Tankless Hot Water Heater Buying Guide

There are several different makes and models to choose from and mostly you will need to determine the correct size for your home and lifestyle. If your water consumption is moderate, that is if there are three or four people using hot water at different times, you will want a moderate size heater. However, if you are using massive amounts of hot water, like running two showers, a dish washer, and/or clothes washer at the same time, you will require a larger, more powerful system. The best way to determine the size of hot water heater you need it to know how many devices you will be using at the same time. For instance, if you regularly use the shower, while washing clothes or dishes, then that is two devices. Or if you use two showers regularly at the same time, then that is also two devices. You may use a shower and the sink, and it would still be one device, as the sink does not take up as much water as a dishwasher. Then you need to know the average temperature of the water for each device. The chart below will help:

Device Avg. Temp.
Tub 102 F
Shower 104 F
Washing Machine 120 F
Dishwasher 110 F
Kitchen Sink 110 F

Then you will need to know the average temperature of the ground water, which varies by region as well as season. However, the average ground water temperature in the United States is 55°. In the southern part of the US the ground water temperature is slightly higher at 60°.

By knowing these two temperatures you will then be able to estimate the average rise in temperature that you will need. For instance if you live in Dallas, Texas and you want to run your washing machine your water will need to rise at least 60°. The chart below is based on this rise, and how many gallons per minute the heater can produce.

If you are considering purchasing a tankless hot water heater, you will also need to decide if gas or electric is appropriate for you. The best way is to look at your existing system. If you have a gas hot water heater currently, you will need to purchase a tankless gas heater. There is one other consideration when purchasing a gas hot water heater, that is, the vent system for a tank type gas hot water heater is considerably different from the tankless. A Tankless system requires installation by a certified plumber and electrician, because of the intricacies of water, electric and/or gas routing. This adds to the initial cost of the unit and it may take several years before it pays for itself. This is not the case when it comes to electric. Although an electric hot water heater may require installation by a certified electrician, because of the need for additional breakers and specific amperage requirements. Be sure that you always check your local codes, before starting any work of this sort.

A gas powered hot water heater will produce a greater temperature rise faster than an electric one, thus the water will be hotter sooner as it arrives at your shower. Also, you must remember, the water is not instantly available, it will take the same amount of time to travel through your pipes and possibly cool the same amount, as any other system.

Model Comparison

Make and Model // Temperature Rise // Number of Devices in use at the same time // Energy Efficiency // Ignition Type // Outside Vent // Price

GAS
Bosch 1600P // 65° F rise @ 2.9 gpm // 1 device // 78% // Pilot // yes // $659.00
Bosch 1600H // 65° F rise @ 2.9 gpm // 1 device // 80% // Hydro* // yes // $629.00
Bosch 2400E // 65° F rise @ 4.5 gpm // 2 devices // 87% // Electronic // yes // $999.00
Rheem RTG-53PVN // 60° F rise @ 3.9 gpm // 1-2 devices // 82% // Electronic // yes // $669.00
Rheem RTG-74PVN // 60° F rise @ 5.5 gpm // 2-3 devices // 82% // Electronic // yes // $829.00
Rheem GT199DVN // 60°F Rise @ 5.5 gpm // 2-3 devices // 82% // Electronic // yes // $999.00 --commercial

Make and Model // Temperature Rise // Number of Devices in use at the same time // Energy Efficiency // Power Requirements // Price

ELECTRIC***
PowerStar AE115 // 60° F rise @ 1.9 gpm // 1 device ** // 95% // 2 - 40 amps breakers // $499.00
PowerStar AE125 // 60° F rise @ 3.0 gpm // 1 devices // 95% // 3 - 40 amps breakers // $699.00
Stiebel Tempra 24 // 60° F rise @ 2.75 gpm // 1 device // 94% // 2 circuits, 2 - 60 amp breakers // $529.00
Stiebel Tempra 29 // 60° F rise @ 3.25 gpm // 1 - 2 devices // 94% // 3 circuits, 3 - 50 amp breakers // $679.00
Stiebel Tempra 36 // 60° F rise @ 4.2 gpm // 2 devices // 94% // 3 circuits, 3 - 60 amp beakers // $689.00

*The Bosch Aquastar hydro-generated ignition system requires no pilot, batteries or electricity.
** Warm Water Areas Only - where ground water temperatures average above 60° F
***Installation Requirements 220 -240 Volts

The advantage of a tankless system is not in the speed of delivery, or temperature of the water, it is the energy savings that come from the same water is not being heated over and over again.