how effecient is a modern water heater?

Question

for natural gas and electric

since electric has no vent then it is 100% effecient minus what heat warms the room (so would depend on room temperature)

a new natural gas furnace is said to be 80-90% effecient, so only 20-10% of the heat goes up the chimney?
how does this compare to a water heater? (if you are using it continuously and not counting the heat lost while it sits idle full of hot water.)

thanks

Answer 1

"WATER HEATER EFFICIENCY

The energy efficiency of a storage water heater is indicated by its energy factor (EF), an overall efficiency based on the use of 64 gallons of hot water per day. The first national appliance efficiency standards for water heaters took effect in 1990. New standards, which took effect in January 2004, increased the minimum efficiency levels of water heaters.

The most efficient gas-fired storage water heaters have energy factors ranging from 0.60 to 0.65, corresponding to estimated gas use below 250 therms/year. Condensing water heaters have energy factors as high as 0.86. The most efficient electric storage water heaters have energy factors ranging between 0.93 and 0.95, resulting in estimated annual energy use below 4,725 kWh/year. There is little difference between the most efficient electric resistance storage water heaters and the minimum efficiency standard. Fortunately, heat pump water heaters using less than half as much electricity as conventional electric resistance water heaters are becoming commercially available. If you use electricity for water heating, consider installing a heat pump water heater. Otherwise, look for the most efficient electric resistance unit in your size range.

With demand water heaters, the manufacturers provide different specifications: the energy input (Btu/hour for gas, kilowatts [kW] for electric); the temperature rise achievable at the rated flow; the flow rate at the listed temperature rise; and so on. In comparing different models, be aware that you aren’t always looking at direct comparisons, especially with temperature rise and flow rate. For example, while one model might list the flow rate at a 100°F temperature rise, another might list the flow rate at 70°. Until there are industry-standard ratings for temperature rise and flow rates, it will be difficult to compare the performance of products from different companies. Some companies are beginning to publish energy factor ratings for these products and this information should make for easier comparisons."

From: Reference 1.

Answer 2

The efficiency of the water heater means how much fuel charger you will pay later. If the gas of electric energy price goes up, the cost will high. It is said that the fuel energy is 30% of the whole family comsumption per month. It is high for each house.
Nowdays solar water heater or solar heating is quite common. It is cheap. The heater can get 50% energy from the sunshine to heat the water. It is totally free to get the hot water. The solar heater investment is higher than the electric or gas heater for the first time. After 3-5 years payback time, it is free and save a lot.
There are roof and ground type. See http://himinsun.com/

Answer 3

A good gas water heater is around 90% efficient, and an electric one can be pretty much 100%.

However, where I live electric heat is about 3 or 4 times more expensive than gas heat, so a gas water heater is much more economical, even if it is less efficient.

Answer 4

Like most home appliances, water heaters have become much more energy efficient in recent years. A decade ago 25 percent of our home energy dollars typically went to heating water; today the Department of Energy claims water heating accounts for about 18 percent of your utility bill.
Water heaters last 10 to 15 years on average. If yours is more than seven years old, replacing it with a more efficient model could save you money in the long run.Conventional storage water heaters, the most popular type, provide a storage tank of from 20 to 80 gallons of hot water, heated by several possible fuels - natural gas or propane, electricity, or even fuel oil.Tankless or demand-type water heaters heat water directly as it is used without relying on a storage tank. They can be fueled by either electricity or gas.Heat pump water heaters move heat from one place to another instead of generating heat directly for providing hot water, which makes them two to three times more energy efficient than conventional electric resistance water heaters. Using electricity for power, units can be either stand-alone water heating systems or combined into a system that heat water while heating and cooling the home.Solar water heaters use the sun's heat to produce hot water.

https://www.electrikals.com/products/rc-home-appliances/water-heaters?cnid=e767e5db4e4c7d52014e4d4c088a02ae&cid=10000&page=1&pagesize=20

Answer 5

Not all heat is lost to the chimney. Consider conduction, convection and radiation.