Isotherm

Fifty-nine years of one Italian compressor company

Indel B started in Sant'Agata Feltria in 1967 and had sold its 100,000th refrigerator by 1975, a decade in which most boats still ran an ice box. The company's biggest credibility marker predates the marine business entirely: NASA selected Indel B in 1982 to build a refrigerator able to work in zero gravity for the Space Shuttle Columbia, which is the kind of reference a compressor maker does not buy, only earns. Indel B has been part of the Berloni group since 1988 and has been listed on the Milan stock exchange since 2017, and today runs more than 800 employees across vehicle, leisure, marine and hospitality refrigeration.

Indel Webasto Marine is the joint venture that actually sells Isotherm and its water-heater sibling Isotemp, pairing Indel B's compressor engineering with Webasto, the German automotive and marine climate supplier. It is based around Novafeltria and Sant'Agata Feltria in Italy's Rimini province, manufacturing at the historic Sant'Agata Feltria site and at a newer plant in Secchiano di Novafeltria that opened in 2021. Isotherm's own material claims the brand is the choice of more than 160 major boat builders worldwide, a figure the company publishes rather than one this desk can verify independently, but it lines up with how often the name turns up unprompted across owner forums for boats built by yards that never mention their fridge supplier in a brochure.

Twelve volts changes everything about the compressor

Passagemaker's own technical breakdown puts a number on the gap: a Danfoss BD35F compressor, the workhorse behind most small Isotherm units, draws about 3.75 amps at 12 volts, roughly 45 watts, and cools up to 12 cubic feet of refrigerator space or 5 cubic feet of freezer. Running a domestic 120VAC unit off an inverter instead means multiplying its AC amp draw by ten and then by 1.1 for inverter losses, so a 2.4 amp household compressor becomes a 26.4 amp DC load, nearly seven times an Isotherm BD35F pulling its full running current. That gap is why almost no cruising boat carries a household fridge off an inverter as its primary galley cooling.

The direct-drive units most Isotherm Cruise and Drawer models use cycle on and off, running an estimated 40 to 60 percent of the time depending on ambient heat and box insulation. Isotherm's holding-plate systems work differently: the ITC+ range freezes a eutectic solution inside a plate, and that stored cold keeps the box down for hours with the compressor off entirely. Sail Magazine's own comparison is blunt about the tradeoff: a holding plate system is relatively power hungry when it does run, so cruisers time it to when batteries are being charged, while a direct-drive unit's steadier, smaller draw is something a small solar array or an hour or two of engine charging covers easily. Insulation is the other constraint a yacht galley imposes that a kitchen never does. Passagemaker specifies 4 inches of urethane foam for a fridge and 6 inches for a freezer as standard, with vacuum-panel insulation buying the same performance in about a quarter of the thickness for roughly USD 1,000 a unit, useful where the cabinetry simply has no depth to spare. Yachting Monthly's own build guidance lands in a related but not identical place, recommending 50mm on the sidewalls, 75mm on the bottom and 25mm on the lid as a minimum, with 50 percent more again on a freezer compartment, and is explicit that insulation, not the compressor, is the single biggest factor in how many amp-hours a fridge actually draws over a day.

The same Danfoss compressor that keeps a weekend cruiser's beer cold cools a charter yacht's galley, and it fails the same way in both.

The range, and the price nobody publishes

West Marine's live catalogue lists 76 Isotherm SKUs spanning that range: Compact 2010 and 2001 conversion kits at USD 919 and 1,029, mid-range Cruise 65 and 85 Elegance units around USD 1,400 to 1,670 and stainless Drawer and Cruise 195 models running USD 2,100 to 2,879. Fisheries Supply's separate listing cross-checks the top end, pricing a Cruise 130 Clean Touch stainless unit at USD 2,247.71 and a Cruise 195 at USD 3,477.05, both read September 2026, which confirms the top of the line runs comfortably past USD 3,000 at retail rather than being a West Marine-specific markup. Passagemaker's own figure for a small Cruise 36 drawer unit, just over USD 1,000, sits above a directly comparable Dometic CD-030 at roughly USD 800, so Isotherm is not the cheapest name in the category even at its smallest size. The range runs past cooling, too: Fisheries Supply prices a Clear Ice Maker at USD 2,185.35 and Isotemp basic water heaters, the sibling product line sold by the same joint venture, at USD 1,082.86 to 1,364.90, so a full galley refit under this one brand covers refrigeration, ice and hot water rather than fridge and freezer alone.

What none of those retailers, or Isotherm itself, publishes is a labor figure. Passagemaker's advice stops at a warning rather than a number: add the installation, and you are looking at some real money, with a marine yard or qualified electrician recommended for any job involving compressor relocation, a new ventilation path or wiring to ABYC standard. Custom galley integration is a different business again. Frigibar, which has built bespoke yacht refrigeration for more than 45 years, tells buyers to start with the exact dimensions of the space and the finish they want, then approach a manufacturer or builder directly for a quote, because nothing at that end of the market carries a published price until a yard has the actual cabinetry in hand.

What the compressor actually costs the battery bank

The clearest real-world number on record comes from a liveaboard owner who ran a 65 litre Isotherm Cruise-line drawer unit for six years and logged a 2.5 amp draw at 12 volts, translating to under 30 amp-hours a day even in hot, humid conditions, alongside a measured 38 decibel noise level she called whisper-quiet. That figure sits in the same band as Passagemaker's engineering number for the BD35F compressor itself, and against a typical cruising boat's daily budget of 60 to 200 amp-hours, an Isotherm drawer unit is a real load but rarely the one that decides the battery bank size.

The number only holds if the installation matches the unit to its locker. Trawler Forum's long-running thread on the Cruise 130 and 195 models describes owners whose fridges struggled to hold temperature not because the compressor was faulty but because it was undersized for the heat the cabinet had to shed, especially in a tight, poorly ventilated locker near an engine room. Fixes owners reported included adding intake and exhaust fans to the cabinet and re-tuning the analog thermostat down, and in at least one case a unit that could not hold vacuum was replaced outright under warranty. Heat rejection, not the compressor's rated amperage alone, is what decides whether the spec sheet number survives contact with a real boat in a real anchorage.

Same compressor family, different badge on the door

Owner debates on YachtForums and YBW Forum comparing Isotherm against Vitrifrigo rarely turn up a measured performance gap, because both brands specify SECOP or Danfoss compressors, both offer roughly one cubic foot drawer formats, and both use closed-cell polyurethane insulation of similar thickness. What tips an individual buyer tends to be which brand their local rigger stocks parts for, or which one came fitted from the yard, rather than anything in the cooling curve. Frigoboat, which competes in the same tier and is reported as the standard fit on Island Packet's production line, is in fact built by Vitrifrigo itself, so the three-way comparison many forum threads run is really a two-way one with a brand name layered on top. Isotherm's own answer to the same question is scale rather than a technical claim: a self-reported 160-plus boat builders using the brand, against Vitrifrigo and Frigoboat's smaller, more sailboat-concentrated OEM base.

The tradeoff that is specific to Isotherm's design is the quick-connect fitting between compressor and evaporator plate, which lets a unit ship precharged with refrigerant and be self-installed without brazing. YBW Forum's account of a 20-year-old Isotherm type 2001 failure traced the fault to exactly those fittings: the o-rings had degraded with age, the charge had leaked out slowly, and the owner was offered a GBP50 to 60 DIY recharge as a temporary fix, a GBP150 to 200-plus-parts professional repair with proper pressure testing, or a full GBP400 replacement, and chose the replacement rather than gamble on the same fitting failing again. The same design that makes an Isotherm compressor a bolt-in swap rather than a written-off galley is the reason a 20-year-old unit failed at a seal rather than at the compressor itself, and a buyer should read that as the fitting having a service life shorter than the compressor's own 5-year warranty implies about the unit as a whole.

Para quién es: Owners specifying or retrofitting galley refrigeration on anything from a coastal cruiser to a crewed charter yacht who want a drop-in drawer unit or a full holding-plate system from one brand, provided someone checks the locker can actually shed the heat the compressor rejects.