Question for plumbing experts

[Galaxiedan]

I'm in the planning stage of replacing the plumbing lines in a '74 mobile home. I'll be using all pex. All fixtures are approximately in a straight line down one side of the doublewide. Hot and cold all enters on one side. First room by water inlet contains water heater, utility sink, and washer machine. Kitchen is next (10' from water heater) with sink, fridge icemaker, dishwasher, and pot filler spicket above stove. 1st bathroom is next (22' from water heater) with sink, toilet, and tub/shower. Master bath is last (50' from water heater) with sink, toilet, and dual showerhead shower.

I plan on running a 3/4 cold branch line down the length with 1/2 runs to each faucet etc. My question is whether to run a 1/2 or 3/4 branch line for the hot water.

I've been told both ways.
3/4 will cause wasted hot water because it will take 2 min for hot water to reach master bath. And no benefit to volume with such small plumbing job.
1/2 will cause weak volume and temp changes if toilet flushes etc.

Any plumbers wanna share experiences?

 

[JFB]

On a different consideration...The #1 thing I wish I had done....a cut off INSIDE.

 

[Galaxiedan]

I have 3/4 pvc from the well with a ball valve shutoff easily accessible by the water inlet to the house. Plus I will have shutoffs at each fixture. So I should be good there. Should be an easy job since I can crawl everywhere underneath. House currently has a mismatch of galvanized and pvc that's a mess. Planning on having the underneath sprayfoamed so the pipes need to be done right. The foam will insulate them if that makes a difference in the first post question.

 

[eveled]

Run 3/4 to the heater. You can always throttle it back, if you think you need to.

 

[Galaxiedan]

Run 3/4 to the heater. You can always throttle it back, if you think you need to.

It will be 3/4 to the water heater, my concern is the 50' run after the hot water heater to the furthest bathroom.

 

[hdxr750]

I've been an Electrician for 44 years and I've learned, Hot on the Left Cold on the Right, Poop runs downhill, the Boss is a Prince and Pay Day is Wednesday.

 

[JFB]

two comments first;
1st. I use to always bump heads with plumbers
2nd In the last couple months I have noticed (and this is the same), the calculations I use to do no longer make any sense to me.

however I found past notes and think I did this right

I assumed 5 gpm and calculated pressure drop in psi and volume in gallons for the runs
................psi......................gallons
run.....1/2........3/4.........1/2........3/4
10.......2.5.........0.3........0.1.......0.2
22.......5............0.7.........0.2......0.5
50.......11..........1.5.........0.5.......1.2

 

[pleadthe2nd]

Yes you main line should be 3/4" with 1/2" branches for both hot and cold

 

[308dave]

What pleadthe2nd said - you want the main run from the water heater to be 3/4".

 

[Don Lovel]

better yet, install a on demand heater in the bathroom right by the shower, no more cold showers

 

[bobski]

why not put in 2 small heaters on each end? turn on and shut off as needed save electricity.

 

[Galaxiedan]

Thanks for the input, I was leaning towards the 3/4 line myself. Regarding multiple heaters, in my situation its not real practical. Hot water is provided by a tankless gas water heater mounted on outside wall opposite master bath.

 

[Mobuck]

"Hot water is provided by a tankless gas water heater mounted on outside wall opposite master bath."

OK now I'm confused. You said a water heater was first delivery inside the structure and master bath was 50' of run.

 

[powder smoke]

better yet, install a on demand heater in the bathroom right by the shower, no more cold showers

Very good idea no waste at all reheating water in a tank over and over.

The only thing I'll add is try to locate it centrally between baths and kitchen.

Tradition set up 3/4 or 1" main with 1/2 tees Copper Tubing will give you more Volume
due to larger internal diameter. ps

 

[Coogs]

Run all 3/4 Mains. Only problem with a GAS on demand water heater is that they may not be approved for mobile home installation. Not all gas burning appliances, as in furnaces and water heaters are. If you go electric on demand, or gas for that matter, make sure you do follow the service instructions. They need flushed, each year, with an acidic solution to clean the mineral buildup on the interior of the heat exchanger. All manufactures of that type of equipment recommend a certain brand/type. The solution has about the same acidity of white vinegar, which you could actually use in a pinch...............Coogs.

 

[Galaxiedan]

"Hot water is provided by a tankless gas water heater mounted on outside wall opposite master bath."

OK now I'm confused. You said a water heater was first delivery inside the structure and master bath was 50' of run.

picture a 24x60 double wide, tankless water heater is mounted outside on one short wall that the water line comes in from. That wall inside is the laundry room. Clear on the other side of the house is the master bedroom.

Not trying to get into a major project by adding electric or gas lines for a new remote water heater. Just trying to clean up a mess of hanging spliced old pipes underneath.

I've had the noritz water heater for 6 plus years so I'm familiar with the flushing requirements. When it was installed they put in the optional bypass valve system. Have real good water so no issues yet.

House currently has all 1/2 lines and doesn't have the best pressures and you do have to run the hot for 30 to 60 seconds in the master bath before it gets hot. Might blame these issues on the old nightmare of pipes. I just don't want to make the wait for hot any longer. Water waste isn't the main concern since I'm on a well, gas usage is. As I'm slowly fixing this place up I'm trying to make it more energy efficient. And it does suck to wash your hands with cold water when you don't want to wait at the bathroom sink.

Thanks for the input.

 

[eveled]

You say you have not the best pressure, but what is the psi? If you don't have a gauge, they are cheap. Go to the sprinkler section of the hardware store. They'll have a gauge on a hose connection, so you can screw it on a draw off valve (spigot).

Lots of people confuse a volume issue with a pressure issue. (You can have a 100psi drip)

Once you know for sure it is a volume issue, run it all in 3/4. Add a recycle pump to return the cold water to the heater. Wire it to the light switch in the bathroom, turn the light on, by the time you get to the sink the water will be hot. Insulate the hot water pipes.

If it really is a pressure issue, pipe size doesn't matter.

FYI when I do the math, your fixtures don't justify a 3/4 main, but it would be an improvement.

 

[powder smoke]

Good point eveled! Volume is more desirable than pressure. ps

 

[JFB]

... a volume issue with a pressure issue. ...

...Volume is more desirable than pressure. ps

Do you mean Flow versus Volume?

volume to me is the amount of water sitting in the pipe, thus the cold water wasted before the hot gets there (and the amount of wasted heating once shut off)

 

[bogus bill]

I would just hire a plumber.

 

[Galaxiedan]

I would just hire a plumber.

I got a couple quotes and that's were the question started. One said 3/4, one said 1/2 with the statements from my first post. I can easily run pex myself ( and save a ton of money for more Rugers) and I guess either option will work in my situation. Just trying to get more opinions is all. I appreciate the knowledge base that this forum has and am happy to get as much feedback as possible.

 

[JFB]

just curiuos...what is you pump cycle pressures?

 

[blume357]

A lot of the 'approved for mobile home' is because in theory the home is still mobile and can be moved... most 'trailers' are never moved again. Example is wood stoves.... these have to be bolted to the floor so that they can't be bounced around while the 'mobile home' is moved. The problem I have with these on demand gas water heaters is they require electricity to light up the burner.... So, if the power goes out you can't have hot water... might as well have an on demand electric heater.... at least all the ones I see around here have power run to them.... also, these critters use a lot of gas to heat water.... most actually have higher btus than most gas furnaces.... finally 'fault' to on demand hot water heaters of all kinds was explained to me by a customer who had three teenage daughters.... never run out of hot water while showering... and so you can just stay in the shower.... forever....