Supply to Water Heater - After House Feeds OK?

[Shoes]

Hey there -

I am running new plumbing to replace PB. I am bringing 3 house zones together between the water heater and supply line. My original intent was to have cold supply breaking off to the house zones on its way to the water heater 10 feet away (diagram attached). But then I began to wonder if it is not preferable to have the water heater last in this series? Is it bad to have the water heater sequentially *after* the house zones? Should the heater be first? Maybe it doesnt matter - but I wanted to ask the experts. I'd prefer to go with the original design as it would require less re-work with the water heater and be visually cleaner. But I'll do what I need to if there is reason.

So - looking at the attached image, is it ok to have the water heater last in the series? Or should it be first instead, making the house zone manifold last (option 2)?

Thoughts? Thanks for the help.

 

[Reach4]

I don't think it matters significantly. I think most people use very little cold in a shower anyway. Option 1 could deliver a little more volume for cold showers. I think the cold pressure might be slightly better balanced vs hot with option 2.

 

[Sponsor]

 

[Shoes]

Thanks Reach.

 

[Jadnashua]

It all depends on if you've sized the piping properly. The smaller the pipe, the more friction, and if the velocity exceeds recommendations, you can literally wear the pipe out and it can create annoying noises. Higher friction also limits the maximum volume available. The recommendation on max velocity depend on whether the water is cold or hot...cold water, you want things at a max velocity of 8fps...hot, about 5fps. You can work out the math on the gpm based on the size of the pipe used.

 

[Terry]

Sized correctly, it doesn't matter.
https://terrylove.com/watersize.htm

I'm all for using less pipe.

 

[Shoes]

Excellent, that puts me at ease. It looks like I am sized decently with 3/4 based on your chart. Good info, thanks!

 

[Jadnashua]

If you're using pex, 3/4" PEX is not the same as 3/4" copper, if that's what you're considering. 3/4" PEX is closer to 1/2" copper, and depending on the type of fittings and the number of them, those can reduce the flow rate of PEX even further.

 

[hj]

You run the pipe the shortest way from the inlet to the building to the last fixture, and then connect the water heater wherever the pipe goes past it.

 

[Pitterpat]

Looking to re-plumb my home soon (next week or 2), if I am using PEX (Uponor) with a 1.5 bathroom house would it be best for me to use 1" as the supply line to hot water heater or 3/4". BTW, I have 3/4 galvanized now to hot water heater, 1956 house with all original plumbing, and 1/2 galvanized to most fixtures.

I was just getting ready to order the PEX when I came here to read this.

 

[Terry]

Looking to re-plumb my home soon (next week or 2), if I am using PEX (Uponor) with a 1.5 bathroom house would it be best for me to use 1" as the supply line to hot water heater or 3/4". BTW, I have 3/4 galvanized now to hot water heater, 1956 house with all original plumbing, and 1/2 galvanized to most fixtures.

I was just getting ready to order the PEX when I came here to read this.

With a 1.5 bath I would go ahead and run 3/4" PEX to the water heater.
By the way, can you update your email address so that the email notifications don't bounce?

 

[Tally Wacher]

With a 1.5 bath I would go ahead and run 3/4" PEX to the water heater.
By the way, can you update your email address so that the email notifications don't bounce?

Not really sure how to describe my setup but it is close to a 3 bath (2 full bath, 2 half baths), would 3/4" to and from water heater with 1/2" drops or 1/2" home run for hot suffice?

 

[Reach4]

There is no penalty for a little bigger than needed piping to the water heater other than cost and ease of install. The penalty for bigger piping from the water heater is that it takes longer to get the hot water to the faucet.

 

[Jadnashua]

Well, the penalty of too small of a pipe for the demand is that the friction will drop the volume and operational pressure. On hot water, you should not design the hot water distribution system for more than 4gpm with 1/2" copper or 8gpm for 3/4" copper total. Pex might be a slight bit lower, but it depends on the length of the run and the number of fittings compared to copper. If you run your pex like copper with lots of fittings, it can be MUCH worse than copper, otherwise, the lack of them can somewhat overcome the size difference. The Copper Institute has a useful design document you can download for free with all sorts of tables to help determine flow rates and pressure drop. The Pex industry may have a similar one, but fluid dynamics are the same, the IDs are different. The magic water velocity in pipe for hot water is a maximum of 5fps. Higher than that, you can run into problems. Doesn't mean it may not handle it, but in the long-term, there are risks involved, and in the short-term, it can start to get noisy.

How much hot you need would depend somewhat on the WH setting and how cold your cold is, which would determine how much of the say 2.5gpm flow from a standard shower head would be of hot verses cold. In the winter, if say your incoming cold water was near freezing (mine is!), then you need more hot water in the mix since a little of that frigid cold will temper it to showering temperatures. In the summer, you'd be using less hot and more cold.

One study I read calculated that a properly installed hot water recirculation system saved money and the precious water resource. Say you're the first to use hot water in a few hours or more. You may have to run the hot for over a minute before it warms the pipes and hot arrives. You're paying for that hot water that's no longer hot, and the sewer fees to dump it down the drain. The energy used to circulate hot water through well-insulated pipes is usually less, especially if you install a timer so that it only runs when you expect to be using hot water. Done right, you'd have hot water within seconds, minimize any waste.

 

[Pitterpat]

By the way, can you update your email address so that the email notifications don't bounce?

Yep, will update today.

In this house the lines from the water heater are 3/4" too; if I'm reading the thread correctly I should make the lines from the water heater 1/2" lines to speed getting hot water to the fixtures faster. I can't put a manifold because there isn't enough uninterupted wall space unless I put it in the shower area (a thought).

 

[Pitterpat]

Well, the penalty of too small of a pipe for the demand is that the friction will drop the volume and operational pressure. On hot water, you should not design the hot water distribution system for more than 4gpm with 1/2" copper or 8gpm for 3/4" copper total. Pex might be a slight bit lower, but it depends on the length of the run and the number of fittings compared to copper. If you run your pex like copper with lots of fittings, it can be MUCH worse than copper, otherwise, the lack of them can somewhat overcome the size difference. The Copper Institute has a useful design document you can download for free with all sorts of tables to help determine flow rates and pressure drop. The Pex industry may have a similar one, but fluid dynamics are the same, the IDs are different.

Here are the links to each of those sites for their design documents:
http://www.texasinspector.com/files/pex_designguide.pdf PEX

http://www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdf COPPER

 

[Jadnashua]

Pressure will drop because of multiple reasons: friction from the length, friction from fittings changing directions, elevation changes (lose about 0.43#/foot of elevation change), and friction from excessive flow (too high of a delivery speed - on hot, that's 5fps, cold 8fps).

The size of the supply pipe therefore depends on the maximum volume you require, how far away it is, how much elevation change there is, and how many fittings are required along the way to get it there. The simplistic answer that running smaller pipe than is required will not result in a satisfactory situation. IF you need the volume and want hot water there fast, you need to run a recirculation system. Think soda straw verses fire hose. Yes, you can flush a soda straw with less water, but will it be able to supply what you want to the end? There is no free lunch. You may need to compromise, but at least know what you want in the end and try to design it right the first time. Generic rules are just that, something that works in some situations.