Domestic Water System

Recirculating Shower  t Hot Water Tank


Fresh Water Schematic

This system is designed so that no time or water is wasted mixing water to the right temperature.  In addition even the water in the pipes isn't wasted waiting for it to come up to temperature.

The water in the system isn't pressurized, but is pumped by individual pumps at each sink.

bulletAll the tanks are connected to a manifold through shutoff valves, and all the fresh water supply comes via the manifold.
bulletEach tank is filled individually at the tank.
bulletAll the hot water is regulated by a thermostatic valve at the galley sink so it is at a comfortable temperature throughout the boat
bulletEach sink has a locally switched electric pump that is fed through the Mixer Valve and its output is controlled by a Diverter Valve.
bulletThe Diverter Valve sends water either back to the cold water supply line or to the sprayer.
bulletTo use, set the Mixer Valve to "hot" and the Diverter Valve to "cold water supply".  Activate the pump until the hot water in the pipe reaches the Diverter Valve.  Then set the Diverter Valve to spray, and adjust the Mixer Valve if necessary.

Recirculating Shower

The Recirculating Shower uses about a half gallon of water for a luxurious shower of any length.   The temperature is controlled by a thermostatic valve, and the heat is extracted from the hot water storage tank.  After the shower the water is discarded.  

To use, you take a relaxing shower, then at the end you soap up, rinse off, and discard the water.  If you need additional rinsing, then you would use fresh water from the sprayer, and then discard it.


The thermostatic valve controls how much water goes through the heat exchanger to keep the temperature at your setting.

Conbraco Thermostatic Valve "Apollo" 34B-104-02 size 3/4


Circulation pump

Rule 800 Bilge Pump

can pump dry and doesn't need priming


can recirculate or drain out water


can work using only 1/2 gallon of water


Needs external filter


Heater exchanger  keeps the recycled water warm by extracting heat from the hot water storage tank. 

FlatPlate FP5X12L-6 Heat exchanger 



5.1 lbs 


6 oz  shower water


8 oz heating water


Constant shower temperature requires about 150 btu/min (9000 btu/hr)

a fully heated tank will provide about one hours shower time.

bulletWhen the shower is dry, no shower water remains in the "sump", any pipes, or the heat exchanger
bulletThe "sump" and strainer should be very easy to clean and dry


Heat Storage and Use


Hot Water Heater & Storage
bulletIn this system hot water is heated and stored in a 15 gal  storage tank.  
bulletThe tank is about 15" x 15" x 15", designed to hold about 15 gallons thus storing about 10000 BTU's. 
bulletThe stored hot water isn't used up, but circulated through heat exchangers to extract the heat from it at the time of use.  The advantages are:
bulletnever having to worry about backflow accidentally draining the tank and exposing the heating elements
bulletthe hot water does not produce carcinogens during storage, and thus can be used for drinking
bulletThe stored heat is used for:
bulletHeat domestic hot water
bulletHeat the recirculating shower
bulletThe tank's 10,000 BTUs is enough to heat a shower which uses about 150 BTU/min, for about an hour (less some losses).
bulletHeat individual cabins
bulletIndividual air handlers in each cabin are supplied with hot (or chilled) water.
bulletwhen cooling they drain condensate into adjacent sink drains. 
bulletPossibly two air handlers could be used:  one that swivels between the forward cabin and the salon, and the other between the head, salon, or aft cabin.
bulletThe tank can collect and store heat from various sources
bulletGenset coolant
bulletThe heat from the genset is added with a FlatPlate FP5X12L-6 heat exchanger.  The fluid then goes to the regular sea-water heat exchanger for final cooling.
bulletElectric resistance elements
bullet 1900 watt and 2300 watts at 156 Vdc. (Using 4500 & 5500 watt 240 Vdc heating elements) Using two elements of different watts allows flexibility in the storage of excess power generated during sailing and redundancy if one fails.
bulletElectric elements have 1" male NPT threads 
bulletDiesel boiler
bulletRefrigeration compressor (not shown)
bulletThe heat is extracted through two identical flat plate heat exchangers to provide for the boat's heating needs.  
bullet The engine and domestic hot water exchangers can be mounted inside the tank to reduce losses and to provide a limited amount of water to the sinks without turning on the pump. (see tank design below)
bulletone pump can be used to pump the hot storage water through both the heat exchangers for domestic hot water and the recirculating shower
bulletA shutoff valve at the shower will prevent unnecessary circulation of the hot water when the shower isn't used.
bulletthe valve and pipe handling the raw hot water must be rated for 190 degrees or hotter
bulletTank design elements:
bulletThis tank requires a water tight removable top with 10 hose connectors for 3/4" diameter hose.
bulletThe tank fits into a cabinet attached to the hull and lined with foam to provide about 3" of insulation.  The insulation is foamed around the tank such that it can be removed to inspect and replace the tank when necessary. 
bulletHeat exchanger nipples are 3/4" male NPT.
bulletThere needs to be tabs to mount a thermostat and junction box.
bulletPressure in the tank is neutral and can be controlled with an overflow box.

Hot Water Schematic


Hot Water Tank Design

Modified August 14, 2003

Systems that will not be installed initially are shown in gray.  
Ideas that may not be practical are in yellow.