Swap out a 12K unit with a 16?

[tonyiiiafl]

What are your thoughts on me swapping out my 12K A/C unit with a 16K unit? I saw the Mermaid (which I owned previously and loved it!) is a lot less expensive than the Dometic 12K unit I have now. The ST 12K unit I have will swap out with the DTU 12K unit, but I have to buy a new control for another $295.00/ The 16K unit has the control already included for $1800.00. I seem to think I have the power to run both. Just looking for thoughts here.

[Viper]

Would be interesting to see if anyone with the same model boat has the configuration that you're considering so you can get some feedback. What you don't want to do is oversize the AC unit for the space it services or it will short cycle reducing the life of the compressor, fan motor, drivers, etc.

Does this unit service just one cabin or two?

[buster53]

Really depends on do you need more BTU's or not? On my 356, I have a 12k and 16k. On a hot, sunny day, they struggle to keep the boat just somewhat cool. Once the sun goes down, it's more than emough and most nights, I turn off the 16k and just use the 12k when we go to bed.
As it is with everything boat related, everything is a trade off, too much or not enough. Hard to find good balance.

[BenTen]

I think your climate has a lot to do with whether the 16k will work in place of the 12k, will it 'work'? Absolutely. As Viper mentioned if too large for the space/demand it will lead to problems.

In my climate the 12k unit is only large enough for cooler days and evenings and cany keeping on hot days, even when working with the 16k unit on. I have a 16k going in eventually as well to cool my main cabin, bunk cabin and head.

HTH

[tonyiiiafl]

I also have a 16 forward and a 12 aft. On a hot summer day they do struggle. Same at night though they are fine. Tough choice here as the replacement cost is really negligible of 12 versus 16.

[km1125]

How big is your ducting, and would it be easier to go up in size? If you're not able to flow enough air, then having a bigger unit won't buy you much. It will need to be big enough on both the return and the supply side. Going from 12 to 16 doesn't sound like huge change, but it is a 30% increase. Imagine if your ducts were sized correctly for 12K and think of them being 30% larger.

You should also look at the cooling water flow. If your current unit can't keep up, is it possibly starving just a little bit on the cooling water flow? You might fix that and solve your problem. If the current flow only supports a 12K unit, you might have to upgrade the pump (and potentially hoses) to fully satisfy the 16K unit.

[tonyiiiafl]

Good thought. I have a tee splitting the duct to a 6” and a 3”. As for return air Carver wasn’t on their game. The return air is pretty much from the bilge. I would love to make a return duct to draw cabin air but it doesn’t look possible.

[BenTen]

Re return Duct- I would love to do this as well as my forward unit pulls most air from the bilge (yuck). Does anyone have an example of how Carver might have done it on future models?

[Midnightsun]

My experience.

On my previous 32 express I had a single 16,000 btu unit. It was OK but struggled in hot temperatures. Not that it did not work but you did needed to keep the entrance door closed for it to be nice and cool down there. I figured the newer stuff must be improved and that my older unit probably lost a little efficiency over the years. I started shopping around and stumbled on MarinAire. Spoke with the owner who recommended I go with a 14,000 btu unit which I thought rather odd since he was going smaller than what I had? I followed his recommendation only to realize the new unit was freezing up, I enlarged the plenum to except more air and increased the size of the main duct which corrected the issue 100%. Holy moly what a differance. The 14,000 btu unit really performed well, in fact I was able to leave the door open now and it no longer struggled in hot weather.

Bottom line, our units are old, the serpentine gets dirty inside to a point where cleaning is difficult, the compressors get weak as well as the circulation fan. We tend to bandaid the unit here and there however replacement after 15-20 years is probably your best option IMHO. That being said, my AC runs 24/7 when at home port, I like to keep the cabin slightly cool and control the humidity levels in the boat when we are not there. I do dial it down cooler when we arrive at the boat though.

I ordered 3 new units for Midnight Sun over a year ago. The unit in master suite was replaced this spring and all I can say is what a difference in cooling capacity and even more so noise wise as they are really quiet. I chose to go 14,000 for the main as opposed to 16,000 and the forward unit which was an 11,000 was replaced by the same size. The master suite had a 7,000 which I upped to a 9,000. Overall the BTU output has remained the same. Will eventually get around to replacing the remaining 2 units.

I have recommended these units to quite a few people who were all really impressed after installation. This is MarinAire. https://www.marinaire.com

[mjk1040]

In our 1998 355, they cut filtered registers in near each AC unit so it could pull cabin air in along with bilge air. We have to run both 16 & 12 btu units on a hot day to cool the inside of the boat down. Running just the 16 btu unit in the salon will not cut it and have to run the aft cabin 12 btu unit too. Air flow and keeping the units cleaned is a must. Come to think of it even our 1986 Mariner had a return air filtered register in it too. Damn tony, just came back from the Cape, should have looked u up!