Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Viessmann HW inadequate - solution?

Frank Dobbs
Frank Dobbs Member Posts: 27
When I installed a 79 gallon Vitocell 300 to go with a Vitodens 6-24 last year I thought my hot water problems were over. I was criticized by some for the wastefulness of a 79 gal heater in a 1-family home, but I knew I would add a new master bath that would have a big bathtub.

Well, the bathroom is being built, and it will have a 165 gal tub that the Vitocell should just be able to handle if no one else is making demands on the HW. Besides the tub will have an inline heater for the jacuzzi part, so I can cheat a little.

What I didn't count on was the shower!

Those of us who like cutting-edge German engineering keep getting these surprises.

Here is the flow rate for the shower tranlated into our units:
Showerhead - Dornbracht Rainsky M.
Flow rate:
44 psi 9.2 gpm
58 psi 13.5 gpm (highest psi recommended)
73 psi 15.0 gpm

More to the point, the recommended *minimum* "cylinder" for HW is 132 gallons. At 79 gals, I'm a little short of spec.

Now the shower actually consists of 3 units that can be operated independently, so the flow rate will not always be in the stratosphere. But I clearly need to do something.

So what do you hw solons recommend:
An additional Vitocell?
An additional other brand tank?
A supplemental HW heater?
Or is this a case where a large supplemental tankless water heater right by the tub is indicated?



  • hot_rod
    hot_rod Member Posts: 22,120
    You need to determine how many

    gpm's they will draw, and for how long. If not it's just a guess again.

    Have them define the time of "shower' in writing. Then and only then would I spec and size the equipment.

    The more you give some folks with that type of water wasting devices, the more they expect.

    Put a number on the load that is realistic to you and the bather.

    possibly another tank would work if it is a one time load with time to recover. If they want endless all the time a commercial instantanous may be a better choice.

    Of course a solar pre-heat should be included if they have money to waste on 13 gpm showers, at least "green" some of that load.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • ALH_4
    ALH_4 Member Posts: 1,790
    DHW Load

    You need a dedicated domestic hot water system for a dhw demand that large in comparison to your heating demand. At a 60°F rise and 15gpm you need 450,000 btu/h to keep up, and adding enough storage for the 6/24 to work on after your shower is probably not practical and may begin to cause problems with dhw priority versus other dhw demands and heating demand during cold weather.

    A 119 gal SDHW pre-heat system would help a little, maybe giving you 15-20 minutes of shower time if fully charged, but would be unreliable.

    How about the Lochinvar Knight Armor system?
  • J.C.A._3
    J.C.A._3 Member Posts: 2,981
    Just an observation, but.....

    Do you REALLY need a 15 GPM shower or fill speed for a tub?

    Call me old fashioned but I know I don't.

    You've got a FINE SYSTEM, but why would you want or need to make something so wasteful....for something so basic as washing?

    Can it be done? YOU BET!!! But the real question is, does it need to be?

    Just thinking out loud. Chris
  • Ron Huber_2
    Ron Huber_2 Member Posts: 127

    You got it right. What the %#** do you need 15 gpm shower for, nobody is that dirty! We have the same problem on some of our jobs, but at least we usually know in advance. We sometimes have to size our load to the DHW as opposed to the heat load.
  • scott markle_2
    scott markle_2 Member Posts: 611
    GFX recovery unit

    Not sure that you would find a model that could provide that sort of flow, But a gravity film waste water heat-exchanger is a viable way of improving recovery rates. I have one in my modest 2 gpm shower stall and the rise in temperature across the exchanger is quite noticeable.

    I really love the simplicity of this device, and if the manufactures claims on recovery are even close to reality it's seems to me that this device has a much better R.O.E than solar at least in the north east.

    Storing more than 79 gallons gets kind of wasteful in-terms of standby losses. This whole issue of dwh loads that are higher than heating loads is going to be more common as building envelopes improve.

    Over-sizing the boiler to satisfy such a extravagant dhw requirement would lead to inefficient heating operation, but all that standby loss sure seems a waste, and if those sort of dhw uses actually occur there may be a noticeable drop in room temperatures because of dwh priority, or even the possibility of lines freezing in remote areas. The comfortrole has no conditional priority mode as with tekmar, to prevent this.

    Showers that use that much water are probably illegal in Germany.
  • Dave_4
    Dave_4 Member Posts: 1,405

    A Gfx would clearly win here and many other cases,as the 1st hour recovery rates are very impressive. Mine has been in place since Y2K. I'm truly Impressed..Paul. Here is a pic of it installed /partially wrapped and foamed in place
  • Glen
    Glen Member Posts: 855
    Need more horsepower -

    as well as capacity. The 6/24 does not have enough input to adequately drive the htex on the 300 liter tank. It may be OK for your heating needs but will be overwhelmed for the DHW demands.
  • mif
    mif Member Posts: 7
    Viessmann HW inadequate - solution?

    Frank, can you post the performance figures in the original language? I cannot believe that Germans would design such wasteful fixtures.
  • steve b_31
    steve b_31 Member Posts: 1
    Is it legal?

    The shower system's water use seems so extravagant that I had to check it out. First, on one website, I found that this shower costs about $8000, so it is an extravagance in more than one way. Also, it turns out that it is not intended for use in the U.S..The manufacturer's website, http://www.dornbracht.com/en/index.htm?nav=1192&cid=305&id=3301 states that: "THAT FOR THE USA AND CANADA THE RAINSKY IS NOT DESIGNED FOR OR INTENDED TO BE USED IN ANY CIRCUMSTANCE AS A PLUMBING DEVICE, SHOWER SYSTEM, OR FOR USE IN VIOLATION OF ANY APPLICABLE LAW. RAINSKY WILL NOT MEET ANY USA OR CANADIAN BUILDING CODES, PRODUCT APPROVALS OR APPLICABLE LAW FOR USE AS A PLUMBING DEVICE."
  • Weezbo
    Weezbo Member Posts: 6,232
    my sincerest hope is...

    that this was not within your original proposal.

    if so, then there are ways to make that much flow happen, however not in any way that could be considered inexpensive..
  • Weezbo
    Weezbo Member Posts: 6,232
    Electric rate High?

    Because if it is , it may have to be weighted against the space storage and re circulating pumps and motors and the space that they occupy.
  • Dave_12
    Dave_12 Member Posts: 77
    Where the blame lies

    Needless to say the GC and the HO are furiously trying to blame each other for the lack of planning. And that's kind of sad, because they both of them are me. ;>} (Although a real GC and an architect are on board, I take all the blame. My GC assures me that no regular GC would be able to work with me, unless he billed change orders several times the cost of the project.)

    I didn't bring up the reason for this kind of bathroom, since my question is technical. But since the heatinghelp chapter of the plumber's philosophical society has spoken up, perhaps I can broaden their horizon a little. The idea of washing one's body efficiently as if one were being processed through a meat factory is appealing in its own right to all of us Americans, and often very welcome. However, there is another tradition where washing is an act with deep emotional resonance --spiritual, social, esthetic, health-restoring, connected to the deep mystery of flowing water and its nearly universal use for purification. Briefly, societies like Ancient Rome, Central Europe, Russia, Turkey, Korea and Japan have made the bath a central part of their individual, family and social lives. The Germans are not only about efficiency in such matters, and they make many fixtures, including Kneipp hoses and elaborate shower heads, that are designed to make the bath more like a spa, or an ancient temple than like a factory unit for washing away dirt. Our 165 gal bathtub is based on a Japanese design. And when I told my daughter who is studying Japanese in college about it, she got all excited about how in Japan families bathe together. Needless to say, we are also getting one of Japanese Neorest toilets that do everything but whistle dixie (as far as I know at least). And even though I am as red blooded a conservative as you can find politically, I think we Americans must admit that not only in boiler design and efficiency, but also in Design and Technology we have a lot to learn from Europe and the Far East. I just learned from a relative of mine who is a distributor for Hansgrohe fixtures that they have a facility in Fla. where each year the distributors put on their bathing suits and try out more than 20 kinds of shower heads to see what they are like. It's not for the efficiency!

    Likewise, I just ordered European (Velux) skylights and the distributor told me that they never leak, but I must follow specs exactly when building the curb, (just as the Veissmann distributor for NYC told me that they do not allow you to exceed maximum venting allowance in the slightest.) But besides working flawlessly, they also have a wide variety of gizmos -rain sensors that close automatically, electronic shades and venetian blinds, and even electronic glass that will darken at the flick of a switch. So just because they are conscious of efficiency and technology, don't think that European and Japanese manufacturers are ashamed of design or luxury. In fact, they revel in it. C'mon, think of the hydronic radiators you can buy in Europe. I've seen some that are actually sculptures.

    If you want to see how decadent showerheads can get today, here is a good link


    Be sure to check out all 4 pages.

  • I'd be a hypocrite if I blamed you for an extravagent bath--I built on for myself. While the tub is "only" about 1/2 that size, the 9' x 3 1/2' shower (all Grohe) can move about 12 gpm if you have all the heads/sprays cranking.

    I let my attic renter as well as the renters in my next-door house use the "carwash" or the Jacuzzi for a mandatory $2 donation. Since the shower uses true thermostatic control, and there have been a number of different users, I can offer a important observation:

    As the quantity of water hitting the body in the shower increases, ALL users turn down the temp. Even those who take what I consider scalding hot showers (say 130F) with a single "standard" low-flow (1.5 gpm) head will reduce the temp considerably as they add more sprays. My personal preference when everything is running is about 85F-90F in the summer and 100F-110F in the winter.

    I agree that your Vitocell will be "barely adequate" for the tub--provided you run it very near the maximum setting of 158F. (Make sure you change coding address 007:001 or the default 007:000 will limit DHW temp to 140F). If your tub heater is anything like mine though, its real purpose is to offset the heat losses--not to raise temp. It will raise temp, albiet quiet slowly.

    At present, I'm using a stand-alone 80-gallon water heater set fairly low (about 130F) and it has never run out of hot water when filling the tub and I've never heard anyone complain of running out of hot water in the shower. I have a 120-gallon Vitocell that I need to attach to my Vitoden 6-24 once I get a "round 2it"... An NO, I have ZERO problems with a 6-24 driving such a huge tank.

    Unless you have utterly enormous piping I have a real feeling that your maximum flow rate in the shower (with everything on) will be down near the bottom PSI flow. I have a 1" meter with 1 1/4" feed. DHW piping all in 1" with only about 6' of 3/4" in the final dedicated branch to the shower. Cold is a 3/4" "home run" back to a pressure balance loop that ensure equal pressure throughout my domestic water system. Entrance pressure about 65 psi with the shower about 18' above the entrance. Water heater in use has 1" connections. Even then I find that the piping significantly impacts pressure in a fully running "car wash" shower.

    My recommendations:

    If at all practical, I would consider a heat recovery unit for the shower drain. Of course the domestic side of the HX will have to be BIG (I'd say at least 1 1/4" tube) to avoid causing excessive pressure drop when the shower is cranking... This alone is likely to give you any "extra" you might need as the hotter the water you run through the shower, the more heat you will recover.

    Try it with the present indirect and the Vitodens set for max DHW temp, but plan ahead in case modification is required.

    The simplest thing I can think of is a tempering tank for incoming fresh water. Use the largest plain uninsulated tank you can fit (bottom connection in, top connection out) in series with the indirect. During the winter when incoming water is coldest you can likely expect incoming water to the indirect only slightly below ambient temp. That alone can give thousands of "free" btus.

    With the heat recovery unit from the shower drain and a tempering tank I have a real feeling that you'll get full use of your "decadent" bathroom.
  • scott markle_2
    scott markle_2 Member Posts: 611

    Mike, just a reminder nothing is "free". The btu's that will warm this holding tank water will come from the building envelope.

    It's only "free" if this heat is being recovered from a waste source or outside the building envelope, solar, geo. Even here, FREE belongs in quotes ,because it's not conjured from nothing just harnessed.

    GFX link; http://gfxtechnology.com/
  • tim smith
    tim smith Member Posts: 2,752
    size of dhw system

    I think for the flow rates you are looking at, I would guess that another 79 gals indirect is what you will probably need. I would assume you will run realistically at 12 gpm w/ an average shower time of 10 minutes. That would take most of the real volume of the 2 tanks, storage only. With still some buffer from recovery, albeit only 10 minutes. jmho, Tim PS, man that is a lot of water useage.
  • Dave_4
    Dave_4 Member Posts: 1,405
    Plan of action

    Thanks to everyone. Here is my current thinking:

    The first thing we are going to do is take my wife's advice and wait and see how much water we use in actual practice. The shower head consists of 3 separate units, and it's not clear we will often want to run all three of them at full blast very often.

    We will also install a gravity film waste water heat-exchanger. A hat tip to Scott Markle for suggesting it. They do have models with for 3/4" supply connections. The only cost would seem to be a modest installation cost. It only "operates" when we need it. It has no operating cost. It reduces the hot water flow rate for a given shower temperature and thus has the effect of expanding the effective size of the water tank and making the recovery rate less inadequate. It seems to be basically maintenance-free, as well.

    Mike raises the question of whether the GFX will reduce the pressure significantly on my 3/4" riser which is part of a circulating loop. Any thoughts on that?

    We have gas in the floor just below the shower and seriously considered a demand water heater like the Rinnae. But that means installing and maintaining a new boiler, with all that entails. So we will pass on that.

    If experience shows the HW inadequate, then we will install an additional HW tank. That will increase our heat loss, though effectively so only when the heat is not on. During heating season, the thermistatic valve on the nearby panel radiator will adjust for any heat gain from the HW tank.

    The tempering tank idea confuses me. It would not make sense to put it between the 6-24 and the Vitocell, that would only increase heat loss. So it would only make sense to put it between the city water and the 6-24. Right? So, in effect, the 6-24 would be heating it by heating the ambient air. But an additional HW storage tank placed after the Vitocell would also be heated by the 6-24, but would actually add a
    larger quantity of BTU's to the system.

    In the first scenario, burner heats water, heats panel rads, heats air, heats domestic cold water. In the second scenario, burner heats water (air temp declines through heat loss to the outside).

    I am really glad to hear about your experience, Mike, with your "carwash." It accords with what I think is likely, that I will not have super high flow rates (I've got a 40' rise) and will find the existing Vitocell enough to muddle through with, but I need to be prepared for all contingencies, since I have committed so much to this project.
  • Dave_4
    Dave_4 Member Posts: 1,405

    Maybe the flow rates are correct but being German, it is designed for ice water, you girly men!


    The engineers are working on the "shrinkage" problem now.
  • Dave_4
    Dave_4 Member Posts: 1,405
    You Vant Real Men, try this Mein Herr!!!

    "WATER TUBE is the first Kneipp hose to do justice to a high quality, stylish bathroom. Design-oriented and minimal in its shape. Maximum, on the other hand, is the beneficial effect of the cold streams of water after a visit to the sauna or the alternating hot and cold streams of a Kneipp hydrotherapy. The result: physical and spiritual freshness. WATER TUBE is available with integrated valve."

    Look on the Dornbracht website for Balance Modules, then Water Tube

    These are very popular in parts of Europe, for health - ice cold water after a sauna, or alternating ice cold and scalding hot water on every limb. My Polish contractor had one once.

    We are going to use it to water the garden in our bath, clean the tub and help fill the tub.

    Who was Kneipp?

    "Sebastian Kneipp (May 17, 1821, Stephansried, Germany – June 17, 1897 in Wörishofen) was a Bavarian priest and one of the founders of the Naturopathic medicine movement. He is most commonly associated with the "Kneipp Cure" form of hydrotherapy, a system of healing involving the application of water through various methods, temperatures and pressures.

    In Norway he is mostly known for his bread recipe based on whole wheat. Kneipbrød (Kneipp Bread) is the most commonly eaten bread in Norway.

    Although most commonly associated with one area of Naturopathic medicine, Kneipp was the proponent of an entire system of healing, which rested on five main tenets:

    * Hydrotherapy
    * Herbalism – The use of botanical medicines.
    * Exercise
    * Nutrition - A wholesome diet of whole grains, fruits & vegetables with limited meat
    * Spirituality - Kneipp believed that a healthy mind begot a healthy person

    During his time in Bad Wörishofen, Kneipp was able to counsel many people. Tens of thousands came from all over the world to receive his healing advice. He was the author of the books "My Water Cure", "Thus Shalt Thou Live", and "My Will"."

    He was Germany's answer to our own John Harvey Kellogg:

    There is a hilarious movie about Kellogg: The Road to Wellville with an all-star cast. I'm sure Herr Kneipp's hydrotherapy was nowheres near as effective as Kellogg's corn flakes, and his yoghurt enemas.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    The tempering tank would be installed in series with the indirect. e.g. fresh water enters the tempering tank from the outdoors and its outlet feeds the indirect inlet. It does not in any way connect to the boiler. The object is to use a tank of sufficient size such that incoming water from the ground has enough time to sit in the tank to reach nearly ambient air temp. Even in an unheated basement this can result in a significant increase in the temp of the water entering the indirect.

    Are you on city water? If so, what size meter? Water meters have VERY steep pressure drops as flow increases above "typical".

    I have a separate 1" meter for in-ground irrigation. All main piping (and the required backflow preventer) is 1 1/4". Individual circuits (zones) in 1" with a max design flow of 19.5 gpm--the other two are 18 gpm. Dynamic (running) pressure drops to about 12-15 gpm as per design but it's only usable (with the backflow preventer) during the wee hours of the morning when static pressure is highest. (It works perfectly any time of the day without the backflow preventer.) In the time between I got the initial permits and had the final inspection the backflow preventer was required despite the fact that I used vacuum breaking zone valves installed at least 18" above the highest outlet in each zone. Here in MO the requirement for backflow preventers was nicknamed the "plumber's enrichment act".
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
    Anyone Remember \"Green Acres\"?

    Shower was OUTDOORS supplied by an overhead ambient air temp water tank. Truly not uncommon for the time in rural areas even if an old c. 1900 "Guide to Everything" book that I truly LOVE suggested shower baths were suited only to those of "highest constitution". It was also suggested that shower baths were useful for "treatment" of various mental ailments.

    After watching "The Road to Wellville" I did some checking. That movie was just as accurate as the South Park episode titled, "All About Mormons". People certainly did and do benefit from both. Faith is an amazing thing...

This discussion has been closed.