Hot water recirculating pump to conserve water

S

smckean (Tosca)

New member
I have a hot water heater on my CD25. I never use it. I am at anchor 85% of the time so no shore power and water is precious. Indeed, it is that last value, conserving water, that is the primary reason I don't use the heater since one has to run over a quart of water into the sink (or saving container) before the hot water can make the long trip from the heater to the galley faucet. The power issue can be solved with my Honda 2000i generator; but how to not waste water? I've thought of ways around this, but my ideas were always too cumbersome to actually bother to implement. Then talking to a contractor last night about circulating hot water systems in houses, a simple solution dawned on me. Question is....will it work? So I thought I'd ask this august body for opinions.

The idea is to install a small switched pump under the galley sink that interconnects the hot and cold water lines just before the galley sink. When you want hot water, you turn on the switch and the pump takes hot water from its line and pumps it into the cold water line -- this should result in water circulating round and round thru the hot water heater (note the main fresh water pump would not be on at this time). One will have learned to count the seconds it takes for hot water to reach the faucet (say 10 seconds), so you count off those seconds and turn off the circulating pump. Now you have hot water right at the hot water tap.

Now, thinking thru what other consequences there are....I don't think cold water will find a path thru the recir pump since pumps have check valves to stop reverse flow. There may be some leakage thru the recir pump from the hot water line to the cold if you are running hot water, but so what. The recir pump is not running so there can't be very much water flowing thru the recir pump considering the main water pressure pump will now be on; so the pressure in both the hot and cold lines will be nearly the same. And even if a little hot water does leak thru the stopped recir pump, it wouldn't hurt much since you are using hot water anyway.

What do the experts think? Where's the flaw in my logic?
 
Well, only positive displacement pumps have check valves to ensure the water goes one way. Centrifugal pumps which are cheap just suck in the water and expel the stuff at higher pressure, so you'd need a check valve.

We have a recirculating hot water system in our house which ran continuously during the day. That wasted a lot of propane and I took it out. Your idea is only on demand, which doesn't waste heat. That's good. You would have to route the return line back to the hot water tank to replace the water you're drawing out.

I assume the Honda generator will handle the load if it's the only load. If you have problems, install a 240 V heating element and you cut the current by a factor of 4. I've done that and it works well, though it takes longer for the water to heat.

Boris
 
I feel the solution is to get rid of the 6 gallon water heater with dual lines where the water has to go over 15 feet to get to the galley or head shower. This also opens up a huge storage space. Most of us have put a shelf in the space where the water heater was.

We (and a couple of other 25's) put in a Bosch 2.5 gallon water heater basically under the galley faucets. We epoxied in a plywood (saturated with epoxy) platform. We have a mixing valve in the shower, to keep temperature constant. I keep the heater near the max temp. (easy to adjust the temp). We waste less than an ounce or two of water when use at the galley. I have no idea why the factory doesn't put the Bosch in to begin with. It holds heat overnight, costs less, and works beautifully!

DSC00441.jpg

We have a selective recirculating system in our house. One leg goes to the kitchen, the other leg to the furthest bathrooms. Each leg is turned on or off with a simple bypass valve under the counter. The pump is on a timer, so it runs and circulates water only at peak times.

In our Cal 46, I put in a bypass valve. Basically I put a "T" in the hot water line, just below the galley faucet, the bypass went into the water tank directly via a "T" into the vent line at the tank. I know exactly how long it took to get hot water, and timed it (about 25 seconds). No extra pump, no switch, no check valves. The extra pump to the cold water system seems to present several problems, I believe that the other solutions are easier.
 
First off, I think your idea is brilliant! I have always had a bit of old Rube in me and even though your plan is quite a ways to go for the gain, it would work and work well - almost well enough to be worth the effort which is good enough for me.

On the other hand, I have the exact Bosch water heater under my kitchen sink in the house and it works really well. I have to warn people of the 130º water in two seconds. If the power draw of the Bosch is less than the draw of your existing water heater it might be better to do as Dr. Bob suggests.

But if you go with the Goldberg plan, I support you all the way!
 
One other thought, is that probably a positive flexible vane centrifugal pump would be best (like a "water puppy" or similar to our outboard motor water pump. A check valve would be desirable, but probably not essential.
 
Thanks for the feedback.

journey on":2eb8i2g2 said:
Centrifugal pumps which are cheap just suck in the water and expel the stuff at higher pressure, so you'd need a check valve.
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Noted. If I use a centrifugal pump, I'll add the check valve. BTW, what kind of pump is typically used for the main freshwater system pump? (Or maybe there's a check valve there I don't know about.) Certainly on my CD25 that pump does not allow water to leak back toward the tank (note there is zero pressure on the tank side). Indeed, I'm always amazed that I don't lose any pressure for dozens of hours, or even longer, as long as I have all the fittings snug.

You would have to route the return line back to the hot water tank to replace the water you're drawing out.
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Hahahahahaha......you missed the central design point of my idea. The whole purpose of the scheme is so I don't have to run a return line. Read my post again.....I'm using the existing cold water line as the return line similar to how they do this in houses when you want circulating hot water without laying new pipe.

thatway":2eb8i2g2 said:
I feel the solution is to get rid of the 6 gallon water heater with dual lines.....
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You are right on of course. I'd love to have your solution, but I don't want that big a project. This seemed like a quick and dirty way to improve things.

Tyboo":2eb8i2g2 said:
First off, I think your idea is brilliant!
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:embarrased :embarrased :embarrased :)
 
One of my first projects was to pull the space and water waster 6 gallon water heater and put a Bosch under the sink so much more efficient and an obvious solution to a lazy factory setup, I did mention it here in a post at the time that Bob noticed and tried it also, then verified how well this stup works. In our Ranger Tug at least it made some sense as the water was also heated by the inboard diesel.
 
We believe in keeping things simple. We only wash dishes at night after dinner to save water, and fill our coffee pot first to keep from wasting any.
 
Your idea sounds good, but adds more complications to the system. We have a 22, so no water heater or shower. Being farmers and having lived in an old farm house with outdoor plumbing for nine years, we got used to the simplicity of a path and a pail. On the boat we usually fire up the Wallace every morning, to warm and dry the cabin and make our breakfast. The kettle is always full and the excess goes into a thermos bottle for the day. So if we need some hot water during the day, there is always a thermos bottle full. This is in my opinion the ultimate way of saving water and energy.

A foot note on the path and pail lifestyle. Since we built our modern house almost 20 years ago, our water consumption has gone up considerably, but probably is much lower than the average household, since we learned to conserve when had to carry a 5 gallon pail in from the pump. The outhouse, now reserved for emergency use only, was chilly at 40 below, but our main complaint of having indoor plumbing is that we rarely see the northern lights anymore.
 
Peter & Judy, when we are off the dock that is the way we do it also, to also save water I installed old school salt water foot pumps in the galley and head. The water heater is nice for when Dana is off the ranch in town for work and stays on the boat.

Micah & Dana, Apple Pie Ranch, Big Sur
 
Well, I did it!

It works and it works well. The idea was to inexpensively add recirculating hot water to the boat (much like is done when retrofitting houses), so I can make use of the factory installed 6 gallon hot water heater. Until now, I never use the hot water heater because of the "wasted" 1.25 quarts of water it takes for the hot water to get from the heater to the galley faucet. This recir set up allows for near instant hot water (less than a second delay). The whole project cost less than $125, but it could have been done for under $50 (see below).

I did it by installing a fresh water pump under the galley. I was going to go with a cheap pump ($30), but the cheaper pumps would take 30 seconds to bring hot water to the galley; so I went with a more expensive one ($100). I didn't need to go that expensive, but I decided to go with the identical brand and model that is installed in the boat as my main fresh water system pump (Jabsco ParMax 2.9) since that way the new pump would do double duty as the recir pump and also as a backup main pump should the main pump ever fail. (BTW, I set things up so that I can have the new recir pump take over the main pumps duties by removing 3 hose clamped barbed fittings and running a 1/2" hose to bypass the failed pump -- uninstalling and reinstalling the pump is not necessary -- quick and easy fix until a more permanent fix can be done.)

Pump.sized.jpg

To make this work you must disable the pressure switch in the recir pump. I did this by cutting the wire that runs to the pump's "relay", and stringing all 4 resulting wires to a terminal strip. This way I can run the new pump as the recir pump or reconfigure it as the main freshwater system pump by simply moving some jumpers around on the lower half of the terminal strip.

Wiring.jpg

To get "instant" hot at both the galley sink and at the shower, one holds down a momentary toggle switch for 10 seconds. No fuss, no waste. The down side is that since I use the cold water line as the hot water recir return line, once the recir pump does its thing, the cold line is partially filled with warm water (not hot if you time it right); but I don't find this a problem since I rarely want truly cold water anyway....even from the cold tap. My drinking water is a separate system; and of course, there is always the cool sea if I don't care about salt.

Switch.sized.jpg

There are some other advantages to this system besides low cost over the alternative Bosch etc instant hot unit mounted under the sink:

1. It takes a lot less room

2. It makes use of the factory installed hot water heater that would otherwise not be used

3. I can easily control the temperature of the hot water coming from the faucets by how long I enable the hot water heater circuit.

4. The hot water tank is a sort of "energy storage" system since I can use surplus electrical energy to heat the water, and then reclaim that energy at a later time.

This last point is a bit subtle. Here's how it works. As part of these enhancements to my boat, I am also replacing the 1500 watt hot water heater element with a 1000 watt element. The reason for that is so I can run the hot water heater AND my 36amp battery charger at the same time off my Honda 2000i genset. I often need to run that genset for 30 to 90 minutes a day to recharge my batteries depending on whether I run the main engine that day or not. Since I can heat the hot water warm enough for dishes or a shower in 30 minutes with the 1000 watt element, I wanted to be able to run both the hot water heater and the charger at the same time (with a little genset head room to spare) .So now I sort of get the water heater "for nothing" since I am running the genset anyway. The charger needs 200-400 watts depending on the battery SOC, so if all I am doing is charging the batteries, a lot of the genset capacity is going to waste. True, the genset uses more gasoline at full running speed than under light load; but I consider that small amount of fuel as essentially free -- the "real" cost of running the genset is noise in the anchorage. So this way I get hot water for essentially the same amount of noise as I produce charging my batteries. Also the alternative Bosch-type systems must use a gob of amps out of the battery, and since I want to use the hot water while at anchor without creating even more noise, the hot water heater is a sort of "time shifter" of electrical energy.....if you get my meaning.
 
Nice install! Glad it works!

I would disagree with:
1. It takes a lot less room
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By removing the 6 gallon hot water heater under the port aft dinette seat you open up about of 8 cubic feet of storage, and virtually loose no storage under the galley.
 
thataway,

What I meant was that the recir pump takes up less space under the galley sink area than a Bosch type system. I don't know about yours, but my "under the galley sink" area is quite crowded (for one thing the Wabasco diesel heater is installed there).

Clearly, the hot water heater takes up a huge amount of volume in the boat. I guarantee you that if I had a new C-Dory factory-built for me today, I'd instruct them to install the Bosch-type system under the galley counter, and definitely not to install a 6 gallon hot water heater (altho I do like the energy-time-shift feature I mentioned :wink:)
 
Oh, I need to add one more comment to respond to some of the observations by others above.

As I looked into pumps etc, what I found was that all (nearly all?) fresh water systems on small boats such as a C-Dory use diaphragm pumps (not centrifugal pumps). Diaphragm pumps use separate chambers and valves to create the pressure differential between the input and output side. As such, and unlike centrifugal pumps, water doesn't pass thru either pump unless it's running. There is no need for any check valves in this installation.
 
You are correct--no heater under the galley counter--mostly just storage.

The smaller Bosch water heater is well enough insulated, that it will still be hot enough (for us) the next day. We have the heater near the max, and use the mixing valve in the shower to keep water temp proper. We find we had as "much usable" hot water as we did with the lower temp setting on the 6 gallon tank.

Yes, great idea to keep a usable spare pump. One of the spares I learned to always have aboard with a boat which had a pressure water system was a full spare pump, quick release fittings and quick disconnect/connect on the electrical.

A wife in the shower and no water pressure, can be a bad situation....
 
thataway":3req7how said:
The smaller Bosch water heater is well enough insulated, that it will still be hot enough (for us) the next day.
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DUH! (sound of palm hitting forehead)

Bob, your sentence just had me realize that I had a total misconception of the Bosch heater you and others have installed. Somehow I got the impression that the Bosch was one of those "instant hot" heaters with no tank. I see now it has a 2.5 gallon tank; so really it is just a smaller version of the factory installed 6 gallon unit (and more efficient too I'd bet).

So for anyone reading this thread forget my comment regarding "energy time shifting". Even if it is a real benefit, of which I am far from certain, the smaller 2.5 gallon tanked Bosch unit clearly would provide that same benefit.

Now, I have to re-think this entire project I just completed. :roll:. 2.5 gallons would likely do me just fine, and I see the Bosch units are pretty cheap ($150 on Amazon....not too much more than I paid for the new pump). True, I have little room under the counter for it, but I probably could have made it work somehow. Then I could have removed the Seaward heater and used that space for storage or for a freezer (which I would love to have). Oh well, it works, and I do get the advantage of having the dual uses for the new pump of recir hot water and a spare main pump.
 
I had to have little laugh. With my first 25, I pulled out the 6 gallon tank, replumbed the system and put in one of the "instant" water heaters...Turns out it didn't work, because it was not designed for constant pressure. So I had my "Duh" moment along the line too.
 
Well, I checked under the counter of my galley, and even though I said above "...I probably could have made it work somehow", I don't see a way to install a cube of 14"x14"x11" (the Bosch 2.5 gallon heater) without major surgery. The only way would be to remove the sliding racks that the previous owner installed (David McKibben -- clever man that he is). The racks are extremely useful, so I would hate to give them up.

25_galley_storage.sized.jpg

All this just means, that in spite of my confusion, I am still glad I installed the hot water recir system. It was relatively cheap, takes little room (hangs from under the counter which was dead space anyway), and gives me a backup freshwater pump should the main pump fail.

It does seem to work well in spite of its rube nature :wink: :lol:
 
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