It's unclear acording to the title and message what the options are. 2 small tankless? 1 large tank? 1 large tankless?
Tankless of either size is better than a single tank. Two tankless imo,offers benifits if one is located in oppisite corners of house. Two would also be nice if one failed. If heaters must be located side by side,I would ask for ball valves that alowed either or both to supply all parts of house. Circulating pumps are great for instant hot water but can wear pipes as time passes.

Contractor is asking for 2 tankless. We are thinking about a 70 gal tank (no recirculation pump).

What would be better in this situation?

Appreciate the answer.

No one?

OK, I'll give it a crack. I'm a fellow homeowner, not a plumber.

You're asking two questions - what to use to heat water, and how to minimize waiting times. There's no one answer to your question as I see it.

Some like tankless, others don't. They're unpopular in my area because they're easily clogged by the moderately hard water from our municipal system. They're also more expensive to install AND often more expensive to operate (a unit for your house may have a higher BTU output than your furnace). Some require annual maintenance from a plumber if you're not handy yourself. They're great if you have large tubs to fill frequently or take very long showers, otherwise....I much prefer tank models. Be sure to get a large one or connect two in series. I'd think you need 80 gallons at a minimum and maybe more if you have large tubs. In most areas, heating water with natural gas and tank heaters isn't all that costly. There's little money to be saved by scrimping on capacity.

The second question (which I see as unrelated to the first) is how to reduce wait times and water waste waiting for the hot to arrive. The two reasonable choices are to have a recirc system (which is separate equipment from the heater) or to locate multiple heaters to shorten the runs. If you get a recirc system, klem is right, it can lead to some pipe wear, but lots of people have them and seem to deal with it. Have it set up with a timer so that it runs only during the peak hot water usage periods and not constantly. Don't get the kind that just dumps water from the hot system into the cold supply if you drink your tap water, it could lead to off-tastes you might not like.

Personally, I have a largish one story with two heaters, one at each end. We have all the hot water we need and never run out EXCEPT when someone decides to take an very extra long shower. Otherwise, there's plenty for dishwashing, clothes washing, and showers at the same time.

Good luck.

Wow. The eternal tankless/tank debate continues.

I've had a tankless for 5 years and it's been absolutely trouble free. Even though my current municipal water has 120ppm of TDS (only some of which is actually hardness - some of it is the soda ash or lye added to raise pH) it has never given any signs of clogging or heating poorly, and in fact when it did the vinegar scale removal procedure, there was little evidence that much scale was removed.

I think people are unhappy with them for 2 reasons: yes, they are going to have problems on really hard water, > 200ppm, especially if it isn't munipical water, and also because they don't install them in a way that gives the most benefit. Mine is in a closet near the 2 bathrooms so it provides hot water very quickly. OTOH I know of a huge McMansion where they were all placed in the basement, at the opposite side of the house from most of the bathrooms, so w/o a recirc system it takes a very long time to get water. It seems like luxury home builders are slowly catching on because I know of a house built in 2010 (other was built in 2004) where they were sensibly placed at 3 locations closer to points of use, with 1 on the first floor very near the kitchen, since that is probably the location of the house with the most repeated daily calls for hot water. The owners are happy with that install.

This post was edited by davidrt28 on Sat, Mar 1, 14 at 7:18

BTW for a single guy who sometimes had to travel a lot of work, the cost saving versus the tank heater was definitely noticeable. If you're using the tanked water heater every day, throughout the day, it doesn't make as much of a difference. But there's a reason the people with PhDs at the Energy department were giving a tax break for them until recently. In most situations, they will use less propane.

I always turn "off" my two tank heaters when we travel, gas usage is essentially zero even though the pilots are on. It's simple to do, the temp knobs are always right in front. So, no advantage on that score to a tankless unit.

While I'm not not a "distrust government' fear-monger, I doubt most technical bureaucrats offer much in the way of thoughtful policy choices. If they did, and their advice were followed, we'd not have many of the problems that we have. All the same, tax credits and tax breaks are the work of lobbyists/industry advocates, political contributors and political parties. Don't be naive to think it's otherwise.

One can "waste" a lot of gas keeping tanks warm before having paid the cost to acquire, install, and run 3 tankless units. Although I think newer models are more capable, one of the reasons homes often had several units installed was some tankless models had limited GPM flow rates. If you're a single guy living alone, you wouldn't experience what happens with a tankless when there are two showers and a washing machine running at the same time.

"So, no advantage on that score to a tankless unit."

Yeah but a lot of people don't want the hassle of doing this every time they will be away from this house for a more than a few hours. Also, if I've traveled by any form of public transportation and certainly that includes flying, my first order of business when getting home is to take a shower. I'd rather not wait an hour for the hot water to be ready.

Look, there's a reason those pesky Europeans and Asians have been preferentially using them for over 20 years now. And it's not because they like to pay more for things than we do.

There's no hassle, I can take a shower in 30 minutes after turning the heat up. Just enough time to go through the mail and unpack. Or, I sometimes leave it on if we're to be away less than several weeks. I agree with your comment, no one turns if off for an absence of less than many days or weeks. There's no need, it's very inexpensive to leave on. Heaters consume little gas to simply maintain an already elevated temp. (unless located in a very cold place, which mine aren't).

I lived in Europe for several years, so let me tell you about the pesky Europeans. It's hard to generalize but there are some common factors.

European households uses MUCH LESS hot water than American ones. Here's a few reasons why:
-appliances like dishwashers and front loading clothes washers ALL have internal electric heaters and so are connected to cold water pipes only. That's why the cycles take so long.
-they bathe less frequently than we do (sad but true)
-sinks in a half-bath (ie, just a WC) often have running cold water only, for hand washing

Many European residential structures are older than internal running water as a widespread phenomenon. That's why you see pipes running through rooms and not in walls. In such cases, there's no space to put a tank, a unit that hangs on the wall fills the bill just fine.

The units that historically were common there are much less powerful that what's being sold here today (that are trying to carve a niche in a market that is tank-fixated). The water heater in my flat, that was 3 feet away from my shower, needed to run for a few minutes to warm up enough to allow for a shower. In the wintertime, lukewarm was about all it could do.

Many people don't like the instant on wall hangers, they're thought of as being old fashioned retrofit relics. They're not popular in newer single family construction, where hot water production is usually part of the central heating system.

If you use recirc, the very best system made is the Metlund Design unit. Pricey, but it saves water and energy and will return the cost of investment regardless of which method you use to heat your water. By the time you buy and install that system you are a ways toward a second tankless, if you go that way. Based upon the lay-out of the home I think you should have two systems regardless of type And, you should plumb a separate return (recirc) pipe for each. Better to install it and not need it than find that you do need it and cannot do it. As well, there should be a conversation with your plumber about the lay-out of the system based upon use of the water heater. Reason being, he is going to plumb the house the way he thinks it will be used. You don't want your kitchen sink at the end of a long, large diameter pipe. Time, distance and flow rate are the issue. Tubing size plays into this too. If you haven't drawn water for a while the water will cool beyond hot used temp. If it is all 3/4" feeding a low flow faucet you can go take a nap before getting hot water. If your plumber is using PEX rather than copper be aware that the fittings have a "bushing affect". What that means is your 3/4" pipe is bushed down to about 9/16" and your 1/2" to about 5/16. It matters. Cross sectional area of 1/2" is .19 sq". 3/4" is .44. That equates to vol of water. Insulate with at least 3/4" insulation.

I have been using tankless since 1998. Operation has been flawless AND I have never flushed the HX. Good water and good equipment.

Your GC is going to select the lowest bidder to do your plumbing. I would suggest that you get involved in this decision. If you get a plumber who feels like Snidely about tankless he will be no good to you once the system has been installed. There are many in the trade like that. What you have to keep in mind is that excellent tankless water heaters have been available in the US for the past 15yrs. I represented the largest of them in the 6 New England States for all of that time. We did little but training on application, installation and service. Service training was a free full day hands-on tear down and service class. If a plumber comes to my class he is a better mechanic when he leaves. Over this 15 yrs many professional (?) plumbers have not bothered to get off their duffs to improve their skills. They rationalize this by telling you that the units are a problem. Is that who you want in your home?

I just received the Houzz kitchen &bath survey and those over 45 tend to use tanks where younger folks more frequently go tankless. Interestingly, 45% of respondents forego a bathtub in the master bath. That surprised me.

Snidely, while I respect your opinion on all the topics we post on, many of which we disagree on ;), I want to offer a caution on turning your tank water heater down when you are not there. Some see this as the "boy who cried wolf", but I do have a plumber friend in Colorado who almost died from Legionalla as a result of doing exactly this. It has worked for you, but you need to be heating that water to am minimum of 130 & 140 is actually better to kill the bacteria in your tank. Flush it frequently too to avoid sediment. Again, just a heads up!

I like your knowledgeable ideas, Jackfre, though you're coming at it from a different perspective (as you said).

You're right on about the need to keep hot water hot to control bacterial growth, it's something I'm aware of and have cautioned others about in this forum. You may know that it's a particular problem with electric tank models, which typically have a cool zone below the lower heating element where water never gets hot.

If my family is indicative of the trend, we've certainly experienced a decline of bathtub use. I only have standard-sized models in my older house and they're rarely used. When I see or visit newer houses with the expansive or jacuzzi tubs, I scratch my head. I think these days most people don't have the time to take a bath, and when they soak, it's usually more a social event in a large hot tub at a gym or in the backyard.

Actually, Snidely, I was not aware that electrics pose more of a threat in this situation, although it makes sense given burner/element placement. Thanks for that!

Live4u,

Bringing the conversation back around....
I'm trying to get an idea of where you live so we can factor in cold water temps. You have the option of a tankless unit with a recerc pump as well. Navien even offers a tankless with integrated circ pump.

In any situation where you use a recerc pump, it should have a return loop, as someone else mentioned. Also, all of the hot water lines must be insulated. Otherwise you are wasting a lot of heat (that must be potentially cooled in the summer as well).

If this were my house I would go with two condensing tankless units - no question.

I have had a tankless unit for over 5 years... the requirement for annual maintenance is overstated. I've flushed mine once and have moderately hard municipal water.

I'd like to correct something from some of the other posters though: Despite common misconception, the bulk of the savings from a tankless heater does not come from the fact that hot water isn't sitting in a tank -- it comes from the fact that the induced sealed combustion allows flue outlet temps to be much lower on the tankless - to near condensing on 82% models or below condensing on 92% and above models. Any normally vented gas appliance will have a running efficiency of around 65%. Standby storage tank losses just reduce that overall efficiency more.

Here's the thing: You never know what will happen to energy prices-- but they tend to trend up. Natural gas had gone down momentarily, but now trending back up also. Buy the most efficient stuff you can -- as long as your installation costs are reasonable (should be cheaper for condensing tankless... but isn't) it will pay for the increased cost in about 5-6 years.

The Navien does have a unit with the included circulator as Jake noted. Be aware that it may not be the right circ for your system. Every system has a personality and circulator pumps should be sized to do the specific job required. Lay out the system, calculate the head loss and select the correct circ. That particular Navien unit may be fine, but do not assume one size fits all in that dept.

"sinks in a half-bath (ie, just a WC) often have running cold water only, for hand washing "

THIS IS SIMPLY NOT TRUE !

I've lived in Europe too, and visit often. I have NEVER seen a private bathroom , powder room, 1/2 bath , whatever - that had a sink and did not have both hot and cold water at the tap(s).

I have been in public toilets , golrified outhouse really that only had cold water , and I'm not even sure it qualified as "running water". This was in the 70's and 80's in Eastern Europe and Russia. The civilized, Western World has hot water just like America.

Snidley is on point about the initial cost of on demand vs. tank with respect to acquisition cost. Especially if you have a long or complex vent run or your heater need stainless piping. He has failed basic math if though, if he thinks the actual running costs are less for a tank version.

Snidley - how efficient are most tank heaters ? You know, the thing that determines the amount of hot water you ACTUALLY get from putting a dollars worth of gas into the system? Most tank models are 60ish % efficient while those rinnai models start at 80% + and go to over 90% efficient !

Sure you can get an 80% efficient tank model, but how much do those cost ??? Yep, the same or MORE THAN an large capacity on demand unit. And it will need need vent pipes also, so more cost !!! Now , you will be able to run it with out a fire hose sized gas supply line, which is a consideration (and expense) for a remodel. However, in a well planned new home , this really isn't a factor.

If you want to debate total lifespan cost , that's one thing. But to say a tank model costs less to operate than an on demand heater as a blanket statement is just plain false.

You see folks, no matter the type of heater it takes the same amount of energy to heat a gallon of your incoming water to 100+ degrees , and YOU are paying the same amount for that btu of gas or kW of electricity whether you are pumping it into a tank type heater or a tankless. So , it then boils down to EFFICIENCY !!!

Things start to get more complicated when you add in or try to add costs for convenience , capital outlay to acquire systems, financing costs, maintenance costs, rebates, ect....

If you just want a washer full of hot water or a 4 min. shower, it's hard to find something initially CHEAPER than a 40-50 gallon tank type that are priced around $500 everyday, everywhere.

You haven't seen just cold water service at a sink in a residence's WC, so you conclude it doesn't exist? Awesome!

There's no point in having any further conversation.

(PS, I've never been to Eastern Europe).

Snidley - once again you have misread or at the least msi represented what I wrote.

I never said they don't exist ! What I said was : your characterization that they OFTEN have only one is incorrect. Two TOTALLY different things.

Often would be six (or more) out of ten bathrooms having only cold water and that simply isn't the case with residential bathrooms or powder rooms in modern America or Western Europe today !

I respect your opinion on tankless heaters, but don't let that cloud facts about other matters.

get a tankless water heater. rinnai's probably the best for you since you are using natural gas. if you plan on electric tankless water heaters, then they're no different from regular heaters.