Please tell me about home hot water recirculating pumps (for instant hot water)

[LSLGuy]

Here’s an excerpt from a fairly recent post of mine wherein I evangelized about the system I got about 10 years ago.

@LSLGuy

Instant whole-house hot water can be retrofitted easily & inexpensively to any house with no significant plumbing required. I did it to my former McMansion with looong slooow hot water runs a few years ago. This is what you’re looking for:

https://www.amazon.com/dp/B000E78XHG

The black plastic fitting goes under the sink at the end of each run, so perhaps install one device per bathroom, one for the kitchen, and maybe one for the laundry room. It’s a mechanical thermostat valve that interconnects the hot & cold side pipes. It installs past the angle stops and before the lines to the sink faucet. The single pump is installed in the HWH outlet line near the HWH.

The basic idea is the pump provides a small pressure head so the downstream hot water supply is pressurized vs the cold supply. And the remote thermostats are closed when the hot water supply is hot enough but open a connection between the hot & cold supply when the hot side is only warm-ish.

The net effect is when the sink supply is receiving only warm-ish water the valve opens, the pump pushes fresh hot water from the HWH down the line while the used-to-be-hot water in the hot-side pipes returns backwards up the cold-side supply line towards the house inlet where it then returns to the cold side of the HWH. No water is lost.

You can configure the timer on the pump to only run certain times of day so there’s zero energy consumption moving water around and reheating it during the times of day or night there’s no need. Couple that with insulating the accessible portions of your hot supply pipes and you get almost instant hot water anywhere / everywhere in your house for very little installation cost or difficulty and negligible operating cost.

I would totally do that again if I lived in a single-family house or even a condo with long enough pipe runs. I’m not endorsing that brand and model specifically, but just that general concept of a recirc system.

The biggest concern for you is whether you can adequately insulate the hot water lines. If your lines were embedded in a slab, then insulation is out of the question and the operating cost would be noticeably high. Conversely, most of my runs were along the exposed joists in the unfinished basement. So in a semi-climate controlled area and readily accessible to slip foam sleeves over the majority of the hot water line runs. In my case the operating cost was truly negligible even if the pump was active 24/7/365.

The result is not “instant” hot water, but it’s warm in 5 seconds and hot in 10 seconds even 100 feet from the HWH. Magic I tells 'ya!


Here’s a quote of another poster in another thread with cites to potentially useful articles.

Can I Do This Electrical Thing-Water Heater Recirculating Pump

There is a special device that hooks to the hot and cold taps at the farthest faucet. Inside that is a temperature-sensitive device that is open when the water on both sides of it are cold. On demand, or on a timer, the recirculating pump sends hot water through the hot water line, to this valve, and then forces it back on the cold water line. It does this until the temperature valve senses that hot water is now available at the faucet. At this point the valve closes, leaving hot water at the ho…

I’ll also point out that in the part of my post I did not excerpt I mention another handy hot water gizmo: truly instant near-boiling water for your kitchen sink. Super handy for cooking, making tea, etc. Not useful for washing. If that might be of interest to you, check out the rest of my earlier post.