Tankless water heater

[Glynr]

I’m in the process of replacing my  Rinnai water heater with a Navien.

ok I figured it out. I’m going to use an Insteon on/off module. The Navien has a “hot” button to activate the pump. I’ll will be able to have Alexa turn on the pump when I want. 
 

Thanks for the replies. Unfortunately they didn’t answer my question. 

Edited September 15, 2023 by Glynr

[apostolakisl]

I don't think you want to use a tankless heater with a recirculation system.  The unit will do a lot of cycling.  I suspect it would void warranty as well.  Perhaps you are just manually using the recirc pump moments before using the hot water, which I suspect would be fine.  But having it run for extended lengths of time would not be a good plan.  

[Glynr]

The pump comes with the unit. Once you set the temperature, it will cycle on and off to keep the water, the same temperature throughout the line.

Edited September 14, 2023 by Glynr

[apostolakisl]

1 hour ago, Glynr said:

The pump comes with the unit. Once you set the temperature, it will cycle on and off to keep the water, the same temperature throughout the line.

Seems totally contrary to the whole concept of a tankless heater.  You basically turn the pipes in your walls into a tank that you keep cycling your heater to keep hot.

[lilyoyo1]

1 minute ago, apostolakisl said:

Seems totally contrary to the whole concept of a tankless heater.  You basically turn the pipes in your walls into a tank that you keep cycling your heater to keep hot.

Tankless water heaters cant stop water from cooling down in the pipes. This method allows a person to have instant hot water when they turn on their faucet vs running the water until hot water makes it way through the pipes.

[apostolakisl]

2 hours ago, lilyoyo1 said:

Tankless water heaters cant stop water from cooling down in the pipes. This method allows a person to have instant hot water when they turn on their faucet vs running the water until hot water makes it way through the pipes.

I am aware of the concept.  But it defeats the primary purpose of tankless heaters which is that they do not consume any energy except when the user is consuming hot water.  I have seen systems that have a flow sensor such that when you start to draw hot water it trips a pump that rapidly pumps out the hot water line into the cold water line to get the hot water to you faster, those are still within the concept.

The least efficient place to store hot water is in your pipes.  Even if insulated, they have a low r value insulation and extremely high surface area to volume.  If you live in the north and are heating your house anyway, I suppose no huge loss.  But you also will suffer from a relatively small volume of water that is poorly insulated which will result in constant short cycling of your tankless heater.  The life of you heater will be greatly diminished.  Furthermore, I suspect that the ignition process is the least efficient use of fuel and you will have lots and lots of ignitions.  A big 50 gallon tank heater will have that large volume to buffer the cooling/heating cycle times and thus not short cycle.

[lilyoyo1]

2 hours ago, apostolakisl said:

I am aware of the concept.  But it defeats the primary purpose of tankless heaters which is that they do not consume any energy except when the user is consuming hot water.  I have seen systems that have a flow sensor such that when you start to draw hot water it trips a pump that rapidly pumps out the hot water line into the cold water line to get the hot water to you faster, those are still within the concept.

The least efficient place to store hot water is in your pipes.  Even if insulated, they have a low r value insulation and extremely high surface area to volume.  If you live in the north and are heating your house anyway, I suppose no huge loss.  But you also will suffer from a relatively small volume of water that is poorly insulated which will result in constant short cycling of your tankless heater.  The life of you heater will be greatly diminished.  Furthermore, I suspect that the ignition process is the least efficient use of fuel and you will have lots and lots of ignitions.  A big 50 gallon tank heater will have that large volume to buffer the cooling/heating cycle times and thus not short cycle.

Not necessarily. With tank water heater, your system still cycles to keep a tank full of water at temperature. Even then, when you run hot water, it'll run to re-heat the water that is lost. Depending on how much hot water is used, that process can still require a lot more energy than a recirculating system over all....This is especially so when you consider most can be turned on manually with sensors, a switch, or timer.

While some people may allow their systems to run non-stop, they're probably looking more at convenience than they are at cost. Another thing people take into consideration (such as myself) is the overall cost savings. Its like using smart switches to save money on your light bill. Yes, the devices use power all day which adds to your electric bill. However, what they add is still cheaper than leaving the products on that they are meant to control.

[larryllix]

The additional delay of a tankless water heater sensing the demand for hot water makes users very aware of the length of time it takes to get hot water from a remote faucet. Tankless water heater manufacturers have tried to compensate for this fact by creating hot water pipe reheat systems as well as small tank systems that keep a small tank of hot water ready at all times to avoid hot water response delays, somewhat.

After going through 3 Rinnai, and 2 Rudd tankless water heaters over 15 years before selling my last home, I can tell you I would never touch another gas tankless water heater in a home design. The maintenance and high cost of replacing them every few years made it the most expensive hot water I have had.

There were  times when it wouldn't kick in because the flow sensor could not detect the small trickle of hot water demand required to say... wash you face at night. Sensing very low  flow rates was one of the biggest problems and the newer small tank systems were designed to alleviate that.

Tankless water heaters are promoted by the huge capacity of their burners, typically. This is a mistake for the uneducated in their operation. The gas burner types have a binary valve system that turns on gas burners to match the hot water draw. When a large flow is required to be heated the larger gas burners are ignited and when a smaller flow is detected, smaller burners are ignited. A binary combination is used for most intermediate flow draws. With a limited number of gas burners and a large capacity unit, this means the smallest burner is only needed for usually more than 0.4 gallons per minute with X degrees of temperature rise. When you run a medium flow at a faucet with a medium warm water mix, the hot water demand is less than the 0.4 gpm draw from the hot water source. When you mix hot and cold water at a sink tap you must turn the water on almost full blast to get the tankless to respond to the demand. Then when you set the tap back to a reasonable level of temperature for actual usage, the tankless will shut off and the pipes full of hot water will fill with cold water again.

Edited September 15, 2023 by larryllix

[marcin]

We installed navien in our house and works great, I tied the unit into elk alarm, once motion is detected in the bathrooms, elk triggers the “hot” button function. This works as long as you have return from the highest point in your hot water supply.

I would strongly suggest not to use Alexa for that reason. 

[apostolakisl]

11 hours ago, lilyoyo1 said:

Not necessarily. With tank water heater, your system still cycles to keep a tank full of water at temperature. Even t

Yes, of course, all hot water heaters that keep hot water at the standby cycle, no such thing as perfect insulation.  But a big tank cycles far less often.  You have 50 gallons of water to buffer the rise and fall of temp.  In a tankless you only have a few gallons in the pipes and that water is rapidly cooling because of the poor insulation and high surface area to volume ratio.

[apostolakisl]

1 hour ago, marcin said:

We installed navien in our house and works great, I tied the unit into elk alarm, once motion is detected in the bathrooms, elk triggers the “hot” button function. This works as long as you have return from the highest point in your hot water supply.

I would strongly suggest not to use Alexa for that reason. 

So you don't have a true recirculating system.  I have a true recirculatory that has a dedicated  loop back to the hot water tank and a pump that runs continuously.  You have an on demand system that I very much doubt has a true recirculating loop.  It likely pumps the water from the hot line into the cold water line until a temp sensor detects that hot water has arrived at the destination.  Or I suppose it could be timed once you know how long that takes.  This system will not cycle, it will just run for however many seconds when triggered.  Using a motion sensor in the bathroom I would suggest is not the best plan.  I enter my master bathroom all the time with no intention of using hot water.  There would be many false triggers.  A flow sensor which detects that you started flowing hot water and then trips the pump is the best for energy and wear and tear.  Though you will not get instant hot water, but the hot water will arrive far faster.  For example, you might have a sink that flows at 1gpm and takes 30 seconds to get hot.  If you have a pump that flows at 5gpm, the water will now arrive in about 5 seconds. 

[gregkinney]

I have a Navien tankless with recirculating system and it's worked flawlessly for over 10 years. The hot water isn't instant; I would say it's about 10-20 seconds. The tankless unit stays off and only turns on when hot water is called for.

[apostolakisl]

5 hours ago, larryllix said:

The additional delay of a tankless water heater sensing the demand for hot water makes users very aware of the length of time it takes to get hot water from a remote faucet. Tankless water heater manufacturers have tried to compensate for this fact by creating hot water pipe reheat systems as well as small tank systems that keep a small tank of hot water ready at all times to avoid hot water response delays, somewhat.

After going through 3 Rinnai, and 2 Rudd tankless water heaters over 15 years before selling my last home, I can tell you I would never touch another gas tankless water heater in a home design. The maintenance and high cost of replacing them every few years made it the most expensive hot water I have had.

There were  times when it wouldn't kick in because the flow sensor could not detect the small trickle of hot water demand required to say... wash you face at night. Sensing very low  flow rates was one of the biggest problems and the newer small tank systems were designed to alleviate that.

Tankless water heaters are promoted by the huge capacity of their burners, typically. This is a mistake for the uneducated in their operation. The gas burner types have a binary valve system that turns on gas burners to match the hot water draw. When a large flow is required to be heated the larger gas burners are ignited and when a smaller flow is detected, smaller burners are ignited. A binary combination is used for most intermediate flow draws. With a limited number of gas burners and a large capacity unit, this means the smallest burner is only needed for usually more than 0.4 gallons per minute with X degrees of temperature rise. When you run a medium flow at a faucet with a medium warm water mix, the hot water demand is less than the 0.4 gpm draw from the hot water source. When you mix hot and cold water at a sink tap you must turn the water on almost full blast to get the tankless to respond to the demand. Then when you set the tap back to a reasonable level of temperature for actual usage, the tankless will shut off and the pipes full of hot water will fill with cold water again.

I have multiple tankless heaters both at my home and my inlaws.  I have a heat pump tanked one at the office.

I forget the brand off the top of my head, but the two in my home are both 13 years old and "knock on wood", I have essentially had zero issues.  The only issue I did have was the flame sensor on the unit needed to be rubbed down with some steel wool a few months ago as it was no longer detecting the flame as a result of carbon buildup.  I have flushed the tanks with vinegar every few years as routine maintenance.  The burner fires up very fast, just a couple seconds and it is making hot water.  These are mounted on the outside of the house (I live in Texas).  They survived the big freeze to 6 degrees two nights in a row we had 2 years ago just fine (I did not lose electricity, if I had, I would have needed to drain them very quickly).  The one unit is located on the outside wall just about 8 feet from the one kitchen sink.  That sink gets hot water in just a few seconds.  Maybe 5 seconds.  You can hear the burn come on in less than 1 second when you turn on the hot water and the remaining time is flushing through the water between the sink and the heater.

EDIT: My tanks or Noritz.  I timed the kitchen sink at 10 seconds which is about 8ft away.  The flow rate of that sink is a bit more than 1gpm (3 cups in 10 seconds).

Edited September 15, 2023 by apostolakisl

[larryllix]

12 hours ago, apostolakisl said:

I have multiple tankless heaters both at my home and my inlaws.  I have a heat pump tanked one at the office.

I forget the brand off the top of my head, but the two in my home are both 13 years old and "knock on wood", I have essentially had zero issues.  The only issue I did have was the flame sensor on the unit needed to be rubbed down with some steel wool a few months ago as it was no longer detecting the flame as a result of carbon buildup.  I have flushed the tanks with vinegar every few years as routine maintenance.  The burner fires up very fast, just a couple seconds and it is making hot water.  These are mounted on the outside of the house (I live in Texas).  They survived the big freeze to 6 degrees two nights in a row we had 2 years ago just fine (I did not lose electricity, if I had, I would have needed to drain them very quickly).  The one unit is located on the outside wall just about 8 feet from the one kitchen sink.  That sink gets hot water in just a few seconds.  Maybe 5 seconds.  You can hear the burn come on in less than 1 second when you turn on the hot water and the remaining time is flushing through the water between the sink and the heater.

EDIT: My tanks or Noritz.  I timed the kitchen sink at 10 seconds which is about 8ft away.  The flow rate of that sink is a bit more than 1gpm (3 cups in 10 seconds).

All depends on your water. We have "aggresive water" here and in my former home location and worse here in the city now. It eats through brass fittings (de-zincifies them) and copper pipe with impurities in it. Tankless water heaters last about 2-3 years as is their expected expected life and maximum warranties. Heat exchangers all developed leaks. One Rhudd unit was replaced under warranty before the 1 year mark.

The system must be flushed with 4-6 gallons of 5% vinegar every six months for 4-6 hours or the flow sensors (mainly) would become desensitized with calcium build-up or sodium from water conditioning equipment (ion exchange) . The large capacity (197,000 BTU) meant the minimum burner capacity needed a larger flow with full temperature rise or the logic wouldn't consider turning on or it would have boiled the water into steam.

The pilot flames would blow out every few months when the storm winds blew. 50-90 mph winds were typical on the hill were I was. This took powering down the unit, draining it, and rebooting to remove the lock-out. Rinnai or Rhudd units both had the same problems despite different chimney designs and manufacturers.

The cold water sandwich problem of the tankless concept was much reduced in later designed from the earliest Rinnai units installed. They started having small tanks inside them for carry over of hot water demand.

Later the designs included small circulation pumps to keep an external tank of hot water hot as the problems became public knowledge. The circulation pumps were not for instant hot water in the pipes but that design idea may have changed also, once you have a built in circ. pump.

[keepersg]

Thank you for the point about 'aggressive water' Didn't know about the water in SW Ontario or for that matter here in Portland. Portland's water comes off of Mt. Hood and is chlorinated and then pH adjusted with ammonia (forming chloramine) to a pH of about 8.5-8.8. Then it's treated with sodium carbonate and carbon dioxide which reduces/eliminates corrosion of vulnerable plumbing components.  This is an important point.  Untreated chlorinated water with a pH above 8.3 (alkaline) will dissolve the zinc out of brass fittings (and dissolve lead).  So will significantly acidic water that is not chlorinated.  I've thought about getting a tankless water heater but did not know about this potential complication.  

[apostolakisl]

10 hours ago, larryllix said:

All depends on your water. We have "aggresive water" here and in my former home location and worse here in the city now. It eats through brass fittings (de-zincifies them) and copper pipe with impurities in it. Tankless water heaters last about 2-3 years as is their expected expected life and maximum warranties. Heat exchangers all developed leaks. One Rhudd unit was replaced under warranty before the 1 year mark.

The system must be flushed with 4-6 gallons of 5% vinegar every six months for 4-6 hours or the flow sensors (mainly) would become desensitized with calcium build-up or sodium from water conditioning equipment (ion exchange) . The large capacity (197,000 BTU) meant the minimum burner capacity needed a larger flow with full temperature rise or the logic wouldn't consider turning on or it would have boiled the water into steam.

The pilot flames would blow out every few months when the storm winds blew. 50-90 mph winds were typical on the hill were I was. This took powering down the unit, draining it, and rebooting to remove the lock-out. Rinnai or Rhudd units both had the same problems despite different chimney designs and manufacturers.

The cold water sandwich problem of the tankless concept was much reduced in later designed from the earliest Rinnai units installed. They started having small tanks inside them for carry over of hot water demand.

Later the designs included small circulation pumps to keep an external tank of hot water hot as the problems became public knowledge. The circulation pumps were not for instant hot water in the pipes but that design idea may have changed also, once you have a built in circ. pump.

Well I don't know what to tell you, I have none of these problems.  And in addition, I just remembered, I had another tankless heater for 11 years at my old office before I moved out.  I never did anything to it at all ever.  It would be about 21 years old now, not sure if it still is working, but it would have been a very early generation unit.  My tankless heaters do not have pilot lights, they have electronic ignition.  They have never "blown out" or needed to be drained and rebooted or anything like that.  I don't get a lot of 90mph winds, but during Harvey we had several days of 40mph winds and I never missed a hot shower.  My home heaters I have flushed twice in 13 years.  I have to admit I didn't know I was supposed to flush them and didn't do the first flush till they were 10 years old until my father in law asked me about it (he has tankless as well and is maybe 8 years old). If your water is crap, then it is going to kill any type of heater.  Our water is not particularly good with about 250ppm of dissolved solids.  Of course the details on which dissolved solids will make a difference and I frankly don't know much about that.  Putting a small tank on a tankless heater is not something that I see advertised for sale.  Makes no sense to do that as far as I can tell.  It only takes about 2 seconds for the water to get hot and a small tank would have the same issues as a recirc pump, lots of cycling.  And of course it would have to have a recirc pump to keep the little tank hot.  I would love to see a link to "tankless" heater with such a tank.

Anyway, at 13 years, my tankless heaters have lasted longer than any tank heater I have ever had.  My heatpump unit at my office does have a tank but is a different bird and all being a heat pump.  It is about 11 years old.  I have never done any service to it.  The load on that one is there is no showering at the office.  But we do a lot of loads of laundry on the sanitize cycle.

I am now going to go knock on some wood.

[TheA2Z]

Had a tankless in old house with a chilipepper installed in master bath farthest from tank.  Worked great for 5 years and we moved.

New house had a 12 year old tankless that went out on me.  Started leaking but I think it was due to water.  On City water but lots of red dirt in water.  I put a big spin down filter and two 20" sediment filters in parallel.  I also put a smaller sediment filter on the inlet to the tankless.  New Renai tankless doing great.

I use isy, now eisy to control a pump at water heater on hot line with a Zwave plus plug.  At end of line, I use a 120V solenoid valve plugged into zwave plus outlet that opens when the hot water pump comes on.  Valve stays open until the water gets hot then shuts down the pump and the valve.  Being using it for about 5 years and works great.  Motion in the water spots on far end of house (kitchen, laundry, or bathroom) will trigger the pump valve combination until it gets hot.  I keep a timer on it too as not to come on more than every 45 minutes as water in pipes stays hot enough.

[larryllix]

Well I don't know what to tell you, I have none of these problems.  And in addition, I just remembered, I had another tankless heater for 11 years at my old office before I moved out.  I never did anything to it at all ever.  It would be about 21 years old now, not sure if it still is working, but it would have been a very early generation unit.  My tankless heaters do not have pilot lights, they have electronic ignition.  They have never "blown out" or needed to be drained and rebooted or anything like that.  I don't get a lot of 90mph winds, but during Harvey we had several days of 40mph winds and I never missed a hot shower.  My home heaters I have flushed twice in 13 years.  I have to admit I didn't know I was supposed to flush them and didn't do the first flush till they were 10 years old until my father in law asked me about it (he has tankless as well and is maybe 8 years old). If your water is crap, then it is going to kill any type of heater.  Our water is not particularly good with about 250ppm of dissolved solids.  Of course the details on which dissolved solids will make a difference and I frankly don't know much about that.  Putting a small tank on a tankless heater is not something that I see advertised for sale.  Makes no sense to do that as far as I can tell.  It only takes about 2 seconds for the water to get hot and a small tank would have the same issues as a recirc pump, lots of cycling.  And of course it would have to have a recirc pump to keep the little tank hot.  I would love to see a link to "tankless" heater with such a tank.
Anyway, at 13 years, my tankless heaters have lasted longer than any tank heater I have ever had.  My heatpump unit at my office does have a tank but is a different bird and all being a heat pump.  It is about 11 years old.  I have never done any service to it.  The load on that one is there is no showering at the office.  But we do a lot of loads of laundry on the sanitize cycle.
I am now going to go knock on some wood.

Strangely enough the units were on well water with only about 14 grains of hardness. mostly lime. Water was alkaline, not acidic.

In the city where i had water dissolve the impurities right out of the copper plumbing, the water was extremely hard with calcium and very basic...high pH, not acidic.

After experiencing several piping pea holes and flooding mess, the building codes here outlawed the cheaper copper pipe they had installed for twenty years and now all copper pipe is thicker walled and has some certification requirement. I sold that house. I knew what was coming over the next decade inside those walls. In addition that house was full of aluminum wiring and they used all push in self grabbing receptacles. They didn't know any better and those codes got changed right after also.

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[TheA2Z]

2 hours ago, larryllix said:

Strangely enough the units were on well water with only about 14 grains of hardness. mostly lime. Water was alkaline, not acidic.

In the city where i had water dissolve the impurities right out of the copper plumbing, the water was extremely hard with calcium and very basic...high pH, not acidic.

After experiencing several piping pea holes and flooding mess, the building codes here outlawed the cheaper copper pipe they had installed for twenty years and now all copper pipe is thicker walled and has some certification requirement. I sold that house. I knew what was coming over the next decade inside those walls. In addition that house was full of aluminum wiring and they used all push in self grabbing receptacles. They didn't know any better and those codes got changed right after also.

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My house and neighborhood has the same thin-walled copper and pinholes are popping all over the place.  The main culprit is the red dirt I discussed in post above.  The red dirt is high in iron.  Iron settles in copper pipes and causes pinholes due to dissimilar metal corrosion.

If I replace it in future Im going Pex.  I always preferred copper but after this fiasco, I'm out.  For now, added serious filtration listed above to hold me over.

[apostolakisl]

7 hours ago, larryllix said:

Strangely enough the units were on well water with only about 14 grains of hardness. mostly lime. Water was alkaline, not acidic.

In the city where i had water dissolve the impurities right out of the copper plumbing, the water was extremely hard with calcium and very basic...high pH, not acidic.

After experiencing several piping pea holes and flooding mess, the building codes here outlawed the cheaper copper pipe they had installed for twenty years and now all copper pipe is thicker walled and has some certification requirement. I sold that house. I knew what was coming over the next decade inside those walls. In addition that house was full of aluminum wiring and they used all push in self grabbing receptacles. They didn't know any better and those codes got changed right after also.

Sent from my SM-G781W using Tapatalk
 

?  IDK.  Maybe it is the brand.  I have Noritz as I mentioned.  Maybe it is the water?  I would assume my water has a lot of calcium in it as we are all limestone here and the water comes out of a lake reservoir that is filled with rain water.  All the creeks running into it are "lined" with limestone as is the lake reservoir.  It is highly unlikely that there is any iron in the water as iron is often advertised as a missing ingredient for healthy lawns around here.

Anyways, I am very happy with my heaters.  They consume zero space as they are fitted between the studs.  I have no issues aside from the flame sensor needing to be cleaned.  That just took a quick youtube video tutorial to hook me up with the fix.  They seem to cost me about $30/mo in propane as a rough estimate based on how much I spend keeping my propane tank filled and the fact that almost all the propane use is hot water.  We also have a gas grill, griddle, and kitchen burners.  But I suspect their use is a rounding error.