Tankless water heaters

[Mike Lang]

Have any of you guys installed a tankless water heater? I have one job where the plumber is installing one in small house with one full bath a kitchen sink and an outdoor shower (it's a beach house). They are telling me that the unit draws 120 AMPS at 240 volts. Does this sound crazy to any of you guys? I've seen them already installed in homes 3 times this size and have a 60 amp breaker. Apparently this unit has 3 - 2 pole 40 amp breakers. Currently the house has a 150 amp service although I guess this will have to be upgraded to at least a 200 amp? Does anyone know of a more efficient unit that can be used for such a small house?

 

[gardiner]

Are you sure the one saying 120 Amps is not looking at a two pole 60 and adding the two 60's together?

 

[mivey]

Sounds like a good sized unit. A lot of people bad-mouth the electrics when compared to gas, but the problem is they are putting in too small of an electric unit. I would think 25-35 kW would be about right for a normal sized house. Might be a little too much for a small beach house.

 

[CopperTone]

i wired one 2 years ago - it took 4 - 220volt 30amp breakers. the whole house dimmed when it kicked on. it was a 200amp service - Homeowner had to call the utility company and they had to change out the transformer outside his house. not sure what the problem was though. I guess it works well now.

 

[augie47]

There is a pretty good earlier thread on them here:

http://forums.mikeholt.com/showthread.php?t=99179&highlight=INSTANT+WATER+HEATER

 

[Mr.Sparkle]

Have any of you guys installed a tankless water heater? I have one job where the plumber is installing one in small house with one full bath a kitchen sink and an outdoor shower (it's a beach house). They are telling me that the unit draws 120 AMPS at 240 volts. Does this sound crazy to any of you guys? I've seen them already installed in homes 3 times this size and have a 60 amp breaker. Apparently this unit has 3 - 2 pole 40 amp breakers. Currently the house has a 150 amp service although I guess this will have to be upgraded to at least a 200 amp? Does anyone know of a more efficient unit that can be used for such a small house?

I think you are getting misinformation.

 

[barbeer]

I myself just took the plunge into tankless! Steibel Eltron Tempra 29. Thats right, 28.5 kw........... I have a 200 amp service, it requires 3 50 amp circuits, so far so good. You asked of efficiency. Electric units are 99 % efficient by nature, there may be a smaller unit that would work but my advice is do not cheap out on this. BTW, each circuit draws 30 amps or so, not 50.

 

[barbeer]

I think you are getting misinformation.

The info is more than likely correct!

 

[augie47]

I myself just took the plunge into tankless! Steibel Eltron Tempra 29. Thats right, 28.5 kw........... I have a 200 amp service, it requires 3 50 amp circuits, so far so good. You asked of efficiency. Electric units are 99 % efficient by nature, there may be a smaller unit that would work but my advice is do not cheap out on this. BTW, each circuit draws 30 amps or so, not 50.

according to the math, if they are evenly divided it would be around 39.6 amps per circuit...the ones I have worked with vary the heat (load) continuously depending on the temperature/flow.
In any event, they can significantly load a 200 amp service.

 

[Mike Lang]

I think you are getting misinformation.

I called the tech from EEmax and he says it draws 120 Amps. It has 3 two pole 40 amp breakers. I asked him if that was inrush current and he said no. He told me that was the constant draw although it may use only 1 or 2 heating elements when not at full load. Although at full load while taking a shower it will draw 120 amps.

 

[Mike Lang]

according to the math, if they are evenly divided it would be around 39.6 amps per circuit...the ones I have worked with vary the heat (load) continuously depending on the temperature/flow.
In any event, they can significantly load a 200 amp service.

What would you suggest I do? I can't see putting in anything over a 200 amp service for a house that is about 800 sq ft.

 

[Mike Lang]

Besides at 120 amps FLA the electrical bill is going to go through the roof.

 

[augie47]

I would go to Mike's site and download the residential load calculator and play with your numbers. Guessing at some details, I tried it with 30kw of water heater and determined 200 amp won't handle it, but I was assuming 1-1/2 tons of air, electric range , etc.

 

[charlietuna]

When i built my house two years ago i investigated tankless water heaters since everything i installed i wanted top efficiency. I have a 2 1/2 bath house with a hot tub. The actual cost of the units (gas or electric) were within a hundred bucks of each other. The electric tankless required two 30 amp circuits and one 40 amp circuit. The demand load would have caused my service size to double from a 150 amp to a three hundred amp service. I already had my mind set on gas cooking and clothes drying due to it's efficiency. The tankless gas unit's efficiency was much greater than electric resistance elements in heating water (almost 60 percent more efficient) so i went with a gas unit. My total gas consumption is about 55 gallons every 3 months which relates to about $55.00 a month. The standard tank type water heater's normal operational costs is estimated at $45.00 a month so if i include all my cooking (and bar-b-ques), clothes drying, and water heating i'm getting a good deal. Remember, gas is 60 percent more efficient at heating water than electric resistance elements. And you loose 45 percent of the energy of ANY tank type water heater due to storing it ! The issue with the electric units is their high demand factor which can be controlled by hot water demands. Even though this is a small beach house - the owner could be washing clothes, washing dishes,showering inside and outside,washing pots in the kitchen sink and using the bathroom vanity sink AT THE SAME TIME while trying to maintain a set outlet temperature!! At this point the unit might be drawing 90 to 110 amps. Where the gas unit has a set regulator that just feeds more gas to a burner. When gas is available it is the way to go!!!

 

[Mike Lang]

Thanks for your advice... I just looked at the Rinnai gas units and you're right them seem like a much better idea. Now I just have to call and make sure the customer has gas at this house. If not a 300 amp service will be a major PITA. There really isn't any room for another panel.
Thanks again guys

 

[JohnJ0906]

I called the tech from EEmax and he says it draws 120 Amps. It has 3 two pole 40 amp breakers. I asked him if that was inrush current and he said no. He told me that was the constant draw although it may use only 1 or 2 heating elements when not at full load. Although at full load while taking a shower it will draw 120 amps.

If it is the same one I recently saw (I don't recall the brand), it used all 3 elements if more than 1 faucet was used.

We were called in for "lights dimming". The WH was causing a 9% VD on the service. The XFMR was at least 300 feet from the building (OH service). We recomended calling the POCO.

 

[Fulthrotl]

Thanks for your advice... I just looked at the Rinnai gas units and you're right them seem like a much better idea. Now I just have to call and make sure the customer has gas at this house. If not a 300 amp service will be a major PITA. There really isn't any room for another panel.
Thanks again guys

in 1962, my parents owned a house in a place called rossmoor, that was a
gold medallion home, for you old people who remember such things. there was
NO gas service to the house. all electric. radient ceiling heat, electric range.

we had a pool.... with an electric pool heater. it was used for one
month. when the electric bill came, it was almost double the mortgage at the
time. i remember as a little kid, hearing the noise the electric meter made, and
wondering why it made that sound... you could hear it spinning.... and i remember
my dad swearing, alot.

electric water heating is not an efficient solution, in my not so humble opinion.

i never did get to swim in a heated pool after that first month.... :-(

 

[bigjohn67]

Tankless WH

Tankless WH

We have alot of experience with these. From 120v/20amp undersink up to the 120 amp models. For all of the 120 amp models (3) 40 amp circuits the house required a "320" amp service. When we tell the homeowner or contractor the cost, they usually go with (2) standard units (30 amps each).
If you are going tankless for the entire house, gas is the only way to go.
The biggest mistake people make when selecting a tankless electric unit is they ask for the largest. You have to size it to the increase in temperature, not the amps. Even with the 120 amp model, it wont heat the water any higher, just keep up with the flow.
In most cases, the flow has to be tuned down just to heat the water to allow time for the water to contact the elements.
Electric units, IMO, are only good for sinks in a bathroom.

 

[Mr.Sparkle]

The info is more than likely correct!

Wow, well than I stand corrected.
Man that is a lot of juice for a Residential HWH.

 

[peter d]

i never did get to swim in a heated pool after that first month.... :-(

Are you scarred for life now? Swimming in a heated pool is a constitutional right for all Californians.