We deal with this problem all the time.
- I would recommend an on-demand hot water recirculating pump to solve your problem.
- While theunder-sink tankless water heater is great in situations where instant hot water is necessary, these systems are the least efficient.
- Also, they are going to have the highest operating cost.
If you simply want to stop wasting water, the recirculating system is the best option for you.
On-demand vs. timer
Assuming you do go with a recirculating system, the next decision you have to make is about the kind of pump to put in. These systems can either be equipped with a:
- recirculating pump that works in true on-demand mode, or
- the recirculating system can run continuously on a timer.
Obviously, the on-demand pump is the most environmentally friendly option, as it only operates when it is needed. One product we install a lot here at Recurve is the Metlund Hot Water D'Mand system. The pump eliminates waste water by only allowing water out of the faucet when it is at the desired temperature.
- On average it takes 30-45 seconds for the hot water to be available at the sink.
- The pump may be operated by a switch placed next to the fixture, by a remote switch, or by a motion sensor.
- An added benefit of a circulation pump is that you get hot water readily available to all sinks on that plumbing line, unlike the under-sink option where you get hot water to only one sink.
If the 30-45 second wait is unacceptable, a continuous pump may be used to make hot water available immediately. These operate just like an on-demand pump, except they are running continuously instead of only when needed. If you opt for this system, make sure to put it on a timer so it is only running during peak usage hours.
Electric tankless
Another option is the electric under sink on demand heater, which is preferable in cases where the homeowner needs instant hot water and cannot wait for the on-demand pump.
- The downside for these systems is that they are very inefficient and will cost you a lot on your electric bill due to their heavy electrical draw when activated -- most under sink models use at least 3,000 Watts when called.
- For this reason, we rarely install under-sink electric heaters.
Making a good decision
Summarizing, the key variables when making this choice for your home:
- installed cost,
- ease of use,
- energy savings, and
- water savings of each option.
The installed cost of the recirculation pumps are about the same, with the under-sink electric water heaters usually being slightly cheaper.
For ease of use, the under-sink tankless heater and continuous recirculation pumps are the best options because the hot water is available instantly and it's as easy as turning on the faucet, while an on-demand recirculation pump requires the user to wait 30-45 seconds for hot water delivery.
In terms of water savings, all three eliminate wasted water and are equally effective in doing so.
In regard to energy efficiency, the on-demand recirculation pump is the most efficient option, the continuous circulation pump is in the middle, and the electric under-sink heater is the least efficient as it draws over 3,000 W whenever it's called.
For more information:
Check our hot water recirculating Q&A to see what other homeowners and contractors are saying about on-demand pumps, continous circulation, etc.