Hot Water Return Piping

AugieT

What is the best way to Pipe a hot water return line with a condensing water heater?
I've seen them piped as you would a normal tank heater and I'm thinking every time your pump is running so is your tankless heater. I'm thinking that's not very efficient. What do you think is best? Thank you

EdTheHeaterMan

Really there is not good way to do that. Perhaps a small (5 to 10 gallon) buffer tank would be a good choice, but that defeats the purpose of a tankLESS water heater. The best option is to have a 3/8" PEX home run the the problem shower or faucet. I am installing a ManaBloc system in my home this week for 3 reasons.
1. those 3/8" home runs mean that the amount of cold water in the pipe from the water heater to the outlet is minimum (and takes less time)
2. I want to abandon all the 1976 copper pipes that are buried in my concrete slab.
3. I am getting a complete bathroom remodel so 90% of the walls where the new PEX needs to go will be open.

How many faucet outlets do you consider "Problem Outlets"? How easy would it be to make a 3/8" home run for that (those) outlets for the hot water? Otherwise get yourself a buffer tank and set it up with 2 pumps. one pump to fill the tank with heated water when it falls below a certain temperature. and the other to re-circ. to the buffer tank as needed.

I like the idea of connecting the re-circ. pump the the bathroom light switch. That way it only runs when you are using the bathroom. By the time you are ready to use the hot water... it is already there. When you leave and turn off the light, the pump is off until next time.

Larry Weingarten

Hi @EdTheHeaterMan , A thought. If you have adequate pressure and no more than 1.5 gpm fixtures, and the runs are not too long, you can use 1/4" tube. I just plumbed a small house this way. 60 psi incoming pressure and all runs under 25 feet. I got an engineer to certify it. In worst case, hot water arrives in six seconds. Other taps it takes three seconds. 🤠

Yours, Larry

EdTheHeaterMan

@Larry Weingarten I know that I get plenty of cold water from my refrigerator door and that is only a 1/4" plastic tube.

I selected 3/8" because just about every kitchen and lav faucet I have ever installed uses 3/8" supply tubes from the valve coming out of the wall to the faucet connection. My dishwasher was installed by the previous DIY Homehacker and that is connected with a 3/8" flare connector like I used to use on oil lines. And my shower is only 17 feet of hot and cold water tube from the MANAbloc. I don't think that is going to be a problem. My son just did the same project in NJ 5 years ago and his is working fine. I don't think I would use 1/4 PEX on the shower but it might work everywhere else.