Recirculating pump options -- energy waste?


Old 04-12-07, 10:00 AM
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Recirculating pump options -- energy waste?

Hi - I want to add a recirculating pump to get hot water to my upstairs faucets without wasting water. I am trying to decide between a point-of-use recirculating pump -- one in which you press a button and hot water kicks-in in about 40 second -- and a whole house pump that attaches at the water heater. My concern with the whole house pump is that, because it is circulating hot water even when you don't need it, it is big energy-waster. While the pump itself probably doesn't consume much energy, a lot of heat gets dissipated as the hot water is continually traveling through your pipes. I understand that some have a timer, but even still, this approach seems inefficient.

Anyone know if I am overreacting or missing something in my assessment? Any other pros/cons I should consider with each approach. Thanks much.
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Old 04-12-07, 12:09 PM
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No, you've got the angles covered. I only would add that the water pipes should be insulated, but that's a given when doing the circulating systems, unless the pipes are hidden in walls already.

It boggles me the prices they get for a pump with a timer to do these setups; I don't see where the cost is.

I debated about what to do and settled on a homebrew system with Taco pumps for each half of the house (off eBay), Grundfos thermostatic valves under the farthest 3 sinks to shutoff the hot water when it arrives (bought as aftermarket parts) and a call switch in each room that has water along the way (tied to a timing system in the basement).

Link to instant hot water devices:
Old 04-12-07, 12:23 PM
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Well yes the pump is a big energy-waster. If you want to call it that. You can rework the water pipes if you have the room. so you dont need the pump . The water will do the work for you . Have your hot water line go up hill to the last run. Then on the end there put a 3/8" copper line. run it down to the floor and back to the hot water tank. You will have hot water in the supply line all the time..
Old 04-13-07, 01:36 PM
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dwmdc, I'm putting in domestic recirculation. I bought a Grundfos 10-16 and it has both a 24 hour timer, so you can select which 20 minute periods of the day it runs and also a return temp sensor so it stops pumping once the water comes back warm enough to the tank. This is a 25 watt stainless steel circ. You have to be careful not to use an iron bodied pump for this because all of the oxygen in your tap water will quickly corrode an iron pump.

I have no concerns about the pumping costs (the cost of the pump was another matter!). If the pump were to run 7/24 it would cost less than $25/yr @ $0.11/kWh. Typcially it will only be on around 25% of the day, so pumping will be $6/yr.

If it saves me 1 minute a day, that's 6 extra hours I save and I don't have not-hot-enough water running down the drain. Water is still cheap - approx. $5 per 1000 gallons, but the days of cheap water won't last forever. At 1GPM for 1 minute to get hot water, that's 365 gallons or $2/yr for lost water plus the cost of heating it up. I would suspect the actual water losses for my house actually exceed $25/year and that doesn't include the costs of warming up the water to whatever temperature it was as it went down the drain to get treated, even though it was just treated and didn't get used. Such waste...

My sole energy concerns are more on loop losses during the summer. Any loop losses in the winter are a wash. My boiler heats the house and the domestic water so there is no real loss in the winter. In the summer there is. To minimize the summer losses, continuous insulation and a nice loop design with appropriate heat traps will be key.

I'm a great fan of simplicity and love gravity systems, but at the end of the day they are powered by the water heater. You have to have enough heat loss at the end of the loop for the weight of the water to increase enough to pull warmer lighter water from the tank. The tank has to heat the water to make up for those losses.

This will typically work provided there aren't major dips (heat traps) in the loop and when the ratio of vertical height of the loop is sufficient to cover the horizontal spread of the house. Pumps on the other hand, can work in any shaped structure, can be shut off when away or not needed and the draw of a 25 watt circ is less than a cent a week.

Now if only the &^%$#@ pumps didn't cost $200!!! ;-)
Old 04-13-07, 02:01 PM
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You have to heat the water all the time with a pump running also .

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