water (hydronic systems) and use the hot water to carry the heat to different locations to do its job. As a general rule, boats 30-feet
and smaller can be well-heated by a forced air unit. The actual heater can be mounted in a space where you have access for maintenance, but otherwise it is out of sight. (All of the diesel fired units are noisier than an electric cabin heater that is in good condition. This is another reason to put them in a space that is insulated from your living quarters.) The burner pulls in air from the outside and exhausts to the outside, so there are no combustion gases inside the boat (Figure 2). Both types (forced air and hydronics) do use some electricity- normally 12v DC or 24v DC. An example of this is an 18,000 BTU model that heats a 38’ sailboat or 34’ powerboat and uses 85 watts during normal operation for the hot air heater and 6 to 12 watts per air handler. The fuel consumption for this unit is .17 gal/hr or 1 1/2 gal / day figuring 50% running time. The heater is controlled by a thermostat so maintains something close to a constant temperature. For up to about
There are high efficiency plate heat
Figure 4. This is a high efficiency plate heat exchanger which can be used to create a constant flow of hot water.
a 30’ sailboat one manufacturer builds a cooking stove that has a blower hood that acts as an area heater.
Hydronics These units deserve their own
section. Again, diesel is burned, but this time to heat water which is then circulated in a loop throughout the boat. By using various types of heat exchangers it will perform different jobs. You can heat a cabin as a separate comfort zone, preheat the engine (Figure 3), or heat fresh or raw water for showering, washing dishes, etc.
exchangers that work well for heating a continual flow of hot water (Figure 4). The cabin heaters are small radiators with a fan to move the air past the finned tubes for the heat exchange to take place and circulate about the cabin. On cruising boats, water consumption can be reduced by using hot, raw water for showers, washing clothes, etc and then rinsing in hot fresh water. As far as the heat exchanger for preheating the engine, it is also possible to reverse the process when the engine is running and use its heat. Having said that, there are limitations to how much heat you can take from the engine without a negative effect on the engine. Many novel things can be done like changing from rubber hose to copper tubing when passing through the foul weather gear locker so it is heated at a low level whenever the heater is running. We have installed copper tubing in the head to act as a towel heater. These heaters are mostly designed
for coaches or buses but some are more marine oriented than others. One manufacturer builds a combi unit that already has the domestic hot water
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