Reddit reviews Corro-Protec CP-R Water Heater Powered Titanium Anode Rod (40-89 Gallon Tank) - Eliminate Odor (Sulfur/rotten egg smell), Corrosion and Reduce Limescale

Full disclosure - my day-job is a research microbiologist and my lab works on anaerobic bacteria.

Your water heater has something called a sacrificial anode rod in it that is electrically contiguous with the steel tank. This anode is made from a less noble metal than iron; as a consequence, the anode is more reactive and sacrifices itself to oxidation preventing the steel tank from rusting away (rust is iron oxides).

Anodes are typically made from magnesium with a steel core. Here's where anaerobic bacteria come into the picture. They are present in municipal water supplies, and some of them thrive in an environment that is around 120-130^o F. Many of the enzymes they need for their growth are dependent on divalent cations - especially magnesium, the material the anode is made of. The anaerobic bacteria enter your tank with the municipal water supply and establish themselves in this niche. As indicated by u/wtfgolf4fun, the product of anaerobic respiration is hydrogen sulfide, which smells like rotten eggs.

There are two things you need to achieve:

• Get rid of the bacteria (and therefore the smell)
  
• Prevent the smell (and bacterial growth) from happening again
  
  Let's start with getting rid of the bacteria. Cut the power to the water heater. Remove the existing anode rod. Drain the tank. Add 3-4 gallons of drug-store hydrogen peroxide (3%) and let it sit for 1-2 hours. Then drain the hydrogen peroxide as well.
  
  Next, how to prevent the smell from re-occuring. Aluminum and Zinc are also less noble than steel, and are not used effectively as divalent cations to support the growth of anaerobic bacteria. You can replace the magnesium anode with one made from aluminum or zinc. There are also permanent electrically powered anode rods; these run around $100, and will last the lifetime of your tank (~20 years).
  
  In addition to changing the anode with an aluminum/zinc/powered anode, you should also raise the temperature for the upper and lower thermostats to 140^o F. This is high enough to kill >99.9% of the anaerobes typically present in municipal water supplies. If you do this, be aware that the higher temperature can scald. To prevent that from happening, you should install a water heater tank booster - so that the water temperature at hot water faucets remains 120^o F.
  
  When you're all done, make sure the water heater is filled with water (i.e. cold water comes out of all hot water faucets) before restoring electric power to the heater.

Let's do some math, and see what your water usage is costing you now. I'm going to assume you're not doing laundry with hot water, if you are, stop. Just turn off the hot water to the washer, you don't need it. I'm also going to assume 10 minute showers each, and a load of dishes every two days. And I'm going to assume you have fairly typical equipment, 2.5gpm shower heads and a standard water heater.

An electric water heater with a 3000W element can typically heat 13.1 gallons of water/hour from 50degF to 140degF. [Water heater recovery rate = watts / (2.42 delta t).] And a fairly typical water heater losses about 70watts to standby losses.

So, two 10 minute showers at 2.5 gallons per minute is 20m 2.5gpm = 50 gallons for shower. And lets say another 5 gallons per day for the dishwasher. That's 55 gallons per day.

55gallons / 13.1gallons/hour = 4.20 hours per day that your water heater needs to run to heat that amount of water back up. 4.20 hours $0.0962/kWh 3kW = $1.21/day to heat that water. Add in 0.070kW 24 hours $0.0962 = $0.16 dollars per day in standby losses, for a total of $1.37 per day to run your hot water heater. $1.37 365 / 12 = $41.72/month for hot water.

Now, lets see what can be done with that for much cheaper than the other options you listed.

I have a low flow shower head that I would easily recommend, it's 1.25gpm. You can find them on amazon.com for $8.00

That alone will reduce your usage from 55 gallons per day to 30 gallons. So those calculations then become 30gallons / 13.1 gallons per hour 3kw $0.0962 per kWh = $0.66/day or $24.99 per month.

A drain water heat recovery unit gets more efficient the lower the flow rate is. Lets say that at 1.25gpm a 42inch model is 50% efficient, it's likely better than that, but we'll call that good enough. But lets also consider the temperature losses from the water heater to the drain about 20 degrees F. 140 deg F - 50 deg F = 90 Deg F delta T. 90 deg F - 20 deg F (losses) = 70 deg F. 0.5 70 deg F = 35 deg F 90 deg F - 35 deg F = 55 deg F. So your new delta T with a smallish drain water heat recovery unit is now 55 deg F when water is flowing in both directions through it.

3000/(2.42 55 deg F) = 22.5 gallons per hour that your water heater can now make when showering.

Now your usages will cost: 30 gallons / 22.5 gallons per hour 3kW $0.0962 per KWh = $0.385 per day or $11.7 per month. With a total of $28.3 per month.

Now lets talk about those standby losses. You can get an R10 water heater blanket that will most likely double the insulation on your water heater. Add R10 worth or rigid foam insulation under the water heater to complete the envelope, and heat traps to slow the flow of heat up the pipes, and that should reduce the standby losses by half. So, $0.16 / 2 = $0.08 /day.

With those things, that would effect any water heater and can stay with the house and not with the water heater, you're now looking at $22.53 per month, a savings of $19.2 per month.

Then, you sit back and wait for mini split heat pump water heaters to make it big in North America and then you upgrade. Or just use solar panels to supply that much smaller amount of power you now need to heat water with a traditional electric water heater.

I'd also recommend a powered anode because changing the anode is a pain in the ass, and insulating your water pipes as much as you can.


*I did the calculations for the drain water heat recovery unit while I waited for the American homedepot site to load so I could get a relevant link only to find they don't list the same 42 inch version I'm putting in my place. I'll let you figure out which one to get and where

**If your showers are longer or shower, hotter or colder, than I calculated for, that will obviously impact the number quite a lot.

Look into replacing the anode rod in your hot water tank with a powered titanium rod. We just moved into a house we well water that smelled strongly I sulfur. I shocked the hot water tank with bleach (and then flushed thoroughly afterward) but also switched out the anode rod. I guess the corroding metal of the usual magnesium/aluminum produces a lot of hydrogen which leads to the production of hydrogen sulfide which is the rotten egg smell

Corro-Protec CP-R Titanium Powered Anode Rod for Water Heater (40-80 gal tank) https://www.amazon.com/dp/B01H459TAK/ref=cm_sw_r_cp_apa_vHpVBbGD1GMJ1

I had success with replacing the anode rod with a powered anode

Corro-Protec CP-R Water Heater Powered Titanium Anode Rod (40-80 Gallon Tank) - Eliminate Odor (Sulfur/rotten egg smell), Corrosion and Reduce Limescale https://www.amazon.com/dp/B01H459TAK/ref=cm_sw_r_cp_api_i_MU-jDbQV01TQ3

I also drained a few gallons from the water heater and put in about a gallon of bleach right before I placed the new powered anode