# The incredible volume of my hot water pipes **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [February 8, 2023, 8:46pm UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502 "2023-02-08T20:46:47Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![steronz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steronz/32/11765_2.png) [@steronz](https://boards.straightdope.com/u/steronz)\ **Post date:** [February 8, 2023, 8:46pm UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502/1 "2023-02-08T20:46:47Z")
I know a few things for certain. 1. My hot water heater keeps water very, very hot 2. My hot water heater is, like, 15 feet from my shower 3. 1/2 copper pipes seem pretty small And yet, based on what I estimate is the flow rate of my shower, there’s about 100 gallons of cold water sitting in those hot water pipes that I need to purge while I stand. My math is probably wrong. ---
**Author:** ![DavidNRockies](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidnrockies/32/6279_2.png) [@DavidNRockies](https://boards.straightdope.com/u/DavidNRockies)\ **Post date:** [February 8, 2023, 8:58pm UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502/2 "2023-02-08T20:58:21Z")
Do you know for sure the route your hot water takes from the H2O heater to your shower? It may not be the first stop on the route … unless, of course, it is and you _know_ it is 😉 ---
**Author:** ![steronz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steronz/32/11765_2.png) [@steronz](https://boards.straightdope.com/u/steronz)\ **Post date:** [February 8, 2023, 9:04pm UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502/3 "2023-02-08T21:04:52Z")
Are you suggesting that gnomes are siphoning off my hot water? It’s a possibility I’ve considered but not explored seriously. ---
**Author:** ![MonkeysBrother](https://avatars.discourse-cdn.com/v4/letter/m/3ab097/32.png) [@MonkeysBrother](https://boards.straightdope.com/u/MonkeysBrother)\ **Post date:** [February 8, 2023, 9:10pm UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502/4 "2023-02-08T21:10:53Z")
Because it’s California and I’m trying to be good and save water, I use a bucket to collect the cold water that runs until I get hot enough water to shower. My heater is about 30 feet from the shower. I get three gallons before the water is shower temperature. I’d estimate it’s less than half that before the pipe is purged. I think the rest goes to gradually warming the pipes. 100 gallons sounds high by a couple of orders of magnitude. ---
**Author:** ![gnoitall](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@gnoitall](https://boards.straightdope.com/u/gnoitall)\ **Post date:** [February 8, 2023, 9:42pm UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502/5 "2023-02-08T21:42:37Z")
> [@MonkeysBrother](#): > > 100 gallons sounds high by a couple of orders of magnitude. We can disregard that number as hyperbolic exaggeration. A high capacity water heater is 75 gallons, which would mean that flushing 100 gallons of cold water from the pipes literally drains every drop of hot water from the water heater plus 25 further gallons from the heater’s inlet. ---
**Author:** ![DavidNRockies](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidnrockies/32/6279_2.png) [@DavidNRockies](https://boards.straightdope.com/u/DavidNRockies)\ **Post date:** [February 8, 2023, 10:07pm UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502/6 "2023-02-08T22:07:36Z")
Let’s say it’s PEX: | PEX Tubing size (CTS/Nominal) | Outside Diameter (OD) | Volume gal/100ft | | --- | --- | --- | | 1/2 | 0.625 | 0.92 | The math I did gave me about 35 cubic inches, or about 0.15 gallons. Not too far off. But I drink, so … ---
**Author:** ![steronz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steronz/32/11765_2.png) [@steronz](https://boards.straightdope.com/u/steronz)\ **Post date:** [February 8, 2023, 10:09pm UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502/7 "2023-02-08T22:09:40Z")
Now round up to the nearest 100. ---
**Author:** ![DavidNRockies](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidnrockies/32/6279_2.png) [@DavidNRockies](https://boards.straightdope.com/u/DavidNRockies)\ **Post date:** [February 8, 2023, 10:11pm UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502/8 "2023-02-08T22:11:18Z")
I’m sorry, Dave. I’m afraid I can’t do that. ---
**Author:** ![steronz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steronz/32/11765_2.png) [@steronz](https://boards.straightdope.com/u/steronz)\ **Post date:** [February 8, 2023, 10:36pm UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502/9 "2023-02-08T22:36:00Z")
It’s OK. This is just a mystery that can’t be solved. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [February 9, 2023, 3:28am UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502/10 "2023-02-09T03:28:53Z")
Anyone else read the OP to see what the obvious euphemism really referred to? ---
**Author:** ![steronz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steronz/32/11765_2.png) [@steronz](https://boards.straightdope.com/u/steronz)\ **Post date:** [February 9, 2023, 12:21pm UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502/11 "2023-02-09T12:21:19Z")
Sorry, big sexy bongs are next door. ---
**Author:** ![Seanette](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/seanette/32/9139_2.png) [@Seanette](https://boards.straightdope.com/u/Seanette)\ **Post date:** [February 9, 2023, 1:53pm UTC](https://boards.straightdope.com/t/the-incredible-volume-of-my-hot-water-pipes/979502/12 "2023-02-09T13:53:58Z")
I interpreted the subject line as a comment on how noisy the pipes might be. I just got up, though. Brain is still booting.