Recirculating hot water
 

Fellow Villagers,

The plumbers roughed-in the plumbing for our new home in Well Point yesterday. We opted for recirculating hot water for our tankless heater. Does anyone have experience with how these things are plumbed for new construction?

From the installation manual, there appears to be two acceptable methods: using a dedicated return loop; and, a cross-over valve. The cross-over valve uses the cold water lines as a return path while the dedicated return loop is, well, dedicated to bringing the water back to the heater.

My question is, “how is the system plumbed for new construction?” Dedicated return or a cross-over valve?

The dedicated return seems better to me for some reason.

The water lines in my current Florida home run through the attic. In the summer, the cold water is very warm and in the winter is damned cold. I’ll have warm cold water year-round with the cross-over valve, I fear. (Albeit for just a short while.)

Suggest trying to contact the construction supervisor for your home.

In case not aware, Water heaters are typically placed on the garage wall near the gas meter. Usually the furthest place from point of use.

The number of pipes there could be a clue.

I wish I had contact information for any of those people!

The attached photo shows four fresh water lines originating (or terminating) at the corner of the garage. I’m still analyzing which way all the pipes go.

Kinda sounds like you are doing a custom build…..

If so call your designer (who you worked with) ….or even your realtor.

We have on on the house we bought. It has an electric WH. When we moved in the prior owners had it circulation 24/7. I am sure we saved water but it used quite a bit of electricity. I changed the timer so it circulates only certain times of the day.

When we built we also opted for a recirculating water heater. They ran a dedicated return line from the farthest point of use.

Supervisers number & name may be on the permit posted at the front of the house.

Thanks. I expect that to be the case, but I’m watching the house come out of the ground from the Florida panhandle. My eyesight isn’t quite that good. ;)

Recirculating water defeats the purpose of having tankless, as all the water lines become a virtual tank and your heater will run a lot more. You will save water but use a lot of electricity. Adding a timer as JRcorvett suggests is a good idea.

I agree. A timer is a feature in the model of tankless heater being installed. I appreciate the analogy of the how water lines effectively becoming the tank.

“Recirculating water defeats the purpose of having tankless” is not true. Recirculating water is beneficial to both a hot water tank or going tankless. A tankless gives you instant hot water at the tankless unit in the garage, it takes minutes to get the cold water out of the lines to your shower or tub. Tankless heaters you are not heating the tank 24/7 when not using/needing the water plus you still have to wait this hot water to get to your shower or tub.
We’ve had recirculating water in our last couple of houses and the most critical part of this system was setting the recirculating pump temperature correctly: too high an the pump will run constantly and keep asking the water heater/tankless heater to keep heating the water, too low of a setting, you will have colder water in the lines. I always had this pump setting a couple degrees cooler than the tank/tankless heater.

Adding a recirculating pump (in a timer) and a cross-over valve on your furthest fixture will accomplish the same thing. I checked into adding this on our build, but the $8200 cost was insane. Tho a dedicated return line buried in the slab was their method. This method should be less than $500 installed.

For those that have installed the recirculating pump with timer and crossover valve, does that cause the water in your cold water lines to always be quite warm?

Our recirculating water heater can be programmed to circulate only at certain times. It also has a “learning” mode. It’ll adjust according to your average usage.

$8,200?! Wow! I wouldn’t have done it at that price either. When we built in 2021 it was only an $1,800 up charge.

Hot water recirculating is just another thing that I don't need, along with a water softener, water filter, or painted concrete. In these threads, I have never seen an actual calculation of how much money, if any, you can save. I can wait 40 seconds for hot water to reach my shower. If you can't wait, turn on the hot water faucet and the hot water will come faster.

Only the tank is now at every point of use inside the house instead of in the garage. And your tankless will never run out of hot water.

If a tankless water heater will never run out of hot water, why do they come in different sizes?

Why recirculate cold water?
 

Circulation systems make the hot water from the tank available instantly through out house. There is no hot water in a tankless system until the heater turns on when a faucet is opened At that point you still have to wait for heated water to get to the fixture in use What am I missing here?

Volume. Obviously a household unit doesn’t produce enough hot water to supply a hotel. Depending on outside temperature our unit can produce about 11 gallons a minute. We will never run out. You get the unit that meets your usage requirements. But I’m pretty sure you already knew that.

ChatGPT gives you a direct ; we’re googling gets many links
 

I copied and pasted your post directly into Chat GPT. It provides a direct answer instead of providing many links (and ads) to help you search for the answer.

ACCORDING TO ChatGPT -

“Your reasoning about the advantages and disadvantages of the two recirculation methods is spot on. For new construction, a dedicated return line is generally considered the superior option, provided it’s feasible within the budget and construction plan. Here’s why:

Dedicated Return Line
1. Efficiency: This system keeps the cold and hot water supplies completely separate, ensuring you always have actual cold water when needed.
2. Consistency: A dedicated return line provides more consistent recirculation without affecting the temperature of the cold water line.
3. Energy Savings: When paired with a recirculation pump controlled by timers or motion sensors, it minimizes energy and water waste.

Cross-Over Valve
1. Cold Water Warming Issue: As you mentioned, a cross-over valve uses the cold water line as a return, which can temporarily result in lukewarm “cold” water. This is especially noticeable if water sits idle in the pipes for a while.
2. Simplicity: It’s less expensive and easier to retrofit into existing homes since it doesn’t require additional plumbing for a return line.

In New Construction

For a new build like your Well Point home, the dedicated return line is likely what was roughed in, as it’s the most appropriate choice for construction from scratch. It aligns with modern energy-efficient and comfort standards, especially in areas like Florida where water temperature fluctuations are noticeable. You might want to confirm this with the plumber or builder to ensure it matches your preference.

Additionally, ensure the recirculating pump is configured correctly (e.g., timer-based or demand-activated) to balance comfort, energy use, and longevity of your tankless heater.”

Not sure how
 

Not sure how they plumb their version of recirculated hot water but I'm sure it's not the way I would do it. I would use a flow detection switch in the hot water outlet line that would energize the circulator. When the hot water is turned on the circulator will come on and charge the loop with hot water. When hot water returns to the water heater an aquastat will sense the hot water has charged the entire loop and turn the circulator off. The circulator will charge the loop faster than purging all the cold water in a conventional system. The water heater doen't run unless needed saving on gas usage. Water waste is minimal. I don't see the Villlages builders doing it this way due to the price of all the components. I would get in the car and get on site to see what's going on. Good luck with your build.

Sort of. But, a tank water heater works the same way. If you have a large enough tank and heating element for the volume you use, you will never run out of hot water. So, in terms of never running out of hot water, both systems can achieve the same result. If you have a large family and a small tankless water heater, you will run out of hot water.

Your new circulating pump is going to be costly to run, even if you have a timer, for certain times of the day, when you need to shower. I had one and disconnected it.

Call Mike Scott Plumbing - they do just about all of the new construction plumbing. Very friendly - they'll answer all your questions.

After 21 years our 40 gallon tank water heater sprung a leak. I looked at tankless as a replacement. I chose another old fashioned tank type water heater. Other than springing a leak, there is little to go wrong. No motherboards, no timers, the only thing electrical is the igniter (gas heater) which we would need for the tankless anyway. At the cost of gas here, with a two person household, the energy savings with a tankless would not likely recover the cost in either my or the water heater’s lifetime. The device is located in the garage, not more than six inches from the master bathroom shower head. Hot water can not be much more instantaneous than that.

Difference between being sized for maximum expected flow rate and maximum expected volume. The tankless heater is sized for the rate of flow regardless of the volume used. The tank system is sized for the volume used regardless of the rate of flow.

A recirculation system ensures that hot water is at the tap when you turn it on. It does this by asking for hot water until the temperature at the fixture reaches the set point. Water isn't wasted by flowing down the drain; instead, it is sent back to the heater (recirculated).

With a hot water tank, the recirculated water goes back into the tank and the heating element runs as necessary to keep the tank at the right temperature.

With a tankless system, the element runs every time the recirculation system calls for more hot water. Normally, the element in the tankless system ONLY runs when you turn on the faucet. With a recirculation system in place, the element will run throughout the day to keep hot water in the line.

The tankless system saves money by running only when you need hot water. Adding a recirculation system will increase the need for hot water and decrease the savings.

We have had an after market installation for years and love it, set on a timer. Had the plumber install an electric box in closet in garage. Yes, the cold water line is warm but I don't drink out of that faucet so that is ok. After it runs for a while it becomes cold. Funny thing is that I have a spot in my living room tile floor that stays warm!!

It sounds like you may have a leak. One way to check is to turn off all water in the house and see if the outside meter is running.

Query: The plumbers roughed-in the plumbing for our new home. We opted for recirculating hot water for our tankless heater. How are these things plumbed for new construction?

Answer: In new construction, plumbing for a recirculating hot water system with a tankless water heater involves a few key steps to ensure efficiency and functionality:

Rough-In Plumbing:
Initial Setup: The rough-in phase begins after framing but before wall covering. Plumbers install the main water supply lines, drain lines, and vent stacks. For a recirculating system, this includes planning for the hot water loop.

Supply Lines: For a tankless heater, both cold and hot water supply lines are run to where the heater will be installed. This includes ensuring there's a main shut-off valve and possibly isolation valves for easier maintenance.

Recirculation System Installation:
Dedicated Return Line: A common method involves installing a dedicated return line for the hot water. This line runs from the furthest fixture back to the tankless water heater. This setup allows for the hot water to circulate continuously or on-demand back to the heater, keeping the water in the pipes hot. This system typically requires more planning and piping during the rough-in phase, as it involves adding an extra pipe.

Pump Placement: The recirculation pump is generally placed near the water heater on the return line to push the cooled water back into the heater for reheating. If a timer or on-demand system is used, this can be controlled to run only during peak usage times, saving energy.

Tankless Water Heater Considerations:
Positioning: The tankless heater should be placed in a location that minimizes the distance the hot water needs to travel to fixtures, which can be challenging in larger homes. However, with a recirculating system, this issue is mitigated since the water stays hot in the loop.

System Integration: Ensure that the tankless water heater can handle the constant demand of a recirculation system. Some tankless units have built-in recirculation features or are designed to work with external pumps. Check compatibility with your specific model.

Piping and Insulation:
Pipe Material: Use materials like PEX or copper for durability and efficiency, with PEX being popular due to its flexibility and ease of installation.
Insulation: Insulating the hot water pipes is crucial to reduce heat loss, especially in the recirculation loop, ensuring the water remains hot as it travels through the house.

Regulations and Testing:
Compliance: Ensure the installation complies with local building codes, particularly regarding energy efficiency and water conservation.
Testing: After installation, the system should be pressure tested to check for leaks, especially before covering the pipes with drywall or other finishes.

This setup ensures that hot water is available almost immediately at every fixture, reducing water waste and enhancing user convenience. However, remember that while a recirculating system with a tankless heater can be highly efficient, the initial setup and additional piping can increase costs and complexity.

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Had the floorplan been different such that the master shower was closer to the heater, then I would not have opted for the recirculating pump either. Alas, the shower is quite far.

No experience. I would think the tankless system would be on 24 hours a day. Seems like a very big problem. I have a regular hot water tank and a pump to circulate the hot water. It works on a timer so I only set it to run a couple of times during the day - when we get up, bed time etc. - and when it is freezing I will run it once or twice in the early mornings on freezing days. (cold water return line helps here) Instead of a timer you could use a smart plug and your phone. I circulate back through the cold water pipe. Not a problem sine I do not run it all the time. But if I did it would be a problem as the water would be too warm. For your system you need a way to turn it off and on when you need it. Might take a minute or two to get hot water so you would have to turn it on before you needed it.
How are the pipes protected from freezing assuming the unit is mounted outside?

Two considerations with tank or tankless, without a continuous recirculation pump, there's no "instant hot water." First, a tankless heater's heat exchanger needs to get up to temperature (120F, for most), even if gas. If you put a pan of water on the gas stove and turn it on, the water isn't instantly hot. Second, regardless of the source (tank or tankless), the HW lines are full of cold water that must be displaced. In a recirculation system, it sends the water back to the tank or tankless heater, as applicable. Recirculation is with a separate return pipe OR a thermal bypass valve (several good YouTube DIY videos) located at the sink/shower/tub which send the "unheated" water to the cold-water line and won't shunt water to the HW faucet until it is "hot." I just ran a quick test using my guest bathtub, which I think is furthest from the tankless heater. It took 1 minute to get warm enough at the tube faucet (showerhead flow rate would be lower and usually takes 2 minutes), and it dispensed 10 qt (measured with a 10 qt bucket) in that time. Where I used to work (hospital), they ran the recirculation pump continuously (not cost effective for homes!), so they did have instant hot water. I looked at all the DYI stuff this past summer and decided the cost wasn't worth it since all I was saving was 10 qt of water, as it still takes the same amount of time to heat the water at the source and cycle the cold water from the lines. Additionally, timers are fine, but you're either going to set the timer to start every day at say 7 a.m. or set it to run for a couple minutes every time you flick a switch somewhere in your house. To me, that's just a hassle. IMO, flip the HW on, hit the head or brush your teeth and that should be good enough to at least have comfortable warm water to start.

Thank you for the analysis using your guest bath as the experiment. Only 10 quarts? That’s surprises me. I’ve not calculated the volume of water in, say, 75’ of 3/4” PVC pipe. When we stayed in a lifestyle villa in Kirsten Villas recently, it certainly seemed longer than two minutes to start a warm shower in the master shower.
At the end of the day, I may not engage the pump. It was an expensive upgrade; that’s certain. But isn’t it better to have it and not need it than to eventually want it and not have it?

Approx. 1gal/50ft of 3/4” pipe

My home, horizontal distance from heater to guest bath = 42’. Add vertical distance and it’s close to 50’.

4.5qts to draw warm water to guest bath. I didn’t time it but times will vary with different fixtures.

Agree, I did a similar test with similar results.

Also:

Measured close to a 10 degree temperature drop from the water heater to the furthest bath (~70 ft).

The cold water temperature here stays close to 75 degrees. It takes less than 10 min for the hot water lines to return to that temperature.