Most ac systems are designed to give a temperature difference of 10 - 15 degrees based on normal average temperature. Example if outside temperature is 80 degrees then one could expect to achieve 70 - 65 degrees inside temperature, however other factors have to be taken into consideration that can drastically reduce the units ability to achieve the inside temperature.
1. insulation, on boats is practically no existing.
2. Windows, just like in a car allows tremendous btu heat gain.
3. Internal btu heat gain, such as lights, appliances, fan motors, tv, radios
4. People and pets.
There are much more things to factor in when trying to calculate total btu within a living space, but these are a few big ones to consider.
I have a 34 footer and would have liked to have installed a 20k btu unit but unfortunately had to install a 16k unit due to space and power limitations.
my unit runs almost continuously when outside temperature reaches 85 plus.
My Unit definitely reduces the cabin temperature and it is definitely much more comfortable on hot days however on 90 degree day the best cabin temperature I usually can achieve is 78 degrees. Which is a huge difference from the outside temperature, however the biggest deference is that the humidity level is substantially less. Although the temperature is still pretty high at 78 degrees, it’s much more comfortable then outside in the sun
Things that help reduce the load on my unit is maximizing air flow, lots of discharge vents, and always cleaning the intake filter almost every day the unit is running.
Keeping the raw water lines and strainer clear.
One thing that had made a huge difference is I cut window, port light, and hatch inserts out of automotive windshield aluminum foil foam sun shield. I made all the inserts approximately 1/8 inch bigger than the inside openings so that the press in nice and snug and stay in place on there own.
hope this helps
