There are two main types of energy that operate water heaters. Gas and Electric. There are also units which operate on solar power however most solar water heaters require some source of electrical or battery backup for uninterrupted operation. There are a lot of options to consider when it comes to the selection of water heaters and there appears to be pros and cons with each type of unit so when it comes to making a choice you certainly need to do some research and consult with professionals to determine what your needs are so that you make the appropriate selection.

One very important factor to keep in mind when going thru the selection process is the "Energy Factor". Water heaters with high energy factors are more efficient. Electric water heaters have factors between .75 and .95 vs. Gas water heaters which range from .5 to .7 thus Electric water heaters are more efficient. It should be noted that if electricity costs more than gas; a gas heater might still be cheaper to run even though it is not as energy efficient.

Gas (and/or) Propane Direct Vent Water Heaters expel the (exhaust) combustion gases to the atmosphere directly thru the use of a vertical vent. Direct venting works because heated air is lighter than cool air and in turn will rise naturally due to the difference in buoyancy between the hot and cold air. This system only works when the exhaust gases can be vented vertically and the overall hot water heating costs are low compared to other types of water heaters. This type of water heater is very common and a natural gas unit usually costs less money to operate than a propane unit since natural gas is typically less expensive than propane. This type of unit also does not require any power (electric) to operate.

Gas (and/or) Propane Power Vent Water Heaters expel the (exhaust) combustion gases with the use of a blower and is the type of unit needed when a tank type gas/propane water heater is installed in a location that does not have the ability to vent vertically. The blower will push the exhaust gases through horizontal vent pipes. The main benefit of this type of heater is the ability to save money by horizontally venting the unit to the outside through less expensive vent pipe or in situations where venting vertically is not an option. A power vent unit is not always the least expensive option since the unit will cost more initially due to the extra equipment (blower/fan) and it also requires power to operate the blower. Also some people find that the sound of the blower running is quite loud so use careful consideration when determining where this type of unit will be located.

Electric water heaters do not require venting thus they can be placed almost anywhere. They have a high Energy Factor thus they are very energy efficient. They also last longer since they have fewer parts than Gas water heaters. Electric units are usually less expensive to purchase and they are easier to install plus there is no chance of a fuel leak or the presence of combustible gases. Electric water heaters are the most common type to be connected or fed by Solar Power.

Once you determine the type of energy source you want to use for your water heating there are still a few other decisions you can make and this would be whether or not you want to purchase a standard tank unit (described above) or purchase a tankless unit. Tankless units heat water directly without the use of a storage tank. Therefore, they avoid the standby heat losses associated with storage "tank" water heaters.

If you decide to go tankless then gas-fueled units usually produce more gallons per minute than electric units. Gas units still need an electrical connection in order to operate and they also need to be vented like a tank unit so that the exhaust can be expelled outside the building.

When a hot water tap is turned on, cold water travels through a pipe into the unit. In an electric Tankless Water Heater an electric element heats the water. In a gas-fired Tankless Water Heater a gas burner heats the water. As a result, Tankless Water Heaters deliver a constant supply of hot water. You don't need to wait for a storage tank to fill up with enough hot water. Typically, Tankless Water Heaters provide hot water at a rate of 2 – 5 gallons (7.6 – 15.2 liters) per minute. Typically, gas-fired Tankless Water Heaters will produce higher flow rates than electric Tankless Water Heaters.

Tankless units have become very popular due to their compact and space saving size; also they are appealing in that they do not hold water or continually heat water when it is not needed. There are still a lot of pros and cons with regard to tankless units so be sure to consult with a professional so that you can determine if the pros will outweigh the cons.

Some of the cons for the tankless units are:

• Takes a little time to heat the water once the demand is made; hot water is not waiting in the pipes like in a standard tank unit.
• The initial cost of the unit and installation is higher than a standard tank unit.
• If the unit is turned on/off frequently there could be a "sandwich" affect of cold water mixed in with the hot water.
• Can be expensive to service especially with regard to the electrical components.
• If you lose power you will not have hot water.

Some of the pros for the tankless units are:

• They are typically less expensive to operate than a standard tank unit.
• Space saving – takes up little space.
• Can install multiple units in various areas of the house so that "wait time" for hot water is minimized.

Technology on the tankless units continues to be upgraded. Some manufacturers now make their units with recirculation pumps so that "wait time" for hot water is minimal at best. This includes the fairly new "Hybrid" tankless unit which reuses some of the heat generated from the unit to heat the water passing thru the tank.

Once again; do some research; talk with professionals and make sure that whatever system you are installing is sized properly for the use you need to ensure that your water heating system will service all of your needs adequately. There are still some energy star models and types of units where rebates are possible so be sure to check out this information in your area as well.