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

Stephen Collette stephen at yourhealthyhouse.ca
Wed May 18 05:27:06 PDT 2011

Thanks for the thoughts Steve's I appreciate them and they make sense, as everything is operator and situation specific and the set up and how long the pumps run, etc, etc. 

Great stuff.



Stephen Collette BBEC, LEED AP, BSSO
Your Healthy House - Indoor Environmental Testing & Building Consulting
stephen at yourhealthyhouse.ca

On 2011-05-17, at 3:00 PM, greenbuilding-request at lists.bioenergylists.org wrote:

> 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

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