(206) 949-5683, Top Rated Plumber, Seattle
Page 1 of 2 12 LastLast
Results 1 to 15 of 18

Thread: tankless hot water heaters

  1. #1

    Default tankless hot water heaters

    I'm trying to decide between a convential hot water heater and a tankless hot water heater for my new house. The house has two bathrooms and each bathroom has a shower and a bathtub. One bathtub is actually a whirlpool tub. The tankless model I have been looking at provides water at about 6 gpm. Is this less than that provided by a conventional hot water heater? What are the pros and cons of tankless hot water heaters and what do I need to know? There would usually be two of us living in the house but I don't want to run out of hot water if using dishwasher and shower, or washing machine and dishwasher and tub. Any information on this would be helpful.

    Thanking you in advance.

    Burzmet

  2. #2
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,638

    Default heater

    You are confusing apples and oranges. A conventional heater will furnish as many gpm as the pipe and faucet will allow, until the tank is empty of hot water. The tankless will furnish hot water at that gpm. If you try to exceed it, the heater will either reduce the demand to that level or the water will flow through too fast to be heated and then you have warm water.

  3. #3
    Plumber Cass's Avatar
    Join Date
    Nov 2005
    Location
    Ohio
    Posts
    5,984

    Default

    Will it be gas or electric and do you live in a hard water area?

  4. #4
    Master Plumber Redwood's Avatar
    Join Date
    Dec 2007
    Location
    Connecticut
    Posts
    7,463

    Default

    The tankless is 6 GPM at what rate of rise? If your winter water temp is 34 degrees f then the 6 GPM may actually be 1.5 GPM.

    A tank type water heater will give you 70% of the tank capacity of hot water. A tankless will give you hot water up to its capacity based on the incoming water temperature until you shut the hot water off.

  5. #5

    Default

    It will be gas and the house is in Colchester, VT (just north of Burlington, VT). I don't know the water condition but we are not installing any water treatment unit and it is city water (as opposed to well water).

  6. #6

    Default

    You said that a tankless will give you hot water up to it's capacity... If the ambient water temp is 40 degrees F and I am filling a bathtub with water expected to be at 105 degrees will the gpm of the tankless heater be the same as when the ambient water temp is 60 degrees? Does ambient temp of city provided water change all that much (maybe some simple education on how the tankless works would help me understand all this)?

  7. #7

    Default

    What is the gpm of a typical bathtub faucet with typical piping using city provided water (as opposed to well water)? I guess to put the question another way, what is a good gpm rating on a tankless water heater for a house where it is usually two people (but sometimes more), two bathrooms, both with showers, tubs, and sinks, a dishwasher, and a washing machine?

  8. #8
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,638

    Default heater

    The tankless heater will give a certain amount of water a finite temperature increase. If the water flows faster than the maximum design, then the water will be cooler than anticipated. If the incoming water is colder than the design temperature, then the outgoing water will also be cooler than anticipated. For any given incoming temperature, there will be a specific gpm that will produce the desired water temperature, and since the means to compensate for the variation is not automatic, the user will have to reduce his usage flow when the incoming water is below specifications.

  9. #9
    Plumbing Contractor westcoastplumber's Avatar
    Join Date
    Nov 2007
    Location
    los angeles
    Posts
    115

    Default

    I have an important question.....was the house piped for a tankless unit?

    once the plumbing has been done for a tank type water heater, then you should stay with that.

    If when you plumber your "New House" fromt he ground up, and plumbed it with the correct size gas and water, then great.

    I went to 2 calls last week, one was a remodel and one was a ground up, both were plumbed for tank water heaters, then the owners changed their mind, it was a costly mistake. Both were installed incorrectly and one failed to even operate at all.

    You can do a retro fit, but if you do not size everything properly, the unit will not operate properly and you will be very unhappy.

    You need to size the tankless to both your demand and your water temp.

    If you go on www.foreverhotwater.com , you will find a size chart that can get you close to what you need. some applications need 2 units.

    and remember, this is "endless hot water", not "instant hot water" if you want instant, you need a recirc pump, sized for the application.
    Last edited by westcoastplumber; 04-19-2008 at 11:01 AM.

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,405

    Default

    Where I live in NH, the winter incoming water can approach freezing - I've measured it at 34-degrees. Unless you get a VERY large tankless system, or one designed for series operation and use two of them, with the volume you are looking for and the very cold water that can exist in the winter, you will be either very dissappointed, or quite a bit lighter in the wallet.

    With 1/2" supply lines to the tub or shower, you can probably expect in the area of 6-8 gallons of water from the tub spout. With a tankless, in the middle of winter, you may need all hot, and even then, it might not be all that warm. If you have 3/4" lines, those can flow in the order of 8-14 gallons per minute, and you would quickly overrun the average tankless system filling the tub.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  11. #11
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Location
    Yakima WA
    Posts
    7,246

    Default

    There are many drawbacks to tankless heaters. They are very expensive to buy, very expensive to install, especially is your gas or electric service is not large enough, the plumbing may have to be redone, there is a considerable amount of care that must be given such as frequent cleaning, qualified servicemen are often difficult to find, they are costly to operate, they do not last forever and the replacements are very costly, and if the incoming water is very cold, you may not get much really hot water. What benefits do you think you will get from a tankless that you would not get from a regular water heater? Studies have shown the actual cost of tankless over its lifespan is more than standard water heaters. As pointed out, if you want instant hot water, then install a recirculating pump. You can get them with timers so they only operate during the times hot water is normally in demand.

  12. #12

    Default

    Am I correct that the recirculating pump that was mentioned is just for the tankless operation and has nothing to do with the standard hot water tank set-up?

  13. #13
    Master Plumber Redwood's Avatar
    Join Date
    Dec 2007
    Location
    Connecticut
    Posts
    7,463

    Default

    No recirculation pumps are often used in homes where there is a distance from the water heater to the point of use. This results in a water wasting run the faucet and wait for hot water. With a tankless system if recirculation is used there is a special way to hook it up or, the water heater warrantee is voided.

  14. #14
    DIY Senior Member taysan's Avatar
    Join Date
    Apr 2008
    Location
    Toronto, ON Canada
    Posts
    106

    Default

    I stumbled across this thread, and wanted to thank the writers for the education on tankless heaters. I too have recently been charmed by the apparant 'sense' they make, but hadn't considered all the mechanical factors involved.

    I think I'll just keep paying the $10 monthly my gas heater costs to rent from the utility No repairs, no worries. Just got them to replace it with a brand new unit a year ago which didn't cost me a dime.

  15. #15
    Master Plumber Redwood's Avatar
    Join Date
    Dec 2007
    Location
    Connecticut
    Posts
    7,463

    Default

    Renting a water heater is a waste of money! $10 a month over an average 10 year life span has you paying $1200 for that water heater... Where are you located? If you are close enough I'll rent you one for $9 a month! LOL

    Not a bad ROI for a $500 water heater!

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
  •