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Water heating

Tankless Water Heaters

Tankless water heaters, also known as instantaneous or on-demand water heaters, provide hot water without using a storage tank. Like tank water heaters, tankless water heaters use either gas or electricity to operate. Cold water travels through a pipe into the unit, and either a gas burner (see Figure 1) or an electric element heats the water. Tankless water heaters can be supplementary units placed at the point of use or can replace a centralized tank water heater. Figure 1: Gas tankless water heater When a flow sensor detects cold water entering the unit’s heat exchanger, the f…

Heat Pump Water Heaters

Heat pump water heater (HPWH) systems extract energy content from a heat source, usually air, to efficiently heat water. Depending on cold water and ambient air temperatures and on patterns of hot water use, HPWHs do the same job as standard electric water heaters but use half the electric energy. These systems use a motor to run a compressor that draws a gaseous refrigerant through an evaporator, raising its pressure until it liquefies in the condenser (Figure 1). This familiar process heats the condenser and cools the evaporator. In wringing the heat from air, HPWHs both cool and dehumi…

Gas-Fired Tank Water Heaters

On a life-cycle basis, gas-fired tank water heaters are typically the least expensive means of heating water. One reason is that on a per-Btu basis, natural gas and propane are usually much less expensive than electricity; another is that tank water heaters of 100 gallons or less are mass produced and are less expensive than most other types of water heaters. In some instances, other water heater types—such as electric heaters—are a better choice. But if gas is available and the water heater is in a location where a gas vent can be installed, a gas-fired tank water heater will like…

Electric Resistance Tank Water Heaters

Because electricity is generally more expensive per Btu than gas, electric water heaters are typically more expensive to own and operate over their lifetime compared to gas water heaters. Despite this economic disadvantage, there are four reasons why someone might select an electric water heater instead of a gas heater: Lower initial cost. Because they don’t require combustion gas vents, electric water heaters are usually less expensive to purchase and install. Ease of installation. Electric heaters can be installed in locations in which it would be difficult or im…

Small Gas Boilers

If you are considering the purchase of a gas boiler, add residential boilers (Figure 1) to your list of options. Even though they are designed for a different market, they can play an effective role in commercial buildings as well. Residential boilers are manufactured in larger quantities than commercial units, which makes them relatively inexpensive and readily available with a wide variety of options. Their small size enables them to be easily moved into and out of buildings, and the most efficient residential units exhibit efficiencies similar to those of their best commercial counterparts.…

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