Tankless hot water heater - yes or no?
January 13, 2020 7:46 AM   Subscribe

Our water heater is kaput, and we're thinking of switching from the traditional tank hot water heater to a high-efficiency tankless (specifically, this one). Our motivations are lowering our natural gas bill (I understand we might save about $10/month), and being environmentally friendly. Is there any reason not to switch to tankless, other than the fact that it costs a few hundred more for the heater itself? If you have horror stories, let me know!
posted by ClaireBear to Home & Garden (27 answers total) 8 users marked this as a favorite
Your existing gas line may not be sufficient, thus increasing your installation cost much more than you might save over the life of the water heater.
posted by mkb at 7:50 AM on January 13 [3 favorites]

I can’t think of a reason not to. I never regretted swapping to one in my last house and I had one installed in my new place before I even moved in.
posted by Tell Me No Lies at 7:55 AM on January 13 [1 favorite]

They work best when you have a relatively small distance from the heater to where you need hot water, and really shine if sometimes you want to have several people shower in a row (ie hot water is endless). You will save more money if you use hot water only intermittently, and save less money if you use hot water regularly throughout the day.

The main downside is that it can take a while for the water to heat up and reach the tap. A minute or so is perhaps no big deal to you, but in some cases it could take several minutes, and that may well be a dealbreaker for many.

Get a good rec for a potential installer and have them come out to your place to advise on the points above.
posted by SaltySalticid at 7:58 AM on January 13 [4 favorites]

They're very common here in the UK and much of the rest of Europe. Upside is hot water on demand, so less waste if you're not using a tank-full of hot water every day. And of course when there's extra demand (e.g. guests) you won't run out. The downsides are as follows: 1. it can take a bit longer for the hot water to come through to the tap, as the burner takes a while to bring things up to temperature. 2. These heaters often don't produce really hot water. In my experience, you'll get water hot enough for a shower or bath, but maybe not hot enough for some cleaning tasks. 3. They're complex, mechanically, and really do need to be serviced every year by an engineer.

I'm a satisfied owner, though.
posted by pipeski at 7:59 AM on January 13 [2 favorites]

I don't want to jinx things, but we got one in April and have been very happy. (My previously AskMe about this.)

Our 1994-era gas boiler croaked and the gas water heater was 10 years old (or three years past its expected lifespan, apparently), so we had them rip out both and replace it with a similar unit from IBC.

It takes maybe 30 seconds more for hot water to arrive, but the plumbers noted that our second story is piped with undersize hot water lines. (Thanks, long-gone contractor!) The gas bill seems to be lower: I think my wife noted a $30 decrease over last December, which is awesome. We have four teens, and the availability of water for showers is much-appreciated!

Having all that space back in the basement is nice, though we hang up our laundry to dry, and the lack of waste heat from the old boiler means that it's colder down there (mid-50s!) and the clothes take longer to finish drying.

My brother-in-law took a hard look at our basement and had the same guy put in the same system at his house, and he's happy, too.
posted by wenestvedt at 8:00 AM on January 13

Your existing gas line may not be sufficient, thus increasing your installation cost much more than you might save over the life of the water heater.

in addition to your gas line maybe not being big enough you may need to change your venting setup and you'll need to make sure you have enough air intake.

These are installation issues and not operational problems though.
posted by GuyZero at 8:11 AM on January 13 [3 favorites]

I like the fact that a conventional water heater gives you hot water in a power failure. I have (sort of) heated my house in winter when the power was out for 3 days by running hot water into tub and sinks.
posted by H21 at 8:12 AM on January 13 [2 favorites]

I had one in the house I bought in 2005. The house was built in 1996, and I think the tankless heater, which ran through our oil-fired boiler, was original. After 5 years or so, the hot water flow gradually started decreasing and becoming more tepid, due to mineral build-up in the water heating coil. I ended up replacing it with a stainless steel tank heater, also heated by the boiler, because that has a much longer expected service life. In the tankless heater, the water being heated passes through a fairly small coil, and there's always new minerals coming in. Eventually the mineral deposits get thick enough that they impede the flow and insulate it to some degree from the heat source. Depending on your water's mineral composition, that may not be a problem.
posted by brianogilvie at 8:12 AM on January 13 [1 favorite]

One hidden advantage of a hot water tank is that it serves as an emergency reservoir of water in an emergency where there is no water service. (Ie, an earthquake in San Francisco). You can store water other ways, just consider whether you need that reservoir.

I hate my older tankless because it takes a significant stream of water to activate. I suspect that's a failure of this model though and is better in new ones. But consider that, what's the minimum flow required to activate.

You can't use tankless hot water heaters with recirculating hot water. At least, not reasonably.
posted by Nelson at 8:39 AM on January 13 [1 favorite]

Thanks, all - very helpful! One more question: there's also the possibility of getting a heat pump water heater. This would change the water heater from natural gas to electric. I understand from the ductless mini-splits that I installed in a different house that these are very energy efficient, but any idea how much this would save over natural gas, if any?
posted by ClaireBear at 8:57 AM on January 13 [1 favorite]

I think the climate of where you live with determine too how well they work, or how popular they are. I like in the upper midwest, and I've heard from several plumbers that it's not a good fit just yet.
posted by wocka wocka wocka at 9:02 AM on January 13 [1 favorite]

It depends on your region and how much electricity costs, and where in your house the hot water heater is located. This is a question for HVAC pros who sell both options.

Personally, given that even natural gas gives off emissions, would skew towards electrifying things instead of using natural gas (however much I want a gas range, it's not a responsible thing to 'upgrade' to in light of how significantly we need to decarbonize everything as quickly as we do). Even if it is more expensive, you're allowing your house to (hopefully) be powered by renewables going forward.
posted by furnace.heart at 9:05 AM on January 13

The thing I disliked most about our tankless heater at our last house was for kitchen use. Every time you stop the hot water, the water heater turns off. So you start using hot/warm water again, and the water in the pipes will still be at temp during frquent use, and then you get a burst of 5-10 seconds of cold water that warms up. So if you have your sink temp set and are just trying to do frequent hand washings during kitchen prep, you keep getting blasts of cold water. Or you need to wait 15-30 seconds (depending on pipe length and flow (you don't have your water full blast for hand washing).

Some older HE washing machines will never get hot water because they only do short bursts. Most of the newer HE washing machines have a setting for that, and they'll do larger bursts, in addition to heating it (electrically at 120V). Check how your current washing machine might handle it.

The only thing tankless is good for, IMO, would be multiple long showers right after each other.

If you were sold on $10/month gas savings, I think you were sold a giant exageration (unless your current tank is uninsulated and kept outside the house). During the summer months (to exclude gas furnace heating and we had an electric range), gas heating was pretty much the same the year after we went tankless. Savings were ~$1/month for average of 6 heating free months for a family of five at the time. But year over year with a family of five, the conditions are always different as one kid might be showering more/less, weather, etc...

At Consumer Reports they list a yearly cost of $245/yr for a gas tank, and $195/year for a gas tankless. That's $4.17/month , and larger than I saw (perhaps for houses that do less showering, but more frequent small-batch hot water (cooking, handwashing, laundry) that hurts the tankless? When we were choosing, the tankless was pitched as likely to save us $2-$5 per month, which is in line with the consumer affairs general data.
posted by nobeagle at 9:11 AM on January 13 [2 favorites]

If cost isn't a concern: a friend of mine installed a small hot water heater for his house, and a tankless one just for the master bath. Part of this was because the MBR is at one end of the house and the rest of the plumbing is at the other, and he wanted hot water faster. For times when the house is full of guests, he had a valve installed that lets him share the tankless supply with the rest of the house.
posted by jquinby at 9:28 AM on January 13 [1 favorite]

I work for a natural gas utility, on the energy efficiency programs. Possibly your utility, though I'm not sure where you live.

Tankless water heaters can work great; if you go that way you should check with your utility on whether they offer any rebates (we'd give you $250 for the model you linked, for example). That unit does draw as much gas as a large furnace, so you would for sure want to make sure your gas supply is adequate. But unless you're in a pretty old home, I wouldn't expect there to be a problem - we haven't seen any issues arise, and wouldn't expect any unless all the customers in a particularly old (low pressure) part of our system decided to adopt tankless.

As folks note, there can be operational issues; not every home is well-laid-out for a tankless heater. The more central the location of the water heater (and thus the lower the length of pipe the hot water needs to travel through) the better. The need for proper venting is also important, as noted (the water heater achieves those high efficiency levels by sucking all the heat out of the exhaust, which means it needs to be mechanically exhausted, generally requiring horizontal venting). You may also need to run a line to dispose of condensate, though that should be pretty straightforward.

Given the need to assess both the gas supply and the ventilation, I strongly recommend you work with a plumber to get the unit installed rather than trying a DIY approach. We generally encourage that for any water heater replacement (or any other time you're messing with gas connections), but it's especially important here.

I know less about heat-pump water heaters; generally you should not expect a rebate from your gas utility for those though some electric utilities may offer one. They're generally larger (taller) than traditional tank-style heaters so if you're space-constrained that could be an issue. I'm told by folks who have done field studies that heat-pump water heaters do best if they're in a mild climate where you can put it in unconditioned space, but that even somewhere like Minnesota (where I am) the heat pump is efficient enough that it more than makes up for the additional heating requirements it puts on the furnace.

Happy to chat more if you want to offer more detailed info (like location) by MeMail.
posted by nickmark at 9:30 AM on January 13 [5 favorites]

I would agree that the monthly cost savings are exaggerated. One way to estimate is to look at your gas bill in August when you presumably aren't running a gas furnace (although maybe a gas stove). But be careful. Your gas bill will include fixed service charges in addition to the amount of gas you use. So don't just use the bill total. Your bill should break down the actual gas usage, typically in therms or BTUs and the price per unit so you can work out the actual gas cost alone.

Your monthly savings might be around 25% of that total. Typical might be a couple of dollars a month.

The thing about traditional gas water heaters is that they are dirt simple technology that works for years with little or no service. They don't require electricity to operate and will work even in a power outage.

Given the small amount of energy savings compared to the much higher cost of tankless, my recommendation is to stick with the traditional heater and apply the savings to a high efficiency gas furnace. That's were you can really save energy, particularly if you are in a region that has cold winters.
posted by JackFlash at 10:15 AM on January 13

They don't require electricity to operate and will work even in a power outage.

This is true only of units with a standing pilot light. Most modern gas-using appliances (of all kinds) are now made with electronic ignition systems, which eliminate the pilot light and also mean that if I lose power, I also lose heat, hot water, and cooking. (There are probably still a few pilot-light models of various appliances out there, as I don't believe they've been completely prohibited except maybe for gas fireplaces, but they're very much the exception anymore.)

Aside from the ignition, only the least-efficient tank-style water heaters won't need electricity for disposing of exhaust (anything above about 70% efficiency will require a power-vented exhaust, as the exhaust isn't buoyant enough to rely on a chimney).
posted by nickmark at 10:52 AM on January 13 [3 favorites]

No reason at all. We love ours. Our current propane line was converted to natural gas and needed no resizing, we have all the hot water we can use and our costs are significantly lower. Go for it!
posted by summerstorm at 10:59 AM on January 13

Just a couple of things to note :

They don't really save water over a tank; outside of minor outlets, the only way water in a hot water tank leaves is through your taps. Otherwise it just sits there until used.

For environment, cost and efficiency, nothing beats a heat pump. They are generally more expensive to buy, but they save so much energy, they pay for themselves surprisingly quickly. If you have solar panels, set it to run during the day, otherwise set it to run overnight on off peak power.
posted by smoke at 11:53 AM on January 13 [1 favorite]

The thing I disliked most about our tankless heater at our last house was for kitchen use.

That's what a close-in (electrical) tank heater is for. It's commonly installed right under the sink, 5 to 20 liter depending on your requirements, so you get hot water with minimal delay. With the only two houses I had without one in one case the combo central heating/hot water unit was right in a corner of the kitchen, and the other had a tankless heater over the sink. The others I installed one almost immediately after moving in.
posted by Stoneshop at 12:20 PM on January 13

I am really happy with mine. The two things that have helped me love it is we bought a larger capacity one than what our household "needs". This really helps with multiple users (showering and laundry at the same time, for example). I would definitely size up.

Also, the way my home is set up, the laundry/bathrooms/kitchen are very close to one another and we put the heater in that side of the house, directly next to laundry and right below the bathroom and very close to the kitchen. The water is dependably hot in a short amount of time because it's not traveling long distances across the house. If you don't have a similar set-up, getting a couple of smaller heaters that live next to where the water use is most intensive is a common solution.
posted by quince at 2:54 PM on January 13

We had a heat pump water heater installed last year. The economics of this decision depend on a few factors:
  • Energy costs to operate the heater
  • Purchase and installation costs of the heater
  • Maintenance costs, if any
We did not find a big difference in energy costs between heat pumps and gas tankless. Raw efficiency of a good heat pump is about 4x larger than a good tankless heater. But electric energy costs 5x more than gas energy in our area. Given moderate hot water usage, the difference between them was only going to amount to a few dollars per month. This might be a different story for you if you have solar panels or another source of cheap electricity.

Purchase costs are usually like you said, a few hundred dollars higher than a gas tanked heater, for either a heat pump or a gas tankless. Keep in mind that heat pumps work more gradually than a typical gas tanked heater, and of course, much more gradually than a tankless. If you often use lots of hot water in a brief time (such as filling bathtubs or back-to-back showers), you may need to purchase a larger tank size for a heat pump to avoid running out of hot water.

Installation costs will be higher if you need to run a larger gas line for the tankless, or new electric service for the heat pump. Also, heat pumps need ventilation to exchange heat with their environment, and although they can be pretty quiet, they are not silent. This may create problems and costs for you, or it may not, depending on where your water heater is located. A big unoccupied space like a garage or basement would be ideal.

Manufacturers recommend that tankless heaters are descaled regularly (like once per year). If you would need to hire someone to do that work, then the tankless heater has a significant additional maintenance cost.

For us, the bottom-line ownership cost came out nearly the same (within a few dollars per month) for a gas tank, gas tankless, or heat pump water heater. Environmental impact was the deciding factor. Only the heat pump can give you hot water that is totally fossil free, if powered by your solar panels or clean electricity from your utility. And even if your electricity sources are not so clean, the extremely high efficiency of the heat pump makes it the clear winner from this perspective.
posted by ContinuousWave at 3:38 PM on January 13 [3 favorites]

Are you on well or city water? Well water can be a problem with mineral build up and more.
posted by Raybun at 5:13 PM on January 13

I'm quite happy with our tankless unit, and it gets hotter than I ever need (a max setting of 140ºF). Previously, we had a traditional hot water heater whose tank failed catastrophically, flooding the basement and ruining a lot of LPs and 78s that I really should've stored on a higher shelf. I know that pipes can still burst, but it's worth it to me to have one less point of potential failure. And oh man, can I take some long, long showers now.
posted by mumkin at 5:43 PM on January 13

i would look at heat pumps over gas heating, especially if you are considering getting solar panels at some point. up front costs will be higher, but your heating costs and overall emissions will be significantly reduced. if your solar panels and inverter were set up to be grid agnostic, in the event of a power outage / gas supply interruption you would still be able to produce hot water.

renew (the sustainable technology association of australia) has this useful comparison overview.
posted by pipstar at 12:22 AM on January 14 [1 favorite]

Hi all, thanks so much for the advice: all of your thoughts were extremely helpful. With apologies for the dleay, I wanted to update for anyone reading this in the future. We ended up getting this - an A. O. Smith 40-gallon natural gas tank-style water heater that is basically standard but a bit higher efficiency than typical. It was only $400 (plus install) and we'll be getting a $30 rebate from our utility company because of its energy efficiency.

I really wanted to try tankless, but a few things dissuaded me. This is a modest house and I wasn't sure future buyers would be willing to pay a premium for an unusual luxury good (as it would be seen in this area). We're a bit pinched at the moment and would rather use the cost difference elsewhere. We will likely be selling within 5 years, so we couldn't recoup much of tankless's marginal energy savings ourselves. The extra cost of tankless over tank was additionally unknown as our installer said he didn't know how much more difficult the install would be and he charges by the hour. The water heater is also going in our unfinished basement: if our basement were finished or we lived in an area with a higher per-square-foot value of real estate, I would have been more tempted by tankless. The water heater is also - bizarrely - entirely across the house from all the plumbing, and I was concerned about increased time for hot water to reach the kitchen/bath with tankless. We also have very hard water, and while we'll also be using a water softener, if we ever rent out the house and don't have control over the softness of the water running through the pipes, I don't want to risk water heater or water pressure problems. We're also having enough renovation stress at the moment that swapping like for like ended up being much more appealing. The idea of paying extra for unknown cost and potential problems was too much. That said, in a future house I do plan potentially to try out tankless.

I was also very intrigued by the idea of heat pump water heaters (in a different property, on the East Coast, I had four mini-splits installed and was very happy). I also found out that our energy company here would have given me a $350 rebate on a heat pump water heater, which would have brought the cost down to about $1000 plus install. I was tempted to try this, but my installer had never seen this type of thing and I, again, was afraid of complication. I had also read some cautionary tales about its ability to rebound when called on to warm up lots of hot water after the tank is depleted, and since this is a family home, I was hesitant. I would more more inclined to put a heat pump water heater in an apartment intended for fewer occupants, or wait until the product line has matured enough to work out those kinks.

Anyway, I feel that I have a much better understanding of the various options and pros/cons now, should I never need to make this decision in the future, and I thank you all for your help!
posted by ClaireBear at 2:21 PM on January 27 [2 favorites]

Update: Don't buy a Navien. Google the complaints on them... they're rampant.
posted by summerstorm at 5:05 PM on April 16

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