Hot Water 'Dump' Circuit

[nhschneider]

Even though our watermaker (Spectra Cape Horn) has an adequate capacity for our consumption, I hate to waste fresh water. Since we prefer to use our water heater for washing dishes, showering, etc. and our water heater is located in the lazarette, it takes a fair amount of flow of water before the hot water arrives at the spigot in the galley, about 20 seconds worth. Whereas that’s only about a gallon of water, it drives me wild to watch it run down the drain. At one point, I installed a recirculating pump but it didn’t improve the amount of cold water down the drain. I even called in a friend who engineers pumps for a living (mostly industrial and sewage treatment) but despite all his skill and knowledge, he couldn’t figure out why the recirculation pump wouldn’t work.

So, I came up with another idea. Right where the hot water hose meets the galley spigot’s inlet, I installed a tee. I threaded onto the tee (using a ½” close nipple) a 12-volt ½” NPT stainless steel motorized ball valve (available on amazon.com - US Solid part number USS-MSV00007) and used a ½” hose barb x ½” MNPT fitting in the opposite side. I put a length of ½” hose that extended from the electric ball valve to one of my fresh water tanks (port side, in my case) where I teed it into the vent line. I tapped off the 12-volts from the fresh water pump and extended the circuit to a convenient spot near the galley sink where I installed a small normally-open, momentary contact switch (the current draw from the electric ball valve is very low). Once everything was installed (it’s a pretty simple project – I don’t think I had two hours involved from beginning to end), I can press and hold the switch, the valve opens, the fresh water pump begins to cycle and the water from the water heater flows into the port water tank for as long as I hold the button down, which, for our installation, is about 20 seconds. As soon as I release the button, the valve closes and I have hot water at the galley spigot.

There is one potential problem with this installation: If you have multiple fresh water tanks and you’re drawing from one and ‘dumping’ to another, it’s possible that the receiving tank could fill to the point where you’re pumping fresh water overboard through the water tank’s vent fitting if the receiving tank were completely full.

I think I had less than $100 in the parts necessary for this project. You might argue that it doesn’t cost justify the savings in fresh water and I would agree but I’m delighted with the results just the same.

Fair winds and calm seas.

[CaptTom]

You might as well go all the way and invest in a circulator to create a loop back to the water heater. Not uncommon in dirt houses. You can hook up an occupancy sensor in the head or galley, or use a light switch, existing or dedicated. The circulator comes on (or is turned on) before using the water. The cooler (but maybe still warm) water in the hot water plumbing is returned to the water heater, saving some energy there. And by the time you turn the spigot on, you have almost instant hot water. No worries about returning water to the wrong tank, or heating up your cold water inadvertently.

[nhschneider]

Capt Tom-
Thanks for the post and your comment, however, if you had read my post, you would have found that I tried - unsuccessfully - to install a recirculating pump. I have one in my home that works great.

Fair winds and calm seas.

[CaptTom]

Oops. Sorry. Carry on.

[Lou-In-NJ]

It sounds like part of the issue is you are using 1/2" tubing, at that diameter, you have 23 cubic inches of unheated water for every 10' of tubing length, and then, even when the heated water gets to the cold tubing, it loses heat to the tubing; you should down-size the hot water side to 3/8".

3/8" tubing is only 13 cubic inches per 10' and your water velocity will increase, that, along with a reduction in surface area of the tubing, will both help with the exchanging of heat from the hot water with a cool tube; and you will not likely be able to tell the difference in flow at your fixtures since most faucets use 3/8" I.D. tubing or smaller for their service connection anyway.

[Jubilee39]

Your idea is good. I have a similar setup except manual. When I plumbed the boat I installed a balance line to enable me to transfer water between tanks. Manual globe valve in the head returns water from the hot line back to the on service tank. Instant hot water for shower with no waste