Need under cabinet demand water heater recommend

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Old 05-29-16, 05:44 PM
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Need under cabinet demand water heater recommend

I have 2x 50 gallon water heaters I installed a few years ago so I have all the hot water I could ever need. The problem is that my kitchen sink which is 12' from the water heaters takes 5 minutes to deliver hot water. I dont want to waste as much water as I currently am, its really ridiculous how long it takes to get hot water.
Any recommendations for a durable under counter demand water heater?
 
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Old 05-29-16, 06:32 PM
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Not what you asked but have you considered a gravity hot water recirculation loop? Might be too hard to retrofit and the plumbers will have to weigh in on if it might help.
 
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Old 05-30-16, 04:57 AM
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I would not consider a point of use water heater, but a recirculation system to keep water hot at that point. A point of use water heater will run too much, consume too much electricity for a minimum benefit time. The recirculator will work much better, IMO.
 
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Old 05-30-16, 06:16 AM
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Something here is really screwy and I think it is the original post. If the faucet is only twelve feet from the water heater and it is plumbed with 3/4 inch nominal type M copper the total volume of the piping would be about 40 ounces or a cup over one quart. If it is piped with 1/2 inch nominal type L copper the volume would be about half, a pint plus a half-cup.

Using the latter volume if it takes five minutes to get hot water the flow rate would have to be about four ounces (a half-cup) per minute. At that rate it would take eight minutes to fill a one quart pitcher or a full half-hour to fill a pot with a gallon of water to cook a pound of pasta.
 
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Old 06-01-16, 11:17 AM
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Well, O.K I was being a tad dramatic to emphasize the point, but it does take 2 1/2 minutes to get hot water from the kitchen tap.

Im not familiar with a gravity hot water recirculation loop but in researching it I discovered a thread which indicated it wasnt appropriate for a slab home, for whatever reason...

This from the article: "For a gravity recirculating loop to work properly, the water heater must be located at the bottom of the loop. Ranch houses and two story houses with basements are perfect candidates. Houses built on slabs or that have hot water lines below the water heater must use a simple in-line recirculating pump." - My home definitely has water lines below the water heaters, in and below the slab.

Gravity Hot Water Recirculating Loops | Ask the Builder

I guess I'll have to do more research.
 
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Old 06-01-16, 01:43 PM
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From: Hot-water circulation loops
The only type of hot-water circulation loop worth considering is a demand-controlled system that uses a pump activated by a switch near the fixture with the longest wait time. Demand-controlled systems were developed by ACT Metlund, a company that sells the required pumps (called D’Mand pumps) and that licenses other companies (including Taco and Uponor) to sell D’Mand kits. The cost of such a kit is about $520.
 
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Old 06-01-16, 03:39 PM
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Well, your numbers are still from outer space.

I just measured the time it takes to get hot water at my kitchen sink. I had not run any hot water for several hours and it took 44 seconds before the water was noticeably warm, meaning it had a temperature in excess of normal body temperature of 99 degrees F. It took a full 60 seconds until the water was too hot for me to hold my finger in the stream. I have my water heater set to about 140 degrees F.

My water heater is about 25 feet from the kitchen sink measured in the least possible dimension but the way the piping runs is considerably further. Knowing how the piping does run I used a tape measure to guesstimate the total piping run. From the faucet to the tee where it branches off to the back bathroom is about 22 feet of 1/2 inch type L copper. From the tee to the water heater is about 20 feet of 3/4 inch type M copper. I did not remember to add the roughly five feet the piping rises from the crawlspace to the water heater outlet.

Running the numbers the piping between the water heater and the sink holds a little less than one gallon. My Moen faucet has a flow rating of about 1-1/2 gallons per minute. That would mean that I would have to run the water for a full minute before I would get water from the heater outlet to the faucet spout and indeed that IS what happens.

In your case the numbers simply don't add up. You MUST have a whole lot more than 12 feet of piping from the water heaters to the faucet OR you have huge pipes that contain a whole lot of water, OR you have a faucet that for some reason is flowing a tiny amount of water. My GUESS is that the flow rate is your problem. Are the shut-off valves beneath the sink wide open? It the aerator on the faucet spout clear? Do you have water with a high mineral content AND no water softener?

Standing around waiting for the water to get hot seems like it takes forever, I know that well. I don't think a day goes by that I am not irritated by that full minute to get hot water at my kitchen sink. I have all the parts necessary to install a recirculating system but I haven't done it because I also know that while it will increase my comfort it will also increase my gas and electrical bills, even with an "on demand" system. Now theoretically it would decrease my water bills but assuming I run the water until hot ten times a day that would mean wasting about 900 gallons every two-month billing cycle. However, my water cost is so low that even though it is a significant percentage of my total consumption, likely 20%, the savings on the water would only amount to about $2.50 a month. Guesstimating my additional energy costs would likely drop the savings to less than $2 a month.

Your numbers, of course, will be somewhat different but in most cases the advantage to having nearly instant hot water at the faucet is going to be almost all in comfort and nothing on an economic basis.
 
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Old 06-01-16, 05:11 PM
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You could get a cheap 2 gallon WH, and connect inline to the house hot water and the sink and see if that helps. Basically a $150 experiment. If it bothers you this much $150 should be a cheap test.

Or measure the amount of water till it runs hot and buy that size WH.
 
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Old 06-06-16, 05:09 AM
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The amount of water needed to be drawn from the tap before hot water comes out is larger than you would think.

After the first slug of cooled down water sitting in the pipe comes out, the next slug of water loses much of its heat warming up the pipe. Only after the pipe itself has been warmed up does hot water come out of the tap.

So if the pipe between the water heater and the tap hold about a pint of water, you need to draw two pints (more or less) before the water coming out is hot.

Usually it is not a good idea to install a water heater under a counter. Sooner or later (long before plain pipes do) it will leak or break down and you need to be able to get in there to replace it.

(copied from another forum) When running the water waiting for it to get hot you could catch the water in a pitcher, pour it into a nearby bucket, and use it to flush a toilet or water shrubs outside.
 
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