Recirculating pump or POU Tankless?


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Old 12-30-14, 05:49 AM
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Recirculating pump or POU Tankless?

New home, 80 gallon electric water heater approx 50 ft from sink/dishwasher. All water supplies and returns CPVC. Our wait for hot water at the kitchen sink is approx 60 seconds and the excess water is being sent down the drain.

I considering both the recirculating pump (Watts) at local building supply easy to install and priced at under $200 and I'm also considering the Point of Use tankless water heater (Chronomite) for a couple of hundred bucks plus the 60ft of #10/2 and the circuit breaker needed for that job.

Which system have you used with success and which system would you recommend?

Thanks.
 
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Old 12-30-14, 11:22 AM
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I have the same problem at my kitchen sink only my piping is copper. So far (16 years living with it) I have done nothing but to acquire a pump and the piping/fittings to install a recirculating line. It IS a nuisance but the cost of my water is so low as to not have any economic gain in the savings. Since my sewer costs are a single flat rate, rather than a pro-rated charge based upon the water consumption there is no saving in sewerage charges. YOUR situation may be completely different than mine.

I DO have experience in recirculation systems as used in commercial buildings. These are only for the convenience of having hot water almost instantly at the faucet and the energy costs are simply ignored. In a residence these energy costs often will exceed the cost of the water itself even if additional sewage charges apply. In a residential setting the supply and return piping MUST be heavily insulated to reduce the energy costs as well as using a pump that has a small energy consumption. Often the pump is timer controlled so it only runs when hot water usage is expected.

SOME residential recirculation systems, perhaps the one you are investigation, use the existing cold water piping to return the cool "hot" water to the water heater. I dislike such systems as they have a tendency to inject a small amount of genuinely hot water into the cold piping making a shot of hot water out of the cold tap a common occurrence. They ARE easier to install and they remove the necessity of insulating a dedicated return pipe as well as having a thermostatic valve and timer to limit the pump operation. They however also have the disadvantage of sometimes not purging the supply piping of water that has cooled off between uses if the thermostat (at the connection to the cold water) does not cool at the same rate as the water in the supply piping. This will give you a slug of cooler water sometimes from the hot tap.

The point of use heater CAN alleviate these problems and on the surface appears to be the ideal solution. The problems are that you MUST size the instantaneous heater for the maximum flow rate of the faucet, it can only serve one faucet and the temperature rise must be sufficient for the coldest water it will encounter. That often means a fairly high electrical demand, 30 amperes at 240 volts is not uncommon, and all the capital costs involved in supplying that electricity at the heater. Add in that, at least in my experience, these heaters are prone to burning out the elements with the slightest disruption of the water flow and the operating costs can also be significant along with their maintenance.

IF you are interested I will detail the system I will be installing this coming year assuming I regain some semblance of my health.
 
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Old 12-30-14, 01:10 PM
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Furd - Sure, let me know what you plan to do with your system.

BTW, there's a Youtube video from This Old House where Richard installs a small pump with its own on/off button at the sink in need - which is what I would prefer to use since once the hot water reaches the bypass valve, it stops flowing and keeps hot water away from the cold water spigot ... but I can't locate the brand of that product and the one product I found Chilipepper appears to be a poor substitute with lower quality manufacturing along with noisy operation. This Old House did a good job of hiding the manufacturer of the unit they used in their video.
 
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Old 12-30-14, 02:03 PM
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I think a more durable and quiet under the sink pump might be this Autocirc Although it does not have a local on/off switch it does have an electrical timer. This appears to take the place of other pumps as well as other pump's bypass valves.
 
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Old 12-31-14, 11:57 AM
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I've installed only one POU heater under a sink and the homeowner didn't want to pay for a 240 v. circuit, so it was connected to 120 v. Later the homeowner said it was worthless on the lower voltage.
 
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Old 12-31-14, 11:55 PM
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My plan is to install a tee in the riser to the kitchen faucet and run the return piping back to the recirculation pump which will be mounted near the water heater. The pump discharge will be teed into the drain connection of the water heater with a check valve to prevent reverse flow. The recirculation piping will also have a tee to accept piping from my back bathroom as the run to that location is as bad as the kitchen.

The pump itself will be controlled by a timing relay that utilizes a low voltage reset signal. Once triggered the pump will only run long enough to bring hot water back to the pump suction and I suspect this will be a matter of seconds. Once the timer cycles the pump will stop until the timer is reset. At each faucet along the way; laundry room, front bathroom, back bathroom and kitchen I will install a lighted pushbutton switch controlling the low voltage timer reset. The indicator light will signify the pump is running and the pushbutton will be the timing relay reset. In operation I would push the button, the light (and pump) would come on and move the cold water back to the heater.

An additional refinement will be a current-operated switch in the dishwasher electrical supply that will hold the timer in a reset position during the dishwasher cycle. This will ensure a constant supply of hot water to the dishwasher.

Yes, this WILL be a "Cadillac" system but since I already have all the components the cost to me will be minimal. For someone to buy all the components the cost would be high.
 
 

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