Tankless water heater & Recirculation Pump

[pjigar]

While a tankless unit could also leak, it would happen in a different manner and less often.

I have had two tankless leak on me.
An 8 year old unit: Corrosion caused the heat exchanger to leak. Started slow (like a tank heater) and then slowly got worst. We limped along with a leak for over a month until we replaced! The heater was in the attic over a porte cochère so we were note in any danager of s structural damage.
An week old unit: The quick connects inside the unit leaked. It was a manufacturing defect. All it needed was some silicone grease and reassembly.

 

[ERD50]

I don't understand all the failure modes and failure rates, but my understanding is that most (all?) hot water tanks will eventually leak once the anode rod is consumed, though perhaps it can be periodically replaced to avoid this common failure. While a tankless unit could also leak, it would happen in a different manner and less often.

Related to others commenting about the space savings, my old hot water heater was in an unheated attic where there was plenty of space for a tall water tank. When it did finally leak, it was in the middle of the night and some ceiling damage occurred before it was discovered. The tankless unit which replaced it easily fit in the crawlspace closer to the all plumbing. And much less damage would result if a major leak did occur in the future. Years later my neighbor had a similar hot water tank failure and they installed a tankless to the exterior of the home.

I have considered installing a UPS+Battery backup for the tankless electronics and igniter, but so far have had good luck with the power not going out for very long.

I'm not sure there is that much difference in the rates of leaks in tankless vs tank, and the previous post shows their experience.

Water heaters aren't put in attics in this area, so I'm not familiar with the details, but if I were to do that, I'd have a large pan/drain installed, and something to deflect a spray type leak down to that pan. I'm surprised that isn't a standard for that type of installation.

And as mentioned, energy savings is rather debatable. But what is not debatable is the space savings, so if that is a driving factor, you've got your answer (although if you can find an attic installation you feel comfortable with, seems that would take up less living space?).

-ERD50

 

[WestUniversity]

We have a tankless. One of the best things we’ve bought. Both of our conventional tank water heaters were in need of replacement and the cost to do both was almost the same as the tankless heater.

Endless hot water is great. I’m not sure how a pump and a recirculating loop would work as there is nothing to circulate since there is no tank of hot water…

 

[Mike2025]

We’ve had Navien TWH’s. The old house had natural gas, while the new house has propane. You need the larger gas lines, but that wasn’t an issue for us.



We’ve had three showers running concurrently without problems. Perfect for when we have a full house here at the lake.



Also, the units we have are “condensing” which means they use almost all the energy from burning gas (98% efficient). The exhaust gas temperature is "barely warm” and can be vented out horizontally using just a PVC pipe. We like that since we located the unit in a crawl space under the floors so we didn’t need a “utility room”.







Yes, you want to descale it annually. Change your furnace filters and descale the water heater.

No need for descale if there is a water softener installed.

 

[triangle]

I'm not sure there is that much difference in the rates of leaks in tankless vs tank, and the previous post shows their experience.

Water heaters aren't put in attics in this area, so I'm not familiar with the details, but if I were to do that, I'd have a large pan/drain installed, and something to deflect a spray type leak down to that pan. I'm surprised that isn't a standard for that type of installation.

And as mentioned, energy savings is rather debatable. But what is not debatable is the space savings, so if that is a driving factor, you've got your answer (although if you can find an attic installation you feel comfortable with, seems that would take up less living space?).

-ERD50

The original hot water tank had a drain pan but I think the leak was more like a pinhole or high up enough on the tank that it streamed out over the pan which was not much larger in diameter than the tank itself. I do not remember all the details but I was happy about not having a tank above the living space. I think the garage is a better place for most homes, but that was not done in some of the designs in my neighborhood, due to their overall layout in relation to the municipal service hookups.

While the energy savings would be marginal today, if one was away very often that might make enough difference in usage to consider from a waste point of view, though not in the overall lifetime cost. My tankless was installed before fracking when natural gas was expensive and that aspect was touted as a sales point but I don't think the monthly gas usage changed all that much. I have been happy with its reliability, but not happy that it cannot support a low flow application like producing a low flow of warm water to wash a child's hands.

 

[Surewhitey]

We have a gas version of a Navien (don't know the model). We moved it to the attic (including gas line) and the 3 year ago price of $2675.

The home is small and not much travel to the kitchen and bathroom (maybe 10 ft to each) so no recirc was needed. Has worked well for us.

By moving, we gained a pantry in the kitchen too.

 

[mpeirce]

I have been happy with its reliability, but not happy that it cannot support a low flow application like producing a low flow of warm water to wash a child's hands.

I think this depends on the model you have. Our TWH doesn’t have this problem, even when the recirculate pump is turned off.

 

[ERD50]

I think this depends on the model you have. Our TWH doesn’t have this problem, even when the recirculate pump is turned off.

Do you know how it handles low flow? This is/was a common complaint for the TWH (and thank goodness no one is abbreviating that THWH! )

I would imagine a TWH that can provide both high and low flow would either need a multistage/variable burner (or heating elements if electric), or maybe some sort of bypass pump/valve to keep a higher flow through the unit (but where would the water go?)? Is there another way?

-ERD50

 

[mountainsoft]

We have used tankless water heaters at many rentals we have stayed at and enjoy them. I originally wanted to install a tankless water heater when we built our house, but it would have required a major (expensive) upgrade to our electrical service. We have cold well water and would have needed a large tankless heater.

Gas heaters are not an option for me. I have a serious fear of gas. I've seen too many explosions and had a couple friends die from a propane explosion in an RV. I also prefer to minimize use of fossil fuels.

So, I installed a large 80 gallon tank water heater with a recirculating pump and return line to reach our bathroom at the other end of the house. If the pump is off it can take well over a minute for hot water to reach the shower. That's a lot of wasted water and cold standing around in the winter. If the pump is on we get hot water in about 5 seconds.

Unfortunately, thanks to new tank insulation standards, we won't be able to install an 80 gallon tank again. They're too large to fit the space now. So we will be forced to down size to a 50 gallon tank, which ironically, is about the same size now as our 80 gallon tank.

 

[mpeirce]

Do you know how it handles low flow? This is/was a common complaint for the TWH (and thank goodness no one is abbreviating that THWH! )

I believe there is a small (0.5gal?) buffer tank in the unit. It allows lower flow rates without sending cold water out. Also the “cold water sandwich”.

The ComfortFlow Technology is built into some Navien tankless water heater models to deal with the hot water delays as well as the notorious cold water sandwiches that can really ruin your time in shower. Hot water delays happen because the water heater is at some distance and it is taking time for hot water to come all the way to your bathroom. Cold water sandwiches happen when you close the tap for a few seconds for some reason and your tankless unit stops because the water use has stopped. When you open the tap, it takes time for the tankless water to sense the water flow and readjust the water tamperature so you get sporadic hot and cold water for upto a minute.

 

[Out-to-Lunch]

Things have improved over the years.

I installed a Bosch about 15 years ago, and it did not handle low flows that well and generated the cold-water sandwiches in many applications.

I installed a Rheem RTGH-95DVLN-2 last winter. It has exceeded my expectations. It fires up extremely quickly, it can handle flows as low as 0.26 gpm, and there are no noticable cold-water sandwiches. I am thrilled with it.

 

[triangle]

@mpeirce and @Out-to-Lunch, your Navien and Rheem TWH sound like a nice advancement over my older model Rinnai. Something to look forward to if mine breaks beyond repair. That Rheem with a range of 0.26-9.5 gpm is quite an improvement over my 0.6-6(7) gpm unit. I think it would be hard to use 9 gpm unless a large household was really trying hard.

 

[Out-to-Lunch]

@mpeirce and @Out-to-Lunch, your Navien and Rheem TWH sound like a nice advancement over my older model Rinnai. Something to look forward to if mine breaks beyond repair. That Rheem with a range of 0.26-9.5 gpm is quite an improvement over my 0.6-6(7) gpm unit. I think it would be hard to use 9 gpm unless a large household was really trying hard.

Yes, I agree, 9.5 gpm is complete overkill for just my wife and me. But I like overkill!

 

[Lakedog]

@mpeirce and @Out-to-Lunch, your Navien and Rheem TWH sound like a nice advancement over my older model Rinnai. Something to look forward to if mine breaks beyond repair. That Rheem with a range of 0.26-9.5 gpm is quite an improvement over my 0.6-6(7) gpm unit. I think it would be hard to use 9 gpm unless a large household was really trying hard.

My propane Rinnai has the same range (0.26 to 9.5 gpm). The house was built in 2015 and assume the water heater was installed then.

 

[Out-to-Lunch]

Things have improved over the years.

I installed a Bosch about 15 years ago, and it did not handle low flows that well and generated the cold-water sandwiches in many applications.

I installed a Rheem RTGH-95DVLN-2 last winter. It has exceeded my expectations. It fires up extremely quickly, it can handle flows as low as 0.26 gpm, and there are no noticable cold-water sandwiches. I am thrilled with it.

This was mildly amusing: As I said, I installed a Bosch (250SX) about 15 years ago. Its quirks were a bit annoying, but tolerable.

Then, my GE dishwasher broke beyond repair, so I replaced it with a Bosch DW. But the flow rate during filling the Bosch DW was too low to trigger the Bosch TWH! So I decided it was time to replace the TWH, and decided on the Rheem.

Of course, that meant that the Bosch TWH soon decided it was ready to go, too, and it failed soon thereafter!

 

[Breedlove]

Wow , in our house we installed an electric TWH and it has been fine . Our old house used to have a HWT in the attic. It was so expensive to get that replaced. With our current tankless it is in a closet . It can be removed and installed in 20 minutes.For us the function is fine. When we built this house the old plumber said all the same things. Then he told me mice were going to eat my Pex. I ended up plumbing my house myself.

 

[Out-to-Lunch]

. Our old house used to have a HWT in the attic. It was so expensive to get that replaced. With our current tankless it is in a closet .

That is a good point about the small size of the TWH. My old tanked WH was, of course, near the furnace to use the flue (1929 house). This location happened to be on the opposite side of the house compared to the hot water runs to the kitchen and bathrooms. I located the TWH to the laundry room, hanging on a wall near the washing machine, just feet away from the kitchen/bath vertical runs. (There would be no space in that room for a direct-vented tanked WH.) Even with the delays in firing my original TWH, I still got water to the sinks faster than with the tanked heater, and with less wasted energy to boot.

 

[mpeirce]

That is a good point about the small size of the TWH. My old tanked WH was, of course, near the furnace to use the flue (1929 house). This location happened to be on the opposite side of the house compared to the hot water runs to the kitchen and bathrooms. I located the TWH to the laundry room, hanging on a wall near the washing machine, just feet away from the kitchen/bath vertical runs.

That’s what motivated us the first time we bought a TWH. We had two tanks sitting next to the furnace on the opposite side of the house from ALL water usage. It was really dumb and took minutes for the hot water to make its way from one side of the house to the other as well as from the basement to the third floor (for our shower). Drove us crazy.

The TWH got installed in the basement directly below all our water usage. Since the vent was just slightly warm CO2/H2O (it’s condensing system) in PVC it just poked our the side of the house

In the renovated lake house the TWH is literally directly below our shower in the “crawl space” (not really a cs, but...) and the bathrooms are clustered next to and above our master bath. We still need the recirc loop because the kitchen and laundry are over on the other side.

 

[SnowballCamper]

I've got tankless in our new (2015) home and love it. Natural gas is so much more efficient for making heat than electricity. It takes up little space, and no maintenance issues so far. I wouldn't go back to a tank water heater. If you have a large house, it might make sense to have a smaller unit close to the shower/bath, etc.

 

[523HRR]

We have a tankless water heater (Navien NPE-240A). Runs on propane. Produces tons of hot water. Four bedroom house and have never run out of hot water with a house-full of guests. We also have an independent recirculating hot water line to every tap in the house. A tremendous pleasure to have instant hot water at every faucet. I hear many complaints from neighbors in our community about how long they wait for hot water.

 

[mpeirce]

I've got tankless in our new (2015) home and love it. Natural gas is so much more efficient for making heat than electricity. It takes up little space, and no maintenance issues so far. I wouldn't go back to a tank water heater.

I really like having a TWH running on gas for the infinite hot water, but for efficiency, the heat pump water heaters with a tank are better.

They have two big flaws. 1. They have a long cycle time to reheat water and 2. They produce cool air. Great in the summer, very bad in the winter. I really hope they don’t mandate them as a few places are banning new gas hookups.

 

[JT90505]

We have a tankless on one side of the house for bathrooms, a tank on other side of house which supplies kitchen. Minimal wasted water for hot no matter where you are.

Have had tankless 12 years now, its been descaled twice. No other issues. We know several others with tankless, nobody descales annually (or more than annually, or even bi-annually).

Yes, you need electricity to run the tankless. So if power is unreliable where you live a tank would be a better choice for hot water.

Tankless water heaters are expected to last ~20 years (do a google search). Ours at 12 years is still going strong, knock on wood. We are on our third tanked water heater in the 25 or so years we have lived here...all highly ranked for reliability and installed by competent plumbers.

We purchased a tankless sized to run two concurrent showers, we've actually run two showers and concurrently filled bathtub. Ability to do so requires proper sizing.

What is important is the hot water, not whether it comes from tankless or tanked. For us. For us reducing water waste while waiting for hot water to traverse the house was important, having essentially unlimited hot water is a real nice to have when 4 people need to shower, and electricity has been reliable...again knock on wood.

 

[tb001]

I really appreciate all of the input on this thread. We’ve decided to move forward with the tankless, primarily due to the space savings. We’ll gain an outdoor storage closet where we can put all of our gardening tools and clear up some room in the garage.

One of our big hurdles was the power outage thing, as we do lose power frequently and one of the saving graces has been that we still had hot water. We didn’t realize this would be an issue until it was brought up here, so that’s been very helpful. I mentioned this to the installer and asked about the battery backup systems and he point blank told us not to waste our money. That we could throw in a battery back up for a computer or cable modem when we needed it and that would be good enough for a fraction of the cost. We’re due to have a backup generator installed this fall anyway, so worst case scenario we can run an extension cord from a powered outlet, if it ends up not being on a backed up circuit.

The comments on flow have also been very helpful. I’m pretty sure this will be sufficient, but we’ll have them run a large enough gas line that we can add a unit if we need to. A bit of extra $ now, but more flexibility later.

As part of the install, we’re also having a leak detection and auto shut off installed on the house. Hopefully next time we end up with a water leak it’s a little less dramatic!

 

[Out-to-Lunch]

Good. You go, tb!

 

[marko]

FWIW our new house came with a gas tankless. We LOVE it; DW tends to take very long showers and now we never run out of hot water.

In addition, I have kept meticulous records of our gas usage for 20 years; all things being equal, our tankless is using about $40 per month less gas vs our old tank system.