Q: I thought about replacing my old gas water heater with a tankless one to save money. I heard there is limited hot water from a tankless one and the hot water temperature varies. What is your opinion?
A: I would recommend a gas tankless water heater for almost every home because of the significant energy and utility bills savings as compared with a traditional tank-type model. The EFs (energy factor) on the most efficient tankless models are as high as 0.95 as compared with only about 0.65 for a new tank-type gas model. The tankless units are small and hang on the wall.
The hot water output from any tankless water heater, gas or electric, is limited in one sense, but unlimited in another. Let me explain this using a gas model as an example. A tankless water heater has a very large burner to heat the cold water as it is being used from any faucet. Some of the highest hot water output models have almost 200,000 Btuh gas burners.
If the water entering your house is 70 degrees and you heat it to 120 degrees, a 200,000 Btuh tankless model can produce about 6.6 gpm (gallons per minute) of hot water. As long as your family doesn't require more than 6.6 gpm of hot water at any time, the hot water is limitless. This means your family could take 50 consecutive showers and not run out of hot water.
On the other hand, if your family tries to take two showers, wash dishes and wash clothes simultaneously, this may require more than 6.6 gpm of hot water. In this case the water may not be heated all the way to 120 degrees. By staggering high hot water usage tasks a little, this is never a problem.
In the early days of tankless water heaters, the hot water temperature at the faucet would vary. Today's tankless water heaters, both gas and electric, have modulating heating capacity to produce steady temperatures. This means when only a trickle of hot water is needed, such as when shaving, only a small amount heat is produced. Some models with a maximum capacity of 200,000 Btuh modulate as low as 11,000 Btuh.
Tankless water heaters are significantly more expensive to purchase. They also often require a new larger gas line or electric wiring and breakers. However, if you purchase a gas tankless water heater with an EF of .82 or higher, it qualifies for 30 percent tax credit on your federal return and there may also be additional state and local tax credits. Also, a tankless water heater can be repaired if it ever leaks or fails.
The newest gas tankless water heater design uses two heat exchangers similar to super-efficient gas furnaces. The primary heat exchanger transfers the most heat to the water. The secondary heat exchanger, often made of stainless steel, condenses the flue gas vapors to release more latent heat. This heat is used to preheat the incoming cold water.
Send inquiries to James Dulley, St. Petersburg Times, 6906 Royalgreen Drive, Cincinnati, OH 45244 or visit www.dulley.com.