Here’s what I have. A 6 gallon water heater with a recirculating pump that uses check valves that route the water back through the cold water lines. I have this at three locations. I wouldn’t recommend the company I used but the system works great. The only downside is that there is no way to do the showers unless you tear the walls apart.

I have a rather large house up here in the Frozen north and the time it takes to push out the cold water and start the flow of hot can be ages (it seems) So naturally I asked the same question. I found that My Rheem water heater is of an age that it can not be upgraded with a pump. While that might not be in your case it does require a plumber to determine if it is possible.

Assuming you have dual sinks in the master bath just open both hot water faucets and shower. You will get hot water in 30 sec and about a gallon down the drain. Shut off the faucets and take a hot shower. More flow (demand) makes the on demand system kick in to high heat. You can hear outside it if you want to experiment with it.
Might want a small heater under the kitchen sink if that’s an issue.

That is somewhat inaccurate. Yes a tankless system does not store hot water. But water is stored in the pipes from the heater to your various faucets through out the house. When you call for hot water that water in the pipes is typically cold and that's what you get until the new hot water can push it out of the faucets. A recirculating pump removes that cold water and pushes it back into the cold water in front of the water heater. Without the cold water in it's way the hot water can reach the faucets faster.

Different System
 

You are not describing a Watts system which has been retrofitted to an existing house. The Watts system uses a low pressure pump to move water from the water heater through the hot water line to a manifold (valves) placed at the faucet or fixture furthest from the water heater. When the cold side of that faucet or fixture is turned off, the valves in the manifold direct the hot water into the cold water line which carries it back to the water heater. If the cold side of the furthest faucet or any cold side of any faucet in the system is open, the valve in the manifold closes and the hot water flow is stopped. The Watts pump is very low pressure, 2-3 lbs, and the pressure in the cold line is 30-50 lbs, which means that flowing cold water will always control the valve in the manifold.

In contrast to a Watts pump that has been fitted to an existing system, in new construction a separate return line (the 3rd line-hot, return, cold) is installed and the water being pushed by the Watts pump is returned to the water heater by the separate return line and not the cold water line.

When the Watts system is installed in an existing house and the cold water line is used as the return line, the water at the faucet on the cold side will be warm when first opened and will remain warm for the 30 or so seconds it takes for cold water to purge the hot water which has been running in the line. This is the exact opposite of waiting for hot water to reach the faucet when there is no recirculating system. I much prefer having hot water in a 2-3 seconds after opening the faucet and waiting 30 seconds for cold water than waiting 30 seconds for hot water.

Existing houses can have a separate return line installed, although it is expensive. Usually, this would be done in a house with a basement where the pipes are readily accessible. When the house is on a slab and the water lines are installed in or under the slab, it is not practical to install a 3rd line, hence, the ingenious manifold made by Watts which directs the hot water being circulated by the Watts pump into the cold water line and then to the water heater in a closed loop.

Not An Improvement
 

So, when your friend wants to take a shower, he has to find his phone, use it to send a signal to start the pump and then wait for the 30 seconds or so for the "instant" tankless heater to send hot water to the shower. How is that better than just turning on the shower and waiting 30 seconds?

recirculation Pump with a Tank less Hotwater Heater
 

Ok, A thankless hot water heater takes water from the feed and, On Demand, heats it and it flows to the open valve, eg the shower, a sink etc. What, exactly do you think you are going to recirculate, and if you recirculate it where are you goinng to recirculate to? To a tank, then what? Are you going to heat it again?

The plumbers I spoke with said that this system, not brand, see post 16, is the only way to get instant hot water. I mentioned in my previous post that you can’t do it in the shower. So not instant but much quicker. By the way, not cheap. I would gladly have a tank style heater any day, but still have a recirculating pump. Had that at my last two homes in Ohio. JMO

No, most have either a google speaker or alexa speaker where you can set up a routine called "hot water" or whatever you prefer. The routine will turn on the water heater pump for "x" minutes, however long it takes depending on you home, then turn it off. So, when you need hot water for anything like a shower, just say "Hey Google, Hot Water" and by the time you get ready, your shower water will be hot since the circulator pump and by-pass device will have had enough time to push hot water through your pipes.

Works great, simple to set up and uses the least amount of water and energy to get hot water to your shower for example.

Here in the Villages, there might be some larger homes where other solutions might be needed but the Watts circulator and bypass valve solution works well and you don't have to spend a lot of money for a localized hot water heater. The trick is to connect it up to a wifi switch and then control it with your Google or Alexa speaker which many have. If not, for around $50, you can get one on Amazon and set it up.