Calculate Water Leak From Hot Water System - Pipes, Pressure & More

[Mackay Scanland]

Hello PF,

I have a question. I would like to know how many gallons per hour are leaking from a residential hot water system. Here are the parameters: House PSI or H2O pressure=100 psi. Hot water pipe size=3/4” copper. Temperature of piping that is approx. 10’ away from the water heater=120 degrees. Temperature of H2O @ water heater T-stat=130 degree (Delta T of 10 degrees).

My take is that to maintain a temperature difference of only 10 degrees across that length of ¾ pipe, there would have to be significant flow through the pipe, and such, a leak somewhere within the system. So, I thought I’d ask some experts what they thought. Question: How many gallons per minute/hour are leaking? P.S. Not my house, but when I heard about the situation, it seemed like a good question! Thank you in advance for all responses…

 

[CWatters]

Based on the method and data here...

http://jmpcoblog.com/hvac-blog/domestic-hot-water-recirculation-part-4-pump-sizing-example

For 3/4" uninsulated copper heat loss is about 3000 BTUH per 100ft.

So for 10 foot that is 300 BTUH.

Table 2 says that 1 gpm will convey 5000 BTUH at a 10°F drop so the flow rate required for a 10 degree drop is

300/5000 = 0.06 gpm