A/C Btu Size

G

Golfman25

Well-known member
Member
Joined
Jan 1, 2000
RO Number
1239
Messages
747
I need to size a marine air conditioner. Here are the details:

Boat: 1980 Chris Craft 281 Catalina -- large cabit with relatively big sliding glass windows (not the small port holes we see today).

Cabin dimensions: 17 x 10 x 6 to 6.5 high

Location: Chicago -- Lake Michigan. Cold water temps about 60-70 degrees. Air temps been in the 90's this summer.

Looking around a several mfg. sites, my calculations come out be about 14,000 btu.

So I can go down to 12,000 btu or up to 16,000 btu. Mfg. says 12,000 would work for my area. But I am not sure if 16,000 is better -- I think I want it cold durring the day, but don't want any problems with too large a unit. Not a significant price difference.

So I ask -- is more better? Any downside going to the larger unit? Should I just stick with 12,000? What say you? Thank you in advance.
 
Personally I would go with the 16,000 BTU. I have a 1986 Silverton Convertible 34 footer with a 16,000 BTU and this past weekend I could only bring the cabin down to 77 degrees. I also have the large sliding glass door and windows all around the salon. I had those tinted limo black and I have heavy insulated curtains.
 
In home A/C's the conventional wisdom says bigger is not better, because if it's too big, it won't be able to run long enough to get the humidity down to an acceptable level; because the temp will drop too fast. But home units don't have adjustable fan speeds, so I would assume that isn't an issue in a boat. I would go with the 16,000 - as long as the extra amp draw doesn't present any problems for you.
 
quote:
Originally posted by alk

In home A/C's the conventional wisdom says bigger is not better, because if it's too big, it won't be able to run long enough to get the humidity down to an acceptable level; because the temp will drop too fast. But home units don't have adjustable fan speeds, so I would assume that isn't an issue in a boat. I would go with the 16,000 - as long as the extra amp draw doesn't present any problems for you.

Click to expand...


+1
 
No question, 16K. Never heard anyone here complain that they had too much AC.
 
I would go with 12. I have a 5k unit in my 26 and it keeps it meat locker cold. I think a 16K unit will perform as ALK mentions.
 
Personally, I'd go with the 12,000. Your boat is very similar in size and space to mine. I currently have a 7,000 in mine. For sure, it is a bit small and struggles in the middle of the day here in south Florida. if does keep the salon comfortable but it does struggle to do so. But, at night, when I really want/need it, it works just fine and cools the boat very nicely.

When this one craps out I will replace it with a 12,000. Reasons:

1. Size
2. Weight
3. AMP load
4. Longer run time keeps humidity much lower.

But, as I said, that's just my personal opinion.

Bob
 
I have the 16K unit in a similar sized vessel--This weekend I could only get down to about 78 or so (outside temps about 90 F). Definitely the bigger unit. Note the large windows and the minimal insulation of a typical vessel of the same size.

Also as mentioned above the vessel will have better resale value if the unit is appropriate for adequate cooling.
 
You didn't ask but i would add, you can tint those large windows very cheap to do and diy.

I would go with the bigger unit if you can handle the xtra amps it draws, and it won't work as hard to keep you cold.

I know the larger unit is more money. But at this point in your life, whats more important saving a little or being a more comfortable?
 
Slightly off topic, but I wanted to warn folks.

We have 2 acs on our Regal 3780. The aft one is 16000 btu; and it died on us. It was keeping the cabin at 78 - 80 when the outside temp was 95+ so I had a ac person check her out.

The compressor was fried (should be white, is brown now) and the circuit board was fried. He sees signs of a spark/fire on the board. He thinks the cause was low freon and running the unit with low freon. he states he sees this all the time; they get low on freon and folks keep running them.

So, keep them fully charged is his message. If they start to put out "less cold" air, shut it down he says.
 
Welcome to the club Greg, I just replaced my salon unit last season!!
 
with the colder water you will probably be fine with the 12k unit but a 16k BTU may have an easier life... although if you can try to check the actual compressor ratings. 4 of my units are 16k BTU but when i checked the actual compressor rating on the Tecumseh website they're actually 12k BTU compressor...

Greg, there shoudl be a low pressure switch which will trigger a Low Pressure warning on your controllers (assuming you have digitals), protecting the compressor. Sometimes, they are not connected though, so make sure your tech checks the wiring when he replaces the compressor.

There is also a thermal breaker inside teh compressor which will shut it down if it gets too hot (not enough gas to cool it).

2 days ago, I added a 5th air con to my boat. Originally i had 4 16k BTU units and the galley was getting cool with some air diverted from one of the saloon air handlers. it just wasn't enough... when i bought the boat, it came with an extra uninstlled new 9k btu condensing unit. I had the AC guy install it, "only" had to get a new air handler... now the galley is nice and cold, i get more air in the saloon. as a result it also improves cooling the lower level since air leaks into the companionway. Not cheap but well worth it.

within a reasonable limit, there is no such things as enough cooling power.
 
Thanks Pascal

It's always made a buzzing noise on start up. Over the weekend it started flipping the breaker on start up. After 4-5 tries it would not flip the breaker.

I do not recall any codes on the thermostat. What is interesting is I left it on HUI mode the prior weekend. When we returned to the boast this weekend the unit was off and it started acting up after that. I wonder if leaving HUI (Humidity Mode) did something.
 
I have a 15K BTU a/c on my Chris Craft 281. It is not a well insulated boat. In the summer, it takes everything it can
to keep cool. I put limo tint on the windows, put 3/4" insulation board on the ceiling and covered with paneling. That
helped a lot. It now cycles during the day time.
We boat year round, but the summer time is the most brutal. Before the tint and insulation, the compressor never shut
down, it ran till late night time.
We have no issues with dehumidifying the air cause it runs so much. When it is above 90 deg. outside, it will not
cycle much.
 
quote:
Originally posted by Kellyg

Welcome to the club Greg, I just replaced my salon unit last season!!

Click to expand...


I am waiting to hear back from the AC guy on the cost. How much was yours?

It's go new or throw parts at the old...we decided on new.
 
Greg,

I was in the same dilemma as you are now. I had the circuit board replaced a few years ago when my a/c was acting just like yours.
I paid $1500 for parts and labor, but received a discount due to the fact I have been selling Regals for quite a number of years and have directed alot of customers to utilize his services.
 
Do you want it cold or dry?

I would go with the 12k, it will run for a longer period, therefore removing more moisture.

Absolute,

"Suckin Sludge & Havin a Gas"
 
I just put a 16k unit in my 34' sailboat. I wanted to get the 14 but when my ac guy went to order it, Cruise Aire had discontinued it, so it was either the 12 or 16. We went with 16. To be sure, it does a great job during the heat of the day, but I'm more concerned with my sleeping comfort and the compressor doesn't run enough at night to keep the humidity down. We have to keep it in the low 60's to have the compressor run even 30% of the time which is not enough.
I'm starting to think I should have gotten the 12k unit.
 
You must log in or register to reply here.
Back
Top