Tankless Recirculating Line or Thermal?

[karoc]

Guys I’m sorry for beating y’all to death with my tankless questions, but I can’t afford to make a mistake on something this expensive and all options. At first I didn’t want a circulating pump cause my new place is just 1000sq ft. The bathroom is about 32’ away from tankless so I was thinking that it can’t take that long. At my present house the WH is about 10’ away from shower and it takes about minute or so before water get hot. Watching some YouTube’s on this subject I see that gallons water adds up over years time. I have talk to my neighbors about utilities and like everything else cost is going up. LP is high and they saying that city water is also expensive. So maybe over years time maybe going with recirculating line will help. Reason for all this is my retirement is not that good, so wife and I getting small and want our overhead to also be small. Anyway to my question.
I’m not 100% sure how this works but I have received help from member here and also Youtubes. This is new construction so it wouldn’t be problem to run a dedicated line. From what I understand is the 3/4 pex hw line run towards bathroom which will have tee’s for drop off of 1/2 pex to fixtures. Which will be 1st clothes washer, 2rd kitchen sink( no dishwasher machine) then to bathroom sink, then shower. Which at that point make U turn head back to tankless. The other choice for recirculating is the thermal expansion valve that goes under sink in bathroom. So it looks to me that thermal bypass would be easier, but is it better? Part I don’t understand is with thermal expansion valve that it doesn’t seem that there be return water back to tankless. But with loop system there be 100% return. Correct? I’m looking at the Rinnai REP 160IP which has built in circulating pump, and from SupplyHouse.com has cold water isolation valve with check valve all in one, which will help make installation little neater. I couldn’t find this valve at build.com which is strange. I’m not ready for hot water but seems prices going up daily, so want to get what I need. Thanks for putting up with me and for all help. If any links to how to’s or pics, any information, that be big help. And opinions

 

[mike93lx]

A minute for 10' means something is wrong.

My 3rd floor bathroom doesn't take that long to get hot water

 

[whateg01]

I understand not wanting to wait for hot water, but from a cost perspective, is it any cheaper to heat water constantly than it is to pay for the extra water?

 

[D.Gribble]

Only thing I can add is we built our home in 2019. 1400 sf ranch in Massachusetts. At the time I did not know that the recirculation line was even an option. I regret not putting in a recirculation line every time I use my kitchen sink which is about 30' from the water heater. Takes 2-3 minutes before hot water is at the sink.

I have Navien tankless and also would go Rinnai if I were to do it again.

 

[karoc]

A minute for 10' means something is wrong.

My 3rd floor bathroom doesn't take that long to get hot water

Mike when we did plumbing on my house we use 1/2 sch#80 pipe, gray. Which if I remember correctly that is small opening. But that was 40 years ago and we just got use to it, I may not be remembering correctly.

 

[mike93lx]

Mike when we did plumbing on my house we use 1/2 sch#80 pipe, gray. Which if I remember correctly that is small opening. But that was 40 years ago and we just got use to it, I may not be remembering correctly.

PVC for supply lines?

 

[karoc]

I understand not wanting to wait for hot water, but from a cost perspective, is it any cheaper to heat water constantly than it is to pay for the extra water?

I agree and gave it lot thought, plus adding more parts also means more can go wrong as Mike was saying. But over time say over few years time maybe it save little money which help pay for those extra parts. It seems that our water district looks for reasons to increase cost according to neighbors.

 

[mike93lx]

I think your water would have to be very expensive to make a recirc pay back.

 

[Jlanciani]

30' of 3/4" pex holds just over a half gallon of water. A decent showerhead flows at least 2.5 gallons per minute. The water gets from the tank to the shower head in 12 seconds.

 

[JJ Quick]

Off point...
I am planning to add hot water circulating.
My primary reason is to reduce water waste.

 

[boatshoes]

For both dedicated hot return and thermal valve/under-sink return valve setups, there isn't any water wasted down the drain.
The downside to the under-sink valve is that the hot water line gets pumped over into the cold water line to create the return loop. No water is wasted, but it makes your cold water line full of lukewarm water, so you don't get true cold water for a bit if the system has been recently active. You can run them on demand or on a timer schedule.
You also have to consider that this introduces water heater-contaminated water (depending on the age and condition of your water heater) into the cold water line. My water authority considers heated water to be non-potable, which is why they don't recommend you use hot water for cooking, for example. This may not be a concern in a bathroom as long as you aren't drinking the tap water, but I wouldn't want to contaminate the lines to my kitchen sink for instance.

 

[dcg9381]

I understand not wanting to wait for hot water, but from a cost perspective, is it any cheaper to heat water constantly than it is to pay for the extra water?

Depends. But there's a solution to this:
"On demand" re-circulation. There are some modern tankless heaters that have a re-circulation pump built in. You can set it up for "on demand" where a pre-configured amount of recirculation is triggered by pressing a contact switch. In the grand scheme of cost, this cost us one recirculation line.. We have contact switches (low voltage) in 3 bathrooms.

My contact switches are "door bell" looking plates in the bathrooms.

Doesn't waste heat, doesn't waste water.... Our water supply (rain water) is limited so wasting water (not the cost of the water) is our main use case.

 

[mike93lx]

Off point...
I am planning to add hot water circulating.
My primary reason is to reduce water waste.

How are you heating that water?

 

[Sumboodie]

2 gallon 120v water heater near the bathroom.

 

[Sturgeon]

I have no love for tankless h/w tanks, with the capacity of such, wouldn't the tank be constantly short cycling. Personally I'd be looking at adding a boilermate heat exchanger and adding circpump with heat sensor.

 

[JJ Quick]

How are you heating that water?

40 gallon natural gas in the garage.

 

[mike93lx]

40 gallon natural gas in the garage.

Do you live somewhere that water is more valuable than gas? I'd rather not burn fuel even if it means cycling through some water, since the water is recovered

 

[karoc]

Guys sorry, it’s going to be propane. Reason for tankless is it takes up less space which will share with washer/dryer in small utility room

 

[dcg9381]

I have no love for tankless h/w tanks, with the capacity of such, wouldn't the tank be constantly short cycling. Personally I'd be looking at adding a boilermate heat exchanger and adding circpump with heat sensor.

That's not been my experience. The flame can vary. Flow rates of under 1.5GPM are handled just fine. Even a single modern shower head with a flow restrictor and our intake water temps being in the mid 70s I've never had an issue with short cycling or on/off.

I have 3 of these. 2 in the house and a small one at the shop. They work great in all sorts of circumstances.

 

[mike93lx]

That's not been my experience. The flame can vary. Flow rates of under 1.5GPM are handled just fine. Even a single modern shower head with a flow restrictor and our intake water temps being in the mid 70s I've never had an issue with short cycling or on/off.

I have 3 of these. 2 in the house and a small one at the shop. They work great in all sorts of circumstances.

Same here.

My last house had a veissman on demand with a 40ish gal holding tank. Worked great and was very cheap to run

 

[Sturgeon]

That's not been my experience. The flame can vary. Flow rates of under 1.5GPM are handled just fine. Even a single modern shower head with a flow restrictor and our intake water temps being in the mid 70s I've never had an issue with short cycling or on/off.

I have 3 of these. 2 in the house and a small one at the shop. They work great in all sorts of circumstances.

 

[Sturgeon]

Yikes, three of them? Good thing you don't have a big demand for h/w, so your using 1.5 gallons in your shower, what about all the other fixtures , they just get put.pause. Couldn't ever use a on demand tank on a remodel unless we totally replaced gas line main to the source for the fuel they burn. Same with electrical, not enough breaker space = new panel . So high energy demand plus limited output. Did I mention the maintenance portion?

 

[dcg9381]

Yikes, three of them?

3 different structures. Gotta have a shop sink, right?

Good thing you don't have a big demand for h/w, so your using 1.5 gallons in your shower, what about all the other fixtures , they just get put.pause.

Lol. I looked it up, Moen shower heads all come with restrictors these days. 1.5 GPM is about right on low flow. My point was on "low flow" that the water heater doesn't "cycle". It's fine. I really can't tell the difference at all from a normal water heater.

Apparently you're not allowed to exceed 2.5 GPM on shower heads. Our master shower has 5 heads - that sounds ridiculous (it is) and we never use them like that, I just went a little nuts when I figured out how easy (and cheap) it was to build this stuff - I did it for resale. I have turned on all 5 of them (once), water heater keeps up just fine.

I looked up the WH capacity and at 30 degree temp rise, it'll do 11 GPM.

Remember, these are massively influenced by the incoming temp of the water. Our water is pretty warm, even in the winter. Cold water, we'd have less than 1/2 the capacity in terms of GPM.

So high energy demand plus limited output. Did I mention the maintenance portion?

They are definitely high demand if electrical and whole house. Mine is fed by a 3/4" propane line.

Not much maintenance on mine. They are inside interior walls and our water is almost totally free of dissolved solids. I haven't touched them. So a lot of it depends on incoming water quality.

 

[dave*99]

I have no love for tankless h/w tanks, with the capacity of such, wouldn't the tank be constantly short cycling. Personally I'd be looking at adding a boilermate heat exchanger and adding circpump with heat sensor.

No, mine does not short cycle. I have 2 Navien units in master/slave with built in recirc. There is some hysteresis built into the temperature sensing. So it has to heat up above a threshold before it turns off. The pipes have to warm up too, so I suspect the water goes around the loop a few times before temperature is reached. The recirc pump is small and moves water slowly.

 

[dave*99]

I have 2 Navien 180,000 btu NG units in master slave with a built in recirc pump piped to a dedicated recirc line. It's about 70' of pipe between the WH and the master bath.

My recirc pump is on a timer. It runs from 7am to 8 pm.

The plumber claimed it's less than $100 per year for the natural gas to run his 24 hours a day in his house. I use the timer.

There are 3 options to control recirc with my units.

The timer that is already built in.
Push buttons located at points of use.
Adding a WiFi interface and using an app.

I would be capable of operating any of the 3. But family and guests...... Well, I have a timer.

It's great to have instant hot water at all points of use.
If I need a shower before 7am........ In the master bath I turn on HW in both sinks and both shower heads in the shower. And wait a good long time for hot water to arrive. Probably 4 minutes or more in the winter. Remember that the WH takes a few seconds to produce HW and there is a lot of pipe in the path. I understand there is not a large volume of water in those pipes, but without the recirc running, one becomes quickly frustrated waiting for the HW to arrive. Once it does, you get limitless HW.

I'm able to set the WH temperature to 126 degrees. Showers are plenty hot. I probably could have gotten by with 1 WH. But they are complicated boxes and I felt having 2 would lessen the chance of having no HW. There are rare times when 3 showers are in use and the clothes washer is running. Still plenty of HW.

In my application, recirc is a must.

 

[dave*99]

The other choice for recirculating is the thermal expansion valve that goes under sink in bathroom. So it looks to me that thermal bypass would be easier, but is it better? Part I don’t understand is with thermal expansion valve that it doesn’t seem that there be return water back to tankless. But with loop system there be 100% return. Correct?

My limited understanding of this choice is that the dedicated return line is the preferred way to go. The under sink valve is a solution for pre-existing homes that would be difficult to retrofit with a dedicated line. The other comments about having lukewarm cold water etc. seem valid from my reading on the topic.

 

[Notgrownup]

Mine is about 60 feet away and it takes about a full min to get to that bathroo shower, the sink about 75 seconds because of flowi would think. I c@n live with because it’s a 2nd bathroom, my master is about 30’ away and it takes 45 seconds or enough time to pinch a good healthy loaf. You’re overthinking this **** man.

 

[mike93lx]

Mine is about 60 feet away and it takes about a full min to get to that bathroo shower, the sink about 75 seconds because of flowi would think. I c@n live with because it’s a 2nd bathroom, my master is about 30’ away and it takes 45 seconds or enough time to pinch a good healthy loaf. You’re overthinking this **** man.

Fiber FTW

 

[MarcSeattle]

30' of 3/4" pex holds just over a half gallon of water. A decent showerhead flows at least 2.5 gallons per minute. The water gets from the tank to the shower head in 12 seconds.

Thanks for that. How much extra time to heat the pipe, faucet and showerhead?

 

[dave*99]

Thanks for that. How much extra time to heat the pipe, faucet and showerhead?

In my experience (about 70' of pipe) the time to heat all that up hits me like this:

During the hours my recirc system runs, I have instant hot water and I don't have to adjust the mix valve while showering.
If I need to shower early in the morning before the recirc system turns on, I get in the shower when the water is warm enough..... The mix valve gets set to almost full hot. But I need to keep adjusting it colder as all that pipe heats up. There is a few minutes of that until the temperature stabilizes.

Is it the end of the world? Of course not. But hey, you asked....

BTW, I have 2 independent mix valves and 2 shower heads running, so there is 2X the usual volume of water running.

This morning I was up at 5 am so I turned on one of the bathroom sink hot taps. It took 8 minutes to get warm enough to wash your face.

 

[Notgrownup]

I timed mine yesterday. 42 seconds to get to my shower head located about 30’ away from the heater

 

[dave*99]

I timed mine yesterday. 42 seconds to get to my shower head located about 30’ away from the heater

Do you have a tankless heater?
Where does your pipe run? Mine is in a cold space. Probably 50 degrees the whole length.

 

[Notgrownup]

Do you have a tankless heater?
Where does your pipe run? Mine is in a cold space. Probably 50 degrees the whole length.

In my crawlspace. Yes i Have a Rinnai, mounted outside.

 

[kbeefy]

For both dedicated hot return and thermal valve/under-sink return valve setups, there isn't any water wasted down the drain.
The downside to the under-sink valve is that the hot water line gets pumped over into the cold water line to create the return loop. No water is wasted, but it makes your cold water line full of lukewarm water, so you don't get true cold water for a bit if the system has been recently active. You can run them on demand or on a timer schedule.
You also have to consider that this introduces water heater-contaminated water (depending on the age and condition of your water heater) into the cold water line. My water authority considers heated water to be non-potable, which is why they don't recommend you use hot water for cooking, for example. This may not be a concern in a bathroom as long as you aren't drinking the tap water, but I wouldn't want to contaminate the lines to my kitchen sink for instance.

I was going to comment with my return valve experience, but @boatshoes pretty much nailed it.

 

[dave*99]

Climate
Incoming water temp
Pipe length
Pipe location and temperature
All seem to be the major factors