Splicing hot water pipe closer to water heater?

[Sokolq55]

Short version:
Will connecting a hot water pipe to be the first one to T off after the water heater and running that pipe directly to upstairs bathroom solve the problem of upstairs shower losing hot water whenever someone runs hot water downstairs?

note - this happened with the separate old school hot/cold valves in the shower. Those will be replaced with a new single mixing valve in the remodel.

Longer version:
Currently, both the hot water and cold water going upstairs are the last in a series of branchings for all of downstairs. Running hot water downstairs “steals” it from upstairs and the shower gets cold. Upstairs is just one bathroom and that hot line just goes to a single shower and single sink.

I plan to cap off that last branch-off point in the basement that goes upstairs and instead connect that hot pipe for upstairs directly to be the first T that branches off of the water heater.

Will this solve the downstairs “stealing” hot water from upstairs?

Also, is there any advantage to running a whole new separate hot pex line from a basement manifold to upstairs versus just using the existing copper pipe that runs upstairs, capping off its existing branch in the basement, and instead connecting that existing pipe directly to be the first T off of the water heater.

Thank you.

 

[Terry]

Running a new 1/2" hot and a 3/4" cold to the upstairs bathroom from the water heater location would help a lot. I typically for a full bath with tub run a 1/2" hot and 3/4" cold.
for a 3/4 bath, 1/2" on the cold would work.

 

[Sponsor]

 

[Sokolq55]

Running a new 1/2" hot and a 3/4" cold to the upstairs bathroom from the water heater location would help a lot. I typically for a full bath with tub run a 1/2" hot and 3/4" cold.
for a 3/4 bath, 1/2" on the cold would work.

Thanks. As a follow up, wouldn’t connecting the existing 1/2 copper directly to be closest to water heater location achieve the same thing as running a brand new line from the heater to upstairs? Both would be basically straight runs from heater to upstairs at that point.

or perhaps my issue wasn’t the fact that the upstairs hot was the last to branch off and the problem was in the no mixing valve. I guess I want to know whether the sequence of a hot T branch has anything to do with the Ts before it “stealing” hot water.

 

[wwhitney]

When you have two hot water outlets open at the same time, the relative flows to each one are going to depend on the relative distances and sizes of the pipes, starting at the point where the two flow paths separate. Plus of course the characteristics of the outlets.

So for example if you had two tees, one after another, and each side port serves one of the two fixtures, the order of the tees doesn't matter. The only difference it causes is a small extra length for the second tee, which is going to be very small compared to the total distance to each fixture.

I think the temperature drop you are currently experiencing is likely due to the non-pressure balancing valve you have; when hot water pressure drops, cold doesn't, so you get a mix with more cold. The actual reduction in flow of hot water may be fairly small. If you made no changes to the piping but just changed the valve to a pressure balancing valve, then you should experience little/no change in temperature when another hot water tap is opened. You would get a drop in flow due to both sides now dropping in pressure.

If you want to reduce that drop in flow by reducing the pressure drop on the hot to the shower, then you can start looking at pipe sizes and lengths. It would difficult to advise you on that without a complete diagram of the hot water distribution pipe (pipe sizes, types, lengths, fittings, etc).

Cheers, Wayne

 

[Sokolq55]

When you have two hot water outlets open at the same time, the relative flows to each one are going to depend on the relative distances and sizes of the pipes, starting at the point where the two flow paths separate. Plus of course the characteristics of the outlet.

So for example if you had two tees, one after another, and each side port serves one of the two fixtures, the order of the tees doesn't matter. The only difference it causes is a small extra length for the second tee, which is going to be very small compared to the total distance to each fixture.

I think the temperature drop you are currently experiencing is likely due to the non-pressure balancing valve you have; when hot water pressure drops, cold doesn't, so you get a mix with more cold. The actual reduction in flow of hot water may be fairly small. If you made no changes to the piping but just changed the valve to a pressure balancing valve, then you should experience little/no change in temperature when another hot water tap is opened. You would get a drop in flow due to both sides now dropping in pressure.

If you want to reduce that drop in flow by reducing the pressure drop on the hot to the shower, then you can start looking at pipe sizes and lengths. It would difficult to advise you on that without a complete diagram of the hot water distribution pipe (pipe sizes, types, lengths, fittings, etc).

Cheers, Wayne

Thanks a lot for that explanation. I think before I run out and start buying new pex I should just try installing a new mixing valve once the new tub drain is hooked up and test that.

My full system is fairly simple. 1/2 inch out of the heater and 4 branch points (basement sink, kitchen sink, downstairs shower, downstairs sink) before the last branch which goes upstairs. But before getting to that last upstairs branch, it’s a convoluted can of worms with like 20 elbows resulting from previous owners work.

The total length from heater to upstairs bathroom is less than 20 feet if it were just a straight run. Hence my thinking of just capping off that last branch downstairs and connecting the existing pipe that runs upstairs directly closest to water heater, thus bypassing the entire “can of worms”.

 

[wwhitney]

Did not fully parse your photos, but reworking the "can of worms" seems wise. Sizing wise, the following would be typical (given your described branching):

Water heater --3/4"-- tee -- 1/2" for kitchen, basement sink
                       |
                      3/4"
                       |
                      tee -- 1/2" -- upstairs bathroom
                       |
                      1/2"
                       |
                   downstairs bathroom

Basically 1/2" for a single bathroom, 3/4" for any pipe that carries more than that.

Cheers, Wayne