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Thread: Tankless or tank water heater

  1. #1
    DIY Member willl's Avatar
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    Default Tankless or tank water heater

    Alright everyone I really do need help on this one. Just got a whirlpool installed in the home that is 120 gallons. The 85 gallon water heater we have currently clearly won't be able to work at all and it doesn't. About half way into filling the thing the water starts getting cold. There are soooooo many different opinions and articles on this that it gets quite confuzing. One says tankless are excellent while another says they are horrid. I live in north dakota by the way. Not sure how cold the water is but it probably is somewhat cold. It seems like the veridict on this forum is that the tankless do save money but that will have to be considered with the initial cost of installation etc.

    I was looking at the commercial grade rheem model gt199dvn. It has a 80 degree rise at 4.1 gpm. That should be plenty. Cost of unit is around 1000$.

    What about maintenance of these things too etc.

    Any help would be much appreciated. Thank you.

  2. #2
    In the Trades Gary Swart's Avatar
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    The tankless question comes up here often. There are some who swear by them, but most do not. There are several negative points about them. Unless you home was designed for a tankless, you will almost certainly have a major expense getting enough power, either gas or electric. If you live in a cold climate, in the winter the incoming water is very cold and you may find the water doesn't get as hot as desired. Tankless require frequent maintenance. Tankless are more expensive than conventional heaters over the long term when every thing is considered. I would suggest you search the archives of this forum for the discussions on the topic before going tankless.

  3. #3

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    Quote Originally Posted by willl View Post

    Alright everyone I really do need help on this one. Just got a whirlpool installed in the home that is 120 gallons. The 85 gallon water heater we have currently clearly won't be able to work at all and it doesn't. About half way into filling the thing the water starts getting cold.


    What temperature do you have the hot water tank set to?

    I have a tankless, but I would not have the patience to wait 45 minutes to fill a 120 gallon tub with hot water. Not sure if the water would still be hot by the timne the tub filled either.

    You need to add a hot tub water heater to that whirlpool tub!

  4. #4

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    Quote Originally Posted by Gary Swart View Post
    The tankless question comes up here often. There are some who swear by them, but most do not. There are several negative points about them. Unless you home was designed for a tankless, you will almost certainly have a major expense getting enough power, either gas or electric. If you live in a cold climate, in the winter the incoming water is very cold and you may find the water doesn't get as hot as desired. Tankless require frequent maintenance. Tankless are more expensive than conventional heaters over the long term when every thing is considered. I would suggest you search the archives of this forum for the discussions on the topic before going tankless.

    I have a central gas tankless. That being said, I would never install an electric whole house tankless.

    My water temp right now is 50 degrees coming in. That temp is no problem at all to heat water with a gas tankless. Then again, some people claim to like to use the dishwasher, wash laundry with hot water, and take two showers at the same time they are washing the elephant in the back yard!

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    Where I live, in the winter, the incoming water is just above freezing, and I would expect yours in the Dakotas is too. That's about 110 at the source, then lose some along the way...it could be tepid at max flow. Some of them throttle the flow down to maintain the temperature rise, so you may get half of that in the winter. Some just run full bore, and you get what you get. I think you'll be dissatisfied.

    I'd look into two things: first, if you don't have a tempering valve on the outlet of the WH, install one, then, and only then, crank the WH thermostat up. You can only get about 85% of the water out of a WH before it cools off too much. But, if you start out with hotter water and use the protection of a tempering valve to keep it safer, you can get more hot water from the tank since each gallon of super hot is tempered to safer temp with cold as it exits the tank; prevently super hot water from going places where it could scald you.
    Last edited by jadnashua; 12-09-2008 at 09:10 AM.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    DIY Member willl's Avatar
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    At 4 gpm it will probably take about 30 minutes to fill completely. This really isn't a problem for me as I would just plan alittle ahead and do other things while it is filling. The house is under major reconstruction so studs and joists are exposed making installation easier. The natural gas line coming into the house is about 1" while the one on the tankless is only 3/4" so that shouldn't be a problem either. The furnace piping is around 1/2" and I have another small heater in the garage that uses 1/2" pipe. Even though the heater in the garage is 1/2" pipe I doubt that it demands that much gas sense it is not a big heater. Might be a good idea to have a plumber look at it to see if everything is ok.

    With the specs on this heater even if the incoming water was around 40 degrees it has a 80 degree rise at 4.1 gpm. That would be 120 degrees which is considered around scalding.

    I have the temp on the tank model set at its highest 170 degrees.

    I do have a water heater for the hot tub but the water heaters are not meant to heat the water but just to maintain the temparature that it was filled at.

    I talked to the guy at rheem about them and yearly maintenance of filter washing and carbon buildup cleaning is recommended. The manual says monthly but he said yearly would probably be ok, probably that is, sense the water I use is city water and the cleaning of the filter is dependant on how dirty the incoming water is in the first place.

    I have an electric 85 gallon right know which probably isn't efficient at all. Getting a gas would help with efficiency. But why only mention the negatives of having tankless. To give alittle balance on this thread some benefits would be alittle more efficiency. Don't have to worry about scalding yourself. Added room in the house. tankless models claim to last longer.

  7. #7
    DIY Member willl's Avatar
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    Plumber told me the temp. of incoming should be around 48 degrees. Are you sure jadnashua that the temparature of your water is so close to freezing. There might be a problem with you system considering that only 2 degrees lower you would be at freezing point and have bursting pipes. Thanks

  8. #8

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    Quote Originally Posted by willl View Post
    Plumber told me the temp. of incoming should be around 48 degrees. Are you sure jadnashua that the temparature of your water is so close to freezing. There might be a problem with you system considering that only 2 degrees lower you would be at freezing point and have bursting pipes. Thanks


    I live in MA, and my incoming water temp is 50 degrees. Not sure how cold the incoming water ends up in February.

    All you have to do to confirm water temperature is run the cold water for about 5 minutes, then fill up a pot with water. Place a thermometer in the water. Same goes for the water temperature in the hot tub. Measure the temperature rather than guess at things.

    By the way, electric water heaters have a slow recovery rate. Look into a gas tank heater and compare the recovery rate of the electric and gas models.

    Also, look into the minimum flow rate of the tankless heater that you are looking into.

  9. #9
    DIY Member willl's Avatar
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    I understand that but your waterlines aren't 6 feet below ground. My question to the plumber was on the coldest days how cold does the incoming tap water get. He seemed to give me a thorough answer on ground temp etc.The recovery rate did enter into my head and they definitely won't be able to recover fast enough to fill a whirlpool so I would have to install 2 tank water heaters back to back inorder to get the proper gallons to fill a whirlpool. I could stick another electric 85 gallon right next to the current one. That would take up alot of space and probably wouldn't be very efficient as they are electric.

    Installing a gas tank where the current one is is going to be tough as running the exhaust is difficult. If I go with tankless I could stick it on the second floor in a small closet and just go right up through the roof. I presume I could stick a 120 gallon tank model on the second floor as well and go through the roof. I think those 120 are pretty big though so I will have to check and see if they will even fit in the closet I am considering putting it in.

    Do the storage gas tank require any maintenance. You seem to be alittle negative on them Ladiesman271. Are you happy with yours. Thanks

  10. #10

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    I installed a Rinnai R74LSI this past August after a LOT of online research. We have had zero problems with the unit and really don't anticipate any with doing the yearly cleaning.

    Read about the install at the below link.
    http://web.me.com/greg.saulsbury/Cho...Install_2.html
    "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

  11. #11
    DIY Junior Member tombat's Avatar
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    Heed the mention on gas piping. Pipe diameter doesn't indicate pressure. A typical 6" WC meter won't do the job unless the tankless is the only appliance you have using gas. I would have had to upgrade to a 2 psi (55" WC) meter but then all the other devices on the line - dryer, stove, furnace - needed to be regulated back down to 6" WC. The gas piping was one of the major costs, even though the gas company was going to upgrade the meter for no cost.

    Tom

  12. #12
    Retired Defense Industry Engineer jadnashua's Avatar
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    I have physically taken an accurate thermometer and measured my incoming water temp in the middle of winter and it was 33-degrees. This was after it had been running for awhile, so wasn't water that was sitting in an unheated area ( I live inthe middle of a row of townhouses, so it already passed through about 100' of enclosed space in the basement ceiling. Believe me...it is cold.

    Cleaning the burner is one thing, but cleaning the heat exchanger's insides is another. Just like a teakettle, the insides will get mineral deposits which, if aren't cleaned off regularly will cause problems. How often depends on the temp rise and your hardness of the water. On a tank type, it's fairly easy to flush that out, and even if you don't, it would take many years before it built up enough to cause too many problems. A tankless is a different animal entirely.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  13. #13

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    Quote Originally Posted by willl View Post

    Installing a gas tank where the current one is is going to be tough as running the exhaust is difficult. If I go with tankless I could stick it on the second floor in a small closet and just go right up through the roof.

    I understand your logic now. Maybe you should look for a tankless heater with a direct vent (in and out). The unit you selected uses up to 200,000 BTU, and needs room air for combustion. That unit will suck out a lot of heated air out of the second floor.




    Quote Originally Posted by willl View Post

    Do the storage gas tank require any maintenance. You seem to be alittle negative on them Ladiesman271. Are you happy with yours. Thanks

    My tankless works fine. I also insulated the entire length of the hot water pipes. I installed a tankless to save floor space more than anything else.

    My previous tank type heater worked fine.

    No preference of tankless over tank type. Go with what works best in your case.

  14. #14

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    Quote Originally Posted by gregsauls View Post
    I installed a Rinnai R74LSI this past August after a LOT of online research. We have had zero problems with the unit and really don't anticipate any with doing the yearly cleaning.

    Read about the install at the below link.
    http://web.me.com/greg.saulsbury/Cho...Install_2.html


    Do you get the so called "cold water sandwich" with that unit? Does the burner kick on right away, or is there a time delay (like 5 or so seconds) after you turn on the water?

  15. #15
    Retired Defense Industry Engineer jadnashua's Avatar
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    It would be a rare burner today that had a standing pilot, so you've either got a spark ignition or a glow plug. First, the flow sensor has to be tripped (typically at least 1/2-gallon/minute flow - want to use a tricke of hot - functionally say warm, and it won't turn on at all, ever). It would likely take at least a little time for it to turn on, then, start up the burner, and, while the heat exchanger is probably fairly efficient, it does have some thermal mass that needs to warm up, so the water on any would likely take a few seconds at least to get up to the set point, if it can, depending on the flow and inlet water temp.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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