Diesel cabin heaters

Given the enclosed steering capability of most power voyaging yachts, there are few other types of boats better suited to extended season cruising. Voyaging earlier in the spring and later in the fall is a realistic possibility when an inside steering position keeps you out of the weather. To make such passages in cold and wet weather work, however, a cabin heater is a needed piece of gear.

And it’s not only a question of comfort, it can be a question of safety. Steve Dashew, designer and builder of both power and sailboats, and a circumnavigator once wrote, “Of all the systems aboard our boats, none is more important than good heating for the interior and an efficient supply of hot water for bathing.” That may sound a bit strong at first blush, but not when you think about it a while. Everything works better when it’s warm &mdash motors, batteries, engines, and yes, muscles, hands and fingers &mdash such as for gripping a lifeline. Moreover, as luck would have it, cold, raw, wet weather seems to be just when you need these things the most.

But even if it’s not a life-threatening situation, it’s a whole lot more tolerable if you can look forward to getting back into a warm, dry cabin followed by a hot shower. Besides, a good, reliable, economical and efficient heater can not only stretch your cruising season at both ends, it can significantly extend your voyaging range up into some beautiful cruising grounds in the higher latitudes.

Generally speaking, there are two basic classes of heaters, space heaters and central heating systems, and several types in each class. Let’s first consider the characteristics of a good boat heater system. First, it must be capable of keeping the boat’s interior space, or spaces, warm and dry. It should be able to do this safely under at-sea conditions. It should be simple to operate, reliable and serviceable at sea by the user. It should also be compatible with other systems on the boat, particularly the vessel’s fuel system.

Space heaters
Space heaters, small standalone units fueled by propane, kerosene, charcoal, coal and wood are available; however the trusty old diesel pot-burner has the advantage of using the same inexpensive &mdash and high energy content &mdash fuel as the main engine(s). It can be either gravity-fed from a separate tank or piped off the main tank via a low-pressure pump. The diesel space heater is the most widely used, the most basic and the simplest of boat heater types; they’ve been around for years. Give it good clean fuel, preheat it to thoroughly vaporize it, maintain an adequate draft (proper stack diameter and height), clean the burner when it needs it and be sure to adjust the metering valve for the viscosity of the fuel. Diesel No. 2, the most commonly used, is heavier than diesel No. 1 and it will give you dependable service for years. Equally important to the distance power voyager, it can be serviced and maintained by the user while at sea.

These are great little heaters, made by Dickinson, Refleks, Sigmarine, and by a relatively new entry to the North American market, Kabola, a Dutch company. Typically, they have heat outputs ranging from 5,500 to 16,500 BTU and consume from 1.3 to 3.2 gallons of fuel per 24 hours. Some can be fitted with an internal coil of copper tubing and thus supply &mdash albeit in modest amounts &mdash domestic hot water. Others have a cook stove lid on top so you can heat up a can of Beefaroni. Floor or bulkhead mounted, they are quite attractive; with little windows so you can see the flames, they’re about as close as you can come to an open-hearth fireplace without sending your insurance company into a rage. However, the problem is their limited capacity &mdash one heater, one space, and at that, not very large, only about 1,100 cubic feet, typically suited for boats in the 30- to 40-foot range. If your boat is much larger than that, or if you have more than one space to heat, you’ll want to consider a central heating system. 

Central heating systems
Central heating systems are essentially the same type of heating system as those used in residential heating systems. The oil burner and fuel tank are located in an out-of-the-way location. A thermostat in the space or spaces to be heated calls for heat, the burner starts, heats the transfer medium (air or water), delivers it to the space that called for it and stops sending it when the space is warm enough. A miracle of modern science? Not really, the Romans were using central heating in their homes in 100 A.D. They called it their hypocaust, and it was also used to heat their famous Roman baths. Just as with residential systems, there are two basic types of systems in marine use &mdash forced hot air and forced hot water (hydronic).

These units burn diesel fuel drawn from the vessel’s main engine fuel tanks, they are thermostatically controlled and may draw combustion air from both inside and outside the boat. They are fitted with ducting or flexible hose and run through lockers and storage spaces to registers or radiators in the spaces to be heated. The combustion chamber is sealed and the combustion gases are exhausted to the outside of the boat. They are microprocessor-controlled and include such safety features as automatic shutdown in the case of overheating, etc.

Forced hot air heaters
In a forced hot air system, the burner draws combustion air from outside the boat as well as from inside, burns it in a chamber with an air-to-air heat exchanger and a blower that distributes the heated air via 4-inch diameter flexible ducting to multiple registers or outlets in the spaces to be heated. Forced hot air systems are simpler and significantly less costly to install and they have the advantage of being able to accommodate an air conditioning unit, using the duct system for the cool air. One drawback to the forced air system is that control of temperature in individual spaces is pretty much limited to opening and closing the outlet register. Another disadvantage is their inability to heat potable or domestic water. They’re also said to be significantly noisier than a hydronic system.

The major players in forced hot air central heating systems are Espar and Webasto. Espar has four models ranging in heating capacity from 7,500 to 44,000 BTU. Webasto has three models covering the range from 3,000 to 12,000 BTU. Wallas offers two diesel-fired models, with capacities from 2,700 to 14,000 BTU. Prices for these units range from about $1,500 to $3,000 for the basic heater unit, however, necessary ancillary components and fittings &mdash ducting, registers, etc. &mdash can add 20 to 30 percent to the cost, exclusive of installation costs. Fuel consumption can run from about 0.026 gallons per hour (gph) to as much as 1.7 gph depending on size and temperature setting. Electrical power draw may range from about 0.6 amps to a whopping 10 amps at 12 VDC for a really big air heater like Espar’s D8LC.

Forced hot water heaters
In these systems, hot combustion gases in the diesel burner heat the coolant water via an air-to-water heat exchanger. A pump then circulates the hot water to either convection type radiators or more commonly, to fan-forced radiators, a type of water-to-air heat exchanger similar to the heating system in an automobile. The fans on each radiator can be controlled with a room thermostat to provide automatic zone control, or with a manual fan-speed control switch. Another advantage of hot water systems is that they can be adapted to heat domestic hot water for showers, dishwashing, etc. They can also be plumbed with a water-to-water heat exchanger between the vessel’s engine and the heater’s coolant loop so that the boat can be heated by the engine’s cooling system when the boat is under way and thus save fuel. This arrangement can also be used to preheat the engine, making it easier to start in cold climates.

Forced hot water systems are more complex, and while the cost of the basic heater equipment is about the same as that for hot air systems &mdash $1,500 to $3,000 &mdash the ancillary fittings and components &mdash pump, expansion tank, valves, etc. &mdash can add from 85 percent to nearly 200 percent to the total hardware cost. Installation costs are also higher.

Espar has seven hydronic models ranging in heating capacity from 13,000 to 120,000 BTU. Webasto has six models covering the range from 17,000 to 104,000 BTU. International Thermal Research offers three models, the Hurricane, Hurricane II and Hurricane III, at 25,000, 35,000 and 50,000 BTU. Fuel consumption will run from 0.07 to 1.2 gph, and operating current draw will range from just less than 1 amp to more than 10 amps at 12 VDC.

A word of caution is in order here. Installation of these systems is critical not only to the performance of the system but also for crew safety, especially on forced hot water systems. “That’s why we sell a do-it-yourself kit for the air heaters but not for coolant system installations,” says James Cowen, Training Manager for Webasto. “We carefully train and certify dealers for installation of these systems and strongly recommend that users work with qualified dealers on selection and installation.”

 In addition, self-installation would void the warranty. 

By Ocean Navigator