Thursday, January 15, 2009

Hot water.

Reinventing the wheel is sometimes a good thing- like with tanked hot water heaters. I am not a fan of tankless water heaters (they are either terribly inefficient or prohibitively expensive) and I wanted to have a storage tank so that we could add solar-heated water as a future project. However, traditional tanked water heaters are usually poorly insulated and have a limited lifespan (I hate seeing the pile of hot water heaters at our local landfill). There are some well-built models on the market, but they are crazy expensive. Then I found the HH20 water heater ( and just installed ours this week. While it looks like the same old tanked water heater, it actually uses a heater exchanger (the finned copper coil) to transfer heat from the tank to the plumbing. Since this design keeps the water in the tank separated from the water you actually use, the tank is not pressurized and (in theory) should never burst or leak. So the unit can be built inexpensively using a plastic tank and 2.5" thick insulated walls- very efficient and very durable.
Once the lid is put on, a single 3500W electric heating element extends down the center of the coil to heat the tank water. We also purchased a heat pump retrofit kit (, which will be installed in the spring so that we can heat the water more efficiently and use the exhaust air for home cooling...more on that later. Since the tank is not pressurized, I can also modify it to accept solar heated water when we get to that phase in the future. We paid $350 for the heater- a little more than buying a conventional tanked electric heater, but a great price for the benefits of this design.


Jennifer said...

Interesting! How does it's efficiency compare to a natural gas tank? How is the water pressure?

Gene said...

Very interesting! The pressure should be fine, I think (assuming you have decent pressure normally). Going through the coils won't cause much of a drop-off. The main downside would appear to be the need for periodic maintenance (i.e., checking the water level).

Shawn said...

Jennifer, the electric water heater itself is 100% efficient, compared to typical gas heaters at 75-85% efficiency (There are some gas water heaters today that are well into the 90+% efficiency range, however). I can't speak for your area, but here in MN natural gas would be a significantly less expensive heating option due the much lower fuel cost- even after factoring in the lower efficiency. However, we have chosen to go with an all-electric home to best support the renewable energy industry (right now, by purchasing wind credits to offsset our electricity useage).
As for your question about water pressure, Gene is correct in that it would not be noticeably affected by the HH20 water heater- the internal heat exchanger coil is just an extension of your existing plumbing lines.
The other feature that attracted me to the HH20 water heater is its smaller, well-insulated plastic tank. It should not wear out, and the 2.5" of insulation will improve the efficiency by reducing 'standby losses" while the hot water is not being used.