by David Emmitt

Ever wonder what it would cost to leave your car running in the garage all night, just so it would be warm when you leave for work? Or to keep your thermostat at 65%F while you’re on summer vacation, just so your house would be cool when you got home?

These examples of wasted energy are akin to your water tank churning all day when nobody is there to use the water, and all night while you’re asleep. The energy generated by your water heater (at a miserable 60-percent efficiency) is lost through the jacket and chimney, along with the energy created by the water’s natural cooling. These “standby losses” are excessive and unnecessary.

Water tanks also accumulate sediment, which further reduces their already-poor efficiency. By design, a water heater is nothing but a big water kettle with a heat-exchange tube running up the middle to remove flue gases.

In 2004, energy standards mandated by the National Appliance Energy Conservation Act were finally applied to water heaters. You’ve probably seen these ratings on other appliances, like air conditioners—going up to 13 SEER (seasonal energy-efficiency rating) this year—and furnaces boasting 80-percent AFUE (annual fuel utilization efficiency).

But the only way to apply these standards to water tanks was to thin the appliance wall, the government determined. While this improved efficiency by 1.5 percent, all manufacturers had to retool to achieve this minimal increase, causing the cost of water heaters to rise. It also reduced the life span of new water-heater tanks to a mere five to seven years.

So, for an average yearly energy savings of less than $10, a new water heater will now cost more and last half as long as an old one. Plus, water-heater tanks can flood when the bottom drops out or the side splits from a faulty relief valve.

Sweeter Solution

So what’s the alternative? A tankless water heater is a popular option in many countries because a lot of buildings and homes don’t have the space or energy to waste on a tank of water that heats up 24/7. Tankless water heaters never run out of hot water, so why pay to constantly heat water at 60-percent efficiency when you can heat it once at 85 percent and never run out?

Tankless water heaters are roughly the size of a microwave oven and most mount on the wall. As component systems, they have parts that work together to heat water. Every part, including the heat exchanger, can be easily and inexpensively replaced.

Most tankless systems easily handle two showers with 40%F incoming water at high altitude. Much more than that, and the water will go cold or the flow will decrease, depending on the tankless brand. Those two showers can be taken forever, however. So if you have six people needing showers, you can take two at the same time, then two more, then two more. Most water tanks heating two showers at the same time would run out in about 10 minutes and take 20 minutes to reheat. A tankless system supplies hot water indefinitely.

And, if you have a hot tub, even two water tanks would have a hard time filling it. A tankless system can fill a hot tub with 330 gallons of water or more heated at 85-percent efficiency.

Avoiding Surprises

When homeowners understand how a tankless system works, they may be disappointed at first. To keep water hot all the time, a hot-water tank “thermally siphons” continuously. Therefore, it takes less time for a water tank to deliver hot water. A tankless system has to fire up first and heat both the water and the pipes. With a water tank, the pipes are already hot. So a tankless system typically has a 50-percent-longer lag time than a water tank.

However, this problem is easily corrected with a recirculation system, like the Metlund D’mand system (gothotwater.com). Tankless systems also require a minimum flow to activate them, which means you may not be able to trickle water in the sink and still get hot water.

Going tankless is still the wise thing to do, but you should be an informed buyer. Any system you choose should have at least three-gallons-per-minute flow at a 70-degree rise at this altitude, or you won’t get the flow you need. Also, be sure the unit is freeze-protected, even if it’s mounted indoors. A non-freeze-protected tankless system can freeze simply from cold air blowing across the heat exchanger when the furnace is operating.

Additionally, most tankless systems cannot utilize the existing water-heater vent, and require either sealed-combustion venting or additional combustion air. They also may need a larger gas line, buffer-pipe, service manifold with ball valves and boiler drains, and professional installation by qualified personnel—not simply a plumber.

The average payback for a tankless water heater is five to seven years in energy savings. Prices range from $800 to $1,700, depending on the product, and installation costs upward of $500.

More for Your Money

Integrating a tankless system with a forced-air furnace creates additional energy savings. When a furnace is converted, the burner, heat exchanger and gas valve are removed, and a hot water coil (similar to a car radiator) is installed inside the furnace. The unit’s forced-air fan and some controls are retained, but otherwise the furnace now lacks any combustion gases or flame.

Converted systems are safe and reliable, and furnace flues and combustion air holes are eliminated, which makes the building more energy efficient by dispelling air-infiltration sources. It also eliminates gas-fired heat exchangers that can create noxious gases.

After conversion, when the thermostat calls for heat, water from the tankless water heater is pumped through the coil and back to the tankless water heater. This circulation activates the water-heater burners, increasing the water temperature to 140% to 150% F. The burners produce just enough BTUs to keep the water hot, but no more, thereby avoiding waste. The fan on the hot-water air handler then switches on and produces warm air that’s not as dry as a standard furnace’s.

This gentler heat source will likely never need maintenance, with the exception of fan servicing and filter replacement, and the cartridge pump is easily repaired if it fails. The heat produced is at the tankless system’s 85-percent efficiency and does not affect the amount of hot water available for domestic use.

Overall, a tankless water heater is the most efficient choice for green-minded homeowners. It’s a system that countries in Europe and Asia have employed for years. Now it’s time for America to incorporate this proven technology into its homes and commercial buildings. Besides, wouldn’t it be great to never again hear, “Hey, you used up all the hot water!”?

David Emmitt is owner of Direct Drive Service Inc. and Go Tankless of Colorado, and a member of the Boulder Green Building Guild. Call 303-546-0448 or visit www.go-tankless.net for information.

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