Water heating is an important user of energy and it accounts for second largest segment of residential energy use. Around 25 percent of household energy is used for heating water for various purposes such as bathing, laundry and in the kitchen. Therefore, selecting the right water heater is essential for reducing household energy cost and the needs of hot water. Water heaters can be divided into two, storage and tankless (instant).
Storage Water Heaters
Storage water heaters are the most common type and its size ranges from 20 to 120 gallons. It is fueled by electricity, oil, propane, or natural gas. Insulated tanks are used for heating water. The hot water is always in the tank ready for use. This water heater use energy even when there is no use of hot water. New energy efficient water heaters come with higher levels of insulation, which is helpful for reducing the standby heat loss. Distribution loss is a major problem of all types of water heaters.
Heat from storage water heaters lost constantly through the tank walls. Though the tank is insulated, difference in temperature across insulated wall is large. Therefore, even with lots of insulation, stand-by loss is substantial.
Instant Water Heater
Instant or tankless water heaters do not have a storage tank. Electric element or a gas burner heats water only when there is a demand. These water heaters heat water directly without using a storage tank and they do not produce stand-by energy losses. These types of water heaters never run out of hot water, which is one of the greater advantages of tankless water heaters. So, the water heating capacity is large enough to supply the demands for hot water. These types of water heaters use energy only when required.
Size of Heating Elements
Heating element of storage water heater can be fairly small, which is the key advantage of these types of water heaters. Significant volume of water can be stored in storage water heaters, which is enough for providing hot water needs of a family. A large flow of electricity or gas is not required to heat the water.
The burners of gas-fired storage water heaters are relatively smaller. So, half-inch diameter gas line is enough for supplying water heater. So, the air intake will be fairly modest in size.
The burners of instant water heaters are often much larger. Compared to storage water heaters, a large burner is required for tankless water heaters. Besides, these types of water heaters also need lots of combustion air. About 30 cubic feet per minute air is required for operating 125,000 Btu/hour. Around 45 cfm is required for operating larger, 180,000 Btu/hour model. Options for replacement can be reduced if the airflow requirement is large.
The flow rate of some tankless water heaters is very minimum, which is as high as 0.5 or 0.6 gallons/minute. This is a major problem of low flow plumbing fixtures like bathroom faucets. Today, the technology is highly advanced and the manufacturers are also responding to these concerns.
Though instant water heaters can save energy, the cost of them are very high compared with storage type water heaters. The cost of instant water heater ranges from $800-$1500, besides, around $1,200 is needed for installation. On the other hand, the cost of storage water heater ranges from $300-$480 and around $300 is needed for installation.
Water heater repair requirements are very high in instant water heaters than storage models. Some models are designed for outdoor installations. In such case, supplying combustion air is not a problem. These models include sophisticated freeze-protection systems. Scale build-up is a major problem for places with hard water. If the hardness of water is above 11 grains/hour, it is better to install softener water.
Instant water heater is larger enough to serve a whole family that requires a huge current draw. However, most houses need only 200-amp service. Therefore, larger current flows are expensive.
Instant water heaters simply do not make sense for many household applications. Though there are exceptions, storage water heater is more useful than instant water heaters. However, when you select a water heater, you must consider cost, size, energy efficiency, fuel type and availability, etc. Proper installation and water heater repair at right time is also essential, which depends on climate, type, safety issues, etc.
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