Tankless water heaters provide hot water only when needed and are sometimes referred to as instantaneous or on-demand water heaters. The more common traditional style has a water storage tank of various sizes and shapes used to store pre-heated water. These water heaters provide hot water at a preset temperature when needed without storage, thereby eliminating the need for storage tanks.
These on-demand tankless water heaters are heated either by electricity, natural gas, or propane. The gas models were found to be 22 percent more efficient than electric models. This finding equates to about 75 dollars in annual utility savings, based on an average home’s use of 77 gallons of hot water per day (Consumer Reports, Tankless Water Heater Testing, October, 2008).
Tankless systems have two primary types:
- Point-of-Use – these systems are small and heat water for only one or two places. One example is installed near the kitchen sink for its use only. Their small size allows them to be placed inside a cabinet, closet, or under a sink.
- Whole-House Use – these systems are designed to provide hot water for an entire home and are typically located in an attached garage or utility room. This type has a longer lag time than a point-of-use system. Lag time is the time it takes the hot water to travel from the heater to the faucet. In large homes, the lag time can be minutes.
As with any home appliance there are pros and cons with these types of water heaters. The following are some of the advantages of a tankless system.
- Energy Savings – although the initial installation is more expensive than a traditional water heater, this type of hot water heater saves energy and reduces utility bills over the long-term. This is opposed to the waste of energy needed to keep the water hot in a tank; thereby, increasing utility bills even when no one is at home.
- Continuous Hot Water – a tankless water heater provides an unlimited amount of hot water, since it heats the water as it passes through the heater. This is opposed to a storage tank system that requires waiting for more water to be heated, when it runs out of hot water.
- Size – most require less physical space than a traditional system. Often these systems are mounted on a wall and do not take up floor space. Systems with water storage-tanks take up much more space, especially those with large tanks – 50 gallons and above.
- Less Risk of Water Damage – storage-tanks eventually leak or rupture at some point, requiring the need of metal pan to collect leakage if in an interior closet or attic space. While the only risk of water damage with these new type of system is from pipe or pipe-fitting failure.
- Life Expectancy – storage-tank systems typically last about 12 years, while a tankless systems life expectancy is 20 years.
Energy Efficient: However, There are Disadvantages
The following are some of the disadvantages of tankless systems.
- Lag Time – this type of water heater only provides hot water on-demand, causing a start-up delay of hot water at the faucet. Although this is also an advantage, homeowners should not expect instant hot water when the faucet is opened. However, this disadvantage also present with storage-tank systems.
- Irregular Use – when a hot water faucet is turned on and off repeatedly, there are periods of hot and cold water. This is caused by a one-to-three second delay when water starts flowing and the heater’s flow detector turns on the gas or electric heating elements. This is not a problem during continuous use.
- Installation Cost – cost of replacing a storage-tank can be expensive. Whole-house tankless water heaters typically cost $800 to $1,150, compared with $300 to $480 for the regular storage-tank types. Tankless models need electrical outlets for their fan and electronics, upgraded gas pipes, and a new ventilation system. This can bring an additional average installation costs to $1,200, compared with $300 for storage-tank models.
- Sources of Heat – storage-tank systems can use solar energy, geothermal energy, natural gas, propane, electricity, and ground-coupled heat exchanger energy. However, the non-tank system can only use natural gas, propane, or electricity.
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David R. Wetzel - Dr. David Wetzel's experience includes more than 25 years in continuing, adult, and teacher education.
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