Hot Water Circulating Pump ?

[stillbuilding]

Have a 66' boat with 4 bathrooms / showers. Piping is 3/4" circuit with short branch lines. Is it reasonable to include a circulating hot water pump to overcome the delay in hot water arrival and reduce wastage? This would require insulation of HW piping of course.

[atoll]

might be better to reduce the diam of the hw piping and have very good insulation,a circulating system is going to act like a radiator system constantly loosing heat to the boats interiour.

[Juniper]

Are you planning on runnin this pump 24/7 or just have a momentary switch to just get hot water there without wasting it?

[stillbuilding]

Originally Posted by Juniper

Are you planning on runnin this pump 24/7 or just have a momentary switch to just get hot water there without wasting it?

I was thinking of activating the circulation pump only in anticipation of use and then closing down after. I accept that there will be some radiation heat loss but there is some of that anyway.

[atoll]

Originally Posted by stillbuilding

I was thinking of activating the circulation pump only in anticipation of use and then closing down after. I accept that there will be some radiation heat loss but there is some of that anyway.

3/4"piping sounds like overkill,better off going 10mm plastic +sleve or copper pre insulated @ 2.5 bar.

are you going to the arctic!

[Sailmonkey]

We have just such a pump in the house. It's fantastic, when on the delay for hot water is 1/2 a second or so. The drawbacks..............the pump causes the water heater to run almost continuously, so it's only on for morning showers and evening dishwashing. I'll assume on your 20M boat that a generator is running whenever there is a demand for hot water?
This is what's been in use in the house for several years.Circulator Pump, 1/40 HP, 115V, 0.52 Amps - Hot Water Circulating Pumps - Hot Water Circulating Pumps - 3GZW3 : Grainger Industrial Supply

[stillbuilding]

Originally Posted by Sailmonkey

We have just such a pump in the house. It's fantastic, when on the delay for hot water is 1/2 a second or so. The drawbacks..............the pump causes the water heater to run almost continuously, so it's only on for morning showers and evening dishwashing. I'll assume on your 20M boat that a generator is running whenever there is a demand for hot water?
This is what's been in use in the house for several years.Circulator Pump, 1/40 HP, 115V, 0.52 Amps - Hot Water Circulating Pumps - Hot Water Circulating Pumps - 3GZW3 : Grainger Industrial Supply

I accept Atoll's thinking and will change to 1/2" insulated pipe. Well, the Aleutians and Alaska anyway as a first trip anyway. Really not so much into cold so around the North Pacific will do thanks Atoll!

I have had such a circulating pump in a large double story house and found it similarly attractive especially combined with an automatic pre-mixer to get a non-scalding hot water temp. Which is why I was wondering about the yacht. Thanks for the link to the pump.

[knottybuoyz]

I'm not so much worried about wasting heat as wasting water. My boat will be a little less than half the length of yours and I was planning on adding a diverter before the shower head that would bring h/w from the tank and route it back to the f/w holding tank. A temp guage would show me when the h/w had arrived so I could divert the flow to the shower. That way no f/w gets wasted down the drain. FWIW

[sailorchic34]

Here's a link to a hot water circulator that installs under a sink. It uses the cold water line to return the hot water to the tank, so no extra piping to run. Includes a temperature sensor and a time clock so it only runs when you want and only runs enough to keep the hot water hot. It does not run all the time so saves energy too.

Should work well on a boat too.


Undersink Instant Hot Water Circulating System-ACT-E1 at The Home Depot

[atoll]

we are 63 ft and have 10mm hard plastic pipe,normally wait 15 seconds before running hot aprox 1/2 liter waste which is collected in a bucket for use flushing the toilet when the tide is out(we dry out twice a day against a quay wall) so no waste at all

[twistedtree]

One down side of HW circulators is that they can result in heated cold water. We have this in out house, and the instant hot water is great, but when it's on I have to run the tap for a while to get cold water. Mind you, I like my drinking water cold, not luke warm and not warm. In our case we have a dedicated return loop for the hot water, but the cold water pipes still get heated by proximity to the hot water pipes. Using a mechanism that returns the hot water through the cold water pipes will be much worse.

Lessons learned are to 1) use a dedicated return loop, and 2) be sure both hot and cold pipes are well insulated.

[sailorchic34]

Well the idea of the undersink circulator, is that it only runs till you have hot water at the pump, then it shuts down. If the cold water line is not insulated it will cool down pretty quick. Plus it has a time clock so you can set it to only run some times of the day.

Its not perfect put sometimes it works ok. I've specified it a few times on some residential design jobs.

Oh agree a dedicated hot water return is better, just sometimes not easy to install in a completed house or boat. Sometime the Hot water return is Value engineered (hate that term btw) out... to save a few dollars or pounds or Euro's

[sailorchic34]

Oh, it could be that your house may have a bypass installed between the hot and cold somewhere. For testing purposes plumbers will install a cross connection between the hot and cold to pressure test the piping. Sometimes its forgotten and not removed. Also if you have a hose sprayer on a kitchen sink, one with a on / off control at the spray head, then you can get hot water into the cold side. Happens alot with commercial kitchens. Well If I'm not the one designing it anyway...

Unless the hot and cold water piping is touching the cold water pipe for quite a ways, I don't see the hot water heating the cold water. All the times I've seen it it's been a cross connection either in a faucet design or a somewhere else. Its not at all uncommon. BTW Plumbing engineering design through construction is one of my many talents.

[sailorchic34]

Oh darn thread creap......

last thing on the house with hot water in the cold side. 1. Is there a check valve on the cold water line at the water heater prior to the hot water return connection. 2. If the water heater is in the basement then you may need to put a heat trap (A U bend say 20" deep on the cold water line to the water heater.

As the hot water return ties to the cold side of the water heater, you can get gravity circulation in the cold water line. That is Hot water will rise up the cold water pipe caused by the hot water returning via the hot water return line..

[twistedtree]

sailorchic34,

I'll be home in a few days and will drop you a note with the details of the system design. I don't want to rely on my memory. I'd welcome the help improving it. It's 100% new (house renovation) and I have to admit to being a bit disappointed at the cross-heating. I've done lots of plumbing, but not this house, plus the instant-on heat is new to me.

Thanks,

Peter