For the vast majority of homes hot water comes from one appliance, the large tank hot water heater. It runs on a constant cycle to ensure that hot water is ready for when we need it. This article will look at the traditional tank water heater, tankless water heaters, solar thermal water heaters and geothermal water heaters.
Tank Hot Water Heaters:
The large tank hot water tanks typically hold around 50 gallons. In electric versions heating elements are suspended in the tank and much like the burners on your stove heat up when electric current is run through them. This heat is transferred directly to the water in the tank and then circulated through your pipes when the hot water is turned on. A gas version works by heating the water from below with a gas burner.
The temperature of the water inside the tank can usually be regulated, and through blending with cold water, the desired temperatures at your fixtures can be reached. The biggest drawback to this type of hot water heater is that it must constantly monitor the temperature of the water and run a cycle to ensure that the temperature is always at your desired setting. This is a terribly inefficient means to heat water, especially at times when you aren't using any. High efficiency models are typically very well insulated and use high efficiency heating elements, but the drawback of needing to keep a constant reserve of hot water is still present.
Tankless Hot Water Heaters:
The tankless hot water heater solves many of the problems inherent in the tank hot water heater. The concept is that as you create demand for hot water by turning on the faucet, the unit will immediately begin heating the water on demand. These units don’t have to store 50 gallons of heated water to meet the demands of a household, and because you aren't limited by the size of your tank, the supply of hot water is virtually endless.
There are both gas and electric models of tankless hot water heaters on the market, but early electric models are typically less efficient than the gas models. The gas models are the most popular and can be installed either on the interior or exterior of your home. Tankless water heaters have been designed to install easily as retrofits, replacing you inefficient tank water heater.
Solar Thermal Hot Water Heaters:
Harnessing the power of the sun to help heat our domestic hot water has become very popular. Solar thermal panels typically come in one of two types, evacuated tubes and flat plate collectors. The technologies are different, but the concept is the same. Coated metal absorbs solar radiation and conducts that heat into a liquid, either water or a highly conductive coolant. This heated fluid is then used to transfer heat to the domestic water supply. This is typically done through a traditional tank water heater, the heated fluid supply acting as the heating element. Flat plate collectors typically perform better in high sun areas with more regular ambient temperatures, while evacuated tubes perform better in areas prone to swings in temperature and frequent overcast skies.
While either technology can be used to harness the power of the sun, it is usually not feasible to use this as the sole source of water heating. The panels take up a large amount of roof area and require specialized installation. A typical solar thermal installation can reduce the energy needed to heat domestic hot water by 25-30% and pays itself back in a 5-10 year period.
One of the popular uses for these panels is to assist with the heat for a radiant flooring system. Other home owners choose to use solar thermal panels to heat their swimming pools, taking advantage of the overlap of high solar energy seasons and popular times to use an outdoor pool. Most solar thermal installations must be used in concert with another technology to account for night time demand and high demand periods.
Geothermal Water Heaters:
While geothermal systems are typically used for HVAC applications, many manufacturers also have options to provide heated domestic hot water through the system. The temperature in the earth is a constant once you reach a certain depth. In a geothermal hot water system, this heat is absorbed into a coolant that is often under extreme pressure. The combination of the heat absorption and increased pressure can produce enough heat to handle both the heating and cooling of a house as well as most hot water demands.
Installation can be expensive, but with increased efficiency and a free source of consistent energy, a geothermal hot water system can pay itself back fairly quickly. With enough investment, a quality geothermal system can replace your furnace, AC and hot water heater.
Conclusions:
Heating the water in your home has moved past the old tanks to a range of more efficient and even renewable technologies. We advise a combination system. Combining a solar hot water system or a geothermal system with a smaller sized tankless hot water system is efficient, provides hot water when you need it (true on-demand hot water with no waiting at the fixture requires additional hardware that is quite expensive). We favor the solar systems due to the easier installation and integration with existing structures.