TYPES OF TANK WATER HEATERS
Storage Tank Water Heater
Storage tanks are the most common type of water heater. As the name suggests, these consist of an insulated tank in which water is heated and stored until needed, then emerges from a pipe on top of the water heater.
There is also a temperature and pressure-relief valve, which opens if either exceeds a preset level.
Natural gas water heaters typically use less energy and cost less to run (by about half) than electric water heaters, although you should note that gas models cost more at the time of purchase.
Tankless (or On-Demand) Water Heater
Rather than storing water, tankless water heaters use heating coils to heat the water as you need it. They’re more energy-efficient than a storage tank, but provide only a limited flow of hot water per minute—about 3.5 gallons.
They’re best for people who typically aren’t drawing water for more than one use at a time—running a shower and dishwasher simultaneously.
Tankless models are best for homes that use natural gas to heat the water; electric models might require an expensive upgrade of the home's electrical capacity.
Heat Pump (or Hybrid) Water Heater
These capture heat from the air and transfer it to the water. They use about 60 percent less energy than standard electric water heaters. And while they cost more than electric-only models, installation is similar and payback time is short. But they don’t work well in very cold spaces and need to be placed in an area that stays 40 to 90 degrees.
And because the heat pump is on top, a hybrid water heater needs as much as 7-feet clearance from floor to ceiling. You'll also need up to 1,000 cubic feet of uncooled space to capture enough heat from the air as well as a nearby drain to discharge the condensate
Solar Water Heater
A roof-mounted cell absorbs the sun's heat and transfers it to an antifreeze-like fluid in a closed-loop system that runs to the water tank. The best deliver stellar savings in summer, making them attractive for warm, sunny regions. But savings suffer on cold and cloudy days. Most models employ a backup system that kicks in when needed.
Even with federal and local rebates, what you'll spend to buy and install a solar system can mean you wait 10 to 30 years to recoup your costs.
Condensing Water Heater
Condensing water heaters are an option if you heat with gas and need a unit with a capacity of more than 55 gallons.
These models have a tank like a conventional water heater, but capture exhaust gases that would normally go out the flue, which wastes energy. These gases are blown through a coil in the base of the unit, where incoming cold water can absorb most of the heat.