[Leo G]

Trying to figure out how long a shower will last without running out of hot water.

I am using this calculator here

http://www.spiraxsarco.com/esc/Miscellaneous_Mixing_Water_Calculator.aspx?country_id=

Inputs are

Cold Water Temperature 50F
Hot Water Temperature 140F
Mixed Water Flow Temperature 105F
Mixed Water Flow Rate 2 US gal/min

It comes up with a hot to cold water ratio of 61%:39%


So I have a 50 gallon tankful of 140F water. I need to add 39% 50F water to it to get 105F

50gal x .39 = 19.4gal

50gal + 19.4gal = 69.4gal

68.4gal / 2 gal/min = 34.2 minutes worth of 105 shower water.

Is this correct?

 

[Tinstaafl]

You haven't accounted for the recovery rate of the heater.

 

[Inner10]

You haven't accounted for the recovery rate of the heater.

Or loss, or the fact that a water heater's output drops as it's being used.

 

[hdavis]

Trying to figure out how long a shower will last without running out of hot water.

I am using this calculator here

http://www.spiraxsarco.com/esc/Miscellaneous_Mixing_Water_Calculator.aspx?country_id=

Inputs are

Cold Water Temperature 50F
Hot Water Temperature 140F
Mixed Water Flow Temperature 105F
Mixed Water Flow Rate 2 US gal/min

It comes up with a hot to cold water ratio of 61%:39%


So I have a 50 gallon tankful of 140F water. I need to add 39% 50F water to it to get 105F

50gal x .39 = 19.4gal

50gal + 19.4gal = 69.4gal

68.4gal / 2 gal/min = 34.2 minutes worth of 105 shower water.

Is this correct?

Nope, that's wrong. It's a ratio problem:

X/50=39%/61%

X= 50 * 39%/ 61% = 31.98 gallons

2 other responses and no one caught it...:whistling

 

[Tinstaafl]

2 other responses and no one caught it...:whistling

What's the point of even looking at the math when you don't have all the variables? :whistling

 

[The Coastal Craftsman]

I can tell you from experience that you can get a very rough idea but its so inaccurate to calculate like that its unreal. Always work on your worst case on incoming temps, GPM, recovery etc etc then use them figures.

 

[hdavis]

What's the point of even looking at the math when you don't have all the variables? :whistling

First dibs on ribbing people:laughing:

 

[CarrPainting]

I have a 40G Hotwater tank... set at 120ish... and i can relax under the hot water for atleast 20-25 minutes :thumbup:

 

[KillerToiletSpider]

I have a 40G Hotwater tank... set at 120ish... and i can relax under the hot water for atleast 20-25 minutes :thumbup:

I have a tankless, the longest I have sat in the shower is an hour and a half.

 

[Leo G]

You haven't accounted for the recovery rate of the heater.

Or loss, or the fact that a water heater's output drops as it's being used.

Doing theoretical black box calculations.

Wise azzes

 

[Leo G]

Nope, that's wrong. It's a ratio problem:

X/50=39%/61%

X= 50 * 39%/ 61% = 31.98 gallons

2 other responses and no one caught it...:whistling

So it's 50/.61

That doesn't seem right

So 41 minutes of 105F water?

 

[hdavis]

So it's 50/.61

That doesn't seem right

So 41 minutes of 105F water?

If it were 66.7% and 33.3%, you'd use 2 gals hot for each gal cold. 75 gallons mixed - 50/.667

Yup, 41 minutes if the on-line calculator has the right percentages.

 

[Leo G]

This is all because my indirect heater started leaking and I replaced it with a temporary electric water heater. (smart enough not to say hot water heater :w00t

The recovery time on this thing is something in the area of 2 hours. Of course it will recover as it's being used, but nothing like the indirect heater. I could take a shower 24/7 and wouldn't run out of hot water until I ran out of oil. It's a big adjustment for the family. Plus my electrical service is 60 amps, and this extra 18.5 amps of draw has the potential to shut down the main breaker on the house. Doing laundry with the electric washer and dryer going and likely the water heater at the same time gets use near 45 amps without anything else in the house. Add a stove and a MW and you see what I'm talking about.

 

[hdavis]

and you see what I'm talking about.

Home harmony:laughing:

 

[Inner10]

I'd say a better idea would be to buy a stop watch and jump in your shower.

 

[huggytree]

a 50 gallon typically wont give you 50 actual gallons of hot...i think its more around 40-42 and you did not figure for recovery.....

140 degrees will mean a shorter life for the heater also

have you considered a separate 50 gallon storage tank instead of the high temps and the mixer?

 

[Leo G]

How is this separate storage tank going to reach temperature?

 

[Chris Johnson]

Recirc pump back to the water heater

 

[Tinstaafl]

Leo. You installed AC in your shop. You have a smartphone. Come the rest of the way into the 21st century.

Pay my way, and I'll come install a 200A service for you.

 

[Leo G]

Been living in this house for over 20 years. Never once tripped the main. If I did upgrade it would be to 100 amps. No need at all for 200 amps.