For centuries, man's only access to hot water was to find a hot spring. With the discovery of fire and invention of pottery, our forebears began heating water. While it is safe to say the first use of hot water was for cooking, it is unknown when hot water was first used for bathing and cleaning.

Although the ancient history of hot water may be murky, we do know when the first manmade and fully automatic water heater was patented: in 1898 by Edwin Ruud, inventor of the instantaneous water heater, which brought the luxury of hot water to homeowners who could afford the $115 price. At the time, the average salary for a 60-hour workweek was $13!

Since that first cast-iron water heater was developed, many innovations have been introduced, including water temperature controls, porcelain enamel-coated steel tanks (now called "glass lining"), sacrificial anode rods, foam insulation, immersion electrical elements, and — most recently — flammable vapor ignition resistant technology and improved energy efficiency.

Today, we enjoy not one, but two very different water heating solutions, both designed to meet our hot water needs:

  • Tank-type water heaters, which maintain a ready store of hot water; and
  • Instantaneous (tankless) water heaters, which heat water only on demand.

The choice whether to use tank-type or instantaneous tankless water heaters depends upon the specific application as well as the customer's lifestyle and expectations. Many water heater manufacturers are expanding their product offerings to better suit the needs of U.S. consumers by providing both types of water heaters. As a professional installer, you must also "gear up" for the new technology, so you are able to recommend, install and service whichever product type will better fit your customers' applications and fully meet their hot water needs.

Different philosophies
In the United States, tank-type water heaters are the dominant choice among consumers. Why?

  • The initial cost for the water heater and installation is lower.
  • Floor space is readily available in most American homes.
  • Fuel costs are still lower than that of many foreign countries.

The U.S. Department of Energy has continually updated energy-use requirements for tank-type water heaters, and that has resulted in dramatic efficiency improvements on all tank-type heaters over the years.

Instantaneous water heaters, while a niche market in the United States, have been used worldwide for years. Floor space is limited and fuel costs are extremely high in many countries.

Tankless units meet these different conditions by heating the water only as it is needed. In addition, the typical tankless unit is compact, can be wallmounted and is available in outdoor as well as indoor configurations.

While the initial purchase price for an instantaneous unit is higher than that for tank-type, fuel-consumption costs are lower. Again, that's because these products heat water only as needed, sparing the homeowner the cost of keeping a tank full of hot water ready and waiting. Tankless technology eliminates the need for a standing pilot.

Residential standards
Residential tank-type gas water heaters (75,000 Btuh and less) are certified to ANSI Z21.10.1-2002. This standard ensures construction safety and incorporates the new flammable vapor ignition resistant safety standard, which went into effect July 1, 2003.

ANSI Z21.10.1a-2002 addresses the problem caused by improper storage or use of gasoline or other flammable liquids near residential gas-fired water heaters. To meet the new FVIR standard, a tank-type water heater must be designed so it cannot ignite flammable vapors caused by spilled gasoline outside the unit. Initially covering residential gas-fired water heaters with storage capacities of 30, 40 or 50 gal., the new standard will eventually cover all residential gas-fired models.


No one wants a complaint about not enough hot water.


Because of higher Btuh inputs, instantaneous gas water heaters are subject to ANSI Z21.10.3 standard. The main impact of this standard is that these models are not affected by residential FVIR standards.

Residential electric tank-type water heaters (less than 12 kW) are subject to the UL174 standard for "household electric storage tank water heaters." This ensures that the wire gauge, amperage rating and grounding are safe. Also, all electrical components must meet other UL standards and be rated for use in a water-heating appliance. Tanks are also hydrostatically tested and design-certified to meet the standards requirements.

Instantaneous electric water heaters are subject to the UL399 standard for "electric heating appliances." This ensures that the wire gauge, amperage rating and grounding are safe. Also, all electrical components must meet other UL standards and be rated for use in a water-heating appliance

Residential tank-type gas and electric models must meet efficiency standards set forth by the Energy Department. Stated as an "energy factor," water heater efficiency is based on recovery efficiency, standby losses and cycling losses. The higher the energy factor, the more efficient the tank-type water heater. EF ratings for electric tank-type water heaters range from 0.81 to 0.95; for gas tank-type units, from 0.48 to 0.63. High-efficiency gas models run as high as 0.80.

Commercial standards
Commercial tank-type gas water heaters (inputs greater than 75,000 Btuh) must meet ANSI Z21.10.3-2001, which includes the construction, performance, and manufacturing and production of these water heaters.

Commercial electric models are tested to meet UL1453 standards for units that meet at least one of the following conditions: more than 12 kW; storage capacities more than 120 gal.; or water temperature exceeds 185 F. Commercial electric water heater safety is generally concerned with proper wire gauge, wire temperatures, fusing and amperage rating.

American Society of Mechanical Engineers testing requires that each pressure vessel be hydrostatically tested, inspected and approved by an onsite visit from the National Board of Pressure Vessel Inspectors. This typically applies to tank-type commercial products only with inputs more than 200,000 Btuh and storage capacities of 120-gal. or more; or if water temperatures are rated above 185 F.

ANSI Z21.10.3-rated products are designed to meet ASHRAE 90.1b-2001 efficiency standards. Unlike residential models that must meet an EF rating, models in this classification must achieve a minimum thermal efficiency rating of 80%. Commercial models are subject to standby loss requirements as well, and typically require some type of vent-damper to retain the heat lost during non-use periods.

Due to the typically high Btuh inputs of tankless products, these models must also meet these same efficiency standards. Because residential and commercial products are tested and rated to different standards, it is difficult to compare the two.

Installation, life-cycle costs
All water heaters must meet specific construction and efficiency standards, but there are differences in the installed and the life-cycle costs.

Installation costs will vary, based on the location of the water heater in the home or business, as well as whether the unit is a replacement of an existing product or installed as part of new construction.

Items to consider in installations include: the initial product cost; cost of venting, piping and electrical; adequacy of the gas or power supply; and the product efficiency.

Life-cycle costs include: the estimated product life, expressed as years of service; replacement part availability and mean time between failures; and availability of trained local service personnel.

Residential applications

As noted earlier, each application will determine which product — tanktype or tankless — will better fit a

customer's needs. You should consider the customer's lifestyle and the potential for lifestyle changes.

Take, for example, two identical houses, each with three bedrooms, two baths, a washing machine and a dishwasher: The first house belongs to a retired couple — "empty nesters"; the second, a family of four with children younger than 15 years of age.

The empty nesters' hot water usage typically would be minimal: two daily showers, weekly laundry, and twiceweekly automatic dishwashing or daily hand dishwashing. Either a small tanktype or single tankless water heater could supply this application, based on hot water demand. Considering the lifestyle of this household, the installation cost, performance and life-cycle cost could be major influences on product selection.

For the family of four, hot-water usage could be significantly higher than that of their older neighbors. Multiple showers and baths, double or triple the laundry load, and daily automatic dishwashing would drive this additional usage. Considering the lifestyle of this household, we would suggest that either a large tank-type heater or multiple tankless heaters would be required. As with the first example, installation cost, performance and life-cycle costs would influence product selection.

Obviously, proper product selection and sizing is critical to customer satisfaction. No one wants a complaint about not enough hot water.

Commercial applications
Commercial applications offer a wide variety of scenarios. For example, a fast-food restaurant may need hot water only for clean-up operations. In this case, either an instantaneous or a tank-type water heater may provide the amount of hot water needed.

Medium-sized hotels or motels of 100 rooms typically have long recovery periods with high-demand peak periods. In this situation, multiple tanktype water heaters or multiple instantaneous units may be considered.

It is extremely important to properly size commercial applications, so as not to run out of hot water. As with residential, you and the customer should consider each application investment and life-cycle cost. Many manufacturers offer sizing tables and sizing software to aid in sizing these types of applications.

Four key factors
A lot has been written about tanktype and tankless water heaters with regard to energy savings; however, satisfying your customer comes down to four critical factors: time, temperature, quantity and price.

Time: What is the length of time hot water will be supplied? What is the length of time between hot water draws? Are the time intervals regular or sporadic?

Residential hot water requirements can vary, but typically they involve periods of peak demand followed by long recovery time.

Temperature: What is the final temperature of the application? What is the lowest incoming water temperature? (Consider, for example, winter conditions.) If tank-type is used, at what temperature will the water be stored?

Residential applications should not exceed outlet temperatures greater than 120 due to the risk of scalding. Commercial applications, however, often require temperatures of 140 to 180. Incoming water temperature compared with the desired temperature rise will give you the information needed to determine which type of water heater would best fit a particular application.

Quantity: How much hot water is required? What is the total demand? What is the flow rate?

Flow rate is an important factor regarding hot water usage. Will the water heater need to supply one fixture at a time or will there be multiple hot water fixtures and/or appliances in use? Price: What is the total cost of installation? What is the investment payback time?

Upfront cost must be compared to lifecycle costs. Or, more simply put: Save now or save later. Customers are more likely to recommend your business to friends and neighbors if you provide not just products and installation but offer a water heating solution for their home.

You should try to match the factors of time, temperature, quantity and price with your customers' hot water usage and budget. In doing so, you will enhance your reputation as a knowledgeable contractor.

As a professional contractor, you must fully understand what is involved with both tank-type and tankless water heaters.

Take advantage of manufacturers' training, learn about the product lines available, understand installation requirements (for gas piping and regulating, venting, local codes, etc.), and learn the sequence of operations and startup requirements. Also, know your source for parts and service.

With today's products, you are now in a position to offer a variety of hot water solutions to your customers.

Tommy Olsen is the commercial product manager for Rheem Water Heaters and has 15 years of experience in the water heater industry. He holds an MBA from Auburn University and a bachelor's degree in Resource Management from Troy University. Olsen is also an American Production and Inventory Control Society Certified Integrated Resource Manager. He can be reached at 334/ 260- 1500 or tolsen@rheem.com


CEC launches 'Tankless University'
WAITSFIELD, VT. — Controlled Energy Corp., a supplier of tankless water heaters, recently launched its Internetbased Tankless University. Found at www.tanklessuniversity.com, the Website is intended to educate builders, architects and engineers, wholesalers, contractors and sales reps.

Tankless University offers information and training for these professional categories. The section for contractors features a detailed online instructional training course that covers how to install gas and electric tankless water heaters for the whole house as well as point-of-use products. Students learn about combustion air and amperage requirements, venting, sizing and proper maintenance of tankless water heaters. The section features detailed text, diagrams and step-bystep videos for maintenance and installations. After finishing the study material, students are invited to test themselves with an interactive quiz.