Originally Posted by ltcdfancher (Post 2395189)

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?

Originally Posted by Justputt (Post 2395170)

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.

Originally Posted by Wondering (Post 2395106)

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.

Originally Posted by Bill14564 (Post 2395195)

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.

Originally Posted by ltcdfancher (Post 2394843)

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.)

Originally Posted by retiredguy123 (Post 2395284)

Pretty close, but I had to do my own calculation.

The actual inside diameter of 3/4-inch Schedule 40 plastic pipe is 0.804 inches.
The radius is 0.804/2 = 0.402 inches.
The area is 0.402 x 0.402 x 3.14 = 0.507 square inches.
The volume for 50 feet of pipe is 50 x 12 x 0.507 = 304.2 cubic inches
The volume in cubic feet is 304.2 x 0.0005787 = 0.176 cubic feet
The volume in gallons is 0.176 x 7.48 = 1.32 gallons

The Federal regulation for shower heads is 2.5 GPM maximum, so it should take about 32 seconds to get hot water to the shower. But you can reduce that time by about half by turning on a sink faucet at the same time as the shower.

Originally Posted by rsmurano (Post 2395063)

“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.

Originally Posted by circlerman (Post 2395068)

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?

Originally Posted by retiredguy123 (Post 2395083)

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.

Originally Posted by Kenswing (Post 2395084)

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.

Originally Posted by ltcdfancher (Post 2394996)

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. ;)

Originally Posted by Nevinator (Post 2395275)

All of the points mentioned in this thread are well taken. There are benefits to having a system with a dedicated return line and also to having an installation that uses the crossover pipe methodology. Also, depending on the size of your home and the location of your primary bathroom to the water heater, an argument could also be made for doing nothing.

When I built my home about a year ago, we were offered the option to have a system installed with a dedicated return line for a cost of about $8000. This was not a value proposition for me. Clearly, the system using the dedicated return line also uses a different, more expensive water heater. The cost between one that allows for water circulation and one that doesn’t only differs by about $600 in most cases and for that reason does not justify, in my opinion, the $8000 cost.

I opted to install my own system and purchased two crossover pipes that I installed in the master bathroom and in the second secondary bathroom of the home. I plumbed in a recirculating pump which cost me roughly $90. I also added an Alexa plug that allowed me to create a routine in Alexa to turn on the recirculation pump anytime I needed it. The routine is set to run for two minutes and 45 seconds, the approximate time it takes to get hot water to my bathroom. The pump automatically turns off after that time.

While this solution does not provide me with on-demand hot water or instant hot water, it does preclude my having to waste 6 to 7 gallons of water every time I want to take a shower while waiting for the water to heat up.

Obviously this is not the best solution but definitely a fair trade-off for not paying $8000.