Determining Number of Trunks for Logic Hot-Water System
big__o
| Posted in General Questions on
Im planning to do a logic system with either 2 or 3 trunk lines. the farthest outlet is about 30 feet away.
Should I go 2 trunks, like this
or three trunks , like below
will i get hot water to the main bathroom appreciably quicker with 3 trunks vs 2?
thanks
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This depends on the total enclosed volume of water in the lines. With very short runs (I'm guessing maybe 20-30 foot runs here?), there isn't going to be a huge difference between several 1/2" lines and a relatively short 3/4" "main" that branches out to the fixtures in the area of those two bathrooms.
I'd do whichever is less labor and/or less materials cost here, I don't think there will be a big difference in terms of how long of a wait you have for hot water in this particular case.
Bill
Thanks for the response. I think I'm in the same page as you that it won't make that big of a difference.
I'll let my plumber know
It depends. If you use the same size pipe in either case, it won't affect the time to heat up. But:
1. If the pipe is smaller for the 3 trunk than for the 2-trunk, the 2 trunk will heat significantly faster.
2. If the pipe is small in both cases, you might get pressure variations in the shower when you start filling the bath, for example, with the 2 trunk, and not with the 3-trunk.
3. If people use the hot water in one bath and then someone else in the second soon after, the second won't need to wait if they share a trunk.
4. Insulating the pipes can help reduce the need to wait if the draws come close enough together.
Thanks for the input. The water heater will be fed from a well pressure tank if it makes any difference
I've tried a number of ways of plumbing longish runs, my current preferred is to home run the hot water to each tub/shower and run a single hot water feed to all other fixtures. I've never had issue with multiple sinks/washing machines/dish washer sharing a single 1/2" feed.
Exact same setup with cold water supply. You can do a trunk and branch but semi home run is simpler if you have a small manifold near the water heater.
This avoids large 3/4" trunks which will take a while to warm up even on a shortish run of around 20'.
A bit more connections than a full home run system but much less piping.
This is an excellent idea. All I really care about is quick hot water to the main tub, so I could ask my plumber to run a dedicated line to it(1/2”?)
Everything else can be a regular trunk and branch.
So you use half inch lines? Floor all the hot water lines?
1/2 pex is good for around 2 to 3 GPM. This gives around 1psi pressure drop per 10' of length. Generally on city water, you can get away with 15psi loss.
Overall the idea is to put anything that will use a lot of water on its own home run. Rest can be shared especially if the water draws are not at the same time and more than one faucet operating won't cause issues. For example:
outdoor hydrant->own feed
kitchen cold water->maybe
washer->shared, best if you can run a 3/8 line from the 1/2 trunk to it
shower/tub->dedicated hot and cold
Most older houses here were plumbed with 1/2 copper. In almost all cases, the water pressure issues in them is fixed just by running a 3/4 supply line to the hot water tank, so you don't need very large piping for most of the house. A couple of dedicated lines to the high flow fixtures is all you really need.