I have been told by State Industries that my (their product) 50 gallon electric low boy waterheater's performance is acceptable if it only produces 25 gallons before dropping 30 degrees from the set tempature. They said 60 percent of the stated size (50 gallon x 60%=30 gallons) is normal. The fact that mine only produces 25 gallons in the first year of ownership does not qualify for replacement. How much hot water should one expect out of a 50 gallon waterheater? I believe most people would expect more than 60% of the number on the tank. Per the certificate of product performance from AHRI the first hour rating is 55 gallons. Could someone please explain what that means? Any other suggestions? I plan to give this almost new waterheater to Habitat to Humanity and buy a better performing product.

You must realize that for every gallon of hot water you draw from your heater a gallon of cold water enters. The more hot water being drawn off the more cold water enters. Of course the water temperature drops the more hot water used.The good news is that as cold water enters the bottom element begins recovery. You will never get 50 gallons of hot water out of a water heater on a single draw. Regards, Tom

Thank you speedball. Okay, so a 50 gallon water heater will not produce 50 gallons in one draw. But only 25 gallons before the temp drops 30 degrees (153-123)? These numbers came from a draw test suggested by State after setting the unit at the max. I would never set my w/h at that temp. Take 20degrees off those numbers above and you are talking a bath where you have to roll over to get wet and the 26th gallon is a cold 103 degrees. The supplier suggested adding another water heater. Imagine the cost of operating 2x50 gallon hot water heaters so you have enough water to come up over the jets. If there is not enough water in the tub it is like a Robo automatic car wash in your bathroom.
Thanks again,
BP

I found two general rules of thumb: 75% and 2/3. The capacity of the hot water heater needs to be at least 75% of the capacity of the whirlpool. If the whirlpool is 100 gallons the heater needs to be 75 gallon. In the second opinion the heater should be 2/3 of the capacity of the tub. If the whirlpool is 100 gallons the heater needs to be 67 gallons. HGow does yours stack up? Regards, Tom

If you heat up 50 gln tank to desired temperature, close incoming cold water valve ( meaning you isolate heated water from receiving any cold water as refill ) and drain the heater - you get close to 50 gln of hot water. That's why "50 gln" hot water heater. Otherwise, it is as Tom explained above in his response to your question...

They are correct, I see no surprise at all, It should be fairly normal common knowledge that as hot water is used, cold water replaces it. So it starts cooling from the very first gallon used.

The gallon size is merely the holding ability, not how many gallons of hot water is available

I also had problems w/my hotwater heater. w/4 girls in the house we never had enough hot water. A plumber friend told me about the tankless hot water heaters, but they are expensive. However I found a very affordable one at Lowe's. It's made by bosch and we are very pleased. It only uses energy when hot water is running and that keeps energy bills much lower.