Recirculator for tankless hot water heater?

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Kennedy
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Recirculator for tankless hot water heater?

Post by Kennedy »

The water coming out of my faucets take way too long to turn warm. I have a tankless hot water system.

I had a recirculator in a former house with a traditional hot water tank, and the water instantly came out of the faucets piping hot.

Can I have a recirculator installed in my tankless system? If I do that, will I lose the energy efficiency by having to keep some water hot at all times?
margaritaville
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Re: Recirculator for tankless hot water heater?

Post by margaritaville »

Rinnai makes recirculators for their tankless systems:

https://www.rinnai.us/tankless-water-he ... irculation

They have systems that are schedule based (they only keep hot water in the pipes during certain hours of the day) or that work based on you pressing a button when you walk in the room or through a motion sensor. The latter type are more about preventing waste than about the convenience of on-demand hot water.

You will take a hit efficiency wise of course for the convenience of near instant hot water. I haven't seen definitive numbers and some argue that you will save enough by not dumping cold water down the drain to offset the cost of increased gas usage required to maintain hot water in the pipes.
mike_in_ny
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Re: Recirculator for tankless hot water heater?

Post by mike_in_ny »

We also found that when the incoming water is cold (winter) that we could not get the water hot enough
with our tank-less system (to fill up the bathtub, for example).

We added a hot water tank to go with our oil-fueled furnace with baseboard heating. It is setup such that
the tank essentially acts as another zone in the house and we are very pleased with it.

There is undoubtedly some lost heat from that tank which is a drag on efficiency. However, for
a house with 3 teenagers taking long showers, I average ~ 1 gallon of oil per day in the summer
months (when not heating the house) for hot water. It has also been a benefit when we lose
electricity due to storms -- we have still had hot water for a day or two.

I highly recommend that setup.
mkc
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Re: Recirculator for tankless hot water heater?

Post by mkc »

It depends on the tankless model whether a recirculation pump can be used with them. Some of the newer ones are compatible, but often require a system from the same manufacturer. Many, especially older ones, are not.
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Bengineer
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Re: Recirculator for tankless hot water heater?

Post by Bengineer »

We used two on-demand push-button pumps that under the sink plumbed to the hot and cold with a Rheem tankless. Press button, wait 30 sec, hot water, no waste.
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Kennedy
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Re: Recirculator for tankless hot water heater?

Post by Kennedy »

Bengineer wrote: Sat Oct 31, 2020 8:49 am We used two on-demand push-button pumps that under the sink plumbed to the hot and cold with a Rheem tankless. Press button, wait 30 sec, hot water, no waste.
This is an interesting solution, but is this practical in a house with multiple sinks and bathtubs? It sounds like I would have to install a separate on-demand unit attached to each sink and tub?
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TomatoTomahto
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Re: Recirculator for tankless hot water heater?

Post by TomatoTomahto »

margaritaville wrote: Sat Oct 31, 2020 7:31 am You will take a hit efficiency wise of course for the convenience of near instant hot water. I haven't seen definitive numbers and some argue that you will save enough by not dumping cold water down the drain to offset the cost of increased gas usage required to maintain hot water in the pipes.
I have a recirculating pump on my (traditional) tank, and I worried about the inefficiency until (d’oh dawn breaks over Marblehead) I realized that my well pump would be running extra to dump that cold water down the drain. Plus, we are in a perennial drought. So, I put the pump on a smart plug, and run it for most of the day.
I get the FI part but not the RE part of FIRE.
neilpilot
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Re: Recirculator for tankless hot water heater?

Post by neilpilot »

TomatoTomahto wrote: Sat Oct 31, 2020 12:45 pm
margaritaville wrote: Sat Oct 31, 2020 7:31 am You will take a hit efficiency wise of course for the convenience of near instant hot water. I haven't seen definitive numbers and some argue that you will save enough by not dumping cold water down the drain to offset the cost of increased gas usage required to maintain hot water in the pipes.
I have a recirculating pump on my (traditional) tank, and I worried about the inefficiency until (d’oh dawn breaks over Marblehead) I realized that my well pump would be running extra to dump that cold water down the drain. Plus, we are in a perennial drought. So, I put the pump on a smart plug, and run it for most of the day.
In your case, so long as the entire circulation loop is well insulated to prevent excessive heat loss inefficiency is likely minimal.
Lee_WSP
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Re: Recirculator for tankless hot water heater?

Post by Lee_WSP »

If you can't get a recirc pump to work, you can always install a 1 gallon water heater under the sink.
inbox788
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Re: Recirculator for tankless hot water heater?

Post by inbox788 »

Lee_WSP wrote: Sat Oct 31, 2020 1:39 pm If you can't get a recirc pump to work, you can always install a 1 gallon water heater under the sink.
I've been looking for a solution, but most all of them require some sort of construction. At the very least, you need AC power for a pump or for heating local water. Best recirculator is returning water to the heater, but that requires additional separate piping (return line). Sending the water to the cold pipe or down the drain are options, but not great. And you use power, so some efficiency is lost. Also, I have a troublesome distant addition and I suspect my piping is somewhat star shaped (Core and Manifold Plumbing), so even if I loop it around the furthest point, there are probably other sinks that still don't benefit much.

Image
https://basc.pnnl.gov/resource-guides/c ... d-plumbing

Image
https://basc.pnnl.gov/resource-guides/demand-plumbing

There was one interesting solution that didn't require much on the remote end (pump at the heater end), but I haven't figured out whether it makes sense for me yet (tankless water heater and demand flow activated; I think I have to change the settings to circulate on time or temperature and don't know if my heater does that.).
https://www.homedepot.com/p/Taco-Comfor ... /301292327
https://www.amazon.com/Taco-HLPe-1-1-Ho ... 07CW8CDNZ/
https://www.amazon.com/Taco-HLV-1-HOT-L ... B00USBTXTA
https://www.tacocomfort.com/product/hot-link-system/
Lee_WSP
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Re: Recirculator for tankless hot water heater?

Post by Lee_WSP »

inbox788 wrote: Sat Oct 31, 2020 2:04 pm Sending the water to the cold pipe or down the drain are options, but not great. And you use power, so some efficiency is lost. Also, I have a troublesome distant addition and I suspect my piping is somewhat star shaped (Core and Manifold Plumbing), so even if I loop it around the furthest point, there are probably other sinks that still don't benefit much.
Then a recirculation pump isn't going to help you. I'd put in smaller heaters at the points very very far from the heater and just deal with the cold water at first for the closer ones.

FWIW, it's the perennial tradeoff between comfort/convenience vs cost. Personally I just fill a bucket and water the trees with the waste water.
Sprucebark
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Re: Recirculator for tankless hot water heater?

Post by Sprucebark »

It probably has more to do with the location of your tankless heater than tankless vs a water tank. In other words, if you ripped out your tankless heater and put in a hot water tank in that exact same spot, it would probably only be marginally faster to get the hot water (difference being when you initially turn on the water the tankless fires up and maybe 1 foot of cold water moves through the pipe).

I have a same situation. My tankless system is installed in my garage so it take a while to get hot water at the other end of the house. But once you get hot water in the pipes (like doing laundry or a shower) all of the other pipes get warm pretty fast since there is already warm water in the pipes.

If I move the tankless system into the crawl space it would be right in the middle of my house and it would be much faster to get hot water everywhere.
inbox788
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Re: Recirculator for tankless hot water heater?

Post by inbox788 »

Lee_WSP wrote: Sat Oct 31, 2020 2:26 pm
inbox788 wrote: Sat Oct 31, 2020 2:04 pm Sending the water to the cold pipe or down the drain are options, but not great. And you use power, so some efficiency is lost. Also, I have a troublesome distant addition and I suspect my piping is somewhat star shaped (Core and Manifold Plumbing), so even if I loop it around the furthest point, there are probably other sinks that still don't benefit much.
Then a recirculation pump isn't going to help you. I'd put in smaller heaters at the points very very far from the heater and just deal with the cold water at first for the closer ones.

FWIW, it's the perennial tradeoff between comfort/convenience vs cost. Personally I just fill a bucket and water the trees with the waste water.
I'd still have to install wiring and power. It might be easier for me to install a drain pipe to water the plants outside.
Can the Hot Link Valve be used with a Tankless water Heater?
No, the HLV can Not be used with a Tankless Water Heater. It does not allow enough flow through the valve to activate the Tankless Heater.
https://www.tacocomfort.com/knowledge-b ... rculators/

I was afraid the flow rate might be an issue.

I think a wireless control system may be the solution and I just haven't found it, or it's just around the corner. Any Kickstarter or Indiegogo entrepreneurs out there? I'd still have to replace batteries once in a while, but if it's less than once a year, I'd be ok with that.
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Bengineer
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Re: Recirculator for tankless hot water heater?

Post by Bengineer »

Kennedy wrote: Sat Oct 31, 2020 11:41 am
Bengineer wrote: Sat Oct 31, 2020 8:49 am We used two on-demand push-button pumps that under the sink plumbed to the hot and cold with a Rheem tankless. Press button, wait 30 sec, hot water, no waste.
This is an interesting solution, but is this practical in a house with multiple sinks and bathtubs? It sounds like I would have to install a separate on-demand unit attached to each sink and tub?
To optimize, you would put the pump at the end of the main trunk(s), assuming you have trunk & branch supply plumbing. If the trunk is accessible from the crawl/basement, the pump could be plumbed to the farthest point from the water heater. If not, choose a sink at the location(s) that take the longest for hot water to arrive. For us, that was the kitchen sink and the master bath sink.
mpnret
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Re: Recirculator for tankless hot water heater?

Post by mpnret »

Question for those that have the recirc sytem that uses the cold water line as a return. When you turn on the faucet for cold water do you now get warm water and have to wait for it to get cold?
birdy
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Re: Recirculator for tankless hot water heater?

Post by birdy »

My first "tankless" was a hybrid which had a five gallon water tank. I had a recirculator installed in the master bath and I loved it! I did have the problem you mentioned in which my cold water came out warm but it wasn't an issue for me. I am on my second tankless heater and unfortunately I am not able to have a recirc pump with my brand. I miss having instant hot water. I run the tap in my tub to get hot water quicker. The tech that installed this one told me to prolong its life, to have it flushed of sediment every couple of years.

birdy
mpnret
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Re: Recirculator for tankless hot water heater?

Post by mpnret »

mpnret wrote: Tue Nov 03, 2020 9:16 am Question for those that have the recirc sytem that uses the cold water line as a return. When you turn on the faucet for cold water do you now get warm water and have to wait for it to get cold?
birdy wrote: Tue Nov 03, 2020 9:55 am My first "tankless" was a hybrid which had a five gallon water tank. I had a recirculator installed in the master bath and I loved it! I did have the problem you mentioned in which my cold water came out warm but it wasn't an issue for me. I am on my second tankless heater and unfortunately I am not able to have a recirc pump with my brand. I miss having instant hot water. I run the tap in my tub to get hot water quicker. The tech that installed this one told me to prolong its life, to have it flushed of sediment every couple of years.

birdy
So it seems like the only advantage to this type of system is convenience. Without it you have to dump some cold water down the drain and wait for warm. With it you have instant warm water but when wanting cold you have to dump some warm down the drain before it gets cold plus you have the pump initial and operating cost.
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Kennedy
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Re: Recirculator for tankless hot water heater?

Post by Kennedy »

OP here for a follow-up. I had a plumber and his apprentice out to see if they could add a recirculator. They looked at my set-up and both advised against it. Said since the system hadn't been originally built to accommodate a recirculator that they would have to use the cold water line to serve this purpose. As such, we would not have cold water coming out of the taps. (That was my understanding, anyway...)

They further said that doing this would be really hard on our water lines, setting us up (potentially) for problems with the pipes down the road.

They advised increasing the temperature on the heating unit as that is what they both did in their own homes to decrease the waiting time for hot water.

The temp was increased to 135 degrees, but I honestly don't think the water gets warm any quicker. Oh well. Guess there are worse problems in life.
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dratkinson
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Re: Recirculator for tankless hot water heater?

Post by dratkinson »

Recirculating pump.

--When cold water line is used for return, an adjustable pump temperature sensor shuts off pump when the water becomes warm. So not all of the cold water has been flushed from the cold water line.

Can probably set pump sensor for lukewarm water... just so it's not a complete shock to the body to jump immediately into a shower. This would preserve more cold water in cold water line, if that was the intent.

Search: https://www.google.com/search?q=recircu ... ure+sensor

--Not certain I understand plumbers' (journeyman + apprentice) concern about how a water line (copper, PEX,...; HD, Lowes,...) used for both hot/cold water flowing in either pipe direction, can be damaged by flowing the other water in the opposite direction. Would suspect plumbers didn't want to do the job so turned up water heater thermostat and billed for a service call as their easiest option. Would suspect plumbing company owner (master plumber) would have a different opinion.


I could be wrong. But would need to see chapter and verse demonstrating why existing temperature-controlled recirculating pump installations are wrong.
d.r.a., not dr.a. | I'm a novice investor, you are forewarned.
teCh0010
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Re: Recirculator for tankless hot water heater?

Post by teCh0010 »

Kennedy wrote: Fri Dec 18, 2020 7:15 pm OP here for a follow-up. I had a plumber and his apprentice out to see if they could add a recirculator. They looked at my set-up and both advised against it. Said since the system hadn't been originally built to accommodate a recirculator that they would have to use the cold water line to serve this purpose. As such, we would not have cold water coming out of the taps. (That was my understanding, anyway...)

They further said that doing this would be really hard on our water lines, setting us up (potentially) for problems with the pipes down the road.

They advised increasing the temperature on the heating unit as that is what they both did in their own homes to decrease the waiting time for hot water.

The temp was increased to 135 degrees, but I honestly don't think the water gets warm any quicker. Oh well. Guess there are worse problems in life.
Are you setting the sink to all the way hot while waiting for it to warm up?

You want to cause as much hot water flow as fast as you can to kick on the tankless, if you have a single handle faucet set to warm the lower flow rate may take a bit of time to cause the tankless to fire, after that it just comes down to the volume of water in the line.
Nowizard
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Re: Recirculator for tankless hot water heater?

Post by Nowizard »

Get a tank for prime areas of the house, as others have suggested. Better yet, avoid tankless unless there are personal principles involved that make the inefficiency a worthwhile trade-off.

Tim
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