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Hot water recirculation issues at a new home

user-750885 | Posted in Energy Efficiency and Durability on

First the construction facts:

1 Slab on grade house in north Georgia.
2 PEX material water supply run significantly under the slab (I have no confirmation as to whether the plumber insulated the water lines or not).
3 Water heater in the garage.
4 A hot water recirculating loop run and a recirculating pump in place.
5 A timer installed for the recirculating pump.

A couple of scenarios:
On my first visit the home, the homeowner had occupied the home for only a few weeks. I found that the recirculating pump had been running “24-7” for those few weeks.

The homeowner identified some warm spots on the floor ( where the floor covering was 3/8″ glued-down engineered wood flooring.) We verified no leaking in the supply lines (from a visual of the water meter when all valves were closed.)
Also, when turning the cold water on at the kitchen sink and at the bathroom lavatories the water came out cool, then a little warmer and finally cool again.
These two performance characteristics were very upsetting to the homeowner.
I suggested that the timer for the recirculating pump be set for times when hot water is likely to be demanded.

On my second visit a couple months later, the homeowner had turned off the recirculating pump.
When we drew cold water from the kitchen sink, no cold to warmer to cooler issues were noted.
However, it took a couple of minutes for the hot water to reach the kitchen sink.
There were no warm spots in the floor.
The homeowner is now upset that water is being wasted waiting for hot water to produce. The gas bill is now much lower (gas water heater) since continuous heat loss in the hot water line is limited.

My suggestion is to use the timer and / or install a D’MAND hot water circulating system (button or switch engaging).

I’m not sure what home builder performance / warranty issues may be in play.
We are getting the plumber to check the manifold (currently behind drywall) to see if any crossed hot and cold lines occurred as well as a check valve and couple of other things.

I’m also not sure what will satisfy the homeowner.

Any other ideas?

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  1. GBA Editor
    Martin Holladay | | #1

    The solution is to install a demand-controlled circulation pump (not a pump on a timer). Here is a link to an article that discusses the problem:

    Hot water circulation loops.

    To investigate whether the hot water lines are insulated, go to the garage and look at the penetration in the slab where the hot water line from the water heater penetrates the slab. If you can see insulation around the PEX tubing, then the hot water tubing runs are insulated. If you can't see insulation at the penetration, you have to conclude that the lines are uninsulated (which is probably a code violation).

  2. fourforhome | | #2

    Tom, I had my house plumbed for a recirc because I didn't want to fill my septic tank just to get hot water to the tap. The Grundfos I have has all those annoying pins that are difficult to change when the daily schedule changes.
    My solution was to install a TP-Link HS100 Wifi timer and the Kasa app that goes with it.
    I leave the Grundfos plugged into the timer and leave it ON and then control it with the app. The app can be scheduled any way you want AND it can be turned on and off on demand.
    I can turn the pump on and schedule it to turn off in 5 minutes and have hot water at the all the faucets within 90 seconds. ( I did insulate all my pipes, so the water is comfortable even after the pump is off for 45 minutes.)
    This is a cheap and easy solution to reduce waste if the owners don't mind using their smart phones to wash their hands.

  3. Jon_R | | #3

    I installed a small electric heater under the kitchen sink. 3 seconds.

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