Up Close with Tankless Water Heaters
Tankless water heaters have been in use all over the world for fifty years, largely because of smaller homes and higher energy costs outside the United States. In fact, tank water heaters are only used in the U.S. As natural gas and LP prices rise (as they have for the past decade) it will cost consumers more to heat water. Imagine cutting water heating costs by 50 to 70 percent – think tankless water heaters.
Tankless water heaters – often called “on demand” water heaters – only heat water when needed. Tank water heaters, on the other hand, keep the water hot all of the time and, when on standby, loose about 6 degrees an hour. Heat in the form of Btu’s also escapes up through the flue pipe constantly. Tank water heaters are incredibly inefficient and yet are used in the majority of American homes. Tank water heaters have a life expectancy of around 10 years, depending on incoming water quality. Tankless water heaters, on the other hand have a life expectancy of 20 plus years and carry a warranty on the heat exchanger from 10 to 15 years (depending on the manufacturer).
A tankless water heater can save about 70 percent of natural gas or LP expense a year for heating water except when the Teenage Daughter Factor comes into play – more on this later. The major differences, aside from energy savings, are a gain in floor space of about 20 square feet and an endless supply of hot water.
Tankless water heaters come equipped with the latest water heating technology and, as a result, sell for around one thousand dollars. The payback period will depend on how much hot water is used in the home. The more hot water used, the faster the payback.
Tankless water heaters are a good choice for singles or small families simply because the demand for hot water is not as great as for a large family. And yet, a small family pays for heating water 24/7 with a tank water heater.
The Teenage Daughter Factor: While it is true that tankless water heaters can help you realize a substantial savings in gas consumption, this may not be possible in all cases. For example, if you now have a teenager (son or daughter) who likes to spend a lot of time in the shower – to the point of using all of the hot water in the home – you will probably use more gas than you presently do. This is because a tankless water heater never runs out of hot water with the end result being that the previously 20-minute shower can now run forever, or until you lay down some shower-length rules.
A Closer Look
In this short article we will look at gas-fired (natural gas or LP) tankless water heaters that offer an endless supply of hot water for an entire two-bath home. Also available are electrically powered tankless water heaters and point-of-use tankless water heaters, which will not be covered here. For optimum efficiency, tankless water heaters should be centrally located in the home, as this will reduce the time required to get hot water to a tap or faucet. Keep in mind that water is not heated until needed. In fact, the heater will not turn on until a hot-water tap is opened. If the tankless water heater is located on the far end of a home, it may take a minute or two for hot water to begin flowing from the tap.
Tankless water heaters are controlled by a small computer and a bunch of sensors, which note the temperature of the incoming cold water and a number of other operational factors. When a tap is opened, the computer determines the amount of heat required to raise the temperature of the incoming water to the desired hot-water temperature. Then the burner is electronically fired up – there is no pilot light – and the incoming water is heated to the desired temperature as it passes through the heat exchanger. The end result is an endless supply of hot water. When the hot water tap is closed, the burner is turned off and the exhaust fan turns on to vent the unit.
We will look at three of the top gas-fired tankless water heaters currently in use in modern American homes: the Takagi TK-2 Flash Water Heater, the Rinnai Continuum and the Bosch AquaStar 250SX. All of these heaters are top of the line and ideal for supplying an unlimited supply of hot water for the average or large home. While the Takagi and Rinnai heaters can only be purchased and installed by a licensed installer, the Bosch AquaStar is available at home centers and can be installed by a homeowner.
Installing a tankless water heater in new construction is easier than installing in a remodel. Part of the reason for this is that because gas-fired tankless water heaters are capable of generating a great amount of Btu’s (up to 195,000 Btu’s on start-up) an adequate supply of gas must be available to the unit. Gas piping must therefore be sized properly. A gas shut-off valve must be installed below the tankless hot water heater so the unit can be serviced if required.
Generally speaking, 3/4-inch black iron pipe can be run up to about 20 feet of length from the gas meter or regulator, and 1-inch black iron pipe can be run for distances up to 70 feet. If other gas appliances are also in the home (gas range, gas clothes dryer and furnace, for examples), larger diameter gas piping may be required to run all appliances at the same time. Keep in mind that in new construction this is easy to plan, but in a remodel, adding larger gas line piping can add to costs of time and materials. Additionally, elevations more than 4,000 feet above sea level may require adjustments for the unit to run properly.
Tankless water heaters also have special venting requirements and must only be vented with a dedicated, sealed vent system. All manufacturers recommend a specific brand of stainless steel vent pipe. All tankless water heaters’ flue gasses are under positive pressure and must never be vented in combination with any other gas appliance – a furnace, for example.
The tankless water heaters we cover in this article can be vented either horizontally or vertically. Total maximum length differs between manufacturers from 26 to 40 feet vertically and 26 to 41 feet horizontally. Each manufacturer covers venting in their owner’s manual, which should be consulted during the planning stages prior to installation.
Combustion air should also be planned for as well. If the tankless water heater will be installed in an enclosed space – a closet, for example – an adequate supply of combustion air must be supplied. The Bosch unit has a separate pipe for combustion air. The Rinnai heater has a unique combination vent/combustion air pipe. The Takagi unit requires installation in an area that will provide an adequate supply of combustion air to the appliance or, if in a confined space, with venting (a minimum of two 47-square-inch vents, for example).
All manufacturers recommend 3/4-inch water supply lines for efficient operation of tankless water heaters. Water pressure should be in the 30 to 50 PSI range. Additionally, a special pressure relief valve must be installed on the discharge side of the tankless water heater. Shut-off valves, on both hot and cold supply lines, should be installed to isolate the unit for servicing if required.
Tankless water heaters also require a dedicated 120-volt AC circuit. Electrical power is obviously required to run the onboard computer and the electronic ignition system because there are no standing pilot lights.
Bosch AquaStar (Model 250 SX)
The Bosch AquaStar tankless water heater is a relatively new unit combining German engineering and American technology. It’s available through Controlled Energy Corporation, home centers, hardware groups, catalogs, internet stores and dealers. The 250 SX is a powerful tankless water heater (175,000 Btu/h) and can deliver enough hot water to supply two showers simultaneously. It is about the size of a suitcase weighing 47 pounds, measuring 23-1/2-by-15-3/4-by-8-1/2 inches, and is designed to be mounted to a wall. It has an efficiency rating of 87 percent and can produce up to 384 gallons of hot water per hour. This unit should not be installed outdoors, in motor homes or on boats.
This tankless water heater has a positive-pressure exhaust vent system and a combustion air-intake pipe that can be mounted left or right on top of the unit. Intake and exhaust piping can be installed horizontally or vertically. Gas and water connections are 3/4 inch.
An LCD control panel is located on the face of the heater and indicates the output temperature of water passing through the unit (factory preset at 122 degrees F). To change output temperature simply press the + or – keys until the desired temperature is set from 100 to 140 degrees F in 2-degree increments. A wireless remote control is also available. If hotter water is needed, simply use the remote controller to increase the output temperature of the water.
The main LCD control panel also indicates other functions of the 250 SX. When the unit is in use, a flame silhouette appears on the screen and the temperature indicator blinks. Once the desired output temperature is reached, blinking stops and the unit will continue to supply hot water at the preset temperature. The control panel will also flash error codes if a problem should develop. Error codes and possible solutions are covered in the Owner’s Manual.
An extremely knowledgeable technical support department is available for questions about installation or problems with operation. This tankless water heater has a 12-year warranty on the heat exchanger and two years on parts.
The Rinnai Corporation was established in 1920 (Nagoya, Japan) and is the single largest gas appliance manufacturer in the world with American headquarters in Peachtree, Georgia.
The Continuum is the most powerful Rinnai tankless water heater (180,000 Btu/h) and can deliver enough hot water to supply two showers simultaneously. It is about the size of a suitcase and is designed to be wall mounted. It has an efficiency rating of 87 percent and can produce 213 gallons of hot water per hour.
This tankless heater has a unique combination positive-pressure exhaust/combustion air-intake vent system that is mounted on top of the unit. Intake/exhaust piping can be installed horizontally or vertically. Gas and water connections are 3/4 inch.
The Continuum is preset at the factory to deliver hot water at a constant supply of 120 degrees F. An optional master remote control unit is required to adjust output temperature and must be hard-wired before use. The remote control cables carry a low-voltage, 12VDC digital signal. To increase output temperature, simply press the “H” button until the desired temperature is reached; the range is 96 to 140 degrees F. An in-use indicator light glows when the unit is heating water. The remote control also allows for diagnosing certain fault conditions.
The Rinnai Continuum was the quietest tankless water heater we tested and carries a 10-year limited warranty.
Takagi T-K2 Flash Water Heater
The Takagi Industrial Company began in Fuji-City, Shizuoka Japan in 1946. Takagi introduced their first prototype tankless water heater in 1952. In 2001 they introduced the Flash TK-2 tankless water heater and set the standard for the industry.
The TK-2 is a powerful tankless water heater (185,000 Btu/h) and can deliver enough hot water to supply two showers simultaneously. It can also be used for radiant, Hydro or baseboard heating systems at the same time as supplying domestic hot water. It is about the size of a suitcase, measuring 24-1/2-by-16-1/2-by-8-1/3-inches, and is designed to be wall or floor mounted.
This unit can also be mounted on the exterior of the home. It has an efficiency rating of 82 percent and can produce 178 gallons of hot water per hour.
This tankless water heater has a positive-pressure exhaust vent system that is mounted on top of the unit. Exhaust piping can be installed horizontally or vertically. This unit must be installed in an area where an adequate supply of combustion air is available. Gas and water connections are 3/4 inch.
The Flash Tankless Water Heater is preset at the factory to deliver hot water at a constant supply of 120 degrees F. An optional master remote control unit is required to adjust output temperature and must be hard-wired before use. To increase output temperature, simply press the “Hot” button until the desired temperature is reached. The range of the TK-2 is 99 to 167 degrees F. A ‘burning’ indicator light glows when the unit is heating water. Unique to this controller is an ‘Information’ button. Here, you are able to scroll through incoming water temperature, outgoing water temperature and gallons-per-minute flow. The remote control also indicates error codes, in case the heater develops a problem.
As you can see, there are a lot of advantages to installing a tankless water heater. Homeowners want appliances that are energy efficient, and tankless water heaters certainly fill that bill with up to 70-percent savings in water heating costs per year. Add to that an unlimited supply of hot water and you have a winning combination for any home.