[Greenbuilding] Ask Pablo: Will a "Water-Saving" Hot Water Recirculation Pump Really Save Me Money?

natural building naturalbuilding at shaw.ca
Tue May 17 09:52:53 PDT 2011


The amount of energy used by the pump is tiny, even if you run it continuously. My pump is rated at 15W so running it for an entire year would only consume a few dollars of electricity.  However, letting the water cool overnight for 8 - 10 hours overnight and during the day for another 6 - 8 hours during the day will dramatically reduce the heat loss compared to having 120 degree water in the pipes constantly.

When used judiciously, I suspect the water saved / energy used equation may be very close. So the advantage of almost immediate hot water becomes a significant factor.

Regards,
Steve Satow

www.naturalbuildingsite.net
naturalbuilding at shaw.ca

On 2011-05-17, at 9:21 AM, Steven Tjiang wrote:

> Running the recirc pumps on an as-needed basis probably doesn't consume that much more energy since the pump power is small and you end up heating the pipes up whether you use or not use a recirc pump.  The water savings, however, is unlikely to offset the installation costs.
> 
> ---- Steve (KZ6LSD)
> 
> 
> On Tue, May 17, 2011 at 7:41 AM, natural building <naturalbuilding at shaw.ca> wrote:
> Pablo's calculations do not seem to include any insulation on the hot-water supply lines, nor do they account for recirc pumps that have timers and aquastats which are available in any reasonable $200 model (Grundfos for instance). Set up properly, this means that the pump is not circulating water during the night or at low-use times of the day which would dramatically reduce heat-loss. He also implies that the pipes are located in un-conditioned space at an average of 52 degrees F. I would suggest this is unrealistic.
> 
> That being said, his underlying argument that they use more energy than they save in water is probably true. But not nearly as extreme as he makes out IMHO.
> 
> Regards,
> Steve Satow
> 
> www.naturalbuildingsite.net
> naturalbuilding at shaw.ca
> 
> On 2011-05-17, at 5:45 AM, Steven Tjiang wrote:
> 
>> Recirc pumps saves water but are an energy waste if run continuously.  Ours has a button that you press manually 30 seconds or so before you use your faucet, and goes off when the hot water reaches the faucet.  Still I doubt the energy savings will offset the installation cost in any realistic amount of time.
>> 
>> ---- Steve (KZ6LSD)
>> 
>> 
>> On Tue, May 17, 2011 at 5:41 AM, Stephen Collette <stephen at yourhealthyhouse.ca> wrote:
>> Here is a link (hopefully it's not scrubbed) on hot water recirculating pumps. Seems according to Pablo, they do not add up. I have one and unplugged mine as I thought (not verified, but eyeballing my electricity bill and guesstimating) that it was costing too much to run. I would be curious about thoughts on this idea from others, as I know we have had discussions in the past on these units.
>> 
>> http://www.treehugger.com/files/2011/05/ask-pablo-hot-water-recirculation-pump.php
>> 
>> If the link is scrubbed, please go to treehugger . com and search ask pablo - hot water recirculating pumps, and you should find it hopefully. or drop this on the end of it. /files/2011/05/ask-pablo-hot-water-recirculation-pump.php
>> 
>> Cheers
>> 
>> Stephen
>> 
>> Stephen Collette BBEC, LEED AP, BSSO
>> Your Healthy House - Indoor Environmental Testing & Building Consulting
>> http://www.yourhealthyhouse.ca
>> stephen at yourhealthyhouse.ca
>> 705.652.5159
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
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