Corrosion in Hot Water System or Bad Water?

Old 09-27-06, 06:44 PM
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Corrosion in Hot Water System or Bad Water?

I am sorry that this is a long and rambling topic, but I need help with my hot water system.

I have both a gas water heater and an electric one. We use very little hot water in the summer so we have the gas service turned off to the house and switch to electric since the minimum gas bill is based on a much higher usage than just the water heater. Even with the disconnect/reconnect charges it is cheaper to have the gas turned off for the warmer seasons until heating is needed again. During the heating season, when the gas furnace is in use, we go back to gas, which is more affordable. We have been doing this for almost 5 years.

This season, when I switched over to the electric heater in spring, the water pressure in the hot water side dropped drastically, and shower heads, washing machine hose filters, etc. on the hot water side frequently plug up. At first I thought it was junk coming in from the city who was doing major pipe upgrades under the streets, but now I assume the stuff is caused by the electric water heater. I was adding a sink and when I opened up a hot water line to install a "T", there is some sort of bright green scale in it. It is hard little blobs about the size of match heads, but they can be dislodged with a little scraping. The blobs remind me of smaller, green versions of sea barnicles. There were no build-ups in the cold water pipes. All pipes are copper and grounding is good on the electric water heater.

The unused heaters are drained when not used and flushed before using each season. I will soon be going back to gas as winter arrives, but would like to know if I need to do something else before shutting down each season or upon start up. I would assume this would be similar to people who have summer or winter homes and shut everything down during the "off" season.

A neighbor thought I should put the heaters in series instead of parallel -- running the cold water from the city into the cold inlet on the gas heater, then taking the hot water outlet from the gas heater and connecting it as the cold water inlet of the electric heater. This way, neither heater would be abandoned and left "empty" during it's off season. The electric heater would be left on-line all year, but in winter, the majority of the heating would be by the gas heater, with the electric heater only maintaining the temperature of water as it stood waiting to be used. A second suggestion from the inspector years ago when this was first installed was to leave the tanks in parallel, but install a small circulating pump of the time used for "instant" hot water. By placing it between the tanks, it would be possible to use the second tank as a storage tank. The disadvantage is that the pump would have to run all year, and since we never run out of hot water now, it seems like either approach would be keeping both tanks warm and would waste a lot of energy.

So my questions come down to this:
1. What is causing the slow-down in hot water and/or the green scale?
2. Does the electric water heater need a new anode rod or other repair?
3. Should a different shut-down and start-up routine be used as the heating load is transfered from one unit to the other?
4. Would a different piping plan help eliminate this problem in the future?

Any input would be greatly appreciated!
Old 09-28-06, 06:41 PM
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Taking the water heaters off line could cause the still water to corrode the anode , and other metal parts. If you are getting a slight rotten egg smell, then the zinc anode is being sacrificed and may possibly need replacing.
I think you should leave both water heaters with full flow of water all the time. You can turn off the electric one whenever you want, and shut down the gas whenever you want, but don't stop the flow of water.
I am not sure the economics of even having an electric water heater is viable with a gas one on line at any given time, but you seem to have done your homework, and if you can figure it out, then that's good.

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