Domestic Heating & Hot Water

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.

Gone are the days of inverting a flower pot over the propane stove, or taking showers from water heated on the rare occasion we ran the engine.

Starting with Sundeer in the 1980s we began to fit diesel boilers. These units, usually made for heating trucks and buses, would pump hot water around the interior, while at the same time we used them for our domestic hot water requirements. By using really big, efficient spiral coil heat exchangers in the domestic hot water heater – typical with a capacity of 25,000 to 30,000 BTU – we would have essentially an inexhaustible supply of hot water.

We plumbed the heating circuit with a “Y” valve, so we could keep the hot water between the boiler and domestic hot water heater in the tropics.

For many years we used Webasto, a German manufacturer that builds robust, easy to maintain equipment. The problem with these units, however, is the burner technology is not quite up to modern standards, and they do not burn as cleanly as some newer systems. And, when used just for domestic hot water, where the boiler tends to run in short cycles, the inside of the burners get dirty fairly quickly.

On Beowulf, at the suggestion of our heating guru Jim Schimke, we tested a Teledyne “Proheat” truck heater. This had a more modern boiler design and was computer controlled. We were put off by the circuit board, but have to say that the unit worked flawlessly, and spent a lot of its life in the unhappy short-cycle water heating regime. We would have gone back to Proheat for this boat except that they do not make a large enough unit.

For this project we needed more capacity. Given the high latitude environs we planned on cruising we calculated we wanted 50,000 BTU of full time capacity. With most heaters that means 85,000 to 100,000 BTU rating, as typically heaters should not be run at more than a 65% duty cycle. Of course Webasto makes a large model that would work, but when we used this for just domestic hot water, unless we had a huge heater tank, there would be problems from the short-cycling.

In discussing this with Jim Schimke he suggested we look at Kabola heaters. These units are designed from the ground up for full time use on boats and in residences. They are highly efficient, will operate for years without maintenance, and are the heater of choice on many of the yachts built in Europe. There are only two problems: they are relatively heavy, and more expensive – both issues to which we are sensitive.

We did a comparison on weight and cost, taking into account the fact that the Kabola heater had the domestic hot water system integrated, that there were no outside fittings or pumps to buy and install, and that we could use more of the rated capacity. Bottom line, while there is still a cost premium – perhaps 40% all things (including labor savings) considered – the weights are about the same. And 40% cost premium for a superior product is acceptable, especially in light of its cleaner burning (less mess on deck) and more quiet operation.

Below is an image of the front of our unit (B-17 Tap model- 65,000 BTU rating).

This heater works in standby mode to keep the boat “defrosted” in cold climates when we are not aboard. And will turn on when it senses demand for domestic hot water for bathing or the galley. The controls are built in, and can be seen on the upper left corner. The plumbing connections on the right are the in and out for the domestic hot water, and in and out for the heated water which circulates to the fan coils. In addition, there is a very beefy circulation pump.

The coil above is 13 meters (42 feet) long. It is finned for better heat transfer. This is used inside of the Kabola to heat domestic hot water.

That big blue box is what meters the diesel fuel and creates the combustion inside of the heat exchanger. One of the positive things Jim Schimke pointed out was that Kabola assembles their heaters from a variety of high quality industrial parts. This makes the units easier to service and improves reliability.

This is the guts of the burner. Pretty simple, and very efficient.

Having cruised with this system for the past two years we have to say we are very pleased with its quiet, efficient operation. It is also has a cleaner exhaust than that which we are used to.

Posted by Steve Dashew  (October 20, 2011)

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