Reduces the energy used by a
recriculating hot water system by up to 90%

What is Circopt?

Circopt reduces the amount of time the booster pump runs in a recirculating hot water system without needing to learn or predict user schedules or habits.


In a typical recirculating hot water system, a booster pump is kept running in order to ensure the availability of hot water. While reducing water use, energy is consumed by the pump and water heater, even when there is no demand.

Circopt only runs the pump when hot water is being used. It turns the pump on when it detects draw. The existing hot water in an insulated recirculation loop meets the initial demand while the booster pump catches up. This ensures a continuous supply of hot water. After being activated, Circopt periodically checks if water is still being drawn, and leaves the pump on or turns it off, accordingly.

Because Circopt only turns the pump on when hot water is needed, pump running time can drop from as much as 24 hours per day to as little as 3 hours per day. This means a savings of up to 90% on pump energy usage alone.

The Opportunity

I'm currently seeking a partner with experience in the field of recirculating hot water system testing and development to validate its efficiency in a controlled enviroment and proceed with commercialization based on those results.

The Circopt Story

Back in 2012, I completed a major renovation of my house, which involved a complete re-plumbing; and, well, re-everything. Rather than install another traditional tank-based water heater, I went with an on-demand hot water heater tied into a recirculating hot water loop.

Recirculating Basics

In a recirculating hot water system, the hot water line forms a loop through the entire house, circling back on itself. Set in this loop is the water heater, which heats water as it passes through; and, a booster pump, which ensures that hot water is being distributed through the entire loop.

This is a very good thing, especially in drought-ridden California, as you waste less water waiting for hot water to arrive at your faucet.

The Problem

In becoming familiar with this new system, I started to realize it contained a serious inefficiency: the booster pump needs to be running for the heater to activate and keep the entire loop stocked with hot water.

This means that booster pump is likely always on, using power, activating the hot water heater, and generating noise. Needless to say, this was a problem, as I could hear the energy being wasted from my living room.

Some Not-So-Awesome Solutions

When I looked into solutions for reducing pump usage, I found a few options:

1. Put the booster pump on a timer so that it is running when you are home and awake.

2. Run the pump when the temperature of the water in the loop drops below a specified threshold.

3. Install one or more buttons, or a remote, which you use to active the pump for a set period of time, eg. 10 minutes.

Options 1 and 2 still run the pump even when there is no demand. Option 2 also requires installing a temperature sensor, likely at the most distant point in the loop. Option 3 is not intuitive or user friendly. Finally, options 1 and 3 don’t account for hot water usage during off hours or by machines, like dish or clothes washers.

I ended up cobbling together a modified version of the first option: my pump was controlled by my security system using a Z-Wave plug. The security system would turn the pump off late at night and then back on early in the morning. Additionally, it would turn the pump off and on with arming and disarming the system.

Still, this solution suffered from the same deficiencies mentioned above and the booster pump was running far more often than I was using hot water.

A Happy Failure

For a few months I lived with my imperfect solution.

Then, one day I came home, disarmed the alarm, turned on the hot water to my kitchen sink and enjoyed instantaneous hot water. Yes!

For a couple of minutes. Then it turned cold. No!

The Z-Wave signal had failed, and the pump hadn’t turned on. So, why did I have those first few minutes of hot water?

The recirculation loop was insulated and had held enough hot water to trick me before I realized there was a system failure.

This got me thinking.

A Better Way

Since the recirculation loop held enough hot water for immediate use, the booster pump didn’t necessarily have to be already be running when I required hot water.

Instead, the booster pump could turn on when I started using hot water, taking advantage of the hot water in the loop before catching up. When I stopped using water, it could then turn off.

Thus, in 2013, I designed a system which turns on the booster pump when it detects use by sensing the activation of a flow meter. It then periodically turns the pump off to check if hot water is still in use. If so, the pump is turned back on; and, if not, it remains off.

Design to Prototype

Living in the world of software development, it took me another few months before I was able to understand enough about hardware, plumbing, and electronics to build and install a functioning prototype.

Once installed in my house, I was, and still am, thrilled with the results.

I always have instant hot water and my booster pump hardly ever runs. With the help of Porter, I’ve been crunching my own numbers and, in total, the pump runs for about 3.5 hours per day as opposed to 8 to 24 hours per day. I’m optimistic that with further tuning I can reduce that even further.

The Road Forward

With Circopt working and worthy, I’m now navigating the road to commercialization. I’ve never launched a hardware product before, so this is an exciting new adventure.

I’m certainly not able to go this alone: if you or your organization has experince developing and validating new technologies to save water and energy, let’s connect.


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