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Tankless Gas Water Heater

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moneymm
moneymm Member Posts: 10
edited January 2019 in THE MAIN WALL
so im buying a house and the 2 water heaters are rusted out on the bottom, and clearly leaking.

I live in NY.

I want to replace, and I currently have tankless and love what it did to my bills so I want to do the same.

The new house has 3 full bathrooms. 3 total showers (one of which has 2 heads), 1 regular tub, 1 jacuzzi tub. the kitchen has 2 sinks. 1 dishwaser, 1 washing machine.

(the jacuzzi gets used a couple times a year, so i dont need to factor that in) i mean i guess i want the house to be able to take 2 showers at once, along with the washing machine running and a sink), thats the most hot water at a time i ever suspect i would need.

what model would you recommend I get? should i just be looking at GPM, and the rest is just brand name recognition?

Comments

  • bob eck
    bob eck Member Posts: 930
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    Almost all tankless gas water heaters that have 199,000 BYU input will have 5 to 5.6 GPM at a 70 degree temp rise.
    If using one tankless gas water heater I would reduce the shower heads to 1.5 GPM. If they are 1.5 GPM you will use about 1.2 GPM of 120 degree hot water. You can run two to three shower with this size TGWH. If you put 2 tankless gas water heaters in that is almost 400,000 BTU
    You might want to look at the Rinnai Demand Duo RSH19980HEiP tankless gas water heater built on the side of a 80 gallon tank. Check it out.
  • Leon82
    Leon82 Member Posts: 684
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    There will be a pressure drop if two showers are running and a faucet is opened.
  • moneymm
    moneymm Member Posts: 10
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    bob eck said:

    Almost all tankless gas water heaters that have 199,000 BYU input will have 5 to 5.6 GPM at a 70 degree temp rise.
    If using one tankless gas water heater I would reduce the shower heads to 1.5 GPM. If they are 1.5 GPM you will use about 1.2 GPM of 120 degree hot water. You can run two to three shower with this size TGWH. If you put 2 tankless gas water heaters in that is almost 400,000 BTU
    You might want to look at the Rinnai Demand Duo RSH19980HEiP tankless gas water heater built on the side of a 80 gallon tank. Check it out.

    the one contractor said with all the bathrooms and everything i have he said he would recommended a 12 GPM bosch tankless water heater.
  • Leon82
    Leon82 Member Posts: 684
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    That's probably the 225k btu model. What temp rise is the 12 gpm? They have a few ratings. Mine Is 10 gpm at 40 deg rise I think.
  • bob eck
    bob eck Member Posts: 930
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    Are you on city water or do you have a well with a pump in it?
    If you have city water then you should have 12 gpm
    If on a well pump how many GPM does the pump produce?
    You most likely will never run all faucets at one time. Two maybe three showers at one time.
    Reduce shower heads to 1.5 GPM.
    You will need to look at tankless gas water heater temp rise of 70 or 75 degrees.
    Incoming water temp of 40 degrees and you need to take it to 120 degrees and that is a 80 degree temp rise.
    40 degree temp rise will only get the water temp to 80 degrees.
  • JohnNY
    JohnNY Member Posts: 3,231
    edited January 2019
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    moneymm said:

    I currently have tankless and love what it did to my bills so I want to do the same.

    Just curious. What did the tankless do for your bills?
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
    Classes
    kcopp
  • Leon82
    Leon82 Member Posts: 684
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    12 gpm is for 35 degree rise
    55 degree rise is 7.7 gpm

    https://www.bosch-climate.us/files/Bosch_Therm_1210_Series_US.pdf
  • mikeg2015
    mikeg2015 Member Posts: 1,194
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    If you only have a 3/4” water line feeding the house and larger 3/4” meter you won’t realistically get more than 8 gpm anyway. Could add recirculating loop using a Navien and you’ll save even more water. Then use a thermostatic valve and a small 5 gallon buffer tank on the return and create a hybrid system for those spikes in demand. I found 115f is fine except laundry and dishwasher. Ideally you’d pipe insulated 3/8” pex direct to those.

  • mikeg2015
    mikeg2015 Member Posts: 1,194
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    ... if you really need 3 showers and a faucet and laundry simultaneously then you can cascade 2 units. Again Naviens do this easily. We’ve had great luck with them at my work.
  • moneymm
    moneymm Member Posts: 10
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    JohnNY said:

    moneymm said:

    I currently have tankless and love what it did to my bills so I want to do the same.

    Just curious. What did the tankless do for your bills?
    cut everything in half, although i also converted from oil to gas at the same time, so both worked out.
  • Zman
    Zman Member Posts: 7,569
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    moneymm said:

    JohnNY said:

    moneymm said:

    I currently have tankless and love what it did to my bills so I want to do the same.

    Just curious. What did the tankless do for your bills?
    cut everything in half, although i also converted from oil to gas at the same time, so both worked out.
    You changed from oil to gas and only saved 50%?
    I suspect the tankless isn't saving you a dime.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Rich_49
  • moneymm
    moneymm Member Posts: 10
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    Zman said:

    moneymm said:

    JohnNY said:

    moneymm said:

    I currently have tankless and love what it did to my bills so I want to do the same.

    Just curious. What did the tankless do for your bills?
    cut everything in half, although i also converted from oil to gas at the same time, so both worked out.
    You changed from oil to gas and only saved 50%?
    I suspect the tankless isn't saving you a dime.
    i saved a ton on all the bills combined, didnt really keep track before or after and it was 6 years ago.
  • JohnNY
    JohnNY Member Posts: 3,231
    edited January 2019
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    Yeah. Tankless heaters don't save 50% over tank-type water heaters. Unless you really never use any hot water.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
    Classes
  • Gordy
    Gordy Member Posts: 9,546
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    There is no way the tankless saved you 50%. It was the difference in the fuel cost of switching from oil to gas. Much cheaper. Most people don’t realize that when the switch fuels, and appliances at the same time. It’s the fuels unit cost that saves the money. Especially when converting from oil to NG. Next is LP to NG closely tied with electric to NG conversion. NG is probably the cheapest fuel to use in most parts of North America.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    @mikegee I dont agree with your 3/4" pipe and an 8gpm. With city or well pressure you can get that much out of 1/2 copper. Wicked high velocities though!
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • Gordy
    Gordy Member Posts: 9,546
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    https://youtu.be/vffdymvjluk
    Intplm.Rich_49JohnNY
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,315
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    Hello, I'll add that if you have room for a tank, (or tanks) their relative simplicity means durability. If you maintain them, you'll get MANY years from them. I've been getting fifty years with maintained tank-type heaters. For energy savings, go to a condensing tank. Studies have shown condensing tank is about the same efficiency as tankless with no high or low flow issues and much less maintenance needed.

    Yours, Larry
    knotgrumpy
  • moneymm
    moneymm Member Posts: 10
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    so for tankless im gonna spend about double upfront and really wont see that big of a savings everyyear and will potentially have flow and issues and not be able to run multiple things at once?

    maybe look into a condensing tank?

    how many gallons would i need?

  • bob eck
    bob eck Member Posts: 930
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    You need to be realistic how many showers running at one time?
    Tankless gas water heater have their place in the market just like tank type gas water heaters also have their place in the market.
    Each one has its pros and cons.
    Tank type gas water heater most have 6 year warranty and can last 10 to 12 years. You can help them to last longer if you check and replace the anode rode every two years. Plus flushing the tank helps to keep it clean.
    75 gallon tank with 76,000 BTU input delivers 121 gallons first hour and 83 gallons at 90 degree temp rise.
    50 gallon tank type 40,000 BTU input delivers 71 gallons first hour and 43 gallons at 90 degree temp rise.
    50 gallon tank type high BTU input of 65,000 BTU input delivers 116 gallons first hour and 70 gallons at 90 degree temp rise.
    You can put in two water heaters and double your output.
    With this type of gas water heater usually no need to upgrade your gas line.

    Tankless gas water heater has 12 to 15 year heat exchanger warranty. With proper maintenance this TGWH should last 15 to 20 years.
    199,000 BTU input will give you 5.5 GPM at a 70 degree temp rise. You can put two in and double your output.
    With tankless you might need to upgrade and enlarge your gas line.

    If you are using as much hot water as you say you will most likely with either one tank type or one tankless gas water heater you might not have enough hot water.

    With tankless gas water heater you will be able to take two showers back to back to back and not run out. I do not think you will be able to do that with a tank type gas water heater.

    Like I said look at the Rinnai demand duo tankless gas water heater built on a 80 gallon tank.

    If you want this much hot water at all times you will need to pay to put in proper water heaters to produce the hot water and you will be paying for the gas to heat your domestic hot water.

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