Do they still make a 20 inch dia.low boy water heater /

Just a little over 53.3 gallons

first time heard of a tankless that is round

Copy following links:

Electric water heater:
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html
Gas water heater:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html
Tankless water heater:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Today's water heaters have more insulation and are larger.

Reliance does not have a water heater 20 x 38.
http://www.reliancewaterheaters.com/lit/spec/electric/R606E0312.pdf

I checked several manufacturers.

American Water Heater has 18 x 38-1/2"
Model #E62-30H-045DV
Shipping weight 77 lbs, but I don't know who sells it.
http://www.americanwaterheater.com/products/pdf/NRESS00308.pdf

Whirlpool from Lowes has a 30 gallon
18" x 45"

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

1) Low-boy water heater, cold water connects to lower inlet pipe and hot to upper outlet pipe.
Cold enters bottom of heater and then hot water rises to top where it leaves tank.
http://waterheatertimer.org/images/20-gal-heater.jpg

2) With larger water heaters both hot and cold connections are on top of tank, but the cold water goes to the bottom through the dip tube.
http://waterheatertimer.org/Water-heater-dip-tube.html

If pipes are reversed, the water heater will not work.

Question: Do Low boy heaters, have a heater at the bottom, AND at the top?--- and are BOTH of the heaters working, on the 'either/or thermostat?
(By 'either/or'-- I mean, that it first turns the top element on, and when it is satisfied, THEN it turns the bottom on, until the whole tank is heated..) -- I would say this is an advantage of the taller tanks...

The taller tanks stratify VERY WELL--- (And the incoming cold water stays right at the bottom, and you take the HOT water off the top-- until suddnely it all goes to COLD.

I am wondering if the Low boy heaters might MIX more thatn the tall ones,-- thus going to WARM water sooner--- due to poor stratification.
Could you test that out, and try to folow the cold water line up the tank, as the Hot water is drawn off?

Another thought:
The Cold Fill tube, does go all the way DOWN to the bottom of the tank, right?--
And does it gently let the cold water flow across the bottom, and not 'rotatee the waer in the tank, as it replaces the hot water being used?
Otherwise the cold water will mix very early-- and give this same problem...
(I have heard of those center tubes falling off in shipment...
Did you by any chance check that, when you installed it?)

A final thought: What if the water draw was extremely fast?-- (Like if the water pressure is exceptionally HIGH--) might that upset the stratification, and cause the same problem, too?

If the hot water is drawn more slowly, can the customer get 30 or 4 gallons of HOT water, before it all goes cold?

Mack B

Unfortunately, virtually all mass-market water heater blankets are 48" wide. One option is to buy a 32 sf roll of R13 ComfortTherm wall insulation (15" wide) and install in four segments. Unlike regular wall insulation, this product is sandwiched in plastic, making it much easier to handle and install (and neater) than kraft-faced insulation. It's made by Johns Manville and available at Lowes for about $9 (JM product number B011, Lowes item #44026). You'll need a suitable tape for the seams.

By the way, when calculating blanket width, you must add insulation thickness (times 2) to the tank diameter. My heater is 20.5" in diameter, so for 3.5" wall insulation, the effective diameter is 27.5", so the circumference is about 86".

Mass market blankets are 75" wide, and come in 1.5", 2" and 3" thicknesses. These can handle tank diameters up to 21, 20 and 18 inches, respectively.

Mike, water supply is important. Make shure your running a 3/4" dia. supply hose to the pressure washer. The longer the supply hose is the less the water supply pressure is so keep as short as possible. Hopefully your hose hookup is running 3/4" pipe to it. It sounds like you've been diligent in checking everything. I hope this was helpful. Jeff

You say a very new water heater. You won't get 40 gallons of hot water from a 40 gallon water heater because the continuing influx of cold water will cool your hot water down. However, it appears that your bottom water heater element needs replacing. If the top element is bad, you'll get no hot water. If your bottom element is bad, you'll get "some" hot water. Try replacing the bottom element. DON'T FORGET to turn off the electricity AND water first (closeby towels are also handy)!