Pro/Con: Tankless Water Heater. Is it worth it?
November 21, 2014 8:32 AM   Subscribe

We have a storage tank water heater from the mid-90s, meaning that it could go at any time. I'd like to have a plan in place for when it does. I've read a little about tankless water heating and it sounds great environmentally, but maybe not so great on the wallet (at least initially). I've got some questions for those better-educated on subject than I.

We have 1.5 bathrooms in our house and only two occupants presently, but we hope to increase that to three or four as we start a family. I don't know if water quality makes a difference, but we're in Syracuse, NY and get the majority of our tap water from Skaneateles Lake and Lake Ontario. I don't know whether our water is particularly hard, but we don't use a water softener, if that helps. We have copper piping. We're also having a whole-house humidifier installed in the very near future. We do not have a sump pump, unfortunately.

I understand that the up front cost of a tankless water heater is more substantial, but does the increased energy efficiency make up the value difference? That obviously depends on gas/energy rates, but, you know, in general... I don't mind paying a little more now if works out in our favor in the long run.

I also understand that you have to descale a tankless water heater about once a year. It sounds like the maintenance is higher on the tankless, as I believe we only need to flush our existing tank annually. Please let me know if I'm missing something here.

So, thoughts? Opinions? Regrets? Horror stories? I'd love to hear from folks who have been down this road so that I can make a smart call when the time comes. Thanks!
posted by JimBJ9 to Home & Garden (39 answers total) 18 users marked this as a favorite
Northern California, temperate clime. We went with a tank heater for three reasons:
  1. mrs. straw works in education so is around the house during the summer, and I often work from home (and at the time was always working from home). With closer to continuous use (ie: midday, not just morning evening), the tank heater is likely more energy efficient. Tankless are great for weekend cabins, but for regular use it's less clear.
  2. We have an on-demand hot water recirculator, press a button, wait a little while, get hot water. The tankless folks explicitly say "don't do this", and everyone we know with a tankless heater says it takes longer to come up to temperature than just cycling the cold water out of the feed lines with a tanked heater.
  3. That tank heater is an extra 40 gallons of potential potable emergency water.

posted by straw at 8:45 AM on November 21, 2014 [4 favorites]

I understand that the up front cost of a tankless water heater is more substantial, but does the increased energy efficiency make up the value difference?

Part of the value difference is not running out of hot water even when your inlaws are visiting and someone turns on the dishwasher right before everyone needs to shower. To me, that alone made it worth it and the monthly energy bill savings were just icing on the cake. (I also live in a part of the country with extremely cheap energy costs and even so the payback time on a tankless heater was fairly short; I'd guess if you do the math and include the rebates it will make solid financial sense.)

Depending on how your house is laid out (compact box versus elongated ranch style, say) and how long the pipe runs are, you may want to install a recirculating pump at the same time -- the additional cost for the pump is low but it means having instant hot water at the tap, which alleviates what is often people's biggest complaint with a tankless heater, which is waiting for hot water to arrive at a far-off tap.
posted by Dip Flash at 8:49 AM on November 21, 2014 [2 favorites]

According to Consumer Reports, your energy savings would take 22 years to recoup from the cost difference in the actual units and the installation.

I had a tankless and while the continuous hot water was great, but there were some things:

1. Tankless needs exhausting, they moved mine outside, where I had to plug in a heating cord to keep it from freezing on super-cold days in the winter. I'm pretty sure that cord ate up any energy savings.

2. The installation was a hoo-ha! Again, moving it outside, moving water lines, wiring up electrical.

3. When it broke, finding someone to fix it was damn near impossible., not really worth it.
posted by Ruthless Bunny at 8:50 AM on November 21, 2014 [2 favorites]

Wanted to try tankless a few years ago, was told it needed to go against an outside wall of the home, this was not possible so the idea died there.
posted by Cosine at 8:55 AM on November 21, 2014 [1 favorite]

A tankless saves money in northern climates when the heat is on for 8 months. Less than 8 months? Depends what you pay per BTU. Dual systems work better.
I live in the northeast, the electric water heater is cheaper in summer.
posted by Mblue at 8:59 AM on November 21, 2014

..and everyone we know with a tankless heater says it takes longer to come up to temperature than just cycling the cold water out of the feed lines with a tanked heater

I've heard the same thing, and that it causes a big problem when using high efficiency clothes washers. If you want a hot cycle you have to remember to run the hot water (if there's a tap near the washer), to get the heater to kick on and start making hot water. The HE washer doesn't pull enough water itself to ever make the heater start up.
posted by JoeZydeco at 8:59 AM on November 21, 2014 [2 favorites]

If your tankless heater requires a larger diameter gas pipe than the current tank, this adds to the cost to replumb the gas from wherever it enters the house. Find out the current diameter and required installed diameter before arranging for installation.
posted by Midnight Skulker at 8:59 AM on November 21, 2014 [1 favorite]

I am an electrician. I have installed MANY instant water heaters.

In my experience, the gas ones work great. The electric ones, eh not so much.
The gas instant-hot water heaters need minimal electrical power - the electric instant-hot water heaters need a lot of electrical power. For an electric one, expect your electrician's bill to be as large as your plumbers' bill. Also, the electric ones do not heat the water evenly, and they tend to have lots of problems. I have had some serious head-aches with customers over electric instant-hot water heaters (and I am the electrician, not the plumber).

The gas ones though, they are great.
After installing several of these on customer, I install a gas instant-hot water heater on my own house. It is great. I love it. I noticed a substantial dip in my electric bill too. And my gas bill did not go up very much at all.
posted by Flood at 9:02 AM on November 21, 2014 [13 favorites]

was told it needed to go against an outside wall of the home

Just to note -- this may be true for some models or in some houses, but is not the case generally. Assuming it is a gas model, it will need to vent out just like a gas tank heater, but that can be up through the roof, horizontally from an interior room, straight through an outside wall, or as in Ruthless Bunny's situation, actually outside the house.

I'd add to my above comment that while any licensed plumber is legal to install tankless heaters, not all plumbers have much experience with them or can give good advice on brand, sizing, location, etc. Usually there is one or two plumbers locally who install a lot of them and are going to be the go-to guys for this, and you'll be better served working with them.
posted by Dip Flash at 9:03 AM on November 21, 2014

Starting in April 2015 the US DOE (Department of Energy) will be enforcing new energy standards for water heaters. Basically, tank water heaters that only run on electric power will become more or less obsolete. The outside diameter of the tanks are going to grow approximately 2"-4" overall to accommodate more insulation in the tank. Water heaters will now either be a dual electric / heat pump system or gas.

Why this is important to your question has to do with a few factors:

1) Is your existing water heater gas or electric?
2) How much extra space do you have around your existing water heater? If it installed tight into a closet the new models might not fit.
3) The new energy standards for water heaters are going to make the tank type 50+% more efficient, bringing them almost in line with current gas in-line water heaters. Electric in-line are more or less going away.
4) Tankless water heaters also changing and will be the most efficient of all the types.

Here is a good article explaining the different types vs. efficiency.

Now from personal experience, I prefer tank water heaters for a few reasons:

1) Much less maintenance and break down potential. Every in-line I have seen installed eventually fails after a few years.
2) While in-line provides almost instant hot water, you need an in-line unit (well this depends on the size) at each hot water or a large distribution network of pipes. The problem is that in a single point tankless system has heat loss along the length of the pipe. So, you get temperature least in my experience.

My advice is to talk to a reputable plumber in your area to determine the length of pipe run vs. water heater location and determine if tankless makes sense for your layout.
posted by Benway at 9:10 AM on November 21, 2014 [4 favorites]

Annectdotally, and everyone thinks I'm mad when I say this, I like the feel of the water from a tankless gas system more. Also as someones whose current house has a tanked heater with shitty water, I am changing diodes yearly, using the more expensive ones that are supposed to stop the problem and my water still smells like sulfur & feels slimy half the time from bacterial build up.

I would kill for a nice clean tankless system because as icing on the cake there are only 2 people living in our house and we are currently paying to heat a huge hot water tank that we use maybe half of. Having said that I have only used tankless systems in Australia's lot milder climate, but even then I never had to run the water any longer than I do now with a tanked system to get hot water.
posted by wwax at 9:18 AM on November 21, 2014

A tankless saves money in northern climates when the heat is on for 8 months. Less than 8 months? Depends what you pay per BTU. Dual systems work better.

I think the poster was asking about a stand-alone, on-demand water heater. The above comment applies to an older style of tankless heater which attaches to the boiler. With that arrangement, when you need hot water and not heat, you run the whole boiler, which is inefficient in the summer.
posted by mr vino at 9:24 AM on November 21, 2014

We upgraded to a Rinnai on-demand hot water heater a couple of years ago. Ours are installed in the basement & vent through the wall; there were no major problems siting or installing them. We are very happy with the infinite hot water, especially for showers. It does take noticeably longer for the sink tap water to get hot, as you have the pipe run + the time it takes for the heat exchanger to warm up, but that is a minor annoyance that we've gotten used to. One thing we didn't anticipate is the effect on our laundry - we switched to HE front-loaders about a year ago, and they're on the 3rd floor of our house. These units demand water in small, intermittent bursts, and it seems that the water doesn't really ever get up to temperature. I don't think this would be a problem with an old-style top-loader that takes its hot water in 10 gallon gulps. In retrospect, we should have sprung for the high-end washer with an auxiliary water heater.
posted by mr vino at 9:31 AM on November 21, 2014 [1 favorite]

OK some truthiness here based on having them. Some echoes:

The gas ones are amazing. Electric ones stink. Gas ones are in fact much much more economical based on simple anecdotal evidence. Our gas bill went down a lot when we switch off the tank. As for tanks being more efficient: nay. As you consume hot water cold water is added which LOWERS the temp of the remaining water substantially increasing recovery time. Time for hot water to tap is only marginally longer. If it currently takes say 10 seconds in a bathroom you don't use daily it will take maybe 13-14 with the thankless. Again this is simple empirical evidence.

Continuous for ever never end run the dish washer and the washing machine and shower hot water is amazing. With a simple balancing valve installed with it (or whatever the hickydo is called) you don't ever notice someone flushing while you're sudsing.

We had a mid range rinnai. The one that's about $650-700. Its only a small cost bump over a larger high efficiency brand name tank. And the unspoken thing here: its such a huge space savings. It was like adding a bonus room.... Seriously I'd say close to 50 square feet of storage space appeared overnight.

I'm firmly in the do it category. Want to know how much? We're having the city add gas lines at our cost. Its half and half for the kitchen appliances and for the tanklrss hot water. Serial.
posted by chasles at 9:38 AM on November 21, 2014 [3 favorites]

I do not like my gas-powered Takagi T-K2. It's 5+ years old, so maybe newer ones are better, but.. The thing I hate is that it takes a certain amount of water flow to get it to turn on. Some of our faucets are apparently low-flow enough that it's not enough. I end up turning my shower on just so I can schedule some hot water from the sink tap. Also as noted above, they take awhile to come up to temperature. It is nice not worrying about running out of hot water though.

One other thing worth knowing; without a tank, you no longer have a 30+ gallon reservoir of water for emergency purposes.
posted by Nelson at 9:42 AM on November 21, 2014 [2 favorites]

We replaced our tank water heater with a tankless water heater at our old house. It was probably 2007-2008. I hated it. In the morning in the kitchen, it went from 15 seconds to get warm water to 35 seconds. During the rest of the day where the pipes were mostly warmed, it went from 10 seconds in the kitchen to 35 seconds. Even worse, in the upstairs bathroom, it would take about 60 seconds to get warm water up there. I absolutely hated it. Perhaps I'm too obsessive about washing my hands.

Also, consider normal kitchen use. With a tank heater, if you're using warm water for hand washing during food prep, assume that you'll wash your hands 3-10 times. With a tank heater, every time after the first where it might take 10-15 seconds, the others will be instant. With the tankless heater, you'll get 10-20 seconds of hot water, followed by 10-20 seconds of cold water, and then it goes hot again. Every time you start/stop the tap. I hated it. Seriously, I effing loathed that we paid more money for it than a conventional water heater.

My wife however loved it. We could have all five people shower at once, and the 4th and 5th people didn't have to worry about running low on hot water.

I would be happier with putting more money into buying a 80-100 gallon tank water heater than a tankless.

In theory, one can get a small 5-10 gallon tank to follow the tankless water heater to help counteract the 5-10 seconds of water flow before the water heater turns on. But that is a lot more costly, and if that 5-10 gallon tank isn't separately heated, I'd really wonder how warm that water would be in the morning.

In case you didn't realize it, I strongly advise against going with a tankless heater. Hate.
posted by nobeagle at 10:07 AM on November 21, 2014 [1 favorite]

I rent an apartment with a tankless heater which runs on gas, so I can only address how it feels to have one, not the cost issue.

IT'S SO RAD. I can take an hour-long shower, then immediately do a load of laundry. I can fill a bathtub without the water getting cold halfway through. And in my place, at least, the hot water shows up very quickly. You hardly have to wait at all after turning on a tap.
posted by showbiz_liz at 10:21 AM on November 21, 2014 [1 favorite]

You could try to roughly estimate the savings yourself. If you currently have a gas water heater and gas furnace, then you can assume that in July or August that all of the gas is going to heat water, not the furnace. So look at your gas bill in August, multiply by 12 months and that is roughly how much you are currently spending on hot water annually.

When you make this calculation, look at your bill carefully. Usually there is one charge for service and another for just the gas. You only want to count the gas part.

Assume that the best tankless system might save you 30% so multiply your number above by 0.3 and that is how much you might expect to save each year, best case.
posted by JackFlash at 10:41 AM on November 21, 2014

We have one, installed close to 10 years ago, I think. I'm happy with it. The water doesn't take any longer to heat up than it used to with the old tank one. You do have to have a certain amount of water flow to get it to turn on, but you get used to that pretty quickly. Not running out of hot water, ever, is a fabulous thing. Ours vents through the roof, not the wall, but we're on the top floor so that wasn't too hard to set up.
posted by gingerbeer at 10:54 AM on November 21, 2014

I have an older gas-fired tank water heater that's probably 15 years old, and I've started looking at the tankless ones. There are, as this thread shows, a wide range of opinions on them. Some people seem to love them, other people despise them with the hatred of a thousand lukewarm-tapwater suns.

My meta-analysis is this: if you live in an apartment or small house, and can put the tankless heater close to the point of use, you will have a much greater chance of loving it than if you live in a large house and you have the tankless down in the basement.

The people I've talked to who are the most outspoken about loving their tankless heaters either have them located right at the point-of-use (e.g. they have them in the bathroom, Euro style) or their home is just not very big. Weekend cabins seem to be basically the absolutely ideal case for tankless heaters -- lots of water used all at once (4+ people showering on Saturday morning) while nothing used for days in a row, and the pipe runs are short. And if you want to fill a big bathtub or something, no problem.

The people I've talked to who hate theirs have put them in as "drop in" replacements for tank heaters in larger SFHs with only 1-2 people there most of the time. This is where you get into a lot of annoying problems with water taking forever to warm up, or alternating hot/cold/hot/cold as the heater turns on and off because you're not pulling enough water to make it run continuously. Since this is basically my situation it's been enough to put me off getting one.

A neighbor with a tankless actually ended up buying a really tiny tank heater to put under their kitchen sink (I think it's maybe a 3 gallon? It fits in the cabinet, somehow.) to solve the hand-washing problem, which to me is a real deal-breaker. (Although maybe it's still a winning strategy in terms of energy savings...? Could be, I suppose.)

I am hoping that someone will come out with a "hybrid" system--basically put a small, heavily-insulated and continuously heated tank in front of a tankless heater--so that you can get the best of both worlds. With the new DOE requirements coming up, I'm hopeful that we'll get some new developments, so I have just decided to cross my fingers and keep using the current heater for a while yet.
posted by Kadin2048 at 10:58 AM on November 21, 2014 [1 favorite]

I once owned a house that had one; nthing the ventilation of the spot where it's installed. It's really important that it be ventilated, or Bad Things will happen. When it worked, it was pretty great; but often the poor ventilation where it was installed made it shut off prematurely. I live in a house now with two standard water heaters, and I think in the long run it has the same effect and—once they're both full—is fairly energy efficient.
posted by littlerobothead at 11:09 AM on November 21, 2014

The gas ones though, they are great.
After installing several of these on customer, I install a gas instant-hot water heater on my own house. It is great. I love it. I noticed a substantial dip in my electric bill too. And my gas bill did not go up very much at all.

It's worth mentioning, in case you or someone else reading this is considering an electric to gas switch, that we're in kind of a renaissance of gas exploration right now and it's crazy cheap. So there's an appearance of savings that may well last forever... or may change in a year. Someone better versed on gas exploration can weigh in on this; perhaps it's not a concern for the timeline of typical home ownership (under 10y between moves). But every time I see these lofty claims about savings I want to shake people and remind them that the cost of non-renewable energy isn't a fixed point.

That said, I'd totally go gas if I already had gas in my house and was replacing an electric heater. But be careful in doing comparisons as if the exact dollar disparity will persist. It may not.
posted by phearlez at 11:14 AM on November 21, 2014 [1 favorite]

We had a gas tankless heater installed maybe 4 years ago and it overall it is great. We're in Toronto where everyone uses gas for home and water heating.

Infinite hot water - this is important because that means we can take showers after eachother without someone getting a cold shower. This was our primary consideration when we decided to switch.
Space - the heater was installed to a wall in the basement. Now we have a storage closet where the old tank used to be.
You may be able to get rebates from your utility company.

It requires electricity to turn on so during a power outage we don't get hot water.
We have to wait a bit longer for the hot water to kick in.
A hot water tank is emergency water. I don't know how useful this really is, but it you won't get this water reservoir with a tankless.
They aren't as advanced as the ones in Japan. My in-laws have one that co-ordinates with their bath tub. They can push a button in the kitchen (where the main panel for the water heater is) and it will automatically fill the bath tub to the desired temperature and alert them when it is full. They can even re-heat the water in the bath from the kitchen. This is in a fairly standard house.

I don't know if it is any cheaper to use a tankless. Our old heater was a rental and the new one is too so there were no upfront difference. The rental is definitely higher, but it's hard to make a comparison on the bills because we've added kids, and people go out of town for extended periods at random times, guests stay over, if it is colder one year then we will use more gas for heating, ...

One thing I will note is that both in England and Japan the houses I've stayed at had a tankless system. Energy is much more expensive in both those countries so if a water tank (which is cheaper upfront anyway) was more efficient I'd think they'd be using them. Whether that efficiency translates to cost-efficiency in Syracuse is another matter.

I don't see myself every going back to a tank system.
posted by any portmanteau in a storm at 11:21 AM on November 21, 2014

I have a gas tankless water heater/boiler combination (it also heats the house), which sits in the basement and vents out a wall. I've had zero problems with it as a hot water heater--water heats as quickly as it did with the tank I had in my previous house, I don't have the hot-cold-hot phenomenon, and yay, endless hot water. But as a boiler, it's...not great once the temperatures go below twenty F, as I discovered last year when, um, temperatures were frequently below twenty F. So it depends what you're using it for.
posted by thomas j wise at 11:28 AM on November 21, 2014

Not sure what your home heating setup is, but if you can add a hot water heater to your boiler you essentially get free hot water during the winter. Well cheaper, because the boiler is running to heat the house and the water heater siphons heat from the boiler.
posted by Gungho at 11:37 AM on November 21, 2014

Response by poster: Man, yeah, that's a broad range of opinions. I don't know that I'm any more clear on this than I was before I posted. :P

If it helps, I'm in a 1450 sq ft house, 3 bedrooms, the full bathroom is on the second floor, and the existing water heater is in the basement. It's a gas model (water heater, range, and furnace are all gas). The water heater is set up right next to the furnace which is next to the basement wall, so ventilation shouldn't be an issue. I do have a bit of room around it.. not enough to physically squeeze myself between the water heater and furnace, but I can get my arms in there. On the other side, I actually wheeled a shelf in there with room to spare, so there's plenty of access from the front and one side.

As much as I like the idea of using the most environmentally-friendly and energy efficient option, my main concern is cost. As I said, I'm ok paying more up front if I more than make up for it on the back end. Pain-in-the-ass level of maintenance is my second concern. I don't mind waiting for hot water.
posted by JimBJ9 at 11:38 AM on November 21, 2014

I have a gas tankless heater in the basement of a big old house. It's the best thing ever in the world.

Buy the biggest, most powerful one even if you don't " need" it. This is critical, because you do need it.

My top of the range Rinnai was $900 on Amazon, delivered. $3500 at the local store. They said no one would install it if I didn't buy it from them. It's installed!

There are vertical and horizontal venting options, you can make it work as long as the gas like into your house is big enough.

It costs very little to run, certainly less than my old hot water heater. I don't wait any longer for hot water since the old heater was also located in the far depths of the basement.

It is a bit noisy but not much.

Maintenance consists of back flushing it once a year and having the furnace guy look at it when he looks at the furnace.
posted by fshgrl at 12:11 PM on November 21, 2014 [5 favorites]

I will be upgrading to tankless system soon. One reason is so I can run the control circuit on generator power and have hot water during an outage. I cannot do this with my old electric tank system that is aging out anyway.
posted by Raybun at 12:21 PM on November 21, 2014

I'm also in California, so climate issues will be different for me than for you. I switched about a year ago when the last tank heater I bought died almost on the day that the warranty ran out. I looked at buying an industrial/commercial tank heater vs a gas tankless and decided on gas tankless. My house is laid out in a way that both bathrooms, laundry area, and the kitchen are all very close piping-wise from the tank location in the interior of the garage. So, I have very little warm-up time as there's not much pipe to transit.

My gas bill is lower (~25-30%?) and we use hot water at the same times for various things, so the fact that we don't run out is great. I got a Japanese heater as they have the best reputation for longevity and they've been the default in Japan for decades. I'd also echo to get the biggest one you can afford. We're only 2 people and a dog, but sizing up has allowed us to do laundry, showers, and dishwasher at once without issues.

I love the tankless, and while I no longer have a reserve tank of water for earthquakes, I do have peace of mind that the likelihood of a top-heavy tank falling over and causing a fire after a quake is zero.
posted by quince at 12:26 PM on November 21, 2014 [1 favorite]

My top of the range Rinnai was $900 on Amazon, delivered. $3500 at the local store. They said no one would install it if I didn't buy it from them. It's installed!

With your existing water heater being gas and in the same place you'd want to install a tankless, OP, the install effort & cost should be quite low. Any competent licensed & bonded plumber will be able to do it with absolutely no problem; you could well spend as much on disposal of the old tank as you would on the install hours.
posted by phearlez at 12:53 PM on November 21, 2014 [2 favorites]

Oh, on review - I'm somewhat surprised to see all this talk about the tank as a reserve. But if anyone really cared about that enough to do something there's no reason, to my knowledge, that you couldn't inline a water heater tank with your cold water and leave it powered down (though you'd probably want to power the sacrificial anode) so you always had that reserve.

Odds are you could pay whatever plumber does the install to do that for you and be out no more than an hour labor. And you wouldn't have to have your old tank hauled away, though usually you need to replace a tank because its rusted through so probably wouldn't have been forced into a replacement if you didn't want it hauled off.
posted by phearlez at 12:58 PM on November 21, 2014

A few years ago I had a 3 day power failure in the winter. I was able to keep the temperature tolerable by running the hot water. A gas tank-type water heater needs no electric power to run.
posted by H21 at 1:03 PM on November 21, 2014

Given your ambivalence, you might consider just going with a well-insulated tank heater and applying the cost savings to a new high-efficiency furnace in the near future. Water heating is only 10% to 15% of your total energy bill, so the potential savings, even in the best case, aren't that significant. On the other hand, in your area, furnace heating is a much larger portion of your energy costs and potential savings much greater.
posted by JackFlash at 1:17 PM on November 21, 2014

We have an on-demand hot water recirculator, press a button, wait a little while, get hot water. The tankless folks explicitly say "don't do this"

Really, because I've specifically been told that it's okay. It might depend on the exact type of pump and you can't have one that runs all the time (which you can with a water heater) but on-demand pumps are fine.

We have one in our house and it works well. The tankless system also works well, but the process that led to us getting it was such a pain that I really don't like to think about it. The only downside is that a power failure means you get no hot water. This hasn't happened to us very often, but it's something to keep in mind.
posted by It's Never Lurgi at 1:52 PM on November 21, 2014

In my experience, the gas ones work great. The electric ones, eh not so much.

Just as a quick comment on this, my work has the electric ones, my friends house has a higher-end gas one.

The gas one is freaking GREAT. The hot water gets going just as fast, if not faster than a normal water heater. They haven't had a single problem in maybe... 3 years of having it?

The electric ones at my work are older than that, probably more like 6-7 years. They've also had no problems, but they SUCK. The water never gets hot enough, it takes a while, etc.

Another comment is that the control logic of the gas ones seems to run through a power supply. As in, it's obviously not running on straight 120v. It would shock me if there wasn't a battery backup solution to this, if the power outage thing is at all a concern. This might be harder if it uses a hot surface ignition and not a spark ignition though...
posted by emptythought at 2:52 PM on November 21, 2014

What kind of furnace do you have? I feel like my indirect water heater, which uses the furnace boiler to heat water in a tank, is the best of all worlds... great efficiency, only paying and maintaining one heating appliance, lots of hot water.
posted by metasarah at 3:16 PM on November 21, 2014

There are two tankless water heaters in my house. One of them is powerful: Takagi TK-1 - and it requires electricity to operate. That is for the 'big bathroom', showers, tub, washers. The other is less powerful: Bosch Aquastar, which has a (now illegal) standing pilot; that is for the kitchen, dishwasher, and the outside shower we use when the power is out since it does not require any electricity at all. The fuel is propane.

The Takagi has been more of a pain than the Aquastar, requiring several bouts of tinkering to keep operating. I finally learned to take out the burner jets, clean them and re-install them which has made it reliable. The Bosch needs its gas valve re-built every five years or so. If you have ever re-built a (simple, like a Zenith-Stromberg) carburetor it is just like that.

Both have been in service since 2002. The water here has a lot of calcium carbonate in it but it does not build up inside the water heaters.
posted by jet_silver at 4:06 PM on November 21, 2014

We (two of us) had only owned our house for five months before we had to replace a dead heat pump, and since we chose to put in a gas furnace (OMG SO MUCH BETTER, he typed in his warm house during a cold snap) we ended up also replacing the gas-powered tank water heater with a gas-powered tankless Rinnai.

Because we don't have a whole lot of history to go back on I can't really say that our summer gas bill is appreciably less than it was before. In fact, for the same five months this year it seems our gas bill was … almost exactly the same as it was the year before (like, within a buck every month).

We love the tankless heater, not necessarily because it's any cheaper to operate (neither is it more expensive), but because we never run out of hot water. I occasionally shave my face and head in the shower, and I can do that without the water going cold as it did a few times in the months we had the tank. We had seven (7) houseguests for a week last Christmas, and never ran out of hot water. I should note that our water pressure isn't really high enough to support multiple simultaneous showers (even though the heater is rated for them), so I can't really report on how well it works in that circumstance, but everybody could shower one after the other without any problems. And it is definitely not any slower to provide hot water than the tank had been. We have an HE washer that does not seem to have a problem with it at all.

The most difficult thing for us was the installation. We partly replaced the heater because they were going to have to remove the tank temporarily just to install the new furnace, and the HVAC guy gave me a discount on the installation when I asked about replacing the tank at the same time ("so tell me, since this was on our long range list anyway …"). Our utility closet is along an outside wall so venting wasn't an issue (aside from watching the installers cut a big hole in our new house), but the existing gas supply in the utility closet wasn't strong enough to supply the furnace and the water heater. The installers had to tap a new line where the gas came into the house and then run new pipe to the utility closet. We still haven't fixed all the holes they had to put into the basement ceiling to make that happen.

My concern for you would be in the temperature rise. How cold is your tap water? A tankless heater is rated for a certain amount of rise, and if your tap water is so cold the rise isn't enough, you'd need to chain two units together or put auxiliary units closer to the point of need, which could be a very expensive installation. My sister lives in the Netherlands, where they have individual heaters in every bathroom and in the kitchen, so I know it can be done. That said, if the plumber had told me that's what I had to do I might have stuck with a tank.

Also, if you go down this road and find your pipes have too much temperature drop, there's a dipswitch you can adjust that will allow you to set a higher temperature than the Rinnai allows by default. Our kitchen faucet is stupid and doesn't run purely hot water when the lever is all the way hot (every other faucet in the house is JUST FINE). Between that and some weird pipe/AC duct routing, I had to turn the water heater up past the standard limit so the kitchen faucet would be hot enough. Luckily for us, our tap water is warm enough that the heater has adequate rise, but this procedure is not well enough publicized.
posted by fedward at 8:39 PM on November 21, 2014 [1 favorite]

There is a third option, a condensing gas fired tank water heater aka Polaris. Very high efficiency, stainless tank. Not cheap but a solid unit that won't get plugged by scale.
posted by Pembquist at 9:54 PM on November 21, 2014 [1 favorite]

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