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Tankless water heater - a not so hot idea

By Meg Sorrell
Posted Wednesday, January 31, 2007

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Chapel Hill, NC - We were totally in love with the idea with a tankless hot water heater. Just heat the water you're using when you use it, not a whole ginormous tankful all the time. Yep. In *love* -- what a great idea! I couldn't wait to start saving money!

Very expensive -- to buy, to install and to repair. Our unit cost $500, installation was almost $800. But we were sure we were saving soooooo much money buying propane instead of paying a higher electric bill. (That was also before the price of propane went so high after the hurricanes.)

In January of 2005, we came home to a kitchen flooded with water -- "hot" water! With water flowing through the broken unit, the burners continued to fire until we got home. Not pretty. The unit, though installed indoors, had frozen in the restricted copper tubing that makes up the heat exchanger. It had been very cold, and the heavy, frigid air settled down the vent pipe (which should have had a horizontal run and a flapper) causing the unit to freeze. Our pipes never froze, only the HWH heat exchanger froze. With a conventional system, this would never have happened.

Here's another scary quote from the Bosch installation manual: "...there may still be a risk of freezing due to negative draft if all the combustion appliances in the area are not being supplied with a sufficient amount of make-up air. A wood stove or furnace can rob the make-up air in the AquaStar's vent pipe, leaving the cold infiltrating air capable of freezing the cold water in the AquaStar heat exchanger." Guess what -- we use a wood stove.

We had the unit repaired and proceeded to replace the kitchen sub floor and floor and the insulation under the kitchen. In December of 2006, as we got our first cup of coffee on a Saturday morning, the unit ruptured again -- frozen again. Thankfully we were home to stop the well pump immediately so that no further damage to the interior of our home occurred.

Our initial response was to start shopping immediately for a replacement unit (same model). I believe that we were extremely lucky to be unable to find such a unit -- we would be out another $500 (or more) to buy the unit and some smaller amount to have the new unit installed. And we would have been left with the exact same vulnerability.

Instead, we bought a conventional water heater for $250, and did the installation ourselves. We're happy not to have that winter worry anymore, and we would rather pay a higher electric bill than continue to worry about flooding our kitchen.

It seems that you would save money by not heating water all the time, but I'm not so sure that is true. When the unit fires, it uses a "lot" of propane. People tend to take longer showers because 1) they will not run out of HW, and 2) they don't feel guilty because they're not keeping a tank of water hot all the time. The fact that the burners are only on when you're using water is sort of meaningless -- electric tank units do not run constantly either, but rather cycle on and off. I would also rather not have a propane bill in the summer -- you will use hot water every month of the year.

The "endless hot water" was nice, I'll admit... but I've not yet run out of hot water using our new conventional tank. There are only two of us, though, and I understand the teenager thing. One other little problem -- with the Bosch, it was harder to get the correct mix of hot/cold. If the flow through the HWH drops too low, the burners go off and you suddenly have only cold water. OTOH, with the electric tank it is just a matter of getting the mix to your liking.

We were absolutely thrilled to get on-demand hot water, but now, having been through these experiences, I would never, ever recommend this unit to a friend. On an online bulletin board I read, one plumber said regarding on-demand HWH: "There are two great days: the day you hook up your on-demand hot water heater and start using it; and the day you take it out and replace it with a conventional system." His words certainly ring true to me.

I was sad to have to let my disillusions die, but we had to move on.

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Tankless water heater - a not so hot idea

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