(206) 949-5683, Top Rated Plumber, Seattle
Page 2 of 3 FirstFirst 123 LastLast
Results 16 to 30 of 34

Thread: Should I replace tank with Tankless

  1. #16
    Jack of all trades DonL's Avatar
    Join Date
    Mar 2011
    Location
    Houston, TX
    Posts
    3,661

    Default "Should-I-replace-tank-with-Tankless"

    My short answer.

    NO.


    Have fun everyone.
    Theory only works perfect in a vacuum.

    Cyber Security Protection for Windows C:\ > WWW.WinForce.Net

  2. #17
    DIY Senior Member lifespeed's Avatar
    Join Date
    Apr 2007
    Location
    California
    Posts
    319

    Default

    Quote Originally Posted by Dana View Post
    The rational reasons for buying a tankless are space savings, and zero recovery time, not the fuel savings economics. Rare is the house where a condensing tankless is the next-most-cost-effective way to save 75-90 therms/year on fuel use. Yes, it's more efficient than a bottom of the line tank, but the present value of the difference in installed cost of the future fuel savings are negative within the normal lifecyle of the unit, even using a 1% discount rate in your NPV calc.
    True, the space and zero recovery are the main benefits, and appealing enough at least to some. And they do save fuel. So, you are analyzing the cost/benefit of a tankless vs one of those new tank water heaters you can get for nothing? Last I checked the prices for the heaters were not that different, although there can be some installation costs depending on the specifics (gas piping).
    Lifespeed

  3. #18
    Jack of all trades DonL's Avatar
    Join Date
    Mar 2011
    Location
    Houston, TX
    Posts
    3,661

    Default

    Anything that has a fast large change in temperature is under a lot of stress.

    Using the wrong material is a disaster.

    You should look into what the heater is made of, and figure the cost of maintaining it.


    There is more to the formula than fuel savings.
    Last edited by DonL; 09-27-2013 at 06:11 PM.
    Theory only works perfect in a vacuum.

    Cyber Security Protection for Windows C:\ > WWW.WinForce.Net

  4. #19
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,432

    Default

    If you can't perform the annual demineralization on the tankless, the cost savings (if there are any) over a traditional tank will be negative, especially when you consider the rework of the utilities...that service will take at least an hour of labor. If you wish to do it yourself, you'd have the first-year equipment costs, and learning curve.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #20
    DIY Senior Member lifespeed's Avatar
    Join Date
    Apr 2007
    Location
    California
    Posts
    319

    Default

    Quote Originally Posted by DonL View Post
    Anything that has a fast large change in temperature is under a lot of stress.

    Using the wrong material is a disaster.

    You should look into what the heater is made of, and figure the cost of maintaining it.


    There is more to the formula than fuel savings.
    Of course there is more to it than fuel. I did look into the heat exchanger, and bought what I believe to be one of the better units on the market. "100% stainless steel corrosion resistant heat exchanger fused with a commercial grade copper heat exchanger, 25% thicker piping than standard models"

    Apparently there are lots of people who don't like these things. Everyone is entitled to their opinion, but opinion is not a substitute for proven performance. After two years I don't see anything but great performance, economy and convenience from my heater. I guess we'll see how it's working in 10 years.

    Because I live in an area with very hard water I installed a water softener. This has been great for ALL the plumbing in the house, especially the water heater. So I expect to do little to no maintenance on the heater, although I will flush it with vinegar every few years despite it not being strictly necessary.
    Last edited by lifespeed; 09-29-2013 at 04:37 PM.
    Lifespeed

  6. #21
    In the trades Dana's Avatar
    Join Date
    Jan 2009
    Location
    01609
    Posts
    2,725

    Default

    Lifespeed: I definitely don't hate 'em (I even heat my house with one!) but I don't have rose colored glasses about their performance or their economics either. Properly maintained you can get 20+ years out of most of them, and you never run out of hot water. Limitations of max flow rates is their primary down side for tub-filling apps, but since you never run out of hot water you CAN fill a tub of arbitrarily large size, if you have the patience. For most of the past 25 years I've used gas fired tankless HW heaters for my hot water (both in the US and in Europe)- my current HW heating situation is an exception (unless you argued that because the heat source for my indirect happens to be a tankless HW heater it should somehow count, even though I've configured it as a boiler.)

    I don't know what hot water heaters come for free, and would not insert a zero-cost into a lifecycle cost comparison even if it were subsidized to the point where it were indeed free. Taking into account competing subsidies may be appropriate at the point of an particular buying decision though. I assume unrealistic long lifespans or zero maintenance costs tanks either. Apples-to-apples the economics aren't there at buck-a-therm gas, even if you add on a (reasonable) carbon cost to cover some of the externalities.

    Finned water tube heat exchangers have high tolerance for big delta-Ts and rapid slewing of temperature & heat rates- that's the least of my concerns regarding tankless water heaters. There is over a century of history on this type of heat exchanger- they can definitely take it.

    But the toll on efficiency of low volume draw short-cycling is real, as is the electrical power use (even in standby mode) that often doesn't reach the surface many forum type discussions of tankless HW technologies (not that it concerns me very much for this application either.)

    PG & E, the Davis Energy Group, Lawrence Berkeley National Laboratories, et al as well as the US D.O.E. have tons of actual monitoring data on comparative systems, both in lab bench testing, and in-situ measurements in occupied dwellings. This was done quite rigorously in CA in order to determine how much subsidy would be appropriately carried by the retail rate-payers, and how much the utilities could earn on subsidy-investment in customer efficiency. In the CA case the analysis even went as far as to determine how much the efficiency saved the utility & ratepayers in lower market price for fuel, and for the diminished or increased infrastructure capital that comes along with tankless water heaters. This was not a one-off simple process, and it took well over a decade to get there, but the alternatives are now well understood, way beyond marketing hype or armchair opining of either advocates or detractors.

    If you're going to count your personal perceptions as "...proven performance..." of "...great economy..." we'll need to see the test data & financial analysis on both your current & prior systems, and not just take your word for it, eh? ;-)

    For now I'll take the word of the engineers and economists who spent a chunk of their careers on it. If you want to PM me your email address I can send you the PDF of a presentation one of PG & E's engineers (Robert Davis, PE)
    delivered at the June 2008 ACEEE Water Heating Forum entitled, "Testing Water Heaters with Different Draw Profiles". It's not the slickest presenation ever, but it does a pretty good job of describing the real operational efficiency differences of at least a handful of realistic options (including a condensing tankless, as well as condensing tanks), under different scenarios. Yes, they're more efficient, than bottom-of-the-line tanks, but not by nearly as much as we all wished they were.

  7. #22
    DIY Junior Member dsbeck's Avatar
    Join Date
    Sep 2013
    Location
    NE Ohio
    Posts
    4

    Default

    Just a quick update:

    1) You guys have convinced me to keep the tank heater instead of replacing it with a tankless.
    2) Any suggestions on a good 75 gallon tank heater?


    Dave

  8. #23
    Jack of all trades DonL's Avatar
    Join Date
    Mar 2011
    Location
    Houston, TX
    Posts
    3,661

    Default

    Quote Originally Posted by dsbeck View Post
    Just a quick update:

    1) You guys have convinced me to keep the tank heater instead of replacing it with a tankless.
    2) Any suggestions on a good 75 gallon tank heater?


    Dave

    A GE made by Rheem is a good choice, At a nice price and good warranty.

    I think.


    Good Luck.
    Theory only works perfect in a vacuum.

    Cyber Security Protection for Windows C:\ > WWW.WinForce.Net

  9. #24
    DIY Member MikeQ's Avatar
    Join Date
    Jul 2012
    Location
    Washington
    Posts
    53

    Default

    Quote Originally Posted by Dana View Post
    It's not the slickest presenation ever, but it does a pretty good job of describing the real operational efficiency differences of at least a handful of realistic options (including a condensing tankless, as well as condensing tanks), under different scenarios. Yes, they're more efficient, than bottom-of-the-line tanks, but not by nearly as much as we all wished they were.
    In my application (second home, half-time use) an electric tankless is saving me a considerable amount on utilities. I was able to relocate the heater from under the stairs to under the kitchen sink. Previously the hot water had to travel out of the top of the water heater down to joist level and across a considerable run to the far end of the kitchen (the kitchen sink is almost always on an outside wall) then up to the sink. Because this was a 3/4" hot water pipe and the climate is cool (summer) to cold (winter) the water in the pipe was always cold or at best, slightly warm (even after three minutes). No amount of pipe insulation could fix the problem. Because the kitchen faucet had an aerator on it, it would take more than a minute for the water to get warm and another minute for the water to reach full hot. When cooking, washing pans, etc. a considerable amount of water was wasted down the drain. Now, the water is hot in less than 1/4 the time. Cooking and the eventual clean-up is much more fun. And we never run out of hot water, even after multiple consecutive showers, laundry or no laundry.

    I would switch to tankless again even if it were just for the convenience and extra capacity but the savings are very real, not only on the electricity but also the water bill. This house is on a septic system but many municipalities base the sewer portion of the utility bill on water usage so there is another potential savings that may not have been analyzed in the study you mention. On demand water heaters are so small they can be located throughout the house at points corresponding to where the hot water is actually needed, greatly reducing the heat wasted heating long runs of piping. All houses larger than 1000 square feet should probably be built with multiple small on-demand water heaters. That would eliminate almost half of the plumbing in a typical house.

    One of the unexpected bonuses is that I can fill my 385 gallon hot tub in about an hour with hot water rather than waiting 16 hours for it to come up to temperature using it's own built in heater.

  10. #25
    In the trades Dana's Avatar
    Join Date
    Jan 2009
    Location
    01609
    Posts
    2,725

    Default

    You're responding to my comment about a document outlining the differences in labeled vs. operational efficiencies under different use scenarios between different GAS-fired water heaters, with a testimonial about an ELECTRIC tankless? I'm glad you're happy with your decision, but left wondering what your real point is? Was it about the water-waste issue?


    An electric tankless is a very different sort of animal. Considerably more water is wasted with gas-fired tankless than with gas-fired tanks or electric tankless due to the ignition delay, where water flows unheated through the heat exchanger for a few seconds as the flue gets purged and the flame gets lit & tested. Recirculation systems reduce the water waste, but at the cost of an uptick in fuel use.

  11. #26
    DIY Senior Member lifespeed's Avatar
    Join Date
    Apr 2007
    Location
    California
    Posts
    319

    Default

    Quote Originally Posted by Dana View Post
    . . . Considerably more water is wasted with gas-fired tankless than with gas-fired tanks or electric tankless due to the ignition delay, where water flows unheated through the heat exchanger for a few seconds as the flue gets purged and the flame gets lit & tested. Recirculation systems reduce the water waste, but at the cost of an uptick in fuel use.
    More water waste with a gas tankless? I sure don't see this. A few seconds of ignition delay cold water in my system get's mixed with hot water in the 1" hot water main and is completely unnoticeable. And if the hot water pipe is cold from lack of use I have the recirculation button in each bathroom and the kitchen to avoid water waste. The fuel would have been used regardless whether it was cold water down the drain or recirculated, tank or tankless.

    It's all about how you implement it. Not all installations are done equally well. I know my summer gas bill (mostly hot water) has been cut in half compared to a 10-year-old tank.
    Lifespeed

  12. #27
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,432

    Default

    How is comparing using less gas related to switching to an electric unit? It would be a miracle if your gas use didn't drop!
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  13. #28
    DIY Senior Member lifespeed's Avatar
    Join Date
    Apr 2007
    Location
    California
    Posts
    319

    Default

    Quote Originally Posted by lifespeed View Post
    More water waste with a gas tankless? I sure don't see this.
    Quote Originally Posted by jadnashua View Post
    How is comparing using less gas related to switching to an electric unit? It would be a miracle if your gas use didn't drop!
    I use a gas tankless and have greatly reduced my fuel consumption as a result. No doubt the old tank heater wasn't the best, but still quite an improvement.
    Lifespeed

  14. #29
    DIY Member MikeQ's Avatar
    Join Date
    Jul 2012
    Location
    Washington
    Posts
    53

    Default

    Quote Originally Posted by Dana View Post
    I'm glad you're happy with your decision, but left wondering what your real point is?
    It's not that I'm happy with my decision - It's more that I'm relieved the bad things I was warned about before I switched to an electric on-demand heater never materialized. I'm happy with the real world performance of the smaller 29 kW tankless and am glad I did not buy into the perspective that even a 36 kW tankless system would be marginal with my cold supply water.

    Even though my incoming water is only 41-43 degrees (year round) I can take multiple showers and do clothes and dishes without having to schedule them around water heater capacity. I ALWAYS have plenty of hot water even after multiple showers and loads of laundry. I cannot say the same about tank style heaters I've lived with over the years.

  15. #30
    In the trades Dana's Avatar
    Join Date
    Jan 2009
    Location
    01609
    Posts
    2,725

    Default

    lifespeed: The utilities in CA were all over the water wasted in ignition delays this in their investigations of the past decade- it's been measured & documented in several places. Have you even tried to measure yours?

    While installation and potable distribution layout practices can make a large difference in water waste, the ignition delay occurs even in an ideal installation. A 1/2 second delay comprises water flow that wasn't heated, and usually dumped. At 25 draws/day typ usage that adds up to a few gallons even for the comparative quick-starters like Noritz. Some others run 2-3 seconds long, with a correspondingly lbigger daily/annual water waste.

    In most places that water loss doesn't add up to any big deal. In parts of CA (particularly soCA) the energy cost of getting that water to the house in the first place is measurable, and not entirely trivial on the larger scale.

    While I personally don't consider this amount of water waste a big deal, it's silly to deny the obvious- a gas fired tankless can never come up to full power as quickly as an electric tankless, and in an apples-to-apples installation it would be pretty easy to measure the difference in dumped tepid-water volumes.

Similar Threads

  1. Undersized NG tankless - supplement or replace?
    By aberson in forum Tankless Water Heater Forum
    Replies: 6
    Last Post: 04-19-2013, 08:38 PM
  2. Should I replace recirc pump for my tankless heater?
    By philefriendly in forum Tankless Water Heater Forum
    Replies: 4
    Last Post: 11-07-2012, 08:00 AM
  3. tankless or tank
    By stormy4614 in forum Tankless Water Heater Forum
    Replies: 11
    Last Post: 09-09-2011, 03:04 PM
  4. Water Tank Setup - 1-Tank System vs. 2-Tank System vs Tankless
    By Furnace in forum Water Heater Forum, Tanks
    Replies: 1
    Last Post: 04-27-2011, 06:22 AM
  5. Tank or Tankless
    By Newro in forum Water Heater Forum, Tanks
    Replies: 2
    Last Post: 03-15-2011, 02:49 PM

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •