Reddit reviews Frost King SP57/11C All Season Water Heater Insulation Blanket, 3” Thick x 48” x 75”, R10

That's what they're called. Water heater blanket and water heater insulation pad. They sell them on amazon and at home depot. You just need to measure your heater to make sure you get the right size. Most of the blankets are 'universal' cut to fit, so it's more of a question of how thick to get it.

I was going to get this one, but eventually decided that since my water heater was in the same room as my gas boiler - it wasn't really necessary.

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.

Here is how you can get a happy compromise. Purchase a normal water heater with a replaceable anode. Where
I live, that would be anything but the cheapest, 6 year warranty models.

Then, before you install it, remove the anode and coat the threads with a never-seize product. Years down the road, this will allow easy removal.

Then buy a second anode. All the Big Box stores sell them. Replace it every five years or so. This will keep rusting to a minimum, and lengthen the tanks lifespan considerably.

Then buy a water heater blanket. This is a product that offers you an additional R-10 in increased insulation:

https://www.amazon.com/Frost-King-SP57-11C-Blanket/dp/B000BPCWQY

This route will save you several hundreds in cost versus the Marathon system.

http://www.amazon.com/Thermwell-SP57-11C-Heater-Blanket-gallon/dp/B000BPCWQY seems someone needs to tell the manufacturers of the water heater blankets that.