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Pro's & Con's of tankless water heaters

Pete_36 Member Posts: 19
1 large washer can draw 5 gal per minute. A average size laundry of 30 washers would need so many it would not be feasible. Thats why some people put 3 in with a storage tank. I think a modcon with a storage would be more efficient.


  • I was wondering if anyone has had any cronic problem with tankless water heaters, specifically Rinnai. Or maybe someone has a preferred manufacturer. Thanks for any input.

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  • allan_7
    allan_7 Member Posts: 55
    That reminds me......

    I remember seeing an article in Contractor Magazine a while back written by Mr. Dave Yates, a frequent Wall Visitor and accomplished professional, about the long term costs of DHW and the various methods of producing it.

    Paging Mr. Yates, I missed your conclusions. Thanks you for your help.
  • Derheatmeister
    Derheatmeister Member Posts: 1,514

    Yes I've seen some of these systems that require A lot of Maintenance ,these system are mostly on well's,so that also is part of the problem. Anyway mostly they need the cleaning of the exchanger and the screen. i am also a trained installer(Big deal) but have yet to find a justifiable situation for a install.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,228
    In general...

    ... tankless have been oversold, with benefits exaggerated and drawbacks ignored. For any water heater, look at ALL the costs over time to arrive at what's best for you. There's more opinion on tankless at www.waterheaterrescue.com .

    Yours, Larry
  • JohnNY
    JohnNY Member Posts: 3,226
    Someone's going to kill me for this, but..

    ...I get emails from my clients, and potential clients, about this all the time so I've prepared a stock reply.

    Here it is:

    Paloma, Bosch, Rinnai, Takagi…..there are lots of tankless, or instantaneous, water heaters out there these days.

    They do a great job and everyone in Europe has one.
    Here in America, though, they present some problems.

    The carbon monoxide-filled exhaust is expelled by a fan out its flue pipe which must terminate at least one foot away from any building opening such as a door or window. That means drilling a 3" hole in the side of your home. That’s not an easy thing to do in an urban building.

    The units themselves use a lot of gas at once. A typical whole-house unit burns around 200,000 BTUs per hour. Compared to your 50-gallon gas fired tank-type water heater, which burns around 50,000 BTUs per hour, that’s a lot of gas.

    What that means is the tankless water heater requires a much larger gas pipe than the tank type is using. And because it burns so much more fuel, it also needs a lot more fresh air for combustion. This adds to their considerable installation cost as very often a large dedicated gas pipe from the meter to the unit is required and a fresh air duct will have to come from outside. That's another 3" hole in the side of the house.

    If your lifestyle is such that you’re frequently using a lot of hot water throughout the day, keep in mind that your tankless heater will be on, probably burning 200,000 BTUs per hour for much of that time. The tank-type will chug along slowly burning its 50,000 BTUs a few times per day and store the water for when you need it.

    Their high efficiency ratings stem from the fact that the unit does not run to simply maintain a constant temperature the way a tank type unit does.

    A tankless water heater’s high efficiency is best realized when installed for someone who doesn’t turn on their hot water very often anyway. It just sits there all day long never turning on until someone comes home and does some dishes and takes a shower.

    That’s the perfect application.

    Many claim to give 6 gallons or more per minute of endless hot water but if you look at the literature included with a common unit, they sort of redefine “hot water”.

    90° F rise / 3.2 gpm

    77° F rise / 3.7 gpm

    65° F rise / 4.5 gpm

    55° F rise / 5.2 gpm

    45° F rise / 6.4 gpm

    Rise is the amount the water temperature will be raised from the inlet of the heater to the outlet of the heater. That means that a 6.4-gallon unit will give you an endless supply of water raised 45 degrees from the temperature it is coming out of your water main at a rate of 6.4 gallons per minute.
    So, during the winter months in our part of the country when the temperature of our incoming water hovers around 40 degrees, you can expect 6.4 gallons per minute of 85 degree water.

    That’s not hot.

    Your shower head might only pass 4.5 gallons per minute so, in this unit, we can expect a 65 degree rise. That will give us 110 degree water. That’s much better but there’s nothing left for another fixture to run simultaneously.

    Of course, in the warmer months this is much less of an issue but it’s not something to ignore.

    This is a speech I’m well-prepared to give as I get calls and emails for these units all the time.

    I am very happy to install them in a person’s home but always with this large disclaimer:

    They simply don’t give you hot water the way we Americans are used to having it.

    After a newly installed unit goes in I sometimes still get the call: “It’s not working!”

    But it is working. Just turning on a faucet may not be enough to turn the unit on. They are activated by an internal device called a “flow switch” that senses water flow through the system (you turned on a faucet) and then turns on the exhaust fan, then the flame, then you start to get hot water. That flow switch needs to sense a minimum amount of water, usually 0.6 gallons, to get the process started. A trickle of water to wash your kid’s hands or to wet a towel isn’t going to do that and that may seem like an eternity to some when standing at the sink. You need to turn the faucet on for stronger flow to get hot water. Is that a waste of water? Probably. At least sometimes.

    As a professional plumber and owner of Gateway Plumbing and Heating, licensed by the Department of Buildings, and a person dedicated to understanding and embracing new technology in my field, I can say that I like tankless water heaters.

    What I don’t like is how they are presented to the public and sold in large retail home centers without giving the consumer any real information on the product. They are very sophisticated, fuel-burning appliances that require significant thought before they are selected, bought, installed or repaired.

    You are right to ask before diving in.

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  • Derheatmeister
    Derheatmeister Member Posts: 1,514

    JohnNY was was a very long post, and very well put!
  • hot_rod
    hot_rod Member Posts: 21,804
    and now plumbers are adding tanks and bronze circs!

    to make them more American-ized. How bizarre, how bizarre.

    I still feel a condensing type water heater is the most efficient single appliance way to get ample DHW.

    With a solar preheat, regardless of your system choice, of course.

    Check out this article.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Bruce M
    Bruce M Member Posts: 166
    I See an Agenda at waterheaterrescue.com

    I don't think you can get an unbiased opinion from a website that sells products for tank type water heaters
  • Thanks Allan

    Here's one: http://www.taunton.com/finehomebuilding/how-to/articles/choosing-water-heaters-tank-and-tankless-options.aspx

    HR has it nailed. In my cost analysis (life cycle cost), the indirect (when properly sized and installed and coupled to a hi-eff boiler) is beat only by solar.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,228
    I don't run...

    ...Water Heater Rescue, but I have given a lot of input to it. I don't profit (or lose) from their business. I have been dealing with water heaters and questions about them for over twenty years. Also, I've collected literature about all types, including tankless. My goal (and WHRs) is to do what's best for the water heater user. That turns out to be good business as well.

    Tankless really have been oversold for many years. A number of brands have come and gone in the US, stranding owners with equipment that quickly become obsolete when parts were not available. Oversold means more was promised that the heaters delivered, both in terms of performance and energy savings.

    My agenda has been and still is to do what's best for the end users. To that, I happily plead guilty.

    Yours, Larry
  • Timco
    Timco Member Posts: 3,040

    So...what are the minimum requirements to meet to consider a tankless / 40 gal combo setup? And what about with a re-circ type setup?

    Just a guy running some pipes.
  • tankless

    I hav had problems with the Bosche I switched to the Noritz, Noritzu in japan. I only put in the biggest residential size and I always check by running to showers on hot only for 30 or 40 minutes and the thermometer nver goes below set point. If you don't have an outside wall to mount it on forget it. The propriatory smoke pipe will kill you. We did one wher the price of the chimney equaled the price of the heater and installation. They do burn up to 200,000 btu's per hour but only at maximum demand. If just the dishwasher is running they're burning more like 30,000 btu's an hour. Bradford-white makes a 25 gollon tank type with a 78,000 btu burner under it. Thats kind of the best of both worlds. If you go tankless get used to washing you hands in cold water.
  • Bruce M
    Bruce M Member Posts: 166
    Oil fired On Demand Hot Water Heater

    I can tell you from personal experience that an oil-fired Toyotomi hot water on demand heater provides an abundance of hot water for a "normal" house. Not talking about whirlpool baths or 5 bathrooms. I keep my water temperature set at 130 degrees and it is possible to take a 4 hour shower and the temperature never varies. After the water is shut off, the unit never runs for more than 25 seconds. During the non-heating season you can shut your primary heating source. The unit has an 88% efficiency rating and can heat up to 240 gallons an hour. The heater can use kerosene as well as #1 or #2 fuel oil. I believe that if used in combination with some form of solar collector it might be even more effective.
  • Kevin O. Pulver_2
    Kevin O. Pulver_2 Member Posts: 87
    I use the Rinnai

    and have had almost zero trouble with them.
    I replaced one water flow sensor under warranty.
    Tech Support was phenomenal! Changeout was simple though a little tight in compact housing. Not bad at all.
    My best recommendation would be Mod-Con boiler with indirect water heater (and insulated recirculating hot water loop rather than manifold plumbing system or you'll still be "washing your hands in cold water").
    With indirect, only one appliance to maintain and one flue penetration. I don't understand the above posted problem with drilling a hole in the house.
    If space is an issue, the Rinnai shines. In my own cramped home, I dumped 2 gas water heaters and hung a Rinnai over the basement toilet. A bronze circ and plate HX in the ceiling supplies my radiant. It's up to the seller to explain the temp rise to GPM relationship to the customer.
    Years ago at training, they made sure we explained them as "continuous flow" rather than "on demand". We have 6 children and NEVER run out of hot water any more. Kevin
  • Mike.C
    Mike.C Member Posts: 43

    What a bunch of closed minded people!
    I have installed over a hundred Rinnai heaters and some even in the unspoken "Open Loop heating system using a tankless" Where's the creepy music? I have no complaints on any heaters we sell. We tell customers the cons of a slightly longer wait, that you can have water all day long just not to run everything in the house at one time. and again no complaints! So that leaves me to believe that you guys for the most part are doing heating of houses and could care less about heating water. If they had a license to own tools I'm sure a few people here would not pass that one! There Just my early morning 2 cents.
  • Elmer Fudd
    Elmer Fudd Member Posts: 8
    tankless with small storage tank

    what about a tankless with a small(5 gallon) storage tank(electric?) Does this help to alleviate the cold water hand washing? I know I have seen this talked about. I feel that the minimum flow is sometimes as important as the max.
    Ya I know not energy efficient but there are other reasons to do a tankless.
  • Home Depot Employee
    Home Depot Employee Member Posts: 329

    Iv'e been using one for 17 years and am on my third but only because I moved into my new house in August. While if I had a boiler due to hydronic heating, the indirect would have been a no brainer. I would never consider ever going back to a tank vessel ever again.
  • Home Depot Employee
    Home Depot Employee Member Posts: 329

    If tankless wasn't a threat, I think every brand of tank type water heater wouldn't have scrambled to add a unit whether relabeled or not to their price book and offering.

    Just a fact-
  • Timco
    Timco Member Posts: 3,040

    Do you have a link or part # for the BW water heater with the 25 gal tank & increased input? I do not see it on their site.

    Thanks, Tim
    Just a guy running some pipes.
  • Al Corelli
    Al Corelli Member Posts: 454

    I have a first generation Bosch at my house (the one with the pilot). As long as we only use ONE faucet at a time, all is well. If two are open, the pressure drop causes flow to almost cease completely.

    The flow to the bathroom sink faucet takes 18 seconds to get hot. Long enough to get the toothbrush prepped. The the hot is there then for the shower with a minimum of waiting. The heat of the water is consistent and never ending.

    The consensus here is that incoming water is only as low as 40 degrees. I routinely see 32-33 degree water in the winter, and as high as 50-52 in the summer. I swap the gauges and periodically test with electronic means to verify accuracy,
  • Pete_36
    Pete_36 Member Posts: 19

    They are pushing these units for commercial use in laundromats. There is no way they can keep up, so some people recirculate to a tank.
  • jackchips_2
    jackchips_2 Member Posts: 1,338

    If you pipe a number of these units to a reverse return header, why wouldn't it work?

    In my home, I have a Takagi, Aquastar 240 in series with my 50 gallon gas fired water heater and not only do I not run out of hot water but I heat my 20,000 gallon outdoor pool through a heat exchanger in the summer.

  • ALH_4
    ALH_4 Member Posts: 1,790

    I think at that point, Aerco water heaters might be a better match.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,228

    This one might be worth watching. It can come with a small tank built in, getting rid of the "cold sandwich" and allowing slow flows. http://www.navienamerica.com/

    Yours, Larry
  • Bruce M
    Bruce M Member Posts: 166
    Navien Tankless

    A fine example of South Korean technology at it's best. Even Rheem has tankless units for sale. It seems that high oil and gas prices have brought higher efficiency to us.
  • Jack
    Jack Member Posts: 1,047

    I've found the on-demand water heater to be ideal for laundry applications. BTW, I represent Rinnai, just so you know. As well, I'm a licensed plumber.

    For reference go to www.rinnaisolutions.com, register and go to the tools section for sizing info. A consumer I would send to www.foreverhotwater.com.

    The coin op laundry has a number of machines typically of varying poundage. Calculate the number of machines to cover the load and where they are to be positioned. As we all know, the closer to the point of use the better.

    One of the advantages of these systems vs tanks is the load factor in laundromats. I always ask the owner how often they are running at capacity. This is important. The answer typically is Sat/Sun mornings. With that info I will ask why would you want to store hot water for 168hrs/wk when you are at demand capacity for +/-10 hrs per week. One of the great advantages of the on-demand is that when only one washer is running, you fire only the gas to satisfy that load. As load increases/decreases, the units modulate up/down to satisfy that load and no more. When no one is running a machine you have no gas consumption. That seems pretty efficient to me. Again, look at the use pattern.

    I sized a system that called for 8 units. That would have been two banks of 4. In discussion with the contractor and the owner I recommended two banks of 3. With the agreement that the units would be installed to accomodate the 7th and 8th units should we have a capacity issue. So, room was left for those units, the piping was designed for simple addition of the additional equipment and the gas line was sized to accomodate them. They have not been necessary in that particular installation, but I was able to "value-engineer" a system to meet the demand satisfactorily. The MSA control package for multiple units, rotates the firing sequence unifies the operation of multiple units and balances the flow within a tenth of a gal. to each unit. Pretty cool! Also, keep in mind, that if on the rare Sat morning everyone looks up and down the line and they all drop their quarters at the same time that the Rinnai system will respond. They are designed to produce only the correct temp water and will activate the flow control to reduce flow to guarantee temp. I would invite you to spend a Sat morning or 10 and tell me how often all the machines draw at the same time. I tell the owner that even in that circumstance, it simply slows down the fill rate for that short period.

    One of the things most laundromat owners really appreciate is the direct venting (no combustion air issues) and room savings these can create. Sq footage in these places is very dear and high wall space is typically available but floor space and storage space is at a premium. I had one laundromat that created a storage area and a small office area when they went to the Rinnai system. That man loved the system and his new found sq ft.

    What is necessary for these to work well? In my opinion, that is a clear thinking, open minded, professional mechanic who knows that a pipe wrench is not a hammer (although I frequently used one as such;) and doesn't leap off of tall buildings in a single bound.

    Having taken my lumps in the mech contracting business I will say that in any new equipment/system, "slow and steady" wins the race. Read, study and then try it out. If we can help...give us a shout.
  • allan_7
    allan_7 Member Posts: 55
    Thank you...

    for access to the technical portal. A lot of info to absorb. Where can a tech obtain the actual manuals??

    Thanks again. Off to work..
  • Jack
    Jack Member Posts: 1,047

    You can access installation, service/troubleshooting, parts, manuals etc in the "literature" section. On Rinnaisolutions, you are correct there is a great deal of info to absorb. Check out the calculators in the upper heading. Also when in the troubleshooting heading click on the blue words and it will take you to the things you need to check. When you see the four blue windows click on any one of them and it will give you an exploded diagram of the unit. click on the part and it will giveyou the part number, and if it is an electrical component it will give you troubleshooting information
  • Home Depot Employee
    Home Depot Employee Member Posts: 329

    Good point Jack

    Most people fail to realize that the newer models, more expensive heater(s) deliver consistant water temps, regardless of demand or flow. So what if it takes longer to fill the tubs or washers under high demand periods, whos paying attention or cares anyways.
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