In a nutshell:

You will save 38% or more on hot water heating costs

You will not run out of hot water.

Hard water will require that you clean it (Vinegar).

Water takes a few seconds more to get hot.

The payback is dependent on getting a low cost installation. Look for utility rebates.

Look at the Navien: It is a condensing unit that is higher efficiency than other tankless units. The "A" models also include a buffer tank and circulating pump. It also uses PVC pipe for venting (much cheaper than Stainless Steel).

Are you talking electric, propane, or nat gas?

What jake says applies only to NATURAL GAS fired situations. You will have to do the spreadsheet homework to see if you'll EVER recoup the upfront costs. Tankless typically requires a larger diameter gas feed pipe... ALL the way back to the meter. (HELLO Mr. Plumber!) Bigger venting too... ROOF cuts? (HELLO Mr. Roofer!) Gas-fired tankless also requires electricity for its controls and ignition; there may be no outlet near your current WH. (HELLO Mr. Electrician!)

For ELECTRIC, tankless is pretty much a NO-GO, since:

a) the standby/idle consumption of modern conventional electric (tanked) WHs is very low (great insulation, no pilot light, no flue losses), so if you use hot water everyday, there's no significant energy savings--i.e. you NEVER recoup your upfront costs;

b) you will need MASSIVELY UPGRADED electric service--often all the way back to the transformer--to get the on-demand flow you expect.

c) thus, ELECTRIC tankless is a fool's errand, applicable only to military field hospitals, and super-tiny apts. which need every sq. inch of floor space.

PS: Don't know the reliability or storm-susceptibility of electric power in your area, but a gravity-vented conventional gas WH works without electricity (all the time, actually), whereas your tankless will be out of action, unless you plug in a genset.

Hard water will require that you clean it (Vinegar).

You KNOW you will NEVER, EVER even THINK to clean your WH, so better find out how long it lasts withOUT that attention.

In general, to date, tankless WHs seem to benefit those who sell them, and those who install them, far more than those who BUY them, LOL!

In summary: tankless WHs are *NOT* a plug-and-play replacement for tanked WHs, but instead require UPGRADES to your "domestic infrastructure". Gather ALL costs... diligently.

As the poster mentioned, they were thinking Takagi or Rinnai, which only make gas-fired units.

"In general, to date, tankless WHs seem to benefit those who sell them, and those who install them, far more than those who BUY them, LOL!"

That's an old timer talking, besides your Oldsmobile being extinct, soon you won't be able to watch TV with the rotary dial set your watching LOL

With all due respect, fixizin is engaging in FUD.

Tankless aren't a plug and play solution. You should do your homework, including knowing your installation costs up front. Don't forget electrical, venting and gas supply.

On the other hand, tankless can solve installation problems. They are small, they can be vented through the sidewall and can save the cost of venting through the roof or lining a masonry chimney. A power vent water heater costs about as much as a tankless. My installation didn't require significant gas line changes and actually saved me money over the cost of a standard tank + installing a vent in the chimney.

The reduction in gas use of about 38% (or more for condensing) is accurate (there are virtually no savings for electric tankless) and the dollar value varies according to the cost of energy in your area. Don't forget that the cost of energy will continue to increase. That said, payback in absolute dollar terms isn't high. As I said, check for tax and utility rebates.

The power issue is a non-issue... I don't know about you, but when the power goes out, my fist thought isn't "hey, I need to take a shower".

12 years ago, we self installed a Myson tankless. We're DIY anyway, but there were zero plumbers or plumber supply houses around that had even heard of tankless in our area> We had to order it from one of those magazines devoted to green and off the grid living. The unit cost us $500. THe venting and piping cost maybe another $300. 12 years ago, that was more than double the replacement costs of a "standard" water heater. Well, we saved $30 a month on our first gas bill. That was easy to calculate for us because it was summer and there was no other gas fired equipment in use. We didn't even use enough gas to get beyond the billng minimum! So, figuring that gas prices have done nothing but go up, I'd figure we saved a minimum of $40 per month for 12 years. That paid for the water heater the first year, and we're over $5000 in savings and counting. It's needed a single replacement pressure sensing diaphragm (around $7) the whole time, and we've cleaned the burners exactly once. We've got good water though. The original tankless water heater that my husband encountered in 1976 that was his inspiration for going tankless is also still in operation. I'll bet you can't say that for any tanked water heater installed in 1972!

Just wanted to give you a personal perspective. The payback timeline is a LOT longer if you aren't DIY and have to pay for the install. It's also a bit quirkier to deal with than tanked in that I can't shower and run the laundry at the same time. But, I can put my dirty gardening clothes into the washer and then shower for 45 minutes and then run the clothes 3x through a hot wash if I wanted to. A minor lifestyle adjustment as far as I'm concerned.

hendricus
I hope you understand the underlying joke was not accepting change and technology advancement

With many tank water heaters headed towards power vented and electronic ignition, those folk wont shower either, at least after the first tank full.

I myself have been tankless for over 20 years, now in my 3rd residence. The nice thing about my units (1 house, 1 vacation cottage) for the last 5-6 years as I can have two showers running and fill the washer. Todays units don't run cold as the older gen did, they continue to put out same temp, your just splitting volume.

One nice thing about the tankless is that you can place them very near the 'point of use'. The installation is small - so no need to put it back in the same spot as the old tank heater. This flexibility frees up space which could be used for other things, and could end up making installation easier too.

We have two of them, both hung an outside wall and outdoors - so venting is a non-issue. If I could redo it, I would have put one of them nearer the kitchen. (Right now it takes about 1 min for hot water to reach the main kitchen sink.) But the nice thing is that if I really wanted to, I could easily install a 3rd unit...

Gas savings? I suppose/hope there is some. But for us, the space savings and flexibility were the major considerations.

Besides recirc, try running a dedicated 1/2" line back to heater for the kitchen and depending on pipe sizes and manifolding you can cut that time by 50-75%

I'd figure we saved a minimum of $40 per month for 12 years.

I think your pretty optimistic with your savings. I have a family of 4 with 2 teenage girls and don't spend $40 a month on hot water total, yet alone save that much. Thats at todays gas prices (~90c/therm, 12 yrs ago it was 25c/therm)and we use more than the average amount of hot water. You can plug in some numbers at this government site.

I would agree that tankless WH are more efficient. I would agree with the govt numbers.

"For homes that use 41 gallons or less of hot water daily, demand water heaters can be 24%Â34% more energy efficient than conventional storage tank water heaters. They can be 8%Â14% more energy efficient for homes that use a lot of hot waterÂaround 86 gallons per day." ref.

I don't think the return on investment is worth making the change for most people. If it was me, I would put tankless in a new construction and replace a tank with a tank in old construction, based solely on avg ROI. I could be swayed to tankless in old construction if I had an extreme needs for hot water, but then you probably wouldn't be worried about ROI if that was the case.

Yes, after much debate and research, this is pretty much what we came to: I would love tankless for enviro-reasons and money-saving - but given that we already have a regular old-fashioned gas water heater (and newly replaced, at that) the upfront expense just doesn't make sense to replace it with tankless. If I were doing new construction, i would definitely do it! Or it I'd known about this 4 years ago when we replaced the old heater...but for now, I think we'll stick with what we've got. Thanks, all for your comments!

chris8796,

Regarding the quote:

"For homes that use 41 gallons or less of hot water daily, demand water heaters can be 24%Â34% more energy efficient than conventional storage tank water heaters. They can be 8%Â14% more energy efficient for homes that use a lot of hot waterÂaround 86 gallons per day."

I looked at that site and it doesn't differentiate between electric and gas (it mentions both) and it also talks about pilot lights on tankless units. None of the gas tankless units we are talking about use a pilot. This isn't particularly good guideline information.

I based my numbers on the DOE Energy Factor ratings. The typical savings for gas is as I have said, about 38%. For Electric, it is only about 3%.

The quoted website qualifies its numbers by saying that higher usage will see less savings. They are making the assumption that the savings comes from not having hot water standing in the tank and the resultant heat loss. That's not where the majority of the energy is wasted, which is why the electric tankless don't have the energy savings.

All that said, even a 38-40% reduction in hot water energy usage doesn't have a big payback. For my small household (1 person) it saved about $70 a year. In other situations (larger household, more expensive utilities) it would be more. With the tax breaks, the additional cost of the tankless would pay back in 5 years. Not a great payback, but I was happy to do it.

The difference is not because of gas vs electric or pilot /no pilot. It comes about because of the DOE test to determine EF. The test is based on 24 hr energy use for providing a set amount of hot water under specific conditions. The test is 64 gals of water in 6 draws.

The biggest loss for tank units is standing loss, which is fixed no matter how much water you use. If you use less water, they appear less efficient because the standing loss becomes a bigger percentage of the total energy consumed. If you use more they appear more efficient, the average family of 4 uses a little over a 100 gals a day.

Likewise, the tankless units lose efficiency with cycling loses. The energy needed to heat up the heat exchanger and pipe inside the heater each time water is demand. My family has hot water draws more than 6 times a day. If your demanding a gallon of hot water once a hour to wash your hands your tankless efficiency drops.

In general, the less water you use and less frequent you use it, the more efficient tankless WH become. The more water you use and the more frequent you use it the more efficient tanked WH become.

Here is a study by Bradford white comparing their models.

Most of the gas tankless units have an EF of 0.8-0.85, while tank units are usually 0.62 with a few high end models 0.67-0.68. The condensing units are 0.95-0.98.

In the end, once you start using enough hot water to worry about the costs, the difference between the models becomes less and the ROI is not there.

Mostly good arguments here

Having had one myself for 20 years, I never thought twice about pulling my 3 month old 50 gallon atmospheric vented Bradford White from my new house and replacing it with a Takagi TK3.

Once you experience a quality unit and install, there is no going backwards for me.

Likewise, the tankless units lose efficiency with cycling loses. The energy needed to heat up the heat exchanger and pipe inside the heater each time water is demand. My family has hot water draws more than 6 times a day. If your demanding a gallon of hot water once a hour to wash your hands your tankless efficiency drops.The primary tricks to efficiency and savings with any tankless unit are: 1) don't overheat the water; 2) be consciously aware of hot water use and change usage habits accordingly.

Many people don't fully understand how tankless works, that it's the flow of water through the unit that activates and keeps it running, and the unit can make hot water all day at exactly the needed temperature without running out. They set the output to 140°F or similarly high temperature same as their previous tank unit (for capacity reserve, but not really conscious of it). No one can stand under a 140°F shower, so they turn the hot flow down to a trickle when showering and complain when the tankless doesn't perform well, the shower keeps running cold because the flow-rate is too low. Set the tankless at 102°F to 105°F and run only the hot tap for showering, much better performance. Or even 110°F with a bit of cold mixed in is better than 130°F to 140°F with a lot of cold mixed in.

Washing hands under warm water, using hot water to rinse the kitchen sink or that dusty serving dish pulled out for Christmas dinner ... don't do that. Think about the fact that hot water does not exist until the faucet is turned on ... and think about whether hot water is *really* needed for the task at-hand. The same thing could be said of tanked heaters, of course, but you've already paid for the heated water standing in the storage tank.

"The biggest loss for tank units is standing loss, which is fixed no matter how much water you use."

No, that's not true. That's the biggest loss for an electric tank unit... and it's not much with a well insulated jacket.

The biggest loss for gas tank units, as I have stated before, is the heat lost up the flue because they have to leave enough heat in the flue gas to reliably vent it via convection. That alone knocks the combustion efficiency down to about 65%. In addition, a gas water heater has a hole up the middle of it (the flue) that works to cool the water in the tank with convection air currents even when the heater is off. Finally, they have pilots which waste gas as well.

Gas tankless use forced air combustion, modulating gas valves and temperature sensors that adjust the firing rate of the burner for the water flow, inlet temps, outlet temps and flue gas temps. They don't waste nearly as much heat out the flue and they often come close to condensing (thus the stainless steel vents) Obviously, some are built to be condensing and the efficiency is higher.

This is why an electric tankless doesn't see the same large gains in energy factors over standard tank units ... because the real issue isn't the heat loss through the sidewalls.

Perhaps there are cycle losses on a tankless heater. The purge cycle pulls some air through and probably cools things down a bit... but I think that's really minor.

My summertime gas bill is $9 amonth average for a water heater only. This is a 40 gal. gas with standing pilot. I can't see saving enough to warrant a tankless unit. 2 person household, empty-nesters.

Me anti-progress? LOL! I'm just against cost-negative gizmos...

Tankless aren't a plug and play solution. You should do your homework, including knowing your installation costs up front. Don't forget electrical, venting and gas supply.
...
... (there are virtually no savings for electric tankless) ... Don't forget that the cost of energy will continue to increase. That said, payback in absolute dollar terms isn't high.,

Umm, isn't that EXACTLY what *I* said? HOW is that sowing FUD? Just don't want folks taken in by the slick-sters who often sell tankless. In my (mostly electric) area it's sold primarily on "chi-chi" factors, seldom any REAL NUMBERS. YMMV.

The power issue is a non-issue... I don't know about you, but when the power goes out, my fist thought isn't "hey, I need to take a shower".

Then you've never been without power for very long. An ice storm can leave you dark for 4+ days. Hurricane Wilma left me down for *14* days... had to cut a LOT of trees, haul a lot of bio-mass, help a lot of neighbors... hot shower... MMMM, nice way to end a day spent back in the 19th Century... natural gas: bad in an earthquake, most EXCELLENT after a hurricane. ;')

"In general, the less water you use and less frequent you use it, the more efficient tankless WH become. The more water you use and the more frequent you use it the more efficient tanked WH become."-chris8796

Thanks for an excellent summation.

Fixin,

Look, when all you do is cite the negatives, don't mention any positives, and talk about the ancillary issues as if they are problems that everyone is going to face, I would call that FUD. When you talk about tankless heaters, not only is the glass half empty, but we are all going to choke when we drink from the glass, drop it, cut an artery on the glass shards and bleed out on the floor. Not all of us live in a hurricane prone area.

There are real advantages on gas installations: Energy savings, continual hot water, small size and potentially lower costs to install are several of those advantages. Tax incentives and utility rebates can sweeten the deal more.

That said, there are some potential drawbacks, as you have pointed out.

My own experience in an older home (1920) is that it was cheaper than installing a powervent unit or a flue liner in the masonry chimney. Little gas piping need to be done (I moved the heater to be closer to the bathroom) and with the tax break, the payback of the difference between that and a conventional heater (which wasn't really an option) is about 5 years at current energy costs. That's not great, but every time the cost of gas goes up, I'm glad I made the decision.

I would say that my experience isn't the same as everyone (a two story stainless steel vent through the roof could make this prohibitive, for example) but it's going to be similar for a lot of folks.

My point is to get real information out there, not marketing hype, and not FUD, so that people can make good decisions.

Alphonse, if you were following along with the real reasoning that gas tankless are more efficient (less wasted heat in the flue gases) you would realize that the above summation isn't correct.

The summation is fine as long as you limit it to comparing the calculated EFs as defined by the the DOE test.

You should also keep in mind in most cases your comparing atmosphere tank WH (EF=.62) to atmosphere tankless (EF=~.82), like the OP was doing. If you try to compare to condensing heaters, then you should compare tankless (EF=.95) to storage tank condensing units (EF=.85), which provide the same direct vent capabilities (PVC). To further complicate matters, some of the new WH are essentially hybrids, a storage tank with a moderate btu condensing unit that can provide 3 gal/min indefinitely.

The good thing is most of us at least agree the ROI is not compelling to make the change (to any of the others WH), when you still have a working WH and it depends on individual needs which is best for your install.

Personally, the best reason to go to tankless is unlimited hot water. If you want to go green or be enviromentally friendly you should be looking at solar, heat pump recovery and drain heat recovery (non fossil fuel methods). Unfortunately, most of these don't have a good enough ROI unless its new construction with reasonable installers or you can DIY, even then it helps to have some tax/rebate incentives.

I agree that the payback doesn't justify replacing a working tank heater with a tankless.

That said, the rest of what you said doesn't follow: I don't see any need to compare a condensing tankless with a condensing tank or that if you want to go green you need to go solar and heat recovery.

Look tankless heaters are going to continue to move to condensing in order to eliminate one of the big installation costs, the stainless steel vent. At least one manufacturer is producing a 100k BTU/H, including small buffer tank and circ pump in the unit for $1400. You will start to see a lot more of these. This is a far more reasonable price point than a $3000 Polaris condensing tank unit, for example.

If I can save 40-43% on water heating (condensing tankless) for about $800 difference between a standard tank + venting vs condensing tankless + PVC vent then that seems like a potentially reasonable (and green) thing to do.

I grew up in europe and gas tankles heaters were the norm. As far as I remember, we never had any problem w/it.
Here in USA I replaced my old tank w/ electric tankless two years ago and I am thrilled. It cost me less every month and I never run out of hot water in my bathtub.
I only got unit from HD, medium size and it works great. Had to pay extra for electrician.
I only have warning for people w/ children.When I turn hot water on, it takes just a tiny turn w/ the nob to adjust the water temperature. If I had kids, I would worry they might get burned. I know temperature can be adjusted on the tank itself too so it might help. We have it on really hot setting.
I personally love the tankless and I didn't mind the extra cost, hope it will last as long as regular water heater.

Unless you buy a quality unit and the remote temp control is located right next to my thermostat and I can control/ observe my outlet water temp at a glance/push of a button.

czechchick2,

Why do you have it set so high? What's the benefit?
Set it at 120 or less and call it good. I can't quite decipher zl700's post, but some of the units have a remote control that you can put in say the bathroom, and set your shower temp right there.