Carver Owners Forum

Well, I came to the boat last night to find that the A/C in the stateroom would not work . Spent the morning troubleshooting it an it appears that the compressor has locked up. It’s a 12,000 btu unit from Marine Air and it’s original to the boat, so it’s given 30+ years of service. The salon unit was replaced a few years ago with a new Dometic (Cruisair) 16,000 btu and has never struggled to cool it portion of the boat. I have spent the most of the day shopping for a new unit.

I’ve looked at Marinaire and according to the website and their calculator I only need a 9,000 btu unit for the stateroom. I also ready on their website where they cautioned against over sizing a unit. Leading me to believe it’s better to go smaller that to go larger. I can get a 9,000 btu unit from them for $1489 including shipping. They do have an 11,000 btu unit, but it will cost around $1750 with shipping.

I also found a 12,000 btu Wabesto unit from Marine Parts Source for $1549 including shipping. While I do like some features of the Marinaire unit a little better, I don’t think those features are worth $200 more, but I’ve been known to be wrong!

My question I guess is, would today’s 9000 btu unit be the equivalent to a 30+ year old 12,000 btu unit? I know that todays technology has to be more efficient, but does that translate to capacity?

What say you guys? Go with the 9000 btu unit or stay at or closer to 12,000?

12000 BTU’s is 12000 BTU’s. A newer model will be more efficient meaning it will use less amperage, but it still only puts out 12000 BTU’s.
Yes, you can oversize but the question only you can answer…were you happy with the old one meaning do you think it was properly sized. If it was, then stick with 12k. If your cabin got a little stuffy and humid in the middle of the night, you might want to drop down in size.

buster53 wrote:Source of the post 12000 BTU’s is 12000 BTU’s. A newer model will be more efficient meaning it will use less amperage, but it still only puts out 12000 BTU’s.
Yes, you can oversize but the question only you can answer…were you happy with the old one meaning do you think it was properly sized. If it was, then stick with 12k. If your cabin got a little stuffy and humid in the middle of the night, you might want to drop down in size.

Buster53, I’m not sure that that is an easy answer. For the most part I thought the original did pretty good. Never at night did it get stuffy and/or humid, but I have seen it do that during the day in the stateroom. I never questioned the size of the unit since it was original.

You stated that if it did get stuffy and humid I might want to drop down in size. Please explain why drop as that would seem counter- intuitive. I assume that if it was too small then it would run continuously, never cycle and wouldn’t cool properly either.

Again, when I did the measurement, Marinaire’s size calculator called for 9000 btu, Is it possible that 12,000 btu was the smallest size made 32 years ago. I would have thought Carver would have properly sized it. Is 3000 btu a big difference? I would like to improve what I had, but I don’t want to make it worse either.

I realize that the safe answer is to replace what was there, but if going down in size would improve the cooling, I’m good with that too.

Your thoughts are greatly appreciated.

Thanks!

I have a Webasto. All I ever hear is the air flow. The unit is dro quiet.
And I would hi smaller. It will run longer and condense the humidity much better. May take longer to get to temperature, but it will bfrf comfortable.

I wouldn't downsize.
If you had 12k btu don't go lower than 11k.
If you have a humidity issue, just drop the fan speed to low.
That lowers the coil temp an increases the Moisture removal.

When you have an oversized unit, your cabin will cool down quicker and the compressor doesn’t run as long and doesn’t have a chance to lower humidity enough. When it comes to air conditioning, humidity levels are just as important as the temp.

In my opinion, it is difficult to size AC units in boats as there are more considerations than calculations based on just the cubic footage. The big windows on some create tremendous amounts of radiant heat and wet bilges will also contribute to moisture levels in the cabin.

I guess what I am saying is that even the same model boat can have different requirements based on window coverings, bilges, canvas colors, your slip direction and geographic location. All this said, if your previous unit worked satisfactorily then why not replace in kind. Even with newer units being more efficient, then the new unit at the same size should be as well......good luck with your choice and try to avoid making a decision based solely on cost......

Talk to someone that does marine air for a living. Be careful how you go here, while a BTU is a BTU the older units were built a lot beefier than they are now. Oversizing will cause short cycling which will shorten the life of your compressor and some of the supporting hardware. While the older hardware might have handled this ok for 30+ years, I wouldn't count on today's builds doing the same. It's more important than ever to have a properly rated unit for the space and conditions.

Bud37, your thoughts were my initial thoughts as I was only looking at unit of the same or near the same size. That was until I ran that sizing calculator. That was then when I started to “what if” everything. With that said, the difference between 11,000 and 12,000 btu is negligible and only in like sizes and quality is where cost might become the deciding factor. One of the other things that I noticed was that in addition to the volume of the area, it also took into the consideration where the unit would be located and where you are located, as the climate can also have an affect. That leads me to believe while a smaller unit might be sufficient in one area it might be too small in another. Of course, a builder doesn’t know where an individual boat will eventually be located they are going to go with the worse possible scenario. Thanks for your input.

Viper wrote:Source of the post Talk to someone that does marine air for a living. Be careful how you go here, while a BTU is a BTU the older units were built a lot beefier than they are now. Oversizing will cause short cycling which will shorten the life of your compressor and some of the supporting hardware. While the older hardware might have handled this ok for 30+ years, I wouldn't count on today's builds doing the same. It's more important than ever to have a properly rated unit for the space and conditions.

Viper, thanks for the post! I’m going to call Marinaire tomorrow and talk with them and see what their advise would be on the sizing. It might be that where I live in Ky a 9000 btu might be fine, but wouldn’t be and would need the larger unit if I lived somewhere else like Fla. Like I mentioned to bud37 above, I’m sure Carver built for the worst possible scenario and a hotter, more humid environment to cover their bases. I do like the fact that the Marinaire’s have a built in humidity sensor, I’m just not sure that that is worth an extra $200 over the same sized Wabesto. I guess I really need Midnight Sun to give me a sales pitch…