Hi,

I am replumbing an efficiency apartment - 1 person only.

I want to move the hot water heater from an inaccessible location to a location that I can access in the future when it needs service or replacement. The new location would be about 25 feet away from the living space, with the pipes buried under ground, wrapped in insulation.

One of the disadvantages of this increased distance is the lag time between when the user calls for hot water and when it eventually shows up.

To fix this, my thought is to run 3/4" PEX to the hot water heater, and 1/2" PEX from the hot water heater back to the house. Since the 1/2" pipe carries only about 25% of the water of the 3/4" pipe, the hot water should arrive 4 times faster, and waste much less cold water ahead of the hot. And since there is only one person in the small unit, there will never be the problem of running the sink while taking a shower.

Does this make sense?

There are a number of instant hot water systems available. All cost money in terms of energy lost, but the "on demand system" is probably the least costly.

I have a gravity recirculation system but I also have a multi-story home with the water heater in the basement. Recirculation pumps usually cost about the same as a 60 to 100 light fixture to operate.

The on demand systems have the greater up front cost but would have the least cost to operate. There are even systems with remote sensors for multiple points of use.

A 1/2" Pex supply would probably be inadequate for the entire apartment (kitchen and bath) since 1/2" Pex is slightly smaller than 1/2" copper or CPVC.


Google "hot water recirculation system"

Doesn't make sense and the flow is too low. Pipe with 3/4 and use a recirculator. If I use your logic, why not use 1/4" copper?

I agree, this is not a good solution unless you put in a circulation pump. " Since the 1/2" pipe carries only about 25% of the water of the 3/4" pipe, the hot water should arrive 4 times faster," This is not a correct statement because you did not consider you reduced volume by a significant amount.

Start with a 1'' PEX line, and then move along to 3/4'' at the fixtures. This will keep your volume up and maintain a good flow of pressure.

I agree with above suggestions...

1/2" PEX is actually around 3/8" I.D. You should run at least 3/4" PEX from the water heater - if not 1". The size of pipe should match outlet on the Water Heater - which is 3/4".

Hope that helps

Milo

Thanks for all the input.

I plumbed the hot water (and cold water) using all 1/2" PEX. In total, there was less than 30 feet of each hot and cold. It runs from the hot water heater to kitchen sink to bathroom vanity to shower.

It works fine. Pressure is very good. And hot water seems to reach the shower quickly.

I assume if the runs had been longer, or multiple people were accessing at the same time there would be a problem, but not in this small efficiency.

Glad you are happy with the volume you are getting out of that 1/2" PEX.

Milo

You may understand differences between flow rate and pressure.. if you make supply 3/4" and back 1/2" you rise your pressure but loose you flow rate its doesn't make sense.

You may understand differences between flow rate and pressure.. if you make supply 3/4" and back 1/2" you rise your pressure but loose you flow rate its doesn't make sense.

You don't rise pressure, that is regulated by the PRV. You lose volume but may find flow increased somewhat. Total volume still drops.

I agree with ma, changing pipe size has no effect on pressure, it only alters volume.