How Efficient Can It Be?

When it comes to condensing water heaters, pretty darn efficient.

Over the past decade or so, it's become clear that while energy efficiency is important when it comes to space heating and cooling, realistically, how water is heated has much more of an impact on energy bills, the environment, and the comfort of homes.

Q: How often do you use hot water? A: Every day.
Q: How often do you heat or cool your home? A: Not every day.
Q: Are there climates where heating and cooling is very light? A: Yes.
Q: Are there climates where water heating is very light? A: No.

Thirty-five years ago, just after the first oil crisis, the single largest portion of the so-called energy pie was the energy needed to heat and cool homes. Water heating made up the third largest portion of the energy pie. Gas, oil or propane water heaters had thermal efficiencies of around 75 percent, but the standby losses were quite large due to minimal tank insulation. Electric water heaters had thermal efficiencies of approximately 98 percent, but, again, the tanks had minimal insulation and standby losses were large. There were few if any tankless water heaters around.

Since then, improvement in efficiency has come from a number of areas including: reducing standby losses, better control of the combustion process, and moving away from standing pilot lights.* Until recently, the most energy-efficient water heater was a gas Tankless Water Heater, which is typically rated as 85-percent efficient. By comparison, a gas Condensing Tankless Water Heater has efficiencies that can be as high as 97 percent.

The Rinnai RC80HPe condensing tankless water heater. You can search for other water heaters in our product directory.

The main difference between a standard Tankless Water Heater and a Condensing Tankless Water Heater is the second heat exchanger. The purpose of the second heat exchanger is to capture the residual heat from flue gases to pre-heat incoming ground water, which then circulates to the primary heat exchanger. With the addition of a second heat exchanger, the unit's final thermal efficiency can be up to 97 percent, meaning less consumption and lower costs.

"With increasing energy costs, consumers are looking for new alternatives to the traditional way of heating water," says Rinnai project manager Tracy Young. "Condensing tankless further reduces the amount of energy needed to heat water while maintaining a specific lifestyle."

While higher efficiency standards proposed for residential water heaters developed by the Department of Energy won't go into effect until 2015, this move by the federal government plus tougher standards for Energy Star appliances points to an inevitable outcome: Water heaters across the board will need to boost their efficiencies considerably. Why not start with the one type of water heater that's already ahead of the curve? That's a Condensing Tankless Water Heater.

For more information on condensing tankless water heaters, take our new continuing education course, Condensing Tankless Water Heaters: Using Propane for the Most Efficient Water Heaters on the Market.


*Source: "The Future of Space Heating Is a Very Efficient Water Heater," June 2010, Contractor Magazine

A version of this story, titled "New Tech: Condensing Tankless Water Heaters," appeared in the August 2010 issue of the Propane Energy Update.

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