Tankless water heater wiring very weird!

[hillbilly1]

Incoming water temperature can be effected by some things. When I lived in town I'm not sure what temperature the city water supply was but it was warmer than the water I pump out in the country that is coming directly from the well. That city water warms up some while in the lines vs being used right after it is pumped. During periods of high use in town - like during hot and dry weather and lots of people are watering lawns I had noticed the water was colder - it was not in the lines for as long.

Most municipalities use above ground storage tanks, (towers) if usage is low, this allows the water to be be warmed or cooled by the ambient air temps, with private well systems, most of the water storage is underground, with a small amount in the bladder tank under or above ground, usually in a insulated enclosure to prevent winter time freezing. Tankless waterheaters do not work well on private well systems, as the water pressure does not remain constant which varies the temp of the water. (I know, because I have a gas fired tankless) Most have flow and temp sensors that adjust for this, but do not adjust fast enough to keep the water an even temperature.

 

[mivey]

Incoming water temperature can be effected by some things. When I lived in town I'm not sure what temperature the city water supply was but it was warmer than the water I pump out in the country that is coming directly from the well. That city water warms up some while in the lines vs being used right after it is pumped. During periods of high use in town - like during hot and dry weather and lots of people are watering lawns I had noticed the water was colder - it was not in the lines for as long.

Was it the lines or sitting in a hot, elevated tank? As usage time passes, I would think the lines would be reasonably cool. I suspect it goes from cool water in the lines to warm water from a hot tank to colder water from the well/treatment plant. In the winter, you would go from cold water in the lines to very cold water from the tank to cold water from the well/treatment plant. Pure speculation, of course.

 

[kwired]

Water is put in elevated tank to provide pressure first and extra capacity during high demand second. When demand is low water in the tank pretty much stays in the tank out side of the relatively small amount (when compared to how much the tank actually stores) used between cut in and cut out of the pump. If it were not for the need to pressurize the water system they would have no point in elevating the tank.

Unless you live close to the well your water is likely to be close to the temperature surrounding the supply lines most of the time.

 

[erikd]

One manufacturer (Bosch) calculates the typical user will save a whopping $20.00 per year on their electric bill by installing an electric tankless water heater. The unit costs $700.00, plus installation, plus electrical upgrade costs. The payback for just the unit cost (not including any installation) ... is 35 years ... for a device that will last for 20 years. I work for a large electric utility, and when we inform the customer that to install one of these devices they are required to pay us full cost for any upgrades that we must make to meet the mandated voltage drop and flicker requirements (one upgrade was estimated at $3K), they tend to quickly change their mind about installing one. For the customers that install one without our knowledge, and then call us when their lights dim every time they turn on the hot water ... they usually replace the tankless heater with a tank type instead of paying us to upgrade their service.

 

[weressl]

One manufacturer (Bosch) calculates the typical user will save a whopping $20.00 per year on their electric bill by installing an electric tankless water heater. The unit costs $700.00, plus installation, plus electrical upgrade costs. The payback for just the unit cost (not including any installation) ... is 35 years ... for a device that will last for 20 years. I work for a large electric utility, and when we inform the customer that to install one of these devices they are required to pay us full cost for any upgrades that we must make to meet the mandated voltage drop and flicker requirements (one upgrade was estimated at $3K), they tend to quickly change their mind about installing one. For the customers that install one without our knowledge, and then call us when their lights dim every time they turn on the hot water ... they usually replace the tankless heater with a tank type instead of paying us to upgrade their service.

That along with electric and hybryd cars, solar power plants in your backyard, have the same payback period. Even with the current interest rates only the stupidrich can afford to invest to save what does not seem to be need saving, namely the Planet Earth. Purchasing these are political statements of a dysfunctional layer of society that always seek to blame and not to praise and does not subscribe to the notion thathumans have inevitable rights AND wisdom to determine their life-course without some 'paternal' interference form people who declare themselves smarter than you.

 

[tortuga]

.. save what does not seem to be need saving, namely the Planet Earth..

No of course humans are not destroying the planet that is scientifically impossible, they just need more space for there stuff...:blink:

I have been called out to install these before, usually during a remodel where someone needs a door or closet where the water heater is and there is no gas. These are used to create space where it is limited and expensive.

I look up and see the big "15" meaning 15kva on the utility transformer on the pole feeding four 200A services on the block with #4 XLPE triplex to 4 houses and hook up the 24kva water heater that takes 3 40A ckts.
I don't know what is stranger all the 15kva transformers and #4 triplex or the 125A water heaters?

 

[Jraef]

I just had the opportunity to make a change as my tank rusted through. I went at it with an open mind, I'm all for doing my part if it makes sense. This did not, even with the gas fired unit. When I got done crunching the numbers, there was no economic sense to it whatsoever, and I wasn't convinced of the "carbon footprint" issue either. To me, it make a lot more sense to buy the most efficient (translate BEST INSULATED) tank type gas water heater and pay to insulate all of my hot water pipes (and even the cold pipes that were out in the hinterland of the building, because having them too cold affects the hot water use). My gas bill dropped a good 10% after installing that new water heater and pipe insulation. I think the main thing is not having to run the hot water so much longer waiting to heat up the cold pipes. At the bathroom farthest from my tank, I now have to wait maybe 20 seconds for hot water at the shower, whereas it was well over a minute before. Doesn't sound like much but it adds up over time. Not only do I use less gas, I use less water too, which makes my sewer bill lower. Win win win...

One thing about those tankless heaters is that in Europe and other countries where they use them a lot, they primarily have smaller units installed DIRECTLY at the point of use, i.e. what they call an "Electric Shower" and one under the kitchen sink. Things like washing machines and dishwashers, if they have them at all, have their own separate water heaters built-in, they only plumb cold water to them. I have relatives in Italy and this is how all of their houses are. There is no hot water piping in the house, only cold. An electric shower (I know, the sound of that scares me too) typically uses a 32A 1 phase circuit (one of their standard CB sizes). In terms of water flow, I thought their showers were pretty skimpy by my standards but lately, every hotel I stay at here has become like that too. But temperature wise, I never noticed anything different.

 

[hillbilly1]

I just had the opportunity to make a change as my tank rusted through. I went at it with an open mind, I'm all for doing my part if it makes sense. This did not, even with the gas fired unit. When I got done crunching the numbers, there was no economic sense to it whatsoever, and I wasn't convinced of the "carbon footprint" issue either. To me, it make a lot more sense to buy the most efficient (translate BEST INSULATED) tank type gas water heater and pay to insulate all of my hot water pipes (and even the cold pipes that were out in the hinterland of the building, because having them too cold affects the hot water use). My gas bill dropped a good 10% after installing that new water heater and pipe insulation. I think the main thing is not having to run the hot water so much longer waiting to heat up the cold pipes. At the bathroom farthest from my tank, I now have to wait maybe 20 seconds for hot water at the shower, whereas it was well over a minute before. Doesn't sound like much but it adds up over time. Not only do I use less gas, I use less water too, which makes my sewer bill lower. Win win win...

One thing about those tankless heaters is that in Europe and other countries where they use them a lot, they primarily have smaller units installed DIRECTLY at the point of use, i.e. what they call an "Electric Shower" and one under the kitchen sink. Things like washing machines and dishwashers, if they have them at all, have their own separate water heaters built-in, they only plumb cold water to them. I have relatives in Italy and this is how all of their houses are. There is no hot water piping in the house, only cold. An electric shower (I know, the sound of that scares me too) typically uses a 32A 1 phase circuit (one of their standard CB sizes). In terms of water flow, I thought their showers were pretty skimpy by my standards but lately, every hotel I stay at here has become like that too. But temperature wise, I never noticed anything different.

Down in the DR (Dominican Republic) if you have a 10 gallon water heater, your rich! You take showers fast down there!

 

[jjkind]

Interesting conversation - the idea that you could save money with a tankless water heater never occurred to me. The main selling point for me was the ability to use my tankless unit with a radiant heating system (avoiding the cost/low-efficiency-heating of either a heat pump or forced air furnace).

Energy is energy - you either heat the water up slowly in a tank with an electric element and minimize your energy loss with insulation or you heat it up instantly in a tankless unit and consume as needed. Unless your tank is vastly oversized, in an unheated location or very poorly insulated, your tank heat losses should not be an important factor in the equation (10%?).

I think the more important consideration is gas or electric. Electricity rates are hovering around $0.10/kWh, trending upward. Residential gas rates are currently around $10/MMBtu, or just over $0.03/kWh(th) if you convert the units - and are trending downward. Assuming 90% efficiency for electric heating and 80% efficiency for gas heating (pretty conservative in both cases - my forced air gas unit is actually 85% efficient), your end cost is around $0.11/kWh heating water with electricity and 0.04/kWh heating with gas. Gas is the clear winner in terms of cost, unless you don't have the service already. (0.117kWh/gal to heat water with noted delta-T x 30 gal/day x 365 days/year x [$0.11-0.04] cost savings = approx. $90/year in savings).

The 24kW(electric) unit in question is not that big. I actually have a 30kW(thermal) Caldera (Argentine brand) tankless unit that uses gas and has flame modulation - very similar in heating capacity to the electric unit mentioned when you take into account the relative efficiencies. I use my unit for a 1-bath, 1100ft^2 apartment with radiant heat branched off the water heater.

Assuming that your groundwater is around 60deg F and you want to heat your hot water to about 108deg F to shower, this 24kW unit could only produce slightly over 3gpm of hot water (again, assuming the unit is 90% efficient in converting electrical energy to thermal energy, it could be slightly higher). According the the all-knowing Internet, the average shower head is 2.5gpm. Not a huge unit.

 

[mivey]

Energy is energy

Not so with heat pump water heaters.

 

[kwired]

Interesting conversation - the idea that you could save money with a tankless water heater never occurred to me. The main selling point for me was the ability to use my tankless unit with a radiant heating system (avoiding the cost/low-efficiency-heating of either a heat pump or forced air furnace).

You can use most any water heater you want with your radiant heating system they do not depend on each other.

Where did you get the idea that a heat pump was low efficiency. Only when outside temperature is very low on an air to air heat pump do you run into efficiency issues, otherwise heat pump is likely most efficient heating source there is.

Energy is energy - you either heat the water up slowly in a tank with an electric element and minimize your energy loss with insulation or you heat it up instantly in a tankless unit and consume as needed. Unless your tank is vastly oversized, in an unheated location or very poorly insulated, your tank heat losses should not be an important factor in the equation (10%?).

Unless in an unheated space (not a wise decision with water lines) heat loss from the tank is gained by the surrounding air that you are conditioning anyway lessening the load on the heating system so it is not really lost. It is an inefficiency during cooling season and deserves some consideration for that reason.

I think the more important consideration is gas or electric. Electricity rates are hovering around $0.10/kWh, trending upward. Residential gas rates are currently around $10/MMBtu, or just over $0.03/kWh(th) if you convert the units - and are trending downward. Assuming 90% efficiency for electric heating and 80% efficiency for gas heating (pretty conservative in both cases - my forced air gas unit is actually 85% efficient), your end cost is around $0.11/kWh heating water with electricity and 0.04/kWh heating with gas. Gas is the clear winner in terms of cost, unless you don't have the service already. (0.117kWh/gal to heat water with noted delta-T x 30 gal/day x 365 days/year x [$0.11-0.04] cost savings = approx. $90/year in savings).

Efficiency and cost are two different animals. Efficiency is how much energy was consumed vs how much usable energy goes toward the intended use of the energy. Gas fired heat sources have a flue in which some heat escapes which accounts for most of the inefficiency. Electricity every watt you input is a watt of heat output by the appliance. There are line losses in the conductors but they are well below 10%, more like well below 1% where did you come up with 90%? I cant speak for national averages but electricity cost has been much more stable over the years, gas has been up and down like a roller coaster.

The 24kW(electric) unit in question is not that big. I actually have a 30kW(thermal) Caldera (Argentine brand) tankless unit that uses gas and has flame modulation - very similar in heating capacity to the electric unit mentioned when you take into account the relative efficiencies. I use my unit for a 1-bath, 1100ft^2 apartment with radiant heat branched off the water heater.

Assuming that your groundwater is around 60deg F and you want to heat your hot water to about 108deg F to shower, this 24kW unit could only produce slightly over 3gpm of hot water (again, assuming the unit is 90% efficient in converting electrical energy to thermal energy, it could be slightly higher). According the the all-knowing Internet, the average shower head is 2.5gpm. Not a huge unit.

How well would that work for a family of four or more? How big of a service, feeders, transformers, etc. and extra cost will it take to supply that and how fast will it pay back vs. the much less expensive tank heater and smaller supply? What is life expectancy or average maintenance cost of each? These questions have to be factored in payback period also.

 

[weressl]

The 24kW(electric) unit in question is not that big.

Not that big? US household/apartment services range from 100-200A @240/120V.

 

[jjkind]

You can use most any water heater you want with your radiant heating system they do not depend on each other.

Where did you get the idea that a heat pump was low efficiency. Only when outside temperature is very low on an air to air heat pump do you run into efficiency issues, otherwise heat pump is likely most efficient heating source there is.

I've never seen a radiant heating system that worked with a tank water heater. They probably exist somewhere - no reason you couldn't build one by attaching a heat exchanger to a standard model, too.

And yes, I know that forced air furnaces can have high efficiencies and that heat pumps usually have high performance coefficients.

The efficiency in terms of energy conversion (or energy movement would be more precise for the heat pump) - kWh or BTU from source to thermal energy - is good. The problem I have is 'how' they keep people warm.

I usually consider these heating sources as "low-efficiency" because you have to heat the air mass considerably to feel warm. This is ok when you live in a well-insulated home. I've never had a home that was well-insulated, and I've had a few homes with lots of windows and high ceilings.

My experience with a house and an apartment that I owned/own: one I tried to heat with a forced-air furnace (that I installed) and the other had a heat pump when I purchased it. Both were sized correctly for the space, but I found them extremely costly to run. I had to run the systems continually to keep the inside temperature 20 degrees above the outside temperature, and I still felt cold.

What was the main problem I found? Walls and windows - when you have poor insulation, you tend to feel cold unless the air temperature is very warm, mainly because your body is radiating heat to the surfaces around you that are at the outside temperature. Moreover, convection heat losses are huge when you have single-pane windows and a concrete structure (concrete has a high thermal mass, but it is also a great thermal conductor).

I put radiant heating in my apartment and the difference is incredible. I feel very comfortable even with the air temperature much lower than I kept the place with the heat pump. All the areas where i spend time have a radiator (doing in-floor just was not an option because of the structure).

Not looking to bash forced-air furnaces or wall/window-mount heat pumps. They have their place in the market. I do think that a lot of people should consider other heating options (radiant heating via gas/electricity or a geothermal heat pump), particularly with energy prices threatening to go up, evening out the trade-off between system purchase/installation cost and operational cost. Again, the idea is that radiant heat makes you feel warmer without struggling to keep the air mass warm.

 

[jjkind]

Not that big? US household/apartment services range from 100-200A @240/120V.

Understand. You need a lot of power to heat water. I mean that it's not big in terms of the quantity of water it can heat. I calculated about 3.2gpm considering a 25deg C temperature rise (may be quite high, depending on your water source). With this unit you may run into problems with two people showering at the same time, depending on the flow rate of the showerhead and the temperature of your water source.

 

[jjkind]

There are line losses in the conductors but they are well below 10%, more like well below 1% where did you come up with 90%?

I wasn't considering any sort of calculation from the plant (then you'd have to consider the 30% efficiency of your coal-fired powerplant on top of the 10% line losses, not to mention the energy that goes into fuel production and care of plant waste such as coal ash - if you do this electric heating comes out tarnished). 90% is just a very conservative estimate of how much of the energy from the heating element is transfered to the water versus how much goes into residual heating of the space around the heater. Again, these are conservative. My gas unit (forced-air) claims to have a transfer efficiency of 85%. I suspect that most electric units are probably around 95% efficient, but I really doubt they get much higher than that.

 

[kwired]

I wasn't considering any sort of calculation from the plant (then you'd have to consider the 30% efficiency of your coal-fired powerplant on top of the 10% line losses, not to mention the energy that goes into fuel production and care of plant waste such as coal ash - if you do this electric heating comes out tarnished). 90% is just a very conservative estimate of how much of the energy from the heating element is transfered to the water versus how much goes into residual heating of the space around the heater. Again, these are conservative. My gas unit (forced-air) claims to have a transfer efficiency of 85%. I suspect that most electric units are probably around 95% efficient, but I really doubt they get much higher than that.

Unless the heating unit is completely remote from the space it is heating the heat is not lost, even with gas fired unit, with exception to heat the exits out the exhaust.

I have no disagreement of the benefits of radiant heating.

There is losses with refining and distributing fossil fuels also. When I mentioned line loss I was talking mostly about resistive losses in conductors not at generation.

 

[frenchelectrican]

Bonjour guys.,

I know it been a while in this fourm anyway someone mention about the Whole house tankless water heater and mention about in European area so I will give you a quick cod? related to the tankless heaters used in France.

? They have to be hardwired no cord et plug attachment are allowed in shower area but other area it is ok to use the cord et plug attachement only on 240 volt L-N circuits if used on 415 volts L-L then it have to be hardwired and have a local disconnect means

? All the tankless water heater must have RCD { GFCI } there is no extempt on this set up.

That basically take care the issue with the cod? in France.

If more question on that part just holler I will answer it asap.

Merci,
Marc

 

[kwired]

Unless the heating unit is completely remote from the space it is heating the heat is not lost, even with gas fired unit, with exception to heat the exits out the exhaust.

I have no disagreement of the benefits of radiant heating.

There is losses with refining and distributing fossil fuels also. When I mentioned line loss I was talking mostly about resistive losses in conductors not at generation.

Another issue is initial investment. If you want cooling you still need to invest in similar equipment such as air handlers, ductwork, compressor etc. All of this already exists with a forced air system.

I am well aware that radiant heating systems are more comfortable because of better warming of objects in the room. Does not necessarily mean they use less energy than a heat pump. I am somewhat hot blooded person and personally am usually uncomfortably hot when in a place with radiant heat - if it were my place thermostats would be set lower, but that is just me.

 

[hillbilly1]

Years ago one of my neighbors had the radient heat system using the water heater to also heat the house, he didn't complain about not heating the house well, but a HVAC contractor friend of mine said "yeah, sure you have lots of hot water........." indicating that he thought they didn't do that good of job heating the house.

 

[kwired]

Years ago one of my neighbors had the radient heat system using the water heater to also heat the house, he didn't complain about not heating the house well, but a HVAC contractor friend of mine said "yeah, sure you have lots of hot water........." indicating that he thought they didn't do that good of job heating the house.

The ones I have seen that heat both domestic hot water as well as water for a heating system still have a storage tank for domestic hot water. The boiler system has a heat exchanger piped into this tank. The domestic hot water system gets its own zone in the output of the boiler that has priority over the space heating zones. You do not want to use this boiler as an instantaneous type water heater because it is heating the meduim (recirculated water that could contain antifreeze in some systems) to 160 maybe even 180 degrees, that is just too hot and dangerous for a domestic hot water system.

They all did just fine job heating the space from what I have seen.