creep up to 85 at the hottest part of the day.

What we found works best is to leave the A/C on 24 hours a day and adjust the thermometer or put on jackets as you get cold. The goal is to keep everything inside as cold as possible so as the heat rises outside the A/C can maintain the cold better because the furniture, walls, counters are all cold already.

In addition our blinds are closed, we have awnings over all windows and our patio awning is deployed and dipped to keep the sun from shining onto the side of the trailer. The door stays shut as much as possible, kids and friends either stay in or stay out.

We also use portable fans to move air around to prevent hot spots. Or pointed at us if it gets uncomfortable inside.

Do you just have a single A/C or two units? I like the heating option that some of the upgraded AC units offer and it looks like the Duotherm has a 3 speed fan, might be nice to quieten things down a little. Ours currently only has a 2 speed fan. We do at least have ducting in our unit.

As for the portable unit. I actually have one of those I left back in Bend. We just don't really have the floorspace for it. I would prefer to pay for the upgrade now and just enjoy the benefits going forward IF I know it'll help us with our issues.

[Huntindog]

BuckBarker wrote:
downtheroad has your answer to the AZ heat. Just make sure your extension cord is heavy duty.

X2.

Arizona heat has to be experienced first hand in order to fully comprehend it.

Making the jump from 13.5 to 15.0 is a very small increase in cooling power, at a fairly high cost. Probably a grand or so with installation. Best to do this upgrade when purchasing the unit new.

That 11.0 extra unit will close to double your cooling for around 300.00.....And when you decide you are done with it, you can sell it for a few bucks.

[BuckBarker]

downtheroad has your answer to the AZ heat. Just make sure your extension cord is heavy duty.