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 Mobile ViewWATER HEATERS AGE of WATER HEATERS AIRBOUND HEAT SYSTEM REPAIRS ALTERNATIVE HOT WATER SOURCES Electric Shower Heaters High Efficiency Water Heaters Indirect-fired Water Heaters Instantaneous Water Heaters Multiple water heaters in parallel Multiple water heaters in series Range Boiler Water Heaters Side Arm Coil Water Heaters Solar Water Heaters Tankless Coil for Hot Water Tankless Water Heaters ANODES & DIP TUBES on WATER HEATERS ANTI SCALD VALVES APPLIANCE EFFICIENCY RATINGS AQUASTAT CONTROL Functions BACKDRAFTING HEATING EQUIPMENT BACKFLOW PREVENTER VALVE, HEATING SYS BACKFLOW PREVENTER, HEATER WATER FEEDER BACKUP HEAT for HEAT PUMPS BLEVE EXPLOSIONS BOILERS, HEATING CARBON MONOXIDE - CO CHECK VALVES, WATER SUPPLY CHEMICAL CONTAMINANTS in WATER CHIMNEY INSPECTION DIAGNOSIS REPAIR CLOGGED DRAIN DIAGNOSIS & REPAIR CLOGGED SUPPLY PIPING CROSS CONNECTIONS, PLUMBING DEBRIS in WATER SUPPLY, Water Heater DRAIN a WATER HEATER TANK ELECTRIC WATER HEATERS Electric, Gas, Oil Water Heater Efficiency Electric Shower Heaters Electric Water Heater Checklist Electric Water Heater Controls List Electric Water Heater Element Replacement Electric Water Heater Element Tests Electric Water Heater High Temp Cutoff Test Electric Water Heater Repair Guide Electric Water Heater Reset Switch Electric Water Heater Thermostats Electric Water Heater No Hot Water Electric Water Heater Parts Identification Electric Water Heater Reset & Temp Set Hot Water Temperature & Pressure Valve Timers for Electric Water Heaters Water Heater Anode & Dip Tube Check ENERGY SAVINGS in buildings FLOODED HEATING EQUIPMENT REPAIR FLOODED WATER HEATER REPAIR FREEZE-PROOF A BUILDING FROST HEAVES, FOUNDATION, SLAB GALVANIC SCALE & METAL CORROSION GAS BURNER Flame & Noise Defects GAS FIRED WATER HEATERS DRAFT HOODS - gas fired Gas BTUH & Cubic Feet Gas Conversion LP Natural Gas GAS PIPING, VALVES, CONTROLS SOOT on OIL FIRED HEATING EQUIPMENT SPILL SWITCHES - Flue Gas Detection GAS PIPING, VALVES, CONTROLS HEAT TAPES, Heat, Insulation prevent Freeze-Up HEATING COST FUEL & BTU Cost Table HEATING COST SAVINGS METHODS HEATING SYSTEMS HOT WATER SUPPLY HOT WATER IMPROVEMENTS HOT WATER DELIVERY SPEED UP HOT WATER EFFICIENCY IMPROVEMENT HOT WATER PRESSURE EXPANSION RATE HOT WATER PRESSURE LOSS HOT WATER PROBLEM DIAGNOSIS HOT WATER QUANTITY IMPROVEMENT Alternative Hot Water Sources & Methods Anti-Scald Valves & Hot Water Quantity CLOGGED PIPING & Hot Water Flow Extra Tanks to Increase Hot Water Insulate Hot Water Piping Insulate Hot Water Tank? Larger Diameter Water Supply Piping Water pipe clog diagnosis Water pipe clog repair guide HYDROGEN SULFIDE GAS INDIRECT FIRED WATER HEATERS MANUALS & PARTS GUIDES - HVAC MIXING / ANTI-SCALD VALVES NO HEAT - NO HOT WATER: HEATER DIAGNOSIS NOISE / SOUND DIAGNOSIS & CURE NOISE CONTROL for HEATING SYSTEMS NOISE, PLUMBING CHECKLIST NOISE, WATER HEATER ODORS GASES SMELLS, DIAGNOSIS & CURE ODORS IN WATER OIL FIRED WATER HEATERS PIPING IN buildings, Clogs Leaks Types PLASTIC HEATER VENT RADIANT HEAT RANGE BOILERS RELIEF VALVES - TP Valves on Boilers RELIEF VALVES - Water Heaters RELIEF VALVES - Water Tanks SAFETY, HEATING INSPECTION SCALE REMOVAL, WATER HEATERS SEWER GAS ODORS SOLAR ENERGY SYSTEMS SOLAR HOT WATER HEATERS SOOT on OIL FIRED HEATING EQUIPMENT SPILL SWITCHES - Flue Gas Detection TANKLESS COILS AQUASTAT CONTROL Functions Clogged Pipes / Tankless Coil De-Scale MIXING / ANTI-SCALD VALVES Tankless Coil Conversions Tankless Coil Leaks Tankless Coil Hot Water Increase TANKLESS WATER HEATERS Electric Shower Heaters Guide to Tankless Water Heaters Operation & Characteristics Problems & Defects Hot Water Delivery Speedup Installation Requirements & Costs Should I Convert to a Tankless Heater? Calculate Water Heater Requirements Capacities of Tankless Water Heaters Life Expectancy & Applications Temperature Pressure Relief Valves - Water Heaters THERMOSTATS, HEATING / COOLING THERMOSTATS, WATER HEATER AQUASTAT CONTROL Functions Electric Water Heater Thermostats TIMERS for ELECTRIC WATER HEATERS VALVES, PLUMBING WATER CONTAMINANT LEVELS WATER HAMMER NOISE DIAGNOSE & CURE WATER HEATERS WATER HEATER ALTERNATIVES WATER HEATER ANODES, DIP TUBES WATER HEATER AIR INLET WATER HEATER DEBRIS FLUSH WATER HEATER DRAIN PROCEDURE WATER HEATER EFFICIENCY WATER HEATER FLUSH PROCEDURE WATER HEATER NOISES WATER HEATER PROBLEM DIAGNOSIS WATER HEATER PROPERTIES Electric, Gas, Oil Water Heater Efficiency Water Heater Life Expectancy Comparisons Water Heater Operating Cost Comparisons Water Heater Purchase & Maintenance Costs Water Heater Water Quantity Comparisons Water Heater Recovery Speed Comparisons Water Heater Safety Comparisons WATER HEATER EFFICIENCY WATER HEATER SCALE - De-Liming Procedure WATER HEATER SCALE PREVENTION WATER HEATER SAFETY WATER HEATERS for HOME HEATING USE? WATER ODORS, CAUSE CURE WATER PIPES, Clogs Leaks Types WATER PRESSURE & FLOW MEASUREMENT WATER PRESSURE VARIATION CAUSES WATER PRESSURE TOO HIGH: DANGERS Definition of Static Water Pressure Definition of Dynamic Water Pressure Measure Municipal Water Pressure Measure Pump & Well Water Pressure WATER FLOW RATE MEASUREMENT HOT WATER PRESSURE EXPANSION RATE WATER PRESSURE GAUGE ACCURACY WATER PRESSURE LOSS DIAGNOSIS & REPAIR WATER PRESSURE REDUCER / REGULATOR WATER PRESSURE REPAIR GUIDE - WELLS WATER PUMPS, TANKS, TESTS, WELLS, REPAIRS WATER PUMPS & WELLS WATER PURIFIERS WATER QUALITY TESTS, CONTAMINANTS, TREATMENT WATER QUANTITY IMPROVEMENT WATER SOFTENERS & CONDITIONERS WINTERIZE A BUILDING More Information |
This article explains the operating characteristics of tankless water heaters, also called instant water heaters or "on demand" water heaters. InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers nor with topics or services discussed at this website.© Copyright 2010 InspectAPedia.com and Carson Dunlop Associates, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website. A Guide to Tankless Water Heaters
The original text of this article was 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. Our OPINION is that readers looking for plenty of hot water heated efficiently should also consider the heater we describe at Indirect-fired Water Heaters. A tankless water heater saves energy by turning off completely when no hot water is being drawn - there are no standby losses - no tank of hot water needs to be kept hot when hot water is not being used. Sketch of a point of use tankless water heater (at left) courtesy of Carson Dunlop. Although some instantaneous water heaters can provide up to 9 GPM (and use 200,000 BTUH), smaller units cannot provide very large hot water flow rates in gallons per minute. If the hot water usage rate is expected to be high, a very high BTUH unit (efficient but not necessarily economical) or multiple smaller point of use tankless water heaters may be needed to satisfy all building occupants and uses. Consumer Reports points out that a tankless water heater may be efficient but not necessarily economical to operate. What they mean is that it is certainly efficient to avoid heating water when no one is using it. But if water usage is high, a high-BTU tankless water heater may consume more total energy than a large but more conventional oil or gas fired hot water tank and burner. Tankless Water Heater Operation & Characteristics
No stored hot water means no standby losses, and, if you match the heating capacity of your tankless heater to your hot water flow rate requirements, there is no delay in hot water supply and no running out of hot water. The Instant-Flow® water heater shown is a Model S-48L/240 240-volt unit rated at 4800 watts and is installed on a 20-A electrical circuit. Tankless heaters are supplied in all-electric models (shown here) and gas (or possibly oil) fired units that include a burner, heat exchanger, venting system, and the necessary controls. When a hot water faucet is opened or the dishwasher or clothes washing machine calls for hot water, the tankless heater detects the water flow and ignites the burners. These powerful burners quickly heat the water inside the small diameter heat exchanger. As hot water is drawn out, fresh cold water is drawn in and the cycle continues. A significant advantage of this system is that you can't empty all of the hot water out of the tank because there is no tank - just continuous hot water. No Stored WaterThe other major advantage over conventional water heaters is energy savings. Tankless water heaters have no large reservoir of water that has to be kept hot around the clock in case hot water is needed. One side effect of the lack of storage is that all of the water in the system is cold when the system has not been in operation recently. When a hot water faucet is operated, it may take more time for hot water to be delivered than in a conventional system. Small Size
However for non-electric tankless heaters, the burner on a tankless or demand water heater must be much larger than on a conventional heater since it has to instantly heat incoming cold water to its target hot temperature. Tankless Water Heater Fuel and VentingMost tankless water heaters are either electric, or they are fueled by natural gas or propane and are vented through a side wall of the house. As Rheem points out, "The venting must be Category III, Stainless steel, and it applies to the adapter, the vent pipe, all elbows, and terminal vent. This is important because the flue gases and by-products of combustion can cause condensation. Stainless steel will not deteriorate like type B venting under these conditions." Tankless Water Heater EfficiencyTankless water heaters are often much more efficient than conventional water heaters, using modulating burners, direct venting and/or condensing combustion systems. Mixing Valves / Flow Control Valves used on Tankless Water Heaters
In one sense, there should be no need for a tempering valve, since we do not need to keep the reservoir water at 140° to prevent Legionnaires Disease. On the other hand, since we don't know the flow rate of the water through the heater, the tempering valve may be needed since the burner cannot modulate to deliver exactly the temperature we want due to the infinitely variable water flow. If the flow rate is low, the water moves more slowly through the heater, and picks up more heat from the burner. Tankless Water Heater Remote ControlSome tankless systems include a remote control, which can be used to monitor the performance of the system, display error codes or change the desired water temperature. List of Tankless Water Heater Manufacturers & Brands
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