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• An owner's guide to installation & costs of tankless water heaters - hot water on demand
• Tankless water heaters = demand water heaters = instantaneous water heaters
• Detailed explanation of how tankless hot water heaters work, what they cost, what are their operating characteristics, pro's and con's.

Here we discuss the special installation requirements, purchase & installation costs, & operating costs of of tankless water heaters, also called instant water heaters or "on demand" water heaters.

Readers should also see ALTERNATIVE HOT WATER SOURCES to distinguish among these types of hot water producing systems. Portions of this article were provided courtesy of Carson Dunlop - that text has been edited and may not entirely reflect CD's views. Page top sketch of a point of use tankless water heater courtesy of Carson Dunlop.

© Copyright 2009 Daniel Friedman & Carson Dunlop Associates, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

Installation Requirements & Operating Cost of Tankless Water Heaters

As we discussed at Problems & Defects, conventional water heaters are relatively inexpensive due to their simplicity while tankless water heaters are more expensive to purchase and install.

In 2009 in Toronto, Ontario a high capacity instantaneous water heater installation could cost $4000. CDN. Their complexity also means that maintenance and repairs can be more expensive.

Dedicated isolating valves help simplify draining and other regular maintenance.

Below we discuss some of the special requirements for installation of tankless water heaters, followed by a discussion of the operating cost of tankless water heating systems.

Minimum Hot Water Flow Rate for Tankless Water Heaters

The burners are triggered by sensors that detect the flow of water. If the flow of water is too low, typically less than ½ gallon per minute, the burners will not turn on and no hot water will be delivered.

Water-saving shower heads, for example, may not allow enough flow to turn the water heater on, especially when the water heater has a high minimum flow rate. Rheem, for example, requires a .66 GPM flow rate to ignite the burner. (This is probably to avoid overheating in the heat exchanger.)

High Elevation Requires Special Modification for some Tankless Water Heaters

Some tankless water heaters may not operate properly at high elevation installations. Some manufacturers address this specifically. For example, all Rheem tankless water heaters can be programmed to operate at elevations up to 9,840 feet.

Tankless Water Heater Relief Valve

The temperature/pressure relief valve lets water escape if the temperature or pressure is too high. This valve should be connected to a tube that discharges no more than six inches above floor level so hot water won't scald anyone nearby.

Some codes require that the tube discharge outside the building. The tube should be as large as the tank fitting and the tube end should never be threaded, capped or plugged.

The tube should be able to withstand 250°F temperatures, should have no shut-off valve, and should be as short and as straight as possible.

Combustion Air for Gas-Fired Tankless Water Heaters

Inspecting several rental properties owned by the same landlord we found that the plumber she used to install tankless water heaters at multiple apartments didn't realize that each gas fired unit needed combustion air.

Each tankless water heater had been installed on an exterior wall and to avoid tenants fooling with the heater, the plumber enclosed each unit in a steel box with a lock.

The tenants complained of gas odors and of constant loss of hot water. Because the units were installed outdoors the dangerous carbon monoxide that was being produced had not resulted in a catastrophe.

LP to Natural Gas Conversion for Tankless, Demand, Instantaneous, or Point of Use Water Heaters?

Be careful. At least some demand water heaters (such as those made by Rheem) are sold in models designed for a specific fuel such as Natural gas OR LP Gas. These units cannot be converted from LP to Natural Gas or vice versa. So be sure you are specifying the proper model and fuel type when buying a tankless water heater.

Operating Costs For Tankless Water Heaters

Tankless water heaters are considerably more expensive than conventional tank-type heaters, and although tankless units are more energy efficient, it may take a long time to recoup the extra investment.

As we mentioned above, people pay up to $4000 for these units installed (February 2009).

Consumer Reports points out that a tankless water heater may be efficient but not necessarily economical to operate.

The organization reported that tankless water heaters cost $800 to $1,150, compared with $300 to $480 for a conventional tank type electric water heater.

We pose that this gap may also need adjustment for differences in installation cost and equipment life. (Tankless units may need higher maintenance.)

Unexpected Instantaneous Water Heater Installation Costs

One of the issues is that the large burners require larger gas piping. In some cases the gas piping into the house is not large enough to accommodate the other appliances plus the tankless water heaters. The requirement to install new gas piping adds considerably to the installation cost.

There are also often challenges about where venting can be placed. Exhaust cannot terminate close to building openings, close to air intakes, at inside building corners, too close to grade, etc.

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

  Tankless Water Heaters
    Guide to Tankless Water Heaters
    Operation & Characteristics
    Problems & Defects
    Hot Water Delivery Speedup
    Installation Requirements & Costs
    Should I Convert to a Tankless Heater?
    Endless Hot Water?
    Calculate Water Heater Requirements
    Capacities of Tankless Water Heaters
    Life Expectancy & Applications

• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Consumer Reports offers an article on the efficiency versus the economy of tankless water heaters - see http://www.consumerreports.org/cro/appliances/heating-cooling-and-air/water-heaters/tankless-water-heaters/overview/tankless-water-heaters-ov.htm
• Bosch Tankless Water Heaters - http://www.boschhotwater.com/
• Chromolite Tankless Water Heaters
• Bradford White Everhot Tankless Water Heaters - Bradford White offers this step by step hot water retrofit installation file (large, slow PDF) - www.bradfordwhite.com
• Eemax Tankless Water Heaters - http://www.eemaxinc.com/
• Noritz Tankless Water Heaters - http://www.noritz.com/
• Rheem Tankless Water Heaters - http://www.rheemtankless.com/content/
• Rinnai Tankless Water Heaters - http://www.rinnai.us/tankless-water-heaters/
• Stiebel Eltron Tankless Water Heaters - http://www.stiebel-eltron-usa.com/
• Takagi USA Tankless Water Heaters - http://www.takagi.com/
• Titan Tankless Water Heaters - http://www.titanheater.com/
• U.S. Department of Energy on Tankless Water Heaters - http://apps1.eere.energy.gov/consumer/your_home/water_heating/index.cfm/mytopic=12820

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