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Hot water recirculating pump to conserve water
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smckean (Tosca)



Joined: 18 Jan 2014
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City/Region: Guemes Island (Anacortes)
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Vessel Name: Tosca
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PostPosted: Tue Feb 25, 2020 8:05 pm    Post subject: Hot water recirculating pump to conserve water Reply with quote

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?
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journey on



Joined: 03 Mar 2005
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City/Region: Valley Centre
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PostPosted: Tue Feb 25, 2020 8:52 pm    Post subject: Reply with quote

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
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thataway



Joined: 02 Nov 2003
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City/Region: Pensacola
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PostPosted: Tue Feb 25, 2020 9:18 pm    Post subject: Reply with quote

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!



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.

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Thataway
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TyBoo



Joined: 23 Oct 2003
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PostPosted: Tue Feb 25, 2020 9:42 pm    Post subject: Reply with quote

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!

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thataway



Joined: 02 Nov 2003
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PostPosted: Tue Feb 25, 2020 9:55 pm    Post subject: Reply with quote

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.
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smckean (Tosca)



Joined: 18 Jan 2014
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City/Region: Guemes Island (Anacortes)
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PostPosted: Tue Feb 25, 2020 11:23 pm    Post subject: Reply with quote

Thanks for the feedback.

journey on wrote:
Centrifugal pumps which are cheap just suck in the water and expel the stuff at higher pressure, so you'd need a check valve.

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.

Quote:
You would have to route the return line back to the hot water tank to replace the water you're drawing out.

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 wrote:
I feel the solution is to get rid of the 6 gallon water heater with dual lines.....

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 wrote:
First off, I think your idea is brilliant!

Embarrased Embarrased Embarrased Smile
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Micahbigsur@msn.com



Joined: 27 May 2019
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PostPosted: Wed Feb 26, 2020 12:38 am    Post subject: Reply with quote

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.
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outbackbill



Joined: 23 Apr 2011
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PostPosted: Wed Feb 26, 2020 8:45 am    Post subject: Reply with quote

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.
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Peter & Judy



Joined: 03 Dec 2014
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PostPosted: Wed Feb 26, 2020 10:18 am    Post subject: Reply with quote

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.

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Micahbigsur@msn.com



Joined: 27 May 2019
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PostPosted: Wed Feb 26, 2020 10:52 am    Post subject: Reply with quote

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
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smckean (Tosca)



Joined: 18 Jan 2014
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PostPosted: Tue Jun 09, 2020 10:19 pm    Post subject: Reply with quote

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.)



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.



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.



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.

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thataway



Joined: 02 Nov 2003
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PostPosted: Tue Jun 09, 2020 10:59 pm    Post subject: Reply with quote

Nice install! Glad it works!

I would disagree with:
Quote:
1. It takes a lot less room
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.
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smckean (Tosca)



Joined: 18 Jan 2014
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PostPosted: Tue Jun 09, 2020 11:09 pm    Post subject: Reply with quote

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)
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TyBoo



Joined: 23 Oct 2003
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PostPosted: Tue Jun 09, 2020 11:12 pm    Post subject: Reply with quote

Good job, Rube!
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smckean (Tosca)



Joined: 18 Jan 2014
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PostPosted: Tue Jun 09, 2020 11:15 pm    Post subject: Reply with quote

Thanks Tyboo. Believe it or not, I remember your "rube" comment. It helped motivate me to get it done. I love the challenge of rube-type projects Wink Laughing
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