Tankless water heater & Recirculation Pump

[tb001]

Does anyone have any experience with a tankless water heater used on a house with a recirculation pump? Pros and cons?

Up until two weeks ago, we had two 50gal water heaters daisy chained together to supply our house. It’s large and a long run to the master suite from the water heater closet. One of our water heaters failed in spectacular fashion a few days before we left for vacation. I suppose better than while we were away, but still made a heck of a mess.

The plumbers are recommending we replace it with a tankless heater. The pitch is that it’s twice as much but will last twice as long and be more energy efficient. Which if you’re only heating on demand makes sense. But if you’re constantly recirculating the water, it seems like it needs to be firing on high all the time? It just intuitively doesn’t make sense to me that it would be more efficient in this scenario, but maybe it’s no worse than keeping 100gal of water warm all the time?

We just want HOT water and lots of it, with good water pressure, in our master suite. And don’t want to wait for 5 minutes for the shower to warm up or be spending far more for the more ‘efficient’ solution. And I have this vague notion that the water doesn’t get as hot, or it won’t be able to maintain adequate flow or pressure, but I don’t know if that’s a dated experience.

Any opinions would be appreciated. We’re in a holding pattern until I make a decision. I would actually love to reclaim the space in the water heater closet, and it would be worth paying the extra money for that alone, but I don’t want to pay up for something that is going to cost more to operate and give us a subpar hot water solution.

 

[skyking1]

Tankless plus recirc makes no sense.
If you want to go tankless, put a second heater near where you need it to get rid of the hot water lag.
If you like a recirc system then get a traditional tank heater and keep the recirc.

 

[triangle]

The re-circulation part should help avoid wasting cold water at the tap, for the unheated water sitting in the line. Though I am not sure it would play nicely with the tankless heating mechanism (which does not want to overheat the water for safetly reasons).

A few advantages of a tankless over tank is not having a tank full of water sitting around for the eventual day when the tank fails. And one can effectively get endless hot water. Both big pluses.

The biggest disadvantage is that many (some? most?) units do not cut on at a low flow rate. That when sizing for a whole house, which takes into account the number of bathrooms, taps, etc. a unit sized for home with more than one bathroom may not work very well when only a single person is needing hot water. If you like high volume showers there should be no problem, but if you want a little hot water to wash your hands then the unit may not turn on at this lower rate. Also it does take longer for the hot water to reach the tap, as the pipes near the heater are not leaching heat like with a tank unit. That has been my experience after installing a natural gas powered tankless unit in our home with copper water lines. It works well enough for taking a shower, though I have to use a little extra water beyond my minimal satisfaction, a flow of 0.6/0.7 gpf flow rate is needed for the flame to be lit. This is not good for light duty tasks. Current tankless units may work better in this regard at working at lower flow as well as higher demands like taking a shower and washing the clothes at the same time, but you should examine this flow aspect closely.

 

[frank]

something else to consider is the gas usage. I have considered these tankless water heaters and they tell me you have to have the gas company assess your gas volume to make sure you have enough gas supply to run them.

 

[mpeirce]

We gave a gas powered TWH and a recirc pump. No problem. Our last house had a similar setup.

We have the recirc pump turn off over night and when we leave the house.

Our motivation wasn’t really efficiency, but convenience. We love the unlimited hot water - especially when we have guests. We also really like have hot water without waiting for it.

The TWH even has the recirc pump built in. So it’s built for this usage pattern.

 

[ShokWaveRider]

Tankless plus recirc makes no sense.
If you want to go tankless, put a second heater near where you need it to get rid of the hot water lag.
If you like a recirc system then get a traditional tank heater and keep the recirc.

Absolutely Not true, we have had one for 12 years with the recirc pump at the furthest point. It is on demand. Works great. You just have to get the right one. Easy to install one's self.

Our Rinnai is in the garage and our master bath shower is at the furthest possible point it can be. I installed the pump under one of the vanities. The new ones are radio controlled with a remote, so we can turn it on from the kitchen or anywhere. Takes about 30s to one minute depending on outside temperature to heat up.

Ours had a 10 year life span, we replaced it with another from the same company.

https://chilipeppersales.com/

 

[Aerides]

something else to consider is the gas usage. I have considered these tankless water heaters and they tell me you have to have the gas company assess your gas volume to make sure you have enough gas supply to run them.

Yes, this, or if you are on electric, get that looked at. We were interested in going tankless but our central electrical system is insufficient (at least that's what we were told a few years ago when we looked into it). Either way, get more than just a plumbers input before you proceed.

 

[ExFlyBoy5]

I think it just depends on how much your energy costs. We thought about converting to a tankless system (currently have a recirculator set to run during the day) but the savings of on demand just isn't there...for us.

 

[ERD50]

...
The plumbers are recommending we replace it with a tankless heater. The pitch is that it’s twice as much but will last twice as long and be more energy efficient. Which if you’re only heating on demand makes sense. But if you’re constantly recirculating the water, it seems like it needs to be firing on high all the time? It just intuitively doesn’t make sense to me that it would be more efficient in this scenario, but maybe it’s no worse than keeping 100gal of water warm all the time? ...

First of all, that whole "keeping 100gal of water warm all the time" is not as big a deal as most people think.

It takes a lot of energy to raise the temperature of water from ground temperature to the 130F or whatever you have it set to. Theoretically, it takes no energy at all to maintain that temperature - but in the real world, heat is lost to the surrounding air and that loss must be made up. But modern tanks are very well insulated, the losses are low (especially electric water heaters, as they have no flue).

Consider the other issues that posters have mentioned, installation isn't always easy for a TWH, you can run into considerable expense if you have to upgrade the electrical or gas supply.

Absolutely Not true, we have had one for 12 years with the recirc pump at the furthest point. It is on demand. Works great. You just have to get the right one. Easy to install one's self. ...

Ours had a 10 year life span, we replaced it with another from the same company.

https://chilipeppersales.com/

I see that is a high volume pump, so it would trigger the TWH to turn on. The standard type of low volume recirculating pump either wouldn't trigger the TWH, or would cause the TWH to run a lot - as you say, you need one designed for TWH.

I guess if you are manually triggering the pump, you don't solve the 'problem' of having to wait for hot water, but you have eliminated the water waste (maybe a little energy is saved, as the warming water is cycled back to the tank, doesn't have to be fully heated).

-ERD50

 

[ERD50]

.... A few advantages of a tankless over tank is not having a tank full of water sitting around for the eventual day when the tank fails. ... .

Not sure this makes much difference. Your water supply is going to be at least 5 GPM, and since your water supply would keep 'feeding' the leak, it would all get replaced from the supply. You could have a 50 gallon tank or a 2 gallon tank, the leak would be the same.

Even in the case that the tank just totally collapsed/ruptured and spilled it's guts instantly (never heard of that), yes, you'd have an extra 50 gallons dumped, but that's just 10 minutes or less of water flow - unless you catch it right away and can turn off the supply, it's not going to make much difference.

-ERD50

 

[tb001]

We gave a gas powered TWH and a recirc pump. No problem. Our last house had a similar setup.

We have the recirc pump turn off over night and when we leave the house.

Our motivation wasn’t really efficiency, but convenience. We love the unlimited hot water - especially when we have guests. We also really like have hot water without waiting for it.

The TWH even has the recirc pump built in. So it’s built for this usage pattern.

This sounds like what they’re recommending for us. It has a built in pump. I assume we would turn it off overnight, like we do our current pump.

Do you have any problems with flow rate of the hot water if multiple people are taking a shower at once? Is the water getting very hot? They suggested if that was an issue we could always add a second, as long as we ran a 1” gas line when we installed the first.

We have a gas furnace right above the water closet, and an electrical panel with extra space about 10ft away with attic access, so hook-ups should be fairly straight forward.

ERD, you touched on my concern. It just seems like it will use more gas, though I admit I don’t fully understand how the recirculation pump aspect works. If it’s close to what we’re using now for gas/electric, that would be fine. But I don’t want to spend more on the unit and have increased costs!

They’ve also told us that we will need to descale the unit annually to not void the warranty, which is annoying. That said, I want the extra space in the water closet!

 

[someguy]

Our analysis led us to stick with the traditional tank heaters. A couple considerations I don't think have been mentioned:

1) Tankless may require a decent amount of ongoing maintenance (cost or time, same thing in my book).
2) Tankless generally won't run in a power outage.
3) Life expectancy of tankless is a key factor in TCO analysis.

 

[skyking1]

Absolutely Not true, we have had one for 12 years with the recirc pump at the furthest point. It is on demand. Works great. You just have to get the right one. Easy to install one's self.

Our Rinnai is in the garage and our master bath shower is at the furthest possible point it can be. I installed the pump under one of the vanities. The new ones are radio controlled with a remote, so we can turn it on from the kitchen or anywhere. Takes about 30s to one minute depending on outside temperature to heat up.

Ours had a 10 year life span, we replaced it with another from the same company.

https://chilipeppersales.com/

I stand corrected. That single loop recirc makes sense. The traditional recircs loop the whole house, and now the supposed energy savings of the tankless are negated.
traditional recircs are on a timer that covers the most likely possibilities, so the tankless would run for 12~14 hours a day for a simple timer.

 

[mpeirce]

Do you have any problems with flow rate of the hot water if multiple people are taking a shower at once? Is the water getting very hot? They suggested if that was an issue we could always add a second, as long as we ran a 1” gas line when we installed the first.

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”.

They’ve also told us that we will need to descale the unit annually to not void the warranty, which is annoying. That said, I want the extra space in the water closet!

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

 

[ncbill]

Keep the tank water heaters & add a recirculation pump for the bathroom.

Tankless are a source of ongoing revenue for plumbers since most homeowners will also hire them do the descaling at $100+ a pop...depending on your local water's mineral content you might have to do that several times annually, not just once.

As for energy efficiency, the amount of gas consumed annually to heat water is a rounding error compared to the annual amount consumed for space heating.

Also, those considering tankless need a plan in case of power failure.

Any amount of water freezing in a tankless heater means...you buy a new one.

 

[tb001]

Just to clarify, we already have a whole house recirculation pump in place in the water heater closet. This unit would theoretically replace both water heaters (our second is ~10yrs old) and the current pump and have a 15yr lifespan.

Our handyman told us his brother has one and hates it, but it was difficult to figure out why. Something to do with having 3-4 people taking showers at once. Maybe not enough flow? We were all set to switch until he told me this.

And yes, the descaling thing is annoying to me. Just another thing to do and I assume you have to pay a plumber to do it, so you have ‘proof’ for the warranty.

 

[Exchme]

The pump for the tank less heater only turns on when you are running hot water. It is there as a minimum flow device to make sure you are heating water, not boiling away the water in the heat exchanger exposed to the flame. That would lead to high wall temperatures and lime build up and premature failure.

Note this type has minimal impact on how long it takes to get hot water at the tap, the big time lag is still the water in the pipes between the heater and the user. Ours is coming up on 10 years old and has been trouble free, except when we had the big Texas Freeze and lost power, we also lost hot water as the burner won't turn on without the pump.

 

[tb001]

The pump for the tank less heater only turns on when you are running hot water. It is there as a minimum flow device to make sure you are heating water, not boiling away the water in the heat exchanger exposed to the flame. That would lead to high wall temperatures and lime build up and premature failure.

Note this type has minimal impact on how long it takes to get hot water at the tap, the big time lag is still the water in the pipes between the heater and the user. Ours is coming up on 10 years old and has been trouble free, except when we had the big Texas Freeze and lost power, we also lost hot water as the burner won't turn on without the pump.

I don’t think this is the case for the unit we’re looking at? It has a recirculating pump built into the unit that, as I understand it, constantly loads the pipes with hot water. That’s what we have now as well, just as a separate unit. Maybe I’m confused as to how it works?

That’s an interesting point about the power use though. We lose power somewhat regularly. We’re in the process of putting in a generator, but it all adds up…

 

[euro]

Our handyman told us his brother has one and hates it, but it was difficult to figure out why. Something to do with having 3-4 people taking showers at once. Maybe not enough flow? We were all set to switch until he told me this.

This is indeed an issue with TWH - the flow is limited and if you need to be able to run several showers plus the dishwasher all at the same time, then you have to get a very large ( and hence expensive) system. That said, most households (especially those with just two or three people) rarely face that problem. In our own experience, even when our 2 teenagers still lived at home, the scenario of 2 showers at the same time almost never happened. So, your situation may be different. Maybe you have 4 people who carpool to work and all get up at the same time and want to take showers concurrently. In that case, definitely don’t use TWH. But if you can go with a fairly small unit, it may well be worth it. I have a system installed in one of my rentals because I too wanted to re-claim all that space the regular water heater took up in the kitchen pantry. Total cost installed was $2000 and the tenants love the extra space and the unlimited stream of hot water.
Really depends on usage patterns, water quality, etc.

 

[mpeirce]

And yes, the descaling thing is annoying to me. Just another thing to do and I assume you have to pay a plumber to do it, so you have ‘proof’ for the warranty.

It’s not hard to do it yourself, look on YouTube for tutorials on how to do it.

At the old house the plumber did it for us the first time and showed us how it’s done. Pretty easy really.

 

[tb001]

This is indeed an issue with TWH - the flow is limited and if you need to be able to run several showers plus the dishwasher all at the same time, then you have to get a very large ( and hence expensive) system. That said, most households (especially those with just two or three people) rarely face that problem. In our own experience, even when our 2 teenagers still lived at home, the scenario of 2 showers at the same time almost never happened. So, your situation may be different. Maybe you have 4 people who carpool to work and all get up at the same time and want to take showers concurrently. In that case, definitely don’t use TWH. But if you can go with a fairly small unit, it may well be worth it. I have a system installed in one of my rentals because I too wanted to re-claim all that space the regular water heater took up in the kitchen pantry. Total cost installed was $2000 and the tenants love the extra space and the unlimited stream of hot water.
Really depends on usage patterns, water quality, etc.

Ah, this is very helpful, thank you. Yes, the person who was complaining has three daughters and his wife all getting ready for school/work at the same time, so that makes a ton of sense. We do frequently have two showers running at once, but not usually more than that. As I understand it, as long as we plumb for it now, if it became an issue, we could add a second unit to increase the flow.

 

[pjigar]

Tankless plus recirc makes no sense.
If you want to go tankless, put a second heater near where you need it to get rid of the hot water lag.
If you like a recirc system then get a traditional tank heater and keep the recirc.

+1.

I installed two zoned manifolds (each with a hot water heater) at two different locations in the center of hot water outlets in the attic when doing a gut-out renovation. I get hot water at any outlet in less than 10 seconds without any recirculation pumps. PEX pipes all around.

 

[Music Lover]

First of all, that whole "keeping 100gal of water warm all the time" is not as big a deal as most people think.

It takes a lot of energy to raise the temperature of water from ground temperature to the 130F or whatever you have it set to. Theoretically, it takes no energy at all to maintain that temperature - but in the real world, heat is lost to the surrounding air and that loss must be made up. But modern tanks are very well insulated, the losses are low (especially electric water heaters, as they have no flue).
-ERD50

We turn the well pump and HW tank off when we leave the cabin. If we come back 3 days later the water is still lukewarm. So, they really don't use that much energy.

Also, if you live in a winter climate then during heating season any "lost" heat is regained by warming the interior space.

 

[triangle]

Not sure this makes much difference. Your water supply is going to be at least 5 GPM, and since your water supply would keep 'feeding' the leak, it would all get replaced from the supply. You could have a 50 gallon tank or a 2 gallon tank, the leak would be the same.

Even in the case that the tank just totally collapsed/ruptured and spilled it's guts instantly (never heard of that), yes, you'd have an extra 50 gallons dumped, but that's just 10 minutes or less of water flow - unless you catch it right away and can turn off the supply, it's not going to make much difference.

-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.

 

[ncbill]

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.

There are gas tankless water heaters that require no electricity...the flow of water provides enough power to the piezo to ignite the gas...natural draft exhaust, of course.

Several of those were retrofitted to the bathrooms at our local Boy Scout camp for hot showers since there's no power at any of the bathrooms.

Water comes from a tank up on ridge behind camp. Added a large propane tank outside each bathroom for the tankless heater.