Converting from Copper to PEX.. Questions at Boiler

[burger]

I am replacing the copper pipe in my house with PEX. I am not sure about the connections to the hot water boiler. The 3/4 cold line from my pressure tank runs up to the boiler, but for some reason necks down 3/8 before entering the boiler and the reducer valve. On the hot outlet to the house hot supply, it is also 3/8 for a short run before entering a 3/4 trunk.

I think I should eliminate the 3/8 sections and replace them with 3/4. I think everything should be 3/4 up to the PEX home run manifold, then 1/2 or 3/8 lines from the home run manifold. Am I missing something?


Thanks!
Ed

 

[DGersic]

Does the boiler need 3/8”?

I agree that you probably want all 3/4” for your main trunk.

 

[acer66]

Seems odd but I am not a plumber and on a side note be aware that same size pex has a lower flow rate than copper.

 

[DGersic]

Is that PEX in there now 3/8” ?

 

[housewolf]

Is that boiler for a closed loop heating water system? If so the CW makeup doesn’t need to be full sized and if the supply (leaving the boiler) has a short length of smaller pipe after a pump, sometimes that’s done to increase the velocity of the water to help the pump along. I’d leave it as is if that’s the case.

If that’s a domestic HW boiler, I’d go all 3/4 or 1”

 

[burger]

Thanks for all the replies!

Is that boiler for a closed loop heating water system? If so the CW makeup doesn’t need to be full sized and if the supply (leaving the boiler) has a short length of smaller pipe after a pump, sometimes that’s done to increase the velocity of the water to help the pump along. I’d leave it as is if that’s the case.

If that’s a domestic HW boiler, I’d go all 3/4 or 1”

The boiler is for a closed loop heater water system and also supplies hot water to the house (kitchen, baths, etc).

Does the boiler need 3/8”?

I agree that you probably want all 3/4” for your main trunk.

Is that PEX in there now 3/8” ?

I added the 3/8 PEX a few years ago to replace a section of 3/8 copper that was leaking. At that point I replaced like with like.

Now that I am replacing all of the copper, I am questioning if it is a good idea to drop the plumbing from 3/4 to 3/8 at the boiler.

Seems odd but I am not a plumber and on a side note be aware that same size pex has a lower flow rate than copper.

Thanks for the heads up. That makes 3/4 PEX look like an even better idea.

 

[fitter30]

Are u changing both the side arm dhw piping and boiler makeup? Pipe size to side arm looks like 1/2" copper with is 5/8" o.d.

 

[Bert_]

It's just an auto fill. The size of the pipe doesn't matter because 99% of the time nothing is flowing through it.

 

[PoorUB]

It's just an auto fill. The size of the pipe doesn't matter because 99% of the time nothing is flowing through it.

And the 1%of the time it barely flows anything! Water flow through an auto fill is probably about 1 GPM.