I am trying to replace an old sink in my bathroom. I shut off the cold water supply. What I thought was the hot water shutoff, however, did not shut the water off to the sink but shut off the hot water line at the point it connected to the COLD water line (after the line branched off to the sink). Why would the hot and cold lines be connected? Right now when I turn on the hot water it runs into the sink and into the toilet.

Thank you for your help.

If I understand description of your plumbing inside your cabinet correctly - than your plumber prepared this set up for retrofit hot water circulating pump, like LAING pump system.

Can you post a photo of it ?

Sorry. The pipes are under the floor so I can't get a picture of them. I will try to describe them better. This is a 1960's house but is new to me. I am in the process of remodeling.

The hot and cold lines run together under the floor of the bathroom. The cold line splits at a T with one line going to the sink the other to the toilet. The hot line also splits at a T with one going to the sink and the other connecting to the cold line prior to the cold water pipe running up to the toilet. There is a shut off valve at the point the hot water pipe connects to the cold water (toilet) line.

Thanks... that draws clearer picture...

If there is a valve, than it indicates that it was put in on purpose - perhaps, it was a set up for future hot water circulation system, after all. Otherwise, it is WRONG. In fact, even if it is set up for LAING pump system, that hot-into-cold connection should be above floor, not hidden under your house.

You have two choices: keep that valve closed and never open it - or cut that connection and plug it with caps.

Thank you very much.

Mixing the hot and cold water for the toilet supply is a way to reduce sweating of the toilet tank. Usually it's done with a special purpose mixing valve.

For more info, look up "dew point". A cold surface meeting warm humid air causes condensation. The conditions that occurs is the "dew point".

Keep it Simple Stupid: Please, post for our enlightenment, where do we find the "poor man's" version of negating dew point in toilet tank addressed in Unified Plumbing Code by connecting hot water supply to cold under via manual valve under a house. Thank You

Quote:

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Originally Posted by Milo Dolezal

Keep it Simple Stupid: Please, post for our enlightenment, where do we find the "poor man's" version of negating dew point in toilet tank addressed in Unified Plumbing Code by connecting hot water supply to cold under via manual valve under a house. Thank You

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Here you go Milo! This is a adjustable mixing valve for controlling tank sweats, (see image), A mixing valve, while a little more complex to install will definitely solve the condensation or sweating problem of the toilet tank.The mixing valve adds hot water to the cold water entering the tank. By setting the tank water temperature to the approximate temperature of the room, condensation cannot form form.There are numerous styles of toilet water mixing valves and they are available at most plumbing supply stores.
And now you know the rest of the story. Regards, Tom

Speedball1: thanks for the visual. I have never seen this device, nor had any of my supervisors in our shop. Now we know it exists. :D I printed your last post and posted it on our bulletin board to introduce this device to our plumbers.

I will ask our inspector about it next week when he comes out to do our rough-in inspections. I will let you know what he had to say...

Here, we all agreed that if we run into toilet tank condensation problem, than we would probably install 3/4" pipe insulation over the cold water pipe instead of using this device.

How would "pipe insulation" help the toilet tank? The toilet tank is sweating? It' agreed that the pipe insulation could raise the temperature of the incoming water a smigeon.

If the toilet tank is sweating, it's likely the pipe is too.

Milo:
I was objecting to cap, remove, and don't open. It's not necessarily the right way, that's why I called it the "poor man's version".

Another application of a mixing valve is on the hot water system. Cold and Hot can be mixed to a desired temperature. You had to know about that application.

Speedball1:

Thanks