When we purchase a product, we usually tend to follow the general maintenance guidelines.  But sometimes we have to pay extra attention to maintenance of certain key  components of the product.  For marine air conditioners, the evaporator is one of these  (If a compressor is the heart of the unit, the evaporator is the lungs!)

In the marine environment, evaporators are subject to different conditions, higher humidity, a much higher temperature variance, and salt!  The evaporators have fins that are made out of aluminum, with  copper pipes passing through these fins that carry the refrigerant. These fins have a typical gap of 0.05”between them; an amount of space that easily gets filled with dust and other particulates in the air.

Over time, this build-up will prevent the air flow and heat transfer needed to cool or heat the environment.  Let’s not forget that, in a cooling setting, the heat absorbed through these fins is used to evaporate the refrigerant passing through. If the fins are covered with dust, not enough heat will pass through and the unit will begin to give the impression that ‘it is not cooling enough’! Hence, we go out and buy a new unit, thinking that the current unit is old or not working.

A simple way to care for the unit is to either vacuum clean the fins occasionally or use an air duster (like those canisters used for electronics, keyboard cleaning etc) with a long nozzle.  It will make a huge difference in the longevity and efficiency of your air conditioner and keep your money in your pocket.

As we field inquiries about our 12VDC marine air conditioner, I regularly find myself in the middle of a conversation about BTU ratings.  There are a number of 110V/220VAC marine air conditioner brands out there.  Did you know you basically have to trust the individual manufacturer to put a BTU rating on its product, and there’s no independent body in the industry to verify it?   If the label on the box says “12,000 BTU”, how do you know if it actually does provide that level of cooling?  

In the US, residential and commercial air conditioners and HVAC equipment adhere to very strict manufacturing standards, which also involve testing in isolated test chambers -- but none of this is applicable in the marine air conditioning industry.  Technically, a marine air conditioner manufacturer can label their product with whatever BTU they deem fit.  There is no controlling body to enforce it for the consumer.   It is a complicated and expensive process to gather performance data for an air conditioner; many marine air conditioner manufacturers don’t have the facility for accurate in-house capacity testing at specified conditions.  

Unless the manufacturer can validate with test chamber results there is only one certain benchmark a consumer can rely on – the compressor rating. Compressors have to be tested to certain performance levels at certain internal pressures; that is the only reliable empirical data in a marine air conditioner.  Most of the marine air conditioner manufacturers simply take this compressor rating at certain conditions and label the complete air conditioner to an estimated BTU level accordingly.  

The photos above are of a compressor from a common marine air conditioner brand, marketed as ’12,000 BTU’.  The compressor manufacturer’s specs for the same compressor show ’11,000 BTU’ rating. 

Let’s not forget that there are many other components in a system besides the compressor and the quality and effectiveness of these other parts, and how they are put together make a significant difference as well.  Price isn’t just a benchmark. Before purchasing a marine air conditioner, make sure to look for the labeling on the compressor. Reputable compressor manufacturers usually make all their test data available on their websites.  If the marine air conditioner manufacturer is not willing to give you the specs of the compressor, run away as fast as you can!!!

I get asked about BTUs in marine applications.  I hear folks installing 16,000 BTU, 24,000 BTU air conditioners on their boats. But the question is, do you need to keep your boat at 68F?  That’s a choice.

Personally, if your boat needs to be at 68F, maybe boating is not the right activity for you. 

The magic of 15F degrees – 

Our body begins to detect ‘cool’ when there is 15F temperate change in the environment.  If outside temperate is 95F, and a cabin down below is reading 80F, your body will feel cool.  

How many BTUs, you ask?

There’s a lot of hype out there about BTUs.  But you don’t necessarily need more BTUs in your marine air conditioner to get relief from the summer heat out on the water.  I hear folks installing 18,000 BTU, even 24,000 BTU air conditioners on their 40-50 foot or even smaller boats.   Here is food for thought: an 18,000 BTU air conditioner equals a 1.5-ton residential air conditioner.  That would be typically installed in a 700-800 sq/ft house (with 10 foot ceilings)!   That’s overkill for a 40-foot boat.  In fact, the AC needs of a boat are measured by one leading marine AC company’s calculations which became the generally accepted standard for sizing BTUs needed for a boat – the same calculations used by companies to determine the AC needs of a house – which has square rooms, good air flow, and is not surrounded by water(!).  Not surprising, the core business of many of these companies is household appliances and residential air conditioning (https://www.dometic.com/en-us/us/about-us/our-brand/history). 

Apples and oranges, we say.  To determine efficient air conditioning of a boat, you need to factor in all the consequences of its environment, including the water temperature!  What boaters really need to be more comfortable down below is removal of humidity. That’s achieved by installing a longer running variable speed compressor in a smaller unit that actually goes through its full cooling cycle.  This way, opting for a few smaller units in one boat will be more economical and makes for a less energy-hungry boat.  As we all know, the interior design of a boat usually has irregular corners and nooks and obstructions which would prevent good air flow in the cabin, so more than one unit would be a better choice.