How can I setup a recirculating system on a tankless hot water heater?

[mdk0420]

Hello all. My boiler is finally up and running and everything is great. But I have a need to make it a better system. Currently it takes probably half a minute or longer from my hot water heater to my shower. I want to setup a loop that'll keep the water hot, but I also don't want the boiler to run 24/7. I heard of some valves that might do the trick but it seemed like they connect the hot water to the cold water to perform that circulation system. Wouldn't that mean both hot and cold water lines would now be hot?

I've also seen diagrams of a return line. How would I go about that? Would it be a return line coming off the farthest hot water line, coming back into the cold water line right before it enters the tank? I would also need a pump. Do timers work the best in that case? I like the idea of motion detection but I have pets and they'll probably just trigger the sensors. I could turn the timer on when home and the timer off when not home. What are you recommendations? Thanks!

 

[Jamesplumbing06]

If you must have instant hot water then yes you need to recirculate. But you also need a insulated tank. 30 gallon electric might be cheap enough. 1/2” return from furthest fixture yes. Battery back up for pump or time will be messed up every time electric goes off. And finally bigger monthly budget for gas bill. Washing hands takes 2 minutes accomplish. Haveing instant hot water at the sink will force heater to run for a whole 30-45 minutes. Must firmly insulate hot line on loop to reduce heat loss. I ask my customers which is more important. Instant hot water or endless hot water? Or just go back to a tank heater and circulate with a solenoid valve system.
I love tankless water heaters. And use to sell customers on a circulating line. Most of them unplug the pump and haven’t complained. The rest complained constant. Gas bill too high. Water isn’t hot at correct time of day. My opinion is a circ line is a waste of money for tankless units.
Electric will only go up about $15 a year with pump. Minimal compared to the rest.
Maybe somebody else has had better luck but not this ole plumber.

 

[mdk0420]

If you must have instant hot water then yes you need to recirculate. But you also need a insulated tank. 30 gallon electric might be cheap enough. 1/2” return from furthest fixture yes. Battery back up for pump or time will be messed up every time electric goes off. And finally bigger monthly budget for gas bill. Washing hands takes 2 minutes accomplish. Haveing instant hot water at the sink will force heater to run for a whole 30-45 minutes. Must firmly insulate hot line on loop to reduce heat loss. I ask my customers which is more important. Instant hot water or endless hot water? Or just go back to a tank heater and circulate with a solenoid valve system.
I love tankless water heaters. And use to sell customers on a circulating line. Most of them unplug the pump and haven’t complained. The rest complained constant. Gas bill too high. Water isn’t hot at correct time of day. My opinion is a circ line is a waste of money for tankless units.
Electric will only go up about $15 a year with pump. Minimal compared to the rest.
Maybe somebody else has had better luck but not this ole plumber.

Oh why would it need to run 30-45 minutes I would think that it would only run a couple minutes every 20 minutes or so to keep the line hot, then when I wash my hands it'll turn on as well but only because there would then be a hot water demand. That was my thought process on it anyways lol.

 

[CST Mechanical]

Grundfos makes a smart re circ pump that has a sensor you zap strap to the hot line leaking your tank. It notes every time there is a call for hot water and after a week or so creates a usage schedule tailored to the specific user. So for instance, if you shower each morning at 7 AM, it will start to cycle at 6:45 to ensure water is hot right away. Still need to bring a 1/2" line from the furthest hot water fixture back to the cold line entering your tank. Also need a check valve so your hot & cold don't get mixed when the pump isn't running.
www.coastmechanical.com

 

[mdk0420]

Grundfos makes a smart re circ pump that has a sensor you zap strap to the hot line leaking your tank. It notes every time there is a call for hot water and after a week or so creates a usage schedule tailored to the specific user. So for instance, if you shower each morning at 7 AM, it will start to cycle at 6:45 to ensure water is hot right away. Still need to bring a 1/2" line from the furthest hot water fixture back to the cold line entering your tank. Also need a check valve so your hot & cold don't get mixed when the pump isn't running.
www.coastmechanical.com

Interesting. My schedule fluctuates though. I'd honestly probably just setup a system where I would time it to be on when I'm home, and off when I'm not. Maybe set it up next to the thermostat for easy on/off functionality. I didn't think of the check valve... should that be right next where the return line would connect to the cold water line? Where it comes from the main right?

 

[Jamesplumbing06]

Not only on the main but also a check valve will go on circulation line and cold line just to keep everything moving in right direction. Need a pump , half inch pipe and timer. Go to furthest fixture. Tee the 1/2” line in and bring straight back to water heater. Check valve goes on this line before it ties into heater.
I am a routine freak. But even then my morning shower is sometimes an evening shower. Dinner might not start on time because kids have practice on Tuesday Thursday and games Saturday. So I am speaking of my experience. Even if it come on 5 minutes early. That’s 5 minutes of sucking double the gas as a tank. And no insulation to keep it warm. I do know of 1 happy customer. I had one guy that wired his pump into his bathroom light switch. So when you turn on light. The water startes heating. It works for them. He says a quick hand wash is usually cold. he may go back and put a dedicated low voltage switch in kitchen but usually flips on bathroom switch on way to kitchen.
Tankless is average 175,000 btu. Tank heater is 75,000 btu. Both are per hour. Be sure that gets figured into thought process.

 

[Mikey]

I've used on-demand circulating pumps with great success, although you do have to have the patience to wait 15-20 seconds for the hot water. You can return the cold water via the existing cold line, or via a separate line if you can get one (better).

 

[FishScreener]

Or add a small, high efficiency, electric water heater at the point of use, and feed through it.

Or, just use hot water to brush your teeth before you shower. You should brush them a couple of times a day, so turn on th hot tap, and draw the water.

If you think through your actions, adapt your actions, and develop better habits, you can then eliminate a lot of energy consuming habits.

I built new Forest Service housing in Challis Idaho. There is an average overnight temperature drop of forty degrees. The buildings don’t have air conditioning. They have computer controlled fans, and ducting, which opens when it is cooler outside, and draws in outside air until, the inside is down to sixty five, and shuts off the fans. The kids living here would turn on the heat in the mornings, and be upset, when the building was up to eighty when they got off work in the afternoon. I had to give classes to train them on how to live in the mountains.

 

[mdk0420]

I wrapped all my pipes with the new install. Should be able to hold heat much better. The line is actually currently a half inch line feeding all the fixtures because of the distance. It takes even longer with the new boiler because it has a flow restrictor on it to limit it to what it can handle. Its a 150k BTU unit. How much more gas usage can I expect from a timer system that goes off every now and then throughout the day? Would it triple the monthly bill?