Home Run vs Trunk & Branch Duct Layouts Which is Better?
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Equivalent length is a way of calculating the amount of friction and turbulence that a fitting causes in any duct run. For example, each 90° elbow adds 50 feet of equivalent length to a duct run. The sum of actual and equivalent lengths impacts the air flow and the pressure needed for each supply or exhaust outlet, and so, determines the size of the ducts.
Not only does the actual length of each duct run to and from the ventilation unit need to be addressed, but each type of fitting comes with it’s own additional ‘equivalent’ length. The sum of actual and equivalent lengths impacts the air flow and the pressure needed to each supply or exhaust outlet, and so, determines the size of the ducts. That is probably true for some houses, it may even be true for a typical house.
What Layout Suits Your Needs?
Then you turn on the water for your shower and wait for the hot water. You have to drain all the cold water out of both lines to get how water. A manifold system helps reduce fluctuations in pressure, but will not entirely eliminate them. For best temperature consistency in the shower, install a pressure-balancing shower valve, such as the Moentrol. Such shower valves keep the same proportionate mix of hot and cold, so what fluctuates is the volume of water, not the temperature.
I would have it drained under the bench seat in shower . This would cut the runs to ~6'-15' compared to 50'. The 2nd WH would not use as much electricity b/c it is always fed by a hot line . I feel this is a better solution than a re-circ system b/c the master bath is the only place where hot water use is most important. A large-diameter (3/4 in.) main water line feeds the manifold; smaller lines run from the manifold to each fixture. Any fixture in the house can be shut off at the manifold.
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No interior partitions to run water line and big engineered beams that can not be drilled. I started off plumbing doing the branch system with copper. Manufacturers are reluctant to say so, but reports from the field suggest PEX can withstand freezing. You should still protect the tubing from freezing. But since it can expand and contract, it’s less likely to break than rigid piping.
Because water pressure variation won't scald or freeze you, home run also allows more latitude with pipe sizing. Say you have 100 feet of 1/2 inch pipe from meter to garage, and another 10 feet to the new shower. Should you put a manifold in the new bathroom, or do you put it in the garage but outside the bathroom ten feet closer to the meter? Then it's either 100 or 110 feet before branching. Some detailed calculations would be required, but probably not worth even thinking about.
PEX Homerun vs T&B with 1/2in Supply
This photo shows clearly why ½ inch copper will flow 3 times as much water as ½ PEX. The showers are fitted with ½ PEX the flow is not strong it is almost acceptable if you use a 50/50 mix of hot and cold! I am seriously considering ripping out the drywall and replacing the pipes. In my current build I have 3 floors + basement. I originally thought I'd do a viega home run system, but based on the amount of vertical travel each line would be, I switched to main and manifold system to save on material and labour.
Based on your floor plan, you don't have many fixtures and they're all very close to the utility room. I'd say it would be easier to splurge on the central manifold and run individual lines in the attic. In my best guess without doing any calcs, and based on big Gary's material, Your wait times for hot water would be minimal in a home run system vs a trunk system without a recirc. Plumbers are making the transition from copper to PEX plumbing (here’s how to literally transition from copper to PEX).
I plan on hanging it just below the floor joists. A 3/4" pex loop the length of my crawl space with Ts in it for the lines up to the fixtures. I've solved my hot water across the house issue. I've made up my mind to install a re-circulation system. I'm thinking you run 3/4" to a manifold under the sink. Or if you have access like a crawl space under the bathroom. But you could fit under a vanity. Especially a double.
A single recirc line at the end of the trunk now serves the whole house. Pressure is fine with any single fixture, but there are noticeable changes when other taps in the house are opened, with some fixtures being affected more than others. I'm sure the 1/2" trunk is a contributing factor to this -- I am just not sure by how much, and if I'll see a difference of using a manifold vs replacing the trunk line with 3/4".
If you increase the diameter of the branch you also increase the time it takes for you to get hot water. In my climate I also like to get ground temperature water so having large branch lines increases the amount of water I have to dump before I get rid of the water in the pipe from the supply entrance to my faucet. This also wastes heat as the branch lines will have hot/cold water and heat or cool the wall spaces - eventually heating or cooling your house. Surprising everything was pretty close with the main labor be clips to clamps as well as total footage. The way my house is set up puts the manifolds right by the first floor bath and right underneath the chase to the second floor bath.
On long runs, it’s a good idea to install a loop as shown to allow for contraction. Another advantage of the loop is that if you mess up and need a little extra tubing, you can steal it from the loop. Also, since PEX moves as it expands and contracts, make sure to drill oversize holes through studs or joists so it can slide easily. Crimp rings are a band of metal, usually copper, that you slip over the fitting and compress with a crimp ring tool.
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