To 1/2" or not to 1/2"?

[Plumberwanabe]

My house is 55 years old with galvanized pipe. In the future I plan to change the location of the hot water tank and flip flop the powder room and laundry room. The laundry room is larger and it will make space for a shower. Presently the entire hot water supply is ½â€. Should I replace the ½†hot water supply with ¾â€? Will a ¾†line with ½†feeds to fixtures improve the wait time for hot water? Or should I simply replace ½†with ½â€? I will use CPVC and do it my self. Any suggestion's?

 

[Terry]

Water Pipe sizing chart

A standard one-bath home with kitchen sink, dishwasher, water heater, clothes-washer, 1.6 tank toilet, lavatory, tub/shower combo and two hose bibs would be counted as 18 fixture units.

Most standard two bath homes consisting of kitchen sink, dishwasher, water heater, clothes-washer, two 1.6 tank toilet, two lavatories, one shower, one tub/shower combo, and two hose bibs would be counted as 23.5 fixture units.

Most standard three bath homes consisting of kitchen sink, dishwasher, water heater, clothes-washer, three 1.6 tank toilet, four lavatories, two showers, one tub/shower combo, one whirlpool bath and two hose bibs would be counted as 34 fixture units.

1" CPVC will have about the same opening as 3//4" copper, the 3/4 will be the equivalent of 1/2" copper, and forget about 1/2" CPVC for anything other than a single fixture, (and keep its length as short as possible), since its bore is miniscule." hj

 

[Sponsor]

 

[Jimbo]

For service to the fixtures, there may be reasons to use 3/4 vs. 1/2. And note hj comment about not trying to equate 1/2 cpvc to 1/2 copper. But, on the other side of your equation, the larger the pipe, the LONGER the wait for hot water will be. Your faucet will flow about the same rate, but there is a lot more cold water in the pipes which has to be flushed out. The solution to that, if it is a big problem, is a recirculation system.

edit: 1/2" copper pipe holds 1.13 gallons per 100 feet, and 3/4" copper holds double, at 2.27 gallons per hundred feet. How signigicant is this? Your faucet would clear 2+ gallons in about 1 minute, vs 30 seconds. With the larger pipe, you waste an additional gallon every time. May not be a huge deal breaker either way.

 

[hj]

You have to balance "wait time" with "volume delivery". That 100' of 1/2" pipe will give you hot water sooner, but if someone opens another hot water faucet, such as the bathroom sink, there may not be enough volume/pressure to take care of both of them. If that happened you would either get less water in the shower, or the water temperature would suddenly become cold, depending on the type of shower valve you have.

 

[Plumberwanabe]

to half inch or not to half inch

I have a 55-year-old house with galvanized pipe through out. I want to flip flop the powder room and laundry room. The laundry is bigger and this will create room for a shower. Presently the hot water pipe system is ½â€. Would it be an improvement to replace the pipe with ¾†and ½†going to the fixtures? Or would it be fine to simply replace ½†with ½â€? By increasing to ¾†will the time for hot water to reach the fixtures improve? I will be using CPVC and doing it my self.

 

[Terry]

I always use only two fixtures on 1/2"
That would be one tub and one lav.
Since your home has a washer and kitchen sink, at some point the hot should be run with 3/4"
The fact that you now have galvanized, that in itself will prevent the pipes from heating quickly. The new clean pipe, with transfer heat from the heater much quicker then the galvanized did. It takes a while to heat steel pipe.
So, take a look at the chart that I posted on pipe sizing, and follow that.

Don't forget to pick up a plumbing permit at City of Bellevue

 

[hj]

Just asking the question a second time does not change the original answers, BUT one consideration for you is that 1/2" CPVC is a LOT smaller than 1/2" steel or copper tubing. 1/2" copper o.d. is about the same size as the steel pipe i.d. so you lose the area of the tubing's wall thickness, but CPVC is the same o.d. as copper so that means you lose even more volume, especially since the wall is much thicker than copper tubing. By the time you get done, you will have the eqivalence of 1/4" to 3/8" steel pipe.

 

[Bsperr]

Not to thread hijack, but I have a similar question along these lines. I'll be replacing the supply lines to our kitchen and laundry room and adding a utility sink in our garage. It's a two bath house. We have a 3/4" copper supply and, currently, everything past the water heater is 1/2" copper. From looking at the supply charts, it seems like 3/4" copper would be more suitable, but we haven't experienced any flow problems in the past. Would it be a good idea to upgrade the main supply lines in the house to 3/4" and stub out to the fixtures in 1/2"?

 

[Jadnashua]

Depending on how many people are in the house and how often simultaneous uses occur, you may really want 3/4" lines. It probably isn't worth it to change unless you are having problems or anticipate more simultaneous uses.