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Thread: Tankless Water Heater for Tub

  1. #1
    Software Engineer BlackNoir's Avatar
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    Default Tankless Water Heater for Tub

    I posted this in the Shower & Tub forum before realizing there was a tankless water heater forum so I thought I'd try over here too.


    Is it plausible to get a tankless water heater for a tub? We have a 50 gallon water heater and we never seem to have enough hot water for our tub. The tub holds ~90 gallons and it's not like we fill it with steaming hot water. The water heater is new so...

    Is it possible to hook up a tankless water heater in series with the regular water heater as an assist?

    Any other advice besides taking a cold bath?

    Thanks,
    BlackNoir

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Depending on how the pipes are layed out, it may be cheaper to put in a second WH rather than a tankless. Feeding warm/hot water into the tankless would decrease it's load and allow it to heat the water hotter, but at some point, you'd be restricted by volume...as the input to the tankless system gets colder, it starts to limit how warm the output is. Since you'd only get maybe 40-gallons out of the WH that was hot, you'd then quickly get down to your normal cold water inlet temp, and that's the thing that dictates the size of the tankless you need. The tankless would need some fairly expensive flue setup and you'd probably need to upgrade the gas line and maybe meter size. You might not need to do that with a second tank WH, depends. A tank has the luxury of taking its time to reheat, a tankless needs to be big enough for the maximum load, so the burner sizes are often quite different.

    I think you'd be better off with a second conventional WH in series. It would have been better if you'd sized what you have to your needs, though.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3

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    Taking the other side... I would add a tankless unit in this case BEFORE messing further with a tank solutions. For one easy, quick reason... unlimited hot water. Whether you fill that 90 gallon tub once a day or march the whole family through one at a time and only half fill it a tankless solutions will fill that need. You 40 gallon unit can't do that as you have found out and adding another tank will only put off the eventual lack of hot water each day.

    I use a tankless unit every day and have not had a single negative issue nor has the family complained... and they would! My unit was installed in a house with 40 year old plumbing so "pipe issues, routes, location" have been overcome or non-existant.
    "Dude, we can fix that. My old man is a TV repairman, he's got the ultimate set of tools!" --Jeff Spicoli


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    Master Plumber nhmaster's Avatar
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    And here we go again !

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    Illinois Licensed Plumber SewerRatz's Avatar
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    Just did a job yesterday, guy called me and begged me to remove his tankless POS and install a 75 Gal Power-vent. He had nothing but troubles from the start. The tankless unit was 2 years old had to be delimed every two months, even though he does have a water softener in working order. Had to have the heat exchanger replaced twice, also if more than one person in the home ran hot water is flow would turn to a trickle. This unit is designed to reduce the flow rate to ensure you get the 120 water temperature. He can not afford to run three units which would handle the demand nicely. Upgrading the gas line is the biggest issue, since adding two more units would be putting a 400K BTU load on his gas system.

    The moral of this situation is only install a tankless system properly sized to handle all your needs with in the home, and plan on doing maintenance on the unit on a regular basis. Remember you are cooking water really fast in these tankless units so they will leave lime and other minerals deposits in the heat exchanger, look at what happens to a pot when you constantly just boil water in it. Also there is no Anode rod (known as a sacrificial rod) for any impurities to attack, so they will attack the heat exchanger and will cause leaks. Takagi just announced it has came out with a a TK-3 Pro, the difference is the copper alloy it uses for the heat exchanger they call it HRS35 copper alloy, for the heat exchanger tubing In their own ads they say it will resist getting pin hole leaks like the standard TK-3 unit. They know there is this problem but of course none of them will advertise that fact. Just like they do not advertise the fact you need to delime these units regularly.

  6. #6

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    Quote Originally Posted by SewerRatz View Post
    Just did a job yesterday, guy called me and begged me to remove his tankless POS and install a 75 Gal Power-vent. He had nothing but troubles from the start. The tankless unit was 2 years old had to be delimed every two months, even though he does have a water softener in working order. Had to have the heat exchanger replaced twice, also if more than one person in the home ran hot water is flow would turn to a trickle. This unit is designed to reduce the flow rate to ensure you get the 120 water temperature. He can not afford to run three units which would handle the demand nicely. Upgrading the gas line is the biggest issue, since adding two more units would be putting a 400K BTU load on his gas system.

    The moral of this situation is only install a tankless system properly sized to handle all your needs with in the home, and plan on doing maintenance on the unit on a regular basis. Remember you are cooking water really fast in these tankless units so they will leave lime and other minerals deposits in the heat exchanger, look at what happens to a pot when you constantly just boil water in it. Also there is no Anode rod (known as a sacrificial rod) for any impurities to attack, so they will attack the heat exchanger and will cause leaks. Takagi just announced it has came out with a a TK-3 Pro, the difference is the copper alloy it uses for the heat exchanger they call it HRS35 copper alloy, for the heat exchanger tubing In their own ads they say it will resist getting pin hole leaks like the standard TK-3 unit. They know there is this problem but of course none of them will advertise that fact. Just like they do not advertise the fact you need to delime these units regularly.
    Maybe a preface is needed regarding my positive post! Geez

    IF, big IF, your water is a problem (pressure, quality etc) then a tankless will not work for you long term and the above begging to have it removed MIGHT apply to you! No if, ands or buts....

    I, real world everday user here of a self installed tankless unit, love my tankless system and will not have it removed as I don't have the problems that a few people on here seem to want to continue to scare people with horror stories. My use of a tankless is a fact and of course this scares the crap out of some on here as they can't see to handle the concept of anything other than a big frikin' tank wasting away in the basement and that future revenue stream of $500 to replace it when it rusts out yet again. FUD.... google it.

    In MY CASE, regular maint will be a ONCE PER YEAR descaling of about 15-20 minutes of my time. No biggy.
    "Dude, we can fix that. My old man is a TV repairman, he's got the ultimate set of tools!" --Jeff Spicoli


    http://web.me.com/greg.saulsbury/ChosatongaSpeaks

  7. #7

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    Quote Originally Posted by SewerRatz View Post

    Just did a job yesterday, guy called me and begged me to remove his tankless POS and install a 75 Gal Power-vent. He had nothing but troubles from the start. The tankless unit was 2 years old had to be delimed every two months, even though he does have a water softener in working order. Had to have the heat exchanger replaced twice, also if more than one person in the home ran hot water is flow would turn to a trickle.


    Maybe he should get rid of the water softener instead!


    From a water softener web site:


    "SALT IS CORROSIVE

    Those in The Navy are familiar with the term "Marine Whites." Sailors used to put their white clothes in ocean water to whiten them. Caution had to be used because if the clothes remained too long in the heavily salt-laden water, they would deteriorate. Salt is corrosive. Softeners use the same salt spread on icy roads, which destroys the underside of cars. Those living near oceans know well the corrosiveness of salt to cars, houses, etc. Many people with galvanized pipes found that salt softened water did prevent scale build-up, but the trade-off was the salt also corroded their pipes.

    Homeowners with salt water softener systems will go through more water heaters because of the salt's corrosive effect on the heating coils. Always check with a manufacturer's warranty related to water. Softened water should not go to a pool or spa. Hard water and naturally soft water have their maintenance issues, however softened water offers potential problems that may imply or outright void the warranty on certain products."
    Samuel James Witwicky

  8. #8
    DIY Senior Member chris8796's Avatar
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    Quote Originally Posted by gregsauls View Post
    I, real world everday user here of a self installed tankless unit
    99% of real world everyday users are incapable of installing a tankless or tank WH and have minimal understanding of plumbing systems. I'm sure most plumbers would rather make their money carrying a tankless unit down the basement, than drag a 75 g tank down the stairs. So I don't think money alone is motivating their opinion.

    Quote Originally Posted by gregsauls View Post
    In MY CASE, regular maint will be a ONCE PER YEAR descaling of about 15-20 minutes of my time. No biggy.

    For the real world everyday user, that means paying a plumber to do this (long after it would be considered preventative). So if you need a plumber for your plumbing needs, you should listen to your local plumbers' advice and what they are comfortable working with.

    For the OP, I would go with a tank or a tankless solution, not a hybrid. Both offer solutions, but only a local plumber can tell you what each will cost and what they warranty. If you had real qoute numbers it would be easier for everyone to offer real world advice. This sounds like a good application for tankless, but if your local plumbers don't like them (for whatever reason), you will pay a steep premium to install and warranty one.

  9. #9
    Master Plumber nhmaster's Avatar
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    Quote Originally Posted by BlackNoir View Post
    I posted this in the Shower & Tub forum before realizing there was a tankless water heater forum so I thought I'd try over here too.


    Is it plausible to get a tankless water heater for a tub? We have a 50 gallon water heater and we never seem to have enough hot water for our tub. The tub holds ~90 gallons and it's not like we fill it with steaming hot water. The water heater is new so...

    Is it possible to hook up a tankless water heater in series with the regular water heater as an assist?

    Any other advice besides taking a cold bath?

    Thanks,
    BlackNoir
    Yes it is possible. However, if you do a little bit of thread searching on this and other sites, regarding tankless water heaters, you will soon see that the majority of professional plumbers, guys that deal with these things day in and day out in many differing scenarios are not particulary impressed with them. Then you can come back here and read the unrealistic glowing praise of them from our two in house protagonists that are under the impression that their opinions are somehow more valid than those of professionals. Tankless heaters are a complete waste of money and nothing but a service nightmare from day one.

  10. #10
    Illinois Licensed Plumber SewerRatz's Avatar
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    Quote Originally Posted by Ladiesman271 View Post
    Maybe he should get rid of the water softener instead!


    From a water softener web site:


    "SALT IS CORROSIVE

    Those in The Navy are familiar with the term "Marine Whites." Sailors used to put their white clothes in ocean water to whiten them. Caution had to be used because if the clothes remained too long in the heavily salt-laden water, they would deteriorate. Salt is corrosive. Softeners use the same salt spread on icy roads, which destroys the underside of cars. Those living near oceans know well the corrosiveness of salt to cars, houses, etc. Many people with galvanized pipes found that salt softened water did prevent scale build-up, but the trade-off was the salt also corroded their pipes.

    Homeowners with salt water softener systems will go through more water heaters because of the salt's corrosive effect on the heating coils. Always check with a manufacturer's warranty related to water. Softened water should not go to a pool or spa. Hard water and naturally soft water have their maintenance issues, however softened water offers potential problems that may imply or outright void the warranty on certain products."
    OK then lets void the warranty on 99% of the Tankless water heaters They say they will not honor the warranty if the water is to hard. I am not trying to scare anyone away from a tankless system. I just want them to know they need to size it properly and understand it nothing like a tank system where if you do not maintain it will just cost more in fuel and will leak sooner. Tankless if you fail to maintain them you stand the chance of leaks but first thing you will notice is a drop in water flow. Rinnai has a nice added feature it will tell you an error code of "DL" when it is time to delime it.

    Oh back to sizing the tankless system someone in one of the posts said a single unit works just fine for them since its just 2 people living in the home. Here is a little blurb from Takagi's website "Remember: Although a home with two or three bathrooms may only have one or two occupants currently, the number may increase if the family changes or the house is sold. Size for the house, rather than the number of occupants." They as well ANY of the other tankless manufactures tell you to size for the house not the number of people living there. It was the mistake my customer with the "begging" me to remove his tankless did. He tried to go about it on the cheap-side and use a single unit in his 3 bath home. He said he was real happy with it the first year it was installed other than the deliming part. But when his kids moved back in and they tried to take multiple showers at once the water pressure on the hot side went down to a trickle. Yea they where getting 120 water temperature out of that trickle. The fix was to add at least one more unit to handle his demand but another 200K BTU demand on the gas would mean the gas meter needs to be upgraded and the pipe coming into the home up-sized. To solve the problem where he can use water with all 3 showers and a dishwasher he would need 3 units to handle it, or replace his first unit with the commercial model and install the second commercial model.

    He did call me today his kids where in two of the shower and he was in his master bath shower and they all enjoyed a good shower at the same time for the first time since the kids came back home.

    Oh for those of you wanting to install a Tankless water heater yourself, get a brand that does not require a licensed plumber as well as having to take their training class. Other wise your warranty is void.

  11. #11
    Master Plumber Redwood's Avatar
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    PFFFFFFFSSSSSSSSSSSSTTTTTT



    Looks like our 2 favorite tankless trolls are back again....

    At least your avitar speaks the truth...



    Now if only we can get laddie boy to pick one that fits...
    Last edited by Redwood; 03-26-2009 at 07:25 PM.

  12. #12
    DIY Member ChuckS's Avatar
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    Quote Originally Posted by SewerRatz View Post
    But when his kids moved back in and they tried to take multiple showers at once the water pressure on the hot side went down to a trickle. Yea they where getting 120 water temperature out of that trickle. The fix was to add at least one more unit to handle his demand but another 200K BTU demand on the gas would mean the gas meter needs to be upgraded and the pipe coming into the home up-sized. To solve the problem where he can use water with all 3 showers and a dishwasher he would need 3 units to handle it, or replace his first unit with the commercial model and install the second commercial model..
    Seamed cheaper to tell the kids to shower one at a time. That's how we did it growing up and how we do it now. Even with a tank heater, with multiple showers going on, you will have to be quick or the hot water will run out. For the life of me I can't imagine the need to run 3 showers and a dishwasher at the same time.

  13. #13
    Illinois Licensed Plumber SewerRatz's Avatar
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    Quote Originally Posted by ChuckS View Post
    Seamed cheaper to tell the kids to shower one at a time. That's how we did it growing up and how we do it now. Even with a tank heater, with multiple showers going on, you will have to be quick or the hot water will run out. For the life of me I can't imagine the need to run 3 showers and a dishwasher at the same time.
    3 showers, dishwasher, washing maching.... Its hard to tell everyone they need to get up an hour earlier so they can shower one at a time. They all already are up at 5 am and out the door by 6 am to head to work or school.

  14. #14

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    Quote Originally Posted by nhmaster View Post
    Yes it is possible. However, if you do a little bit of thread searching on this and other sites, regarding tankless water heaters, you will soon see that the majority of professional plumbers, guys that deal with these things day in and day out in many differing scenarios are not particulary impressed with them. Then you can come back here and read the unrealistic glowing praise of them from our two in house protagonists that are under the impression that their opinions are somehow more valid than those of professionals. Tankless heaters are a complete waste of money and nothing but a service nightmare from day one.

    Consider the above source. An out of touch with the real world "old school plumber". Probably just grasping the concept of indoor plumbing.

    Sorry to inform ALL, no problems with my tankless from day one. I know thats hard to grasp for the "old schoolers" on here.
    "Dude, we can fix that. My old man is a TV repairman, he's got the ultimate set of tools!" --Jeff Spicoli


    http://web.me.com/greg.saulsbury/ChosatongaSpeaks

  15. #15

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    Quote Originally Posted by SewerRatz View Post
    ...It was the mistake my customer with the "begging" me to remove his tankless did. He tried to go about it on the cheap-side and use a single unit in his 3 bath home.
    In all my years of customer service and support (25+) there always seems to be what I call "the rest of the story". When a system is down the blame is placed on the equipment as inferior or defective in nature. It's only after the tech arrives and starts digging into what is wrong that "the rest of the story" comes to light. The customer did "xyz" and the system overloaded and/or failed.

    Whether it's plumbing, heating, a/c, doors, windows, appliances etc they are "man made" and can be "man broke" whether intentional or through neglect.
    I've stated before that to live in this technology rich world it will start requiring a person to know more about technology. If you have know how to keep the virus updates current on your PC then you should know how to call the tankless tech to delime once a year along with all the yearly routine house maint items. Better yet, let plumbers put in place a yearly call system for delime service for customers. Great revenue stream for scheduled service.
    Last edited by gregsauls; 03-27-2009 at 06:57 AM.
    "Dude, we can fix that. My old man is a TV repairman, he's got the ultimate set of tools!" --Jeff Spicoli


    http://web.me.com/greg.saulsbury/ChosatongaSpeaks

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