Mariner 36 in Falmouth in November 2019

Air Conditioning and Heat

Air Conditioning and Heat

Air conditioning and heat is a bit of a luxury on a small boat due more to its high power draw than to its cost. Some marine AC/heat sells for as low as under $2,000 in a 120VAC unit. The maximum power draw for a small unit is in the 500-800W range. There will be a challenge finding room for the unit in the forecabin.

Installation challenges

Whether AC/heat is installed at all depends partly on how much sailing is done in the tropics where it gets hot or in Maine or Canada where it gets cold and how uncomfortable this gets. It also depends on whether room can be found somewhere in the forecabin for the unit.

One unit using being considered (Webasto) measures 11.2"L x 16"D x 11.6"H. Mabru makes a higher quality 5000 BTU unit that measures 14"L x 10"D x 10"H. There may be enough room for this unit aft of the holding tank which puts the air intake facing the v-berth cabin.

Available AC units

Marine suppliers tend to carry the lowest cost units and larger units. For example, Defender carries Webasto, Dometic and Velair. West Marine carries Dometic and Velair. Hamilton Marine does not carry air conditioners. The smallest unit is a 6000 BTU Dometic which costs about $2,300 (as of 2025) and 6000 BTU Webasto which costs about $1,600 (as of 2025) but is out of stock and may be discontinued.

Among all manufacturers the larger units (10000 BTU and up tend to be more efficient. In some cases the larger units share a blower with the smaller units making the blower too large for the smaller units. Some units give a wide range of power indicating a low power consumption capability where the blower speed and the compressor speed are reduced.

The best quality units are from Mabru and are sold directly. The come in 12V systems and 115V/230V. The smaller units are 5000 BTU, 7000 BTU (12V only) and 9000 BTU (115V/230V only). They used to carry 24V systems which would be ideal. The 12V units are very efficient at about 15 BTU/W. The 115V/230V units are fairly efficient at about 10 BTU/W. The copper tubing is 70/30 Cu/Ni rather than the 90/10 Cu/Ni often used and copper fins rather than cheaper aluminum. The compressors come with a lifetime warranty. The variable speed fan and compressor allows very low power operation (less than half power for 115V/230V units) which can maintain low cabin humidity and provide some cooling. These units are more expensive.

Cruise N Comfort USA offers 12V, 24V, and 48V units. The smaller units (7500 BTU and 10,000 BTU) are 12V only. The 11,500 BTU unit is 24V. All units come in the same 304 stainless steel chassis measuring 22"L x 12"W x 10½"H. These are not as efficient as the Mabru.

Mermaid Manufacturing makes small units in 3500 BTU and 6500 BTU. These are 115V/230V only (no heat option in 230V units). They are fairly efficient. They have very high startup transients. Their specs are lacking. The unit appears to be powder coated. Their units may be impossible to fit in the available space on the boat.

Webasto seems to be replacing the older FCF and FCFP series with the BlueCool series. The company no longer lists the smaller FCF and FCFP units, listing only the 12000 BTU and 16000 BTU. The FCF 12000 BTU units are efficient at about 12 BTU/W. The BlueCool 6000 BTU are less efficient at about 10 BTU/W but efficiency improves in the larger units. An old datasheet for the FCFP 6000 BTU unit puts the efficiency at about 11 BTU/W.

Dometic makes 3500 BTU and 6000 BTU models. The 3500 BTU unit does not have reverse cycle heat and is very inefficient at 6 BTU/W. The 6000 BTU unit is fairly efficient at 10 BTU/W. The 10000 BTU unit is even more efficient at 12 BTU/W.

The smallest Velair units are 10000 BTU. They are quite inefficient for units of that size at under 9 BTU/W.

Coastal Climate Control, Inc. is a reseller supplying Climma Compact 4200 BTU marine air conditioners and MarinAir units ranging from 6000 BTU and up. Some of the Climma do not have reverse cycle capability (the 4200 BTU unit does) and have no specs on the Climma web page. These appear to be lower quality units. The MarinAir web page is more useful. Both Climma and MarinAir are less efficient than Mermaid and much less efficient Mabru 12V.

Conclusions

Products come and go. This is partially due to some types of refrigerants being phased out due to concerns about ozone depletion potential (ODP) and greenhouse warming potential (GWP). The choice of refrigerant will impact efficiency. hydroclorofluorocarbons (HCFCs) such as R-22 (freon) are no longer used. R-134A is a clorofluorocarbon (CFC) with no ODP but moderate GWP and moderate efficiency (about the same as R-22). The newer refrigerant R-410A, a hydrofluorocarbon (HFC), provides no ODP but high GWP and much better efficiency than R-134A. R-32 and R-454B are newer HFC with no ODP and low GWP and higher efficiency than R-410A but with slight flamability. A few natural refrigerants (R-290 propane and 600a isobutane) provide very high efficiency but are extremely flamable so not suitable for boats. The industry is mostly moving toward R-410A and more recently R-32.

There are likely manufacturers not listed here. It is possible that if this page is not updated for a few years some of the products will be discontinued or replaced. The AC/heat system may not purchased for a few years and therefore the available products may have changed.