Primary Loop Length

JDJTAJ

I apologize ahead if this question is answered somewhere already. No matter how I phrase this question the answer I get is regarding spacing between close tee's, which is clear.

Question:
What is the maximum length the loop between the boiler and the closely spaced tee's be? (I left out the primary/secondary because there seems to be confusion as to which is which.) I have attached a photo for clarity.

Another company is claiming the heat exchanger failure is because "the manifold is installed wrong". It has been working fine for 8 years however this other company is telling the customer that the manifold has to be right at the boiler.

Thank You

GGross

This depends on the pump used, the flow rate requirement through the heat exchanger, pressure drop through the heat exchanger, and pipe size used. 20-25' is probably going to be just fine though


missed the end of your post, if this is a "post mortem" investigation, you should look at the relevant information mentioned above, some installers undersize the pipe (size it based on the boiler connection, not right) which would make the boiler loop achieve lower flow. Does the boiler have an internal flow switch safety?

Most heat exchanger failures I see on condensing equipment are due to poor water quality, coupled with more makeup water (leaks and an uncontrolled fill valve)

adding one more thing, there isn't a rule about the tees being right at the boiler, that is a common installation though. The reason you pipe the boiler in this way is simply to separate the flowrate from the two loops, this way allowing the flowrate through the boiler to be within spec. It could be possible the flow rates on the heating system loop are too high to be separated by the tees, but I still think it would be water quality related if we are guessing based on most common failures.

GroundUp

There is no "maximum length", only maximum resistance to flow for the onboard circulator (assuming it's a combi as the drawing indicates). 20ft of 3/4" has a whole lot more resistance with an 8 GPM flow rate than 50ft of 1-1/4" would, meaning that the onboard circulator may not be able to provide adequate flow through the heat exchanger if the pipe length and/or diameter is insufficient. The heat exchanger may have simply failed because it's a Navien and that's just what they do, but it may also be piped wrong. If this company did indeed say that the "manifold" needs to be installed at the boiler, that can go both ways. The factory Navien manifold connects directly to the boiler so there is nowhere else to put it. If the closely spaced tees are being referred to as the "manifold", they would then be incorrect. Show us how it's piped and include pipe diameters, and we can assess from there. Also FYI, "worked fine" is a very loosely used term. If it was piped wrong and there was insufficient flow through the HX this whole time, it never "worked fine". It worked, but never fine.

JDJTAJ

It is a Navien Combi which has an internal circulator. The pipe is 1" PEX from the boiler to the tees with no elbows. This was simply to mount the boiler to the wall as the previous boiler was of course near chimney. The other company the referred to the closely spaced tees as the "manifold". Navien did provided a replacement boiler rather than just a new heat exchanger. The other company did install the replacement boiler, sold them a Navien manifold, and removed the close tees.

When I say "it worked fine" I'm referring to this as NOT being the cause of the heat exchanger failure, like the other company told them it was.

JDJTAJ

Also the is a post mortem investigation because the customer is looking for us to pay the other company's $3000 invoice. It was originally installed by my company 8 years ago. They have had it serviced almost every year.

hot_rod

In some cases a primary loop can circle an entire building. Loads taken off with closely spaced tees.
The boiler loop. Is what you are referring to, it could be any length as long as the piping and circulator is sized.
Some boiler manufacturers show you a graph of the boiler pressure drop, that will tell you how much capacity the onboard circ has for additional piping length. If it is a fire tube usually you have extra capacity. With water tube the factory circ may not have much if any extra capacity.

GroundUp

Read the manual- it should tell you the limitations for the onboard circ. If they didn't call you and give you an opportunity to repair/swap the boiler, there is no way they're going to make you cover the cost of having someone else do it.

GGross

JDJTAJ said:

Also the is a post mortem investigation because the customer is looking for us to pay the other company's $3000 invoice. It was originally installed by my company 8 years ago. They have had it serviced almost every year.

Tell them the manufacturer warrantied a whole replacement boiler, which implies they find the issue to be defect related, as their warranty covers only defects in manufacture not installation errors. If an installation error were found to be the cause they shouldn't have covered the cost of the unit. As an installer you can't be expected to cover every instance of an installed system failure in perpetuity, that's absurd, paying for another companies service fees is even more silly. Ask the other installer to provide proof that the boiler didn't see correct flow, they are the ones making claims, they should be able to show the numbers to prove it, you shouldn't have to defend yourself against a claim that is made almost entirely without merit (it's just a guess until someone shows the numbers!)

dko

Zman

Please provide more details.
What model boiler? What size pump? What is the manufacturer's minimum flow requirement?
Keep in mind that the ID of 1" PEX is almost the same as 3/4" Copper. Using PEX and Copper sizes interchangeably can get you into trouble.

JDJTAJ

Problem resolved.
We installed this boiler 8 years ago and have been doing their maintenance yearly. I don't understand why they didn't call us before calling another company. The other company told the customer that the failure was "because too much cold water is coming back to the boiler because the "manifold" is not right under the boiler". There are two circulator zones on the house side loop. I have explained the system operation and why that statement is not true.
I have proven to them that the installation was good and the other company has deceived them. The customers parents live next door in a two family home. We have been maintaining the systems for 10 years and I have no idea why they called another company in the first place. I told them that we will not be servicing any of their equipment at either home going forward.

Thank you for all your input.

HomerJSmith

Fact of life! The customer doesn't want to pay, the boiler manufacturer doesn't want to pay, and the installing company doesn't want to pay. What a conundrum.
Because the HX requires a given rate of flow across it, on long boiler loops, I think, it would be prudent to look at the Delta T across that loop to gain an understanding of the rate of flow. A tight Delta T would indicate an adequate flow. A wide Delta T would indicate a lesser flow. A flow too low, one might get flashing in the HX. A visual of the pressure gauge may show spikes in the reading when this occurs.
As others have stated, resistance is the other half of flow. What was the actual nature of the failure with the boiler? I would like to know.