Maringret’s Refrigeration Research

While we were replacing our galley, it was the obvious time to decide whether to install a fridge or not. When we removed the 20 year old cool box, we discovered it was surrounded with approximately 25 millimeters of styrofoam. The discovery went a ways towards explaining why we put cartons of milk in and were able to take out cartons of yogurt. There is a companion page Refrigeration FAQ which is our collection of wisdom we encountered while researching refrigeration alternatives.

We set out to research the selection of a refrigeration system in a number of ways:

  • Internet sites
  • Magazine articles
  • Books
  • Manufacturers published material
  • Recommendations from chandleries or dealers

We were quite unsuccessful in our search. Specifically we found:

Magazine articles 
Although we have subscriptions to magazines from Sweden, Canada, the US and the UK, no magazine touches the issue of fridges. The one exception is the June 1995 Cruising World article which is now available on the Internet and so we have listed a link to the article under Internet. It is somehow indicative that one of the most complex, expensive and the largest electrical consumer for a boat is not touched by the boating press who seem to be spending their time printing recipes and trip reports. Perhaps the armchair sailers who subscribe to the magazines aren’t interested in refrigerators.

Internet Sites 
The one non-manufacturer website seems to be Cruising World which has an online version (here or alternately here) [Note: both “” and “” are dead as of 2018] of a refrigeration article that first appeared in print in the June 1995 issue of Cruising World. The article reviews units which were available to the US market in 1995. One thing we found is that there is very little cross over between the European and American markets, Sweden’s Isotherm and Germany’s Waeco seeming to be two of the few. Hence the article, which is very thorough, is useful only to those buying an American refrigeration system. Aside from this site we found only manufacturers sites whose links we listed below.

We found information on refrigeration in both “Boatowner’s Mechanical and Electrical Systems” by Nigel Calder and the “Offshore Cruising Encyclopedia” by Steve and Linda Dashew. Both books dealt adequately with the principles of refrigeration but give very little in the way of recommending specific units. Any other publications we found were so generic we questioned why they had been published.

Manufacturers Material 
Once we found out the different manufacturers out there we collected their published materials. The first problem we encountered was that each manufacturer describes the operation of their refrigeration in their own style which makes it very difficult to compare one brand to another. Secondly it is very hard to take any abstract figures and determine how they would apply on your boat.

Recommendations from Dealers 
The advice we got from any dealer of refrigeration products was limited to what they sold and additionally to what they had personal experience with. As far as collecting technical information we found it much more fruitful to directly contact the manufacturers or their agents and speak to the technical support staff as opposed to dealing with retail sales staff.

Refrigeration FAQ
As we dealt with various people and publications we gathered a collection of points on the topic of marine refrigeration. We have collected these into a Refrigeration FAQ (Frequently Asked Questions)

As the research phase of our project progressed, two factors entered the process:

  • We decided that in our case we would not be installing a freezer. This was primarily due to lack of space and need (as well as wariness of power consumption) but it did simplify things in that we only needed to review and research refrigerators and not freezer units.
  • For better or worse, there is a separation of markets between North America and Europe where manufacturers tend to market in one area or the other. This meant we could ignore the US made units as they generally were not available through dealers in Europe. Were we to import such a unit ourselves, access to any parts in the future would be equally complex. Nevertheless we have put a list of American refrigeration websites at the end of this page.

This brought us to the point where we had three manufacturers to look at:

  • Isotherm of Sweden (who marketed under their own name, but now market under Indel Webasto)
  • Veco of Italy (who market under the names Frigoboat and Frigomatic)
  • Waeco of Germany (who marketed under the brand name of Coolmatic but now market under Dometic)

After collecting the manufacturers printed material and contacting their customer support staff via telephone we came up with the power consumption figures given below. One of the many problems we faced was trying to get some common basis with which to compare the figures given by the different manufacturers. As the text below demonstrates we were not very successful, in general we were unable to get one manufacturer to provide their consumption figures for any scenario other than the one they published. This meant that basically we ended up comparing apples to oranges to bananas. For each of the following 3 manufacturers we have tried to list the assumptions made along with a power consumption table based on the figures in their published material as of the fall 2000. Of course their figures may be revised but what we are publishing was current as of late 2000.

Isotherm Projection

ASU SP with up to 125 litre box:

Isotherm ASU SP & 125L box Aver. Max. Comments
Current 0.4 2.5 These figures for the current drawn are the amount drawn from the battery when the engine is not running.
Watts 4.8
Amp-Hours per 24 hour day 9.6 50mm PU insulation
Amp-Hours per 24 hour day 7.2 100mm PU insulation


air temperature: 20C-40C
water temperature: 22C
box internal temperature: 4C


    • 90 % of installations for this model have box sizes between 40 and 60 litres
    • fully charged plate will last for up to 15 hours, consequently the recommended usage is to run engine for 30 minutes twice per day
    • when engine is running the compressor will draw 5 amps
    • without the engine running the compressor current draw will average 0.4 amps (maximum of 2.5 amps), this 0.4 A will be 24 hours per day giving approximately 10 amp-hours per 24 hour day

Veco Frigomatic Projection

Frigomatic divides their power consumption data into two scenarios, waters around the UK (which would be similar to the North Sea and and Baltic) and a separate set of figures for Mediterranean waters (which they caution are not the same as proper tropical waters such as the Caribbean).

Frigomatic K35F (UK Waters) Air Cooled Water Cooled Comments
Current 0.75 0.6
Watts 9 7.2
Amp-Hours per 24 hour day 18 14.4 50mm PU insulation
Amp-Hours per 24 hour day 9 7.2 100mm PU insulation (using 50% of 50mm)
Frigomatic K35F (Med Waters) Air Cooled Water Cooled Comments
Current 1.5 1.2
Watts 18 14.4
Amp-Hours per 24 hour day 36 28.8 50mm PU insulation
Amp-Hours per 24 hour day 18 14.4 100mm PU insulation (using 50% of 50mm)


    • UK Waters:
      48 litre box, air cooled with 50mm PU insulation consumes 750 mA which is 18 Ah per day
      reduce the power consumption by 20% for keel cooled
    • Mediterranean Waters:
      48 litre box, air cooled with 50mm PU insulation consumes 1.5 A which is 36 Ah per day
      reduce the power consumption by 20% for keel cooled

Waeco Coolmatic Projection

Coolmatic seems to have the widest range of compressors and evaporators hence there is more to represent in the tables.

Coolmatic 54 & 55 Low Aver. High Comments
Watts 35 37.5 40
Amps when running 2.917 3.125 3.33
VD-01 Duty Cycle 0.4 0.4 0.4 rated for 100 litres
Amp-Hours per 24 hour day 28 30 32 50mm PU insulation
Amp-Hours per 24 hour day 21 22.5 24 100mm PU insulation
Coolmatic 84, 85 & 86 Low Aver. High Comments
Watts 45 52.5 60
Amps when running 3.75 4.375 5
VD-15 Duty Cycle 0.2 0.2 0.2  VD-15 is rated for 250 litres so cut power for 50 litres by 1/3
Amp-Hours per 24 hour day 18 21 24 50mm PU insulation
Amp-Hours per 24 hour day 13.5 15.75 18 100mm PU insulation
Coolmatic 94, 95 & 96 Low Aver. High Comments
 Watts 60 80 100
Amps when running 5 6.667 8.333
VD-06 Duty Cycle 0.125 0.125 0.125 rated for 250 litres, assume discharge time is 12 hours
Amp-Hours per 24 hour day 15 20 25 50mm PU insulation
Amp-Hours per 24 hour day 11.25 15 18.75 100mm PU insulation


Amp-hours required for a 100 litre box, using either 50mm or 100mm PU insulation, where the internal temperature is 4C
50mm 100mm
Isotherm ASU SP pumpless water cooling 9.6 7.2
Frigomatic K 35F air cooled 18 9
Frigomatic K 35F pump operated water cooling 14.4 7.2
Coolmatic 50 Series & VD-01 evaporator 30 22.5
Coolmatic 80 Series & VD-015 evaporator 21 15.75
Coolmatic 90 Series & VD-06 accumulator 20 15
Averages 18.83 12.78
 Standard Deviation 6.88 6.08

All three manufacturers above use the same Danfoss compressors. As the box construction is not part of what they supply and therefore outside of the manufacturer’s figures, this leaves the evaporator and electrical control circuitry to distinguish one brand from another. The range of values is quite interesting given how little is actually being varied (i.e. only the evaporator and electrical control circuitry). This is born out by a standard deviation of 6.


All the figures on this page were discussed and agreed to verbally by the technical representatives of the various manufacturers or their distribution agents for the UK.
Note: all figures are from 2000 sales material.

Take a look at our two fridge building projects here and here.

There seem to be very few (if any) industry standards when it comes to refrigeration. This severely handicaps any attempt to compare different makes as you end up playing the “oranges and apples” game where one measures in “widgets” while the other measures in “warbles”. It is also sobering to think that for such an expensive undertaking and complex installation the marine publishing industry seems to stay mute. Does this mean it’s too complicated for the magazine experts?

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