more energy efficient gas or electric water heaters?
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Question by tj: more energy efficient gas or electric water heaters?
Need to replace water heater. I have gas now but I think electric may be more efficient.
Can you help? Leave your own answer in the comments!
5 Responses to more energy efficient gas or electric water heaters?
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although rather oxymoronic electric is more efficient but typically cost more to run.
Why? In most areas gas is cheaper.
If you are looking at it from a green perspective if your Utility burns coal then gas is greener
If your Utility is hydro electric is greener
If your Utility is Nuclear electric is greener
If your utility is gas electric is greener
Solar Thermal is the greenest of all and will have a payback and then provide free hot water for a number of years
additional details
AO smith FPSE-40-230e 40 gallon gas water heater
Input 40.000 BTU per hour
Energy Factor .65
Recovery Efficiency .08
AO Smith PEC-66 66 Gallon electric water heater
Input 15,358 BTU
Energy Factor .84
Recovery Efficiency .98
Above are two standard water heater form the same company.
The gas heater which is 16 gallons smaller has an energy factor of 19% more energy needed
( energy factor the larger the number the better same with recovery efficiency)
The gas heater has recovery efficiency of 18 percent less recovery.
The larger electric uses less energy to heat water than the gas.
Almost 3 times the BTU and almost 20% across the board.
The gas unit has a huge hole in the middle that when not convection heating is convection cooling. You cannot completely encapsulate a gas fired unit.
The electric element is completely immersed heater transferring all its heat energy directly to the water. It can be completely encapsulated there by losing less standby heat.
Electric wins hands down and not by a little. As we know energy is neither lost nor gained simply transferred from one state to another.
Electric Water Heaters transfers less energy for the same workload
So why is gas the choice? Economic Efficiency.
In my area a therm is about $ 1.20 (100,000 BTU)
a KwH runs about 26 cents (this is due to are tiered system I have never seen a household with an electric water heater that is not in the top tier. this figure has been averaged out by tier four customers in my area. It includes transmission and all other charges that my utility bills.
So from our btu factor above I pay 3.99 for one hour in our more efficient electric model. (15.38 *.26)
From our BTU I pay 48 cents for one hour in our less efficient gas model (.4 * $ 120)
but lets be fair the electric unit is heating 40% more water so we pay 67.2 cents for the same amount of water or almost 600 percent more
Depending on which efficiency we are talking about depends on which heater we choose. Your mileage might vary. In an area where gas is available it is usually because it is much cheaper to run
Red E3
July 25, 2013 at 7:41 am
i suspect that gas is far more efficient.
consider, something like 1/2 the electricity is generated using gas.
so there are losses generating the electricity.
then there are losses transmitting it to your house.
it is true that some of the heat from a gas water heater goes up the chimney.
but i suspect that you use far less gas to heat your water directly, than would be used to generate electricity, and transmit it to your house.
have a happy hot shower. 🙂
PS: also keep in mind, if you use less electricity, that which you don’t use is the least efficient that the utility is burning at the time when you’re not using it. That is, when less is being used, it’s the worst of the batch that is not being used.
have a happier hot shower. 🙂
linlyons
July 25, 2013 at 7:48 am
There are many factors to consider before updating your HWS. If green energy is an option then it should be thoroughly investigated.
Solar type HWS’s in Australia offer solar panels that connect to a “Smart” very well insulated storage unit. This warm water (heated by the solar panels) is then then fed into an instantaneous gas unit to raise the temperature for use. During colder months warm water from the storage unit is fed back to the solar panel to prevent freezing. As the system only uses the gas necessary to warm the to say 55 degrees celcius it is extremely efficient. In summer the system may not use any gas at all.
For standard systems, due to the cost of fuel, gas is cheaper than electricty here is Australia. My instantaneous gas system is far cheaper to operate than my storage gas system.
Michael Alger
July 25, 2013 at 8:43 am
Depends. The tankless systems are an “on demand item” and might be worth looking at rather than keeping a tank full of hot water all day. Most gas fired tankless systems blast the chamber with 160,000BTu of heat energy or more depending on size. If you talk with one of the manufacturers that might be available in your area, talk with a local plumbing supply house to know who is available, that manufacturer can give you an approximate idea of annual usage cost or volume of gas for your area.
Go with a larger rather than smaller tankless sytem if you have kids or if you have a need to be washing clothes for example while someone is taking a shower.
There are electric tankless units too, they usually are around 30 Kilowatts for size or better and at that size it is usually a 30 second time rating for a 50 degree temperature rise. They are called tankless, but they do have a tiny tank for the heating element.
Sizing the systems it is useful to know what the temperature is of water coming into the house because the tankless sytems are often rated on a “thermal rise” or “temperature rise” often at 50 degrees or 75 degrees F.
Electric “can” be slightly more efficient, only because the heating element is immersed in the tank completely and no waste heat to lose. It really only works well if you use a timer to turn the heater on and off. If you go this route- spend the extra for the 12 year tanks because they are usually made with a high efficiency foam insulation that is usually twice as thick than the lesser warrantied units. Also look at a larger tank like a 60 gallon tank if you are plannig on a bath remodel, especially if you plan on a jet tub. They make up for the cost difference quickly.
If your power goes out, if the hot water is not used in the interem, it will still be hot enough 2 days later for a comfortable shower. If you have back up power- make sure it is adequate if you want to keep the water heater available while power is out. Their drawback is if you plan to go off grid or try to run as much off a solar or wind system, 4Kw for both typical heating elements is often more than most basic systems develop at any given time.
J.
July 25, 2013 at 9:14 am
The most efficient way to go is solar water heater with gas-powered tankless as a backup. The solar heater is an awesome investment – 5-8 year payback means better than 8% on your money. Tankless heaters are fairly expensive but provide an extremely low operating cost for those times when the solar heater can’t keep up with demand.
virtualguy92107
July 25, 2013 at 9:32 am