1/2\" PEX sup. & ret. to 80-gallon indirect?

Brad White_203

Stick to your guns, John. Trust your instincts.

Do it the way you know is right.

Engineers like that make me have to work harder just to show and prove that I can breathe without thinking about it.

JohnNY

Bidding repipe of bad installation.

I'm talking to a potential client with a bad radiant/indirect installation. Everything was designed and purchased from an online company out of Montana and installed by plumbers who seem to have no clue what to do with it. (Staple-up tubing, 17" on center and automatic air vents set upside down on the manifolds, for instance
I could go on and on but I just want to discuss the use of 1/2"pex off the radiant manifold to energize the indirect water heater.
The water moves by a Taco 007.
The boiler is an 80K Peerless mod-con.

I told the client I propose to replace that pex with 1.25" copper from its own loop off the boiler.
The online engineer guy said the 1/2" Pex was fine to heat the tank.
I take issue with that and expressed my concerns.
His reply was "Well, you'd only have to change it if you wanted to achieve the full performance of the water heater."
MY reply was, "Why wouldn't we want that since this is a brand new installation?"

I got no answer except him telling me to leave the PEX in place.

What am I missing here?

Am I being too pushy?



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tim smith

1/2\" pex total BS for the indirect. Now maybe 1\" is adequate

depending on the indirect but 1/2, give me a break. Tim
PS, John, I am demoing a Fluke Thermal imager today on a trap job we are doing, just a footnot. Have you found one yet?? Tim

JohnNY

Thanks, Tim

I got some prices for the new Flir unit and have been too busy to follow up. Looks like it's gonna be a $200/month lease, though.

Tell me if it's worth it after your demo.

I'm thinking it will be for half the year and it'll sit unused for the other half.

That ain't so bad.

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hot_rod

depends on how quickly

they want the indirect to perform. You have about 72,000 BTU available to move from boiler to indirect, at 90% efficiency. 1" should easily move that, 3/4 even with some high FPS 1-1/4 is a bit larger than you need. Compromise at 1" with the engine- ear


Many of those combo boiler DHW use 1/2 tube to run the onboard plate hx or flash tanks. Works fine, just takes twice as long. I have a Teledyne (Baxi) with an onboard DHW flate plate in my mother in laws home. It provideds an honest 2.5 gpm of DHW, non stop, piped with 15mm, about 1/2" copper size tube inside the boiler.

hr

JohnNY

So, I want about 7.5 gpm, no?

I've got about 25 feet developed length between the two appliances.

Anyone have a quick answer to how much head through that PEX?

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hot_rod

1\" pex?

at a 7.5 gpm flow rate of 180F average fluid temperature would be 2.7 psi pressure drop (6.5ft.) per 100 feet of 1" pex. 4 fps

As per the HDS software model.

Depending on the type of indirect and coil, you need to consider that pressure drop. I'd guess that 007 would cover most installations.

Certainly nothing wrong with 1-1/4 copper. probably 3 or more times the cost to purchase and install? I like the large bore PAP or FostaPex for indirect piping. It an easy, clean, fitting free installation.r

hr

ScottMP

1/2\" pex to the indirect ???

HAHAHAHAHAHAHAHAHAHAH

Scott

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Unknown

what's the point of getting full performance of the water heater?

the goal is to meet the demand, and not cycle the boiler during a DHW demand.

if you can meet the actual demand (not the water heater rating) with 1/2", I don't see the problem. Though I wouldn't want to run 180 degree domestic water through PEX.

If you assume 2 GPM or so through the 1/2" with a dedicated pump, or a bit less, you can transfer the full output of the boiler with an 80 degree dt (180 to 100). You won't get that, of course, since the indirect is about 120 to 140, but keep in mind even if the water comes out at 140, that's half the boiler's output being transferred: that's actually a sweet spot for efficiency, if I understand it.

so if you can meet the demand, with this size tank, and roughly half of the boiler output, at a 140 storage temp, 1/2" wouldn't necessarily freak me out.

PEX, however, would. I would only consider that in copper or PAP. but that's me.

Bob Bona_4

why stop

there? They do make 5/16 PEX as well!

(LOL w/ Scott)

This summer I repiped a 240,000 BTU boiler driving an 80 gallon Superstor. 3/4" S/R, with the return reduced to 1/2" b/c they returned it at the point where the water feed fed into the bottom of the boiler. 007, natch.

Some people's kids, to quote ME.

I guess my response would be, "don't expect much".

Andrew Hagen_4

Coils

How many people use Amtrol Boilermates? Don't they have something close to a 1/2" coil? I know the old Bradford White indirects had 1/2 or 5/8" coils.