ohm
Senior Member
- Location
- Birmingham, AL
A lot of juice for a very short time, like striking a welding arc. But, they are still very efficient.
Under the right circumstances, they're the smart choice.
Tankless water heaters
- Thread starter Mike Lang
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A lot of juice for a very short time, like striking a welding arc. But, they are still very efficient.
Under the right circumstances, they're the smart choice.
mivey
Senior Member
Not unless you are billed on demand. To increase the monthly bill, you will have to use a lot more water to go along with it. You will only heat the water you use.
Why not just put in a heat pump water heater or a solar with an electric back-up if you want high efficiency.
Also, if the demand is a problem, just get a Marathon high efficiency water heater and take the high demand off of your electric service and put it in the tank.
charlietuna
Senior Member
I have a Noritz(GAS) unit which is sized for my home's number of hot water outlets and types of use, which no doubt figures the highest number of gallons of hot water AT THE UNIT"S HIGHEST SET TEMPERATURE. It is computerized and can measure all kinds of data it required and can self diagnose it's own internal problems. I went with an external unit that hangs on an exterior outside wall and exhausts directly via a stainless steel vent. It's size is about the size of a large suitecase. Electric requirements is a 120 volt GFIC receptacle under the unit for control power. From the main unit it requires a six conductor thermostat cable to the master control station(my case was the master bathroom). They have optional branch stations that you can install anywhere you want the ability to change the setpoint of the outlet water temperature. The six conductor cable is required from the master controller out to the slaves which can be daisy chained. An example of how this works is the PRIMARY SETPOINT TEMPERATURE is always set at the master controller(say it is set at 130 degrees). Someone in another bathroom likes to shower at 135 degrees, they can set their temperature at "their" slave unit to 135 degrees and take their shower. After 15 minutes of no water flow the master unit resets the outlet temperature back to the PRIMARY SETPOINT. When using tankless units, you get used to just using "full" hot water --no mixing to get the temperature you like. From my own experience the slave unit, in my house, is never used and cost about $100 each plus labor and materials. The tankless unit has a fine filter arrangement inside to assure no restriction of water. Below the unit are a set of bypass and stop valves which allow you to backflush the unit if necessary depending on the clearity of the water. I am on spring fed water and have never had a problem in two years. Now i still have the water stubs in my master bedroom closet that the original plans called for the tank type heater to be installed. Now this is inside my homes conditioned air space and knowing it would be allowing more than half it's energy to escape through the tank walls makes sense alone to be tankless and hanging outside giving me more closet space.
electricguy61
Senior Member
Our company does plumbing as well, and has installed a number of different natural gas brands. I agree that Noritz seems to be the best engineered.
Even if the op's customer doesn't have natural gas, it might still be cheaper to install a propane tank and run the water heating from gas then to install a 320 service and use electricity to heat water. Total electric is not very cost affective.
Even if the op's customer doesn't have natural gas, it might still be cheaper to install a propane tank and run the water heating from gas then to install a 320 service and use electricity to heat water. Total electric is not very cost affective.
mivey
Senior Member
electric is more efficient than gas
electric is more efficient than gas
FWIW, the gas storage units only gets up to about 65% efficiency as compared to 95% capability of the electric storage units.
Gas in heating and cooking:
Gas is not as efficient as electric in heating. Think about the electric heat pump in a home, which can be 300% more efficient than gas heat. In home heating, gas and propane are only about 80% efficient as compared to 98% for resistance heat. The cheaper gas & propane fuel usually make them cheaper than strip heat, but they can't compare to a heat pump.
A gas stove is only about 30% efficient as compared to 70% for a standard electric cooktop and 90% for an induction cooktop.
Back to the water heaters:
In an electric water heater, the element heat is transferred to the water but a gas unit puts a lot of the heat energy out the flue.
The gas storage units have an energy factor of 60-65% compared to 90-95% for electric.
The gas tankless units are in the 82% efficiency range as compared to the 99.3% for electric. The problem with the gas unit is, the loss in the efficiency of the gas unit's heat exchanger due to scaling, will push it's average efficiency down to the 60-70% range in a short time.
The electric heat pump water heaters have an efficiency rating of 220% and the solar with electric back-up about 120%.
But efficiency is not everything as we must consider the life cost. The lowest life cost is the electric heat pump, followed by the electric & gas tankless, then gas storage, then electric storage, then solar with electric back-up (imagine what if we could have cheap solar conversion).
The gas vs electric "myths" live on:
The idea that gas is more efficient than electric comes from the comparison that if you only get 33.3% of the energy out of an old gas or coal generator, then 99% out of the electric heater, you are left with 33% as compared to an old gas heater with 50% efficiency.
That idea is certainly outdated now as the natural gas turbines today are over 50% efficient (51% for combined cycle, simple cycle is still about 33%). Modern fuel cell plants are now at 50-60% efficiency and are expected to be able to reach 70%. Coal plants today are about 39-40% efficient with gasified coal around 44%. Also, our electricity is generated by energy sources other than gas or coal alone.
Most of these "gas is more efficient than electric" myths are based on including the generation losses at old gas and coal power plants and don't take into account the coefficient of performance of modern heat pumps.
electric is more efficient than gas
The tankless gas AND electric units may be more efficient than a conventional electric, but a heat pump electric water heater is more efficient than the tankless units.
FWIW, the gas storage units only gets up to about 65% efficiency as compared to 95% capability of the electric storage units.
Gas in heating and cooking:
Gas is not as efficient as electric in heating. Think about the electric heat pump in a home, which can be 300% more efficient than gas heat. In home heating, gas and propane are only about 80% efficient as compared to 98% for resistance heat. The cheaper gas & propane fuel usually make them cheaper than strip heat, but they can't compare to a heat pump.
A gas stove is only about 30% efficient as compared to 70% for a standard electric cooktop and 90% for an induction cooktop.
Back to the water heaters:
In an electric water heater, the element heat is transferred to the water but a gas unit puts a lot of the heat energy out the flue.
The gas storage units have an energy factor of 60-65% compared to 90-95% for electric.
The gas tankless units are in the 82% efficiency range as compared to the 99.3% for electric. The problem with the gas unit is, the loss in the efficiency of the gas unit's heat exchanger due to scaling, will push it's average efficiency down to the 60-70% range in a short time.
The electric heat pump water heaters have an efficiency rating of 220% and the solar with electric back-up about 120%.
But efficiency is not everything as we must consider the life cost. The lowest life cost is the electric heat pump, followed by the electric & gas tankless, then gas storage, then electric storage, then solar with electric back-up (imagine what if we could have cheap solar conversion).
The gas vs electric "myths" live on:
The idea that gas is more efficient than electric comes from the comparison that if you only get 33.3% of the energy out of an old gas or coal generator, then 99% out of the electric heater, you are left with 33% as compared to an old gas heater with 50% efficiency.
That idea is certainly outdated now as the natural gas turbines today are over 50% efficient (51% for combined cycle, simple cycle is still about 33%). Modern fuel cell plants are now at 50-60% efficiency and are expected to be able to reach 70%. Coal plants today are about 39-40% efficient with gasified coal around 44%. Also, our electricity is generated by energy sources other than gas or coal alone.
Most of these "gas is more efficient than electric" myths are based on including the generation losses at old gas and coal power plants and don't take into account the coefficient of performance of modern heat pumps.
mivey
Senior Member
A Marathon high-efficiency unit only loses about 5 degrees in a 24 hour period.
electricguy61
Senior Member
Bottom line is what I stated: gas is more cost effective.
charlietuna
Senior Member
Mivey,
I notice your location is "BRIAR PATCH" ??? This must be on another planet and where the sun shines 24 hours a day to consider a heat pump only to heat your water. Your numbers on comparing gas vs electric heating ANYTHING - water -food-drying clothes is reversed. Just try googling tankless water heaters to get the true facts. You stated a "Marithon high efficiency water heater only loses about 5 degrees in a 24 hour period" means nothing ! A tankless gas or electric will loose zero degrees in that same period ! Please check your figures because Electric Resistance Element heating is very inefficient !
I notice your location is "BRIAR PATCH" ??? This must be on another planet and where the sun shines 24 hours a day to consider a heat pump only to heat your water. Your numbers on comparing gas vs electric heating ANYTHING - water -food-drying clothes is reversed. Just try googling tankless water heaters to get the true facts. You stated a "Marithon high efficiency water heater only loses about 5 degrees in a 24 hour period" means nothing ! A tankless gas or electric will loose zero degrees in that same period ! Please check your figures because Electric Resistance Element heating is very inefficient !
mikeames
Senior Member
- Location
- Gaithersburg MD
- Occupation
- Teacher - Master Electrician - 2017 NEC
I dont think people realize what they mean when they say efficient. Efficient means the amount of energy going in vs the amount comming out in the desired form. Electric heating is very efficient but LEAST COST EFFECTIVE.
Logic it out, and electric element converts almost all electrical energy into heat. No energy is lost to heating exhaust gases or expelling gas. No energy is lost in the form of light energy or radiant energy as is the case with gas.
The problem is the prime mover or the source of the energy when it comes to electricity is the power plant. The distribution system we pay for when creating or using electricity is where the cost goes. If energy just showed up at your house in the form of gas or electric, electric would be more efficient at heating.
technically it not because we need a source of energy to get electricity. So the word efficiencty is relative when talking about any system. Are we talking about one part of the system or the whole. We pay for the whole which make gas more cost effective.
Logic it out, and electric element converts almost all electrical energy into heat. No energy is lost to heating exhaust gases or expelling gas. No energy is lost in the form of light energy or radiant energy as is the case with gas.
The problem is the prime mover or the source of the energy when it comes to electricity is the power plant. The distribution system we pay for when creating or using electricity is where the cost goes. If energy just showed up at your house in the form of gas or electric, electric would be more efficient at heating.
technically it not because we need a source of energy to get electricity. So the word efficiencty is relative when talking about any system. Are we talking about one part of the system or the whole. We pay for the whole which make gas more cost effective.
mivey
Senior Member
Heat pumps work quite well in my area (while the Briar Patch story is a Cherokee tale, I'm referring to Joel Chandler Harris' home state). For areas staying below 40 deg F, the geothermal would be a better heat-pump option than the air-source heat pump.
Losing only 5 degrees in 24 hours means that your statement of: "allowing more than half it's energy to escape through the tank walls" is an exaggeration.
It sounds like you are going by what you have been told/heard. Perhaps it is you who needs to do some research. These might help you get started:
http://www.sproule.com/Historical-Gas
http://www.energysavers.gov
http://www.energystar.gov/index.cfm?c=water_heat.pr_water_heaters
http://www.aceee.org/consumerguide/waterheating.htm#lcc
http://www1.eere.energy.gov/consumer/tips/index.html
http://www.southface.org/web/resources&services/publications/factsheets/sf_factsheet-menu.htm
Don't confuse efficiency with economics. If you have high electric rates and low gas rates, the economics can make up for the lower efficiency of gas.
add: mikeames gets it. Read his post.
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mivey
Senior Member
Not always.
See the annual savings here:
http://www.energystar.gov/index.cfm?c=water_heat.pr_water_heaters
and the life cycle costs here:
http://www.aceee.org/consumerguide/waterheating.htm#lcc
Also, consider the stovetop and the water heater:
In the water heater case, a high efficiency electric is more efficient (95% vs 65%), but the economics may not work out. A heat pump is so much more efficient (220% vs 65%) that the economics work out in favor of the electric. This is true even if you consider a high-loss prime mover (65% vs 220%*34% = 75%).
In the stovetop case, gas is about 30% efficient:
conventional electric = 70%, so you have 30% vs 70%*34% = 24%
induction electric = 90%, so you have 30% vs 90%*34% = 31%
This does not account for the prime movers of today with 50-60% efficiencies.
In comparing residential heating, and using $12/Mcf gas and $0.10/kWh electric you get the following:
strip heat: $29.92/MMBtu
natural gas: $14.59/MMBtu
heat pump only:
$16.28 at 2 deg F
$14.18 at 12 deg F
$12.56 at 22 deg F
$11.27 at 32 deg F
$10.22 at 42 deg F
$9.35 at 52 deg F
$8.62 at 62 deg F
heat pump with aux strips:
$20.93 at 2 deg F
$17.58 at 12 deg F
$14.65 at 22 deg F
$12.21 at 32 deg F
$10.22 at 42 deg F
$9.35 at 52 deg F
$8.62 at 62 deg F
Using these costs, the gas vs electric breakeven point is about 10 deg F for the heat pump alone and about 22 deg F for the heat pump with aux strips.
vinster888
Senior Member
- Location
- Nature Coast of Florida
Make sure to notify the POCO of these things. I have been across many remodels where the transformer isnt capable of the load and needs upsizing
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