The Basics Typically installed in the garage, basement or attic, tank-type water heaters use propane, natural gas or electricity to produce a large volume of dependable, low-cost hot water. Residential tank-type water heaters typically store between 20 and 80 gallons of hot water, usually at the factory setting of 120°F. The temperature can be adjusted up or down by a control on the unit. If there is high demand over a short period—a family taking back-to-back showers in the morning or a vacation home packed with guests—the hot water can run out. When it does, you have to wait for the water to get hot again. Though they’re well-insulated, to compensate for standby heat loss, tank-type water heaters heat water even when not in use.

Options Abound When choosing a replacement to a tank-type water heater, many people replace it with the same thing. However, advancements in efficiency and technology have made the decision a little more challenging. A new 30-gallon water heater may produce more hot water than a 40-gallon water heater built just 10 years ago. The easiest way to tell is to compare the amount of water both units produce in the first hour (typically listed as FHD or First Hour Delivery on the specs for the water heater). Tankless water heaters offer continuous hot water, but if a remodeling budget is tight, a tank-type water heater will likely be the most affordable choice. Tank-type installation is fast and labor costs are minimal—typically between $500 to $1,000. Upgrading a standard 5′ x 9′ bathroom to a master suite or an in-home spa may require upgrading to a larger gallon capacity unit, especially if the new bathroom will include a deep soaking tub with a multi-head shower system.

Safety First Current gas hot water heaters contain special flammable vapor ignition resistant (FVIR) technology that prevents the ignition of flammable vapors, such as spilled gasoline, outside the unit. First unveiled by Rheem in 2003, the proprietary Guardian FVIR System incorporates an exclusive air and fuel shutoff mechanism that shuts the water heater down quickly and safely should vapors ignite within the combustion chamber. In addition, the Rheem Guardian System is maintenance-free, with no filters to clean—ever.

The Basics Tankless water heaters are more energy efficient than conventional tank-type water heaters because they provide hot water on demand at the precise temperature needed, so there is no storage and therefore no need to expend energy heating that stored water. About the size of a medicine cabinet, these space-saving, compact models can easily be wall-mounted indoors and even outdoors, depending on the climate.

More Hot Water, Fast Many homeowners complain that it takes a long time to get hot water. That’s caused by the hot water between the water heater and the faucet going cold. You have to get that water, which can be up to two gallons out before hot water starts flowing. To solve that, you can install a tankless water heater with a built-in or accessory recirculation pump, which circulates hot water through your pipes so it’s ready when you need it. Another option is to install a tankless electric tankless model, which can be installed at or near the point of use for near-instant hot water.

Continuous Hot Water, Continuous Savings Rheem tankless water heaters combine innovative technology and functionality for a hot water solution that can supply a ntinuous flow of low-cost hot water whenever and wherever you need it. No matter how many body sprays and showerheads, no matter how deep the whirlpool, you will not run out of hot water with a properly sized tankless water heating system. In addition, the Rheem Guardian System is maintenance-free, with no filters to clean—ever.

Solar water heaters are an even greener hot water solution that uses a dark-color solar collector to capture the solar energy that is used to heat the water. Solar water heating systems can be “passive,” where the water flows between the collection area to the storage tank via gravity or some other non-mechanical means; or “active,” which uses a circulating pump to move water through the system. An active system may also be called “forced circulation,” and requires more energy than passive systems.

Even the most efficient solar water heaters sometimes require some auxiliary heating (boosting). This may be because of a large, late-in-the-day hot water usage or after a long period of extensive cloud cover. An electric, gas or other fuel-type booster can be quite effective in enabling a solar water heater to provide a year-round supply of steaming hot water, but it also obviously adds more energy requirements.

Both types of water heaters have their benefits. See the full comparison below to decide which type of Rheem® water heater is right for your lifestyle and budget.

Sizing is the technique that matches the capacity of the hot water source to your needs. For tank water heaters, the key criterion is hot water storage capacity. For tankless water heaters, the key criterion is hot water flow rate. Incoming water temperature is a critical consideration, which varies by region and season. That is, a water heater in the North—either tank or tankless—will need a higher BTU input in the winter than the summer to heat and deliver water to a given temperature.

Regardless of which type of water heater is used, you should start with a lifestyle audit of your typical usage:

1. Baths: How many bathrooms are in the house?
2. Showers: How many showers are in the house and how many showerheads, body sprays and side sprays are in each shower? How much water do they use? Standard showerheads have a flow rate of 2.5 gallons per minute, although new water-efficient showerheads have lower flow rates. Most people are comfortable showering in water temperatures around 102°F to 106°F.
3. Bathtubs: How many bathtubs and whirlpools are in the house? How many gallons are needed to fill each to capacity? While small tubs are usually about 40 gallons, deep soaking tubs can hold up to 140 gallons. As with showering, remember, most people bathe at temperatures between 102°F to 106°F.
4. Schedules: What is the typical bathing and bathroom use schedule in the home? How many occupants are likely to be bathing simultaneously?
5. Other hot water appliances: Are any other hot water appliances in use at the same time? If so, these need to be calculated also, e.g., dishwasher, hot-water laundry, kitchen use, etc.
6. Geography: Where is your home? Consider the winter inlet water temperatures in the area to make sure there’s sufficient hot water flow on the coldest days. The rule of thumb is:
7. Do the math; select the right unit: Add up your peak demand in gallons per minute and see which size of tank water heater will satisfy this peak requirement at the very coldest time of the year; i.e., when the difference between the inlet and outlet water temperatures will range as high as 75°F if you live in the Northeast or Upper Midwest. For example, if a Minneapolis homeowner picks a system that will handle a Delta T of 75°F in the winter (45°F inlet to 120°F outlet) to meet the needs of a household that runs two showers simultaneously every weekday morning, this consumer need not worry about the summer, when the inlet temp should be 20°F to 25°F warmer.

While tankless water heaters do not run out of hot water, if not sized correctly, the flow rate of that water can be adversely impacted. The temperature of the shower will remain the same, but flow could slow to a trickle. So, the first step in sizing tankless water heaters is to add up all the flow rates of showerheads, faucets and appliances that are likely to be in use at the same time. Step two is to consider the incoming water temperature. When inlet water temperatures dip down into the 30s and 40s, larger BTU inputs will be needed. In certain high-volume applications, you may want to specify more than one tankless water heater unit, either installed separately or connected together to operate as a single tankless system.

If you already own Rheem® water heating equipment, you may need to know the serial number for service, warranty information or other reasons. The serial number identification on all Rheem water heating product rating labels contain ten (10) digits.

If follows the example below:

Serial #	12	09	D	01234
Description	Month Manufactured	Year Manufactured	Plant Line Code	Consecutive Serial Number

Your warranty is based on the date of manufacture and the warranty code listed in the model number. To verify if your water heater is in warranty you can call 1-800-621-5622 and listen for the prompt to take you to warranty.

Anode Rod  Because water heater tanks are typically made of steel, they are (or should be) equipped with an anode rod that attracts the minerals in water so they attack the sacrificial rod instead of the tank.

Atmospheric  A type of gas water heater that uses no fans or other assistance to vent flue gases.

Booster  As the water inside a standard tank-type water heater is used, the temperature of the hot water that comes out becomes lower. A booster is a type of tankless water heater that measures the water exiting the tank water heater and heats it.

BTU  Short for British Thermal Unit. The amount of heat required to raise or lower the temperature of one pound of water by one degree Fahrenheit.

BTU/h  The heat transfer rate of water heating equipment is measured in British Thermal Units per Hour.

Capacity  The capacity of a water heater is how much hot water it can store. New rules mandate that two numbers are quoted for capacity: the nominal capacity (typically 30 gal., 40 gal., 50 gal. etc.) and the rated capacity, which is the actual amount of water a water heater can hold (typically 2-5 gallons lower than the nominal capacity).

Dip Tube  The dip tube is on the cold water line of a water heater to direct the cold water to the bottom of the tank both so it can force the hot water out and so it can be heated.

Direct Vent Water Heater  A direct vent water heater gets its combustion air from the outside, rather than the room the water heater is installed in.

EF  Short for Energy Factor, this is a measure of how efficiently a water heater uses its energy input. The higher the number, the more efficient the unit is. EF has been replaced by Uniform Energy Factor.

Expansion Tank  Installed on the water inlet line, an expansion tank regulates the pressure in water lines.

FVIR  All residential water heaters manufactured after 2003 are required to be Flammable Vapor Ignition-Resistant, that is they must not ignite flammable vapors outside the combustion chamber.

Hybrid Water Heater  A hybrid water heater uses heat pump technology to draw heat from the air and transfers it to the water to make it hot. This type of water heater is highly efficient.

NOx  As fossil fuels are burned, oxides of nitrogen are often formed. Because these combustion by-products impact air quality, EPA regulations control the acceptable amount of NOx output of most water heaters.

Point-Of-Use Water Heater  These electric water heaters are compact enough to be installed at or near the place they will be used. They heat water only when it is needed and return to standby when hot water is no longer need. Depending upon the capacity (or flow rate in the case of tankless), point of use water heaters can supply hot water to a sink, an entire bathroom, an addition, a workshop, garage, etc.

Standby Losses  Standby losses measure the temperature loss in a hot water tank over a 24- hour period and are report as an energy loss in BTU/h units.

T&P Valve   An important safety measure, the temperature and pressure (T&P) valve opens when the temperature or pressure inside the water heater exceeds its designed limits.

UEF  In 2017, EF ratings were replaced with the Uniform Energy Factor (UEF), a new industry standard for measuring energy efficiency in water heaters. The new UEF rating method defines consistent standards for measuring energy efficiency performance, simplifies the water heater selection process, and more accurately reflects real-world scenarios that impact energy efficiency ratings.

Watt/Watts  Electrical power, also expressed as ‘W’. For example, a 100W bulb consumes 100 Watts of electrical power. The W in Watt is always uppercased, because it is named after a person.