proper supply and return piping to my indirect

Joseph_4

I've been researching many indirect manufactures to get the best deal of recovery times, cost , warranty etc. for my customers. Ive seen more than one manufacturer that make units with 1" supply and return tappings (which would be less expensive than 1 1/4 by a lot) but want a minimimum of flow of close to 14 gallon per minute. As far as Ive read 1" should be limited to 8 gallons of flow. in that case it would seem to suggest to use 1 1/4 piping but in that case its kind of misleading…plus the coil size itself is 1" in the tank so wont that be a restriction.

Recently an older plumber friend told me one should always pipe in 1 1/4?

Whats your opinion?

Thanks

Joe

HHI

EdTheHeaterMan

Have you ever looked inside a Stop and waste valve? That 1/2" valve has a opening a lot smaller than 1/2" but the flow thru that valve does not seem to make a difference. that is because the approach piping for as many feet as there is and the discharge piping for as far at that pipe goes, is 1/2" with less that a 1/4" of total length of reduced opening. All the water does is go faster thru that small restriction and then slow back down once it gets to the other side.

Another way to figure this is that the supply tube from the stop valve under the sink to the actual fixture on the sink is 3/8" for about 12 inches. That does not seem to restrict that flow out of the faucet. But what would happen if the pipe from the street water main was only 3/8" and traveled for 30 feet from the street to the meter then from the meter to the stop valve under the sink is another 40 feet of 3/8" tubing? All that thin tubing would be a real restriction from all that friction of the small piping. I believe you would see a big difference in the water flow and the water pressure if all your house pipes were 3/8". even if that was the only valve open when you tested that theory.

You want to use a 1-1/4" Copper x 1" male (or female) adaptor in the that heat exchanger coil on the indirect if you want the greatest recovery. But use common sense, if your boiler only has 70,000 BTU input, then you can't get 80,000 BTUs of heat from it. 70,000 gross input with a 58,000 NET won't benefit from a 1-1/4" feed to the indirect. The 1" feed and return will get you the same result as the 1-1/4" feed and return.

Same holds true in the other direction. a 200,000 BTU boiler can not put more that 40,000 BTUs into an indirect when it is pipes with only 3/4" copper supply and return. (Actually it can with a noisier, faster GPM and a larger temperature temperature difference, but you want to keep the noise down in this type system)     

EBEBRATT-Ed

I agree with @EdTheHeaterMan

Take your boiler BTU output and divide it by 10000. That will give you the most GPM you can get from the boiler. No sense oversizing the pipe the boiler can only produce a given BTU.

But you don't want the pipe undersized either.

1" is usually what is used in most cases. Some use 3/4 but that is undersized.

Take the gpm you get from above

3/4" =4GPM

1"=8GPM

1 1/4"= 14 GPM

hot_rod

you can get 10 gpm through 1” copper M in a short length and stay under the 4 fps rule.

But you need at least 100,000 btu of boiler to make it worth flowing that gpm. What size is the boiler that will run the indirect?

IMG_1048.png

Joseph_4

im actually looking at 2 jobs right now , the output on one boiler is 130k and output on the other 200k . Is there anyway to figure out how much more recovery per hour using 1 1/4 over 1"

thx

Joe

ethicalpaul

the peerless tapping for indirect is 1”

But why do you want them to have to heat up 500 pounds of cast iron every time they need some hot water? Sell them a standalone heater instead

Joseph_4

The recovery rate on most indirects are 3x standalone. large family. they run out of hot water with a 75 gallon stand alone

Joe

hot_rod

if you have the appropiate location, I think a heat pump water heater is a good option. I noticed Navian has some stainless tank HPWH now.

Go big, 80 gallons or more so you have enough drawdown.

This is the toughest question to answer as DHW wants or needs vary widely. Put a number to it will make it easier to decide the best options.

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1842954#Comment_1842954

because in many cases, it is much more efficient than connecting a standalone tank to a chimney that will suck the heat out of the water on the way up the chimney.

500 pounds of cast-iron can cool down in four hours. If no one takes any hot the indirect, it may take 10 hours before that tank drops 10° for the burner to come back on run for seven minutes and get that 10° back. A standalone may run every three hours for seven minutes or more depending on how small the burner is just to maintain that same size tank at 120°.

GroundUp

What makes you think you need 14 GPM?

Joseph_4

here is chart from manufacturer. im looking to install the residential model 80 which in reality is 70 gallons hot water. supply and return tappings are 1"

joe

Screenshot_20250216_104021_Gallery.jpg

hot_rod

What size is the boiler?

You mentioned recovery rate of indirect is 3X that of a gas fired tank. But this can only be true if the boilers burner size is 3X that of the tank water heater. Until we know the boilers actual DOE output, it is a question that cannot be answered accurately.

In that graph the minimum boiler size is 115K output. If you have 100- 115K boiler then 10 gpm would be adequate to get the recovery.

You cannot put into the tank what the boiler cannot provide.

Screenshot 2025-02-16 at 8.53.30 AM.png

LRCCBJ

https://forum.heatinghelp.com/discussion/comment/1842952#Comment_1842952

If the coil in the tank is 1", the benefit of piping 1.25" to and from the tank is minimal. The flow rate through the system is going to be governed by the 1" in the indirect. So what if the 1.25" could possibly flow more. You're not going to get more than the restriction posed by the 1".

Also, understand that the recovery per hour decreases only slightly with the larger pipe size and greater flow rate.

As an example, if you flow 10g/minute with 1" piping and the coil temperature drops 20 degrees in the round trip, you have an average water temperature of 170°F in the coil (180°F in and 160°F out).

Now, use 1.25" piping to and from the indirect and manage to get a flow rate of 12g/minute (recall that the flow rate is largely limited by the 1" coil). The coil output does not change. The coil temperature drops 16.6 degrees in the round trip. Average water temperature of 171.7°F. (180°F in and 163.4 out).

So, clearly, the benefit of the 1.25 piping is negligible with a 1" coil.

Now, with the 200K output boiler, you have to make an expensive decision. It has the capability to USE a 1.25" coil. If you procure a unit with that size, you must pipe it with 1.25" . If you don't, the boiler is going to cycle during recovery of the tank because its output is greater than the 1" piping can move, and you can only deliver about 150K (assuming 15 GPM) .

One other point of note:

Take the 1" as an example. Flow at 12 GPM. The pressure drop in 60 feet of 1" (round trip to and from the coil and including the coil) is only 5.5 feet (using Type L). So, it is extremely likely that the system will flow more than the calculated 12 GPM. Even a Taco 007 is going to flow about 15 GPM through that 1" despite your desire to keep the flow rate at about 12 GPM.

Joseph_4

I appreciate the comments. @LRCCBJ .. The manufacturers charts says with a boiler 115k output at 13.7 flow will deliver those numbers. only way i can get 13.7 on my end is using 1 1/4 . They had to know that their 1" coil with my 1 1/4 piping would deliver the posted recovery otherwise it would be untrue. part of the reason i posted it because Im doing this 17 years and I always try to up my game.. It states no where in instructions to use 1 1/4 pipe. If i want to compare units for my customers i need to know what my costs are. It would seem they have to benefit from 1 1/4.

@Hot Rod. here is the chart from a reputable stand alone water heater and the one im using

the stand alone is 125 first hour 81 recovery per hour

my indirect with a 115k output boiler is saying 235 first hour and 175 continuous but for my other customer with 200k output then AHRI chart says 272 first hour im assuming continuous is around 210 per hour.

Im focusing right now on this indirect but with 200k output there are units like Smart 80 from Triangle tube that will deliver even more.

20250216_113959.jpg

thanks

Joe

hot_rod

you can certainly flow 14 gpm through 1” copper.

1” copper type M at 14 gpm would be 5.1 fps velocity, a bit high but workable.

Pressure drop of .046 psi / ft of piping. Your coil and piping length, maybe 30’?

Going to 1-1/4” lowers the velocity and pressure drop.

Do you need this kind of performance from the tank? What’s the hurray🤓

If the goal is performance, efficiency, then a plate HX outside the tank is maybe 7 times better heat exchange. Properly sized a plate HX could deliver 120 dhw temperature with a boiler supply of 125. With two moving flow heat transfer greatly increases.

Reverse Indirects can get a close temperature approach also, or continuous DHW production with a tank jammed full of excellent heat transfer, copper tube.

.

IMG_1051.jpeg

IMG_1052.jpeg

LRCCBJ

I appreciate the comments. @LRCCBJ .. The manufacturers charts says with a boiler 115k output at 13.7 flow will deliver those numbers. only way i can get 13.7 on my end is using 1 1/4 . They had to know that their 1" coil with my 1 1/4 piping would deliver the posted recovery otherwise it would be untrue. part of the reason i posted it because Im doing this 17 years and I always try to up my game.. It states no where in instructions to use 1 1/4 pipe. If i want to compare units for my customers i need to know what my costs are. It would seem they have to benefit from 1 1/4.

Let's look at this more carefully.

The manufacturer claims that you need 13.7 flow. Does he provide the headloss in the coil at that flow rate? Can we "assume" he has 1" piping in the coil?

You are focused on the piping between the boiler and the indirect when the piping of the coil itself is EQUALLY IMPORTANT. There might be 25 feet inside that tank. If the manufacturer utilized 1", then the headloss of the 25 feet in the tank, at a flow rate of 14 GPM is only 2.6 feet. If you connect another 25 feet of 1" to and from the boiler and you flow at 14 GPM, the headloss is another 2.6 feet. Any pump you purchase can manage 5.2 feet. So, in fact, you'd flow more than 14 GPM.

My conclusion is that the manufacturer has no idea how much piping you need to connect to the indirect so he suggests you pipe it with 1.25 to cover himself. The reality, in most situations, is that the 1.25 is complete overkill, buys nothing for the customer, and costs the installer significantly more.

A manufacturer is classic for posting information that would apply only to the very fringe of operation. 98% of the purchasers are not anywhere near that fringe. So, the information is not applicable TO YOU.

Also, I want to reiterate what Hot Rod mentioned.

Let's say you only flow 11 GPM instead of the 13.7 claimed to be required by the manufacturer. The only thing that happens is that the DT in the coil climbs slightly. Instead of a DT of say 20°F, your DT will be 24°F because you are flowing a bit slower. WHO CARES. The recovery time will be ever so slightly longer. There is no customer in the world that would ever realize this.

Joseph_4

ok I got it.. thank you for everyone's time. I greaty appreciate it

thx

Joe

hot_rod

The ∆T through an indirect is a tough number to pin down. You will design for a specific ∆ to size the system piping and pump. The tanks dynamics change constantly and widely. A tank full of 55° water with a boiler supply of maybe 160 will produce a certain ∆.

As the tank warms that ∆ will change. It tightens to near 0° when it turns off.

The stratification in the tank is constantly moving if no flow is going through the tank. So the coil inside is exposed to a varying tank temperature. This makes the math messy for calculating.

Screenshot 2025-02-16 at 1.23.10 PM.png

I lost track of who posted this about indirects, sage advice.

Screenshot 2025-02-16 at 1.26.05 PM.png

ethicalpaul

https://forum.heatinghelp.com/discussion/comment/1842982#Comment_1842982

that’s why I recommend electric.

And I think you can’t compare the firing time of a boiler’s burner directly against that of a water heater’s burner

mattmia2

The area of the coil is at least if not more important and that isn't easy to use to calculate transfer rate even if you ignore all the things that are going on with the water in the tank.

if you need more surface you can buy tanks with 2 coils, usually sold as "solar" tanks.

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1843110#Comment_1843110

As an installer of many different heating and hot water systems over the last 50 years, I have actually had an opportunity to install a 40 gallon electric water heater, a 40 gallon gas water heater, a 40 gallon indirect water heater and a 32 gallon oil fired water heater for 4 different customers… and do a cold start test on each one. I only wish I had a video camera when I did the test so I could be just like you. (L🤣L)

The tests, on the different customers, shows that:

1. The electric water heater with 40 gallons of 55° water in it, consumed electricity for about 3 hours and 51 minutes until the electric meter stopped turning at the faster rate. I then verified this by leaving my Amp Meter clamped on the power line while I was installing a new oil fired boiler for the same customer. That way I could glance at the meter during the entire 4 hours and notice the time it went off within a few minutes of the actual stop time.
2. The gas water heater with a 38,000 BTU burner and a tank full with 56° water tool just under 30 minutes between the time the burner started until the time the burner stoped. So it takes 28 minutes and 30 seconds for that burner to heat 40 gallons of water about 63 degrees. You can do the math backwards to determine the efficiency of the burner in that water heater if you like.
3. The Oil fired water heater with a 0.60 GPH firing rate took less than 15 minutes to heat 32 gallons of 58° water.
4. Finally so not to have the burner on the source boiler do anything but heat the DHW the indirect connected to a boiler with a 138,000 NET rating took only 9 minutes to take the 34 gallons (that is how much potable water was in the 40 gallon indirect) to get from 55° to 120 degrees and shut the burner off by the limit and the circulator stopped within 1.5 minutes after that. The burner of the boiler WAS a direct correlation to heating DHW in my non scientific test. (That is also the day that I discovered that using a larger pipe to supply the boiler water to the indirect  may actually increase the DHW output by perhaps transferring a little bit more of the boiler heat to the indirect, so it may not cycle on the limit because of the reduced pipe size restriction of the amount of  heat transferred)

My conclusion is that

1. A tank that is connected to a vent will have more off cycle loss that the indirect or the electric tank that is not connected to a vent.
2. Electric water heaters have the worst recovery rate out of all the residential water heaters so you need to purchase a much larger water heater if you need more first hour rating or more constant operation.
3. Oil fired stand alone water heaters have the fastest recovery, largest first hour rating and most constant operating capacity of the three most popular stand alone water heaters.
4. Indirects have the advantage of not being connected to a vent, and have the capacity of faster recovery if your source boiler is a greater BTU input that the stand alone water heater that might be substituted for it.

In conclusion, with my personal experience and DYI non scientific testing (like some guy Paul I know who makes videos) you are not going to convince me that an indirect is a bad idea, Like I am not going to convince you that they are a good idea. We will just agree to disagree on this.

Unless you happen to know three other people that have the 3 other water heaters that you don't have and convince them to do this test over the summer and video the results.

Just a thought or maybe a challenge to confirm your hypothesis to be true or false.

PS. if you do make the electric water heater test, you don't need to keep the camera running all 4 hours to prove your point. I will believe you if you just add a 10 second clip every 40 minutes to show the water heater temperature progress. I know how you like to make long videos L🤣L

ethicalpaul

nice info but I think the concern with “first hour” and capacity stuff is generally over-worried-about. Just buy the correct capacity.

The costs are easy to calculate since the definition of a btu is directly relatable to this very topic. But I just don’t think the cost of actually heating the water is a big deal—even I agree the very worst is resistance electric and the cost of that for a whole year is $1000 or less.

So how much can you possibly save? Even free would only be $1000 a year difference 😂

But the indirect has to heat up the whole boiler first, so your cold start test really should have started with a cold boiler too. At least that’s the way it fits my argument best!

Don’t forget the expensive tank, the expensive fittings, the expensive circulator, and the electricity to run it. Oh and the really expensive labor to install all that stuff. Of course that last item probably looks different to a career plumber than it does to a career homeowner 😅

mattmia2

You have numerous options in stainless and plastic indirect tanks. There are only a few option in electric and even fewer in gas. How are the plastic electric tanks holding up? You can heat the boiler a lot of times for the cost of a new tank.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1843225#Comment_1843225

I have seen composite buffer tanks, who makes a composite indirect?

mattmia2

https://forum.heatinghelp.com/discussion/comment/1843257#Comment_1843257

amtrol/boilermate

https://www.supplyhouse.com/Amtrol-2783Z01-8-41-Gallon-HM-41Z-HydroMax-Indirect-Fired-Water-Heater

of course they appear to cost way more than stainless

hot_rod

looks like a steel tank with a HDPE liner. Similar to a thermal expansion tank and the Pro series Extrol

Looks a little like the Amtrol BoilerMate?

Will it last longer than a baked on enamel coating is a steel tank? . Time will tell.

IMG_9708.jpeg

mattmia2

looks like the steel is the outer jacket and the tank is plastic covered in foam insulation unless i'm reading something wrong. maybe the jacket ultimately ends up supporting it

hot_rod

It looks a lot like the BoilerMate construction

The steel tank is the structural component.

One issue with the steel BoilerMate is condensation formed between the steel tank and the foam insulation. It would rust out that belly seam and you would hear a loud pop as the separated😝

Looks like the BoilerMate is now stainless.

I never understood the coil up top in the hottest water?

IMG_9710.png

mattmia2

everything about that top plate, the connection to the inner vessel, the connection of the tappings seems very difficult to get right when someone installs or services it. the water seems more likely to be a small leak of the top plate than condensation.

hot_rod

The early version were problematic, one rep I know hired a full time person just to process warranties.

Allegedly a plumber in Colorado dragged several failed tanks to the wholesaler behind his truck 😯

EdTheHeaterMan

@ethicalpaul said: "But the indirect has to heat up the whole boiler first, so your cold start test really should have started with a cold boiler too. At least that’s the way it fits my argument best!"

That is exactly the test I did when I replaced a boiler and connected it to the indirect. It was summer and there was no reason to operate the heating circulator. I said to myself "SELF, this is the perfect opportunity to put what I have been told to the test." The boiler was filled with room temperature water, and the indirect was filled with 55° water from just filling it after the potable side was just completed.

The exact test that I would like you to duplicate on video.

And the results were that the oil burner heated the boiler to the limit and shut off within 9 minutes and a few seconds. the circulator was still operating for another 3 to 4 minutes Before the call for DHW aquastat was satisfied and the burner did not come back on before the call for DHW was satisfied. So technically the 1" pipe that could only handle between 8 to 11 GPM flow. Based on the circulator pump and the short distance of the piping from the boiler to the Indirect, I believe it was more that 8 GPM that is suggested by the rule of thumb of 1" = 8 GPM = 80,000 BTUh. Technically the call for DHW from cold start was 13 minutes but the burn time was only 9 minutes. So the 1.10 GPH firing rate divided by 60 minutes times 9 minutes is the actual input to compare to the 4500 watt elements of an electric water heater. The bottom line is to not run out of hot water while you are in the shower.

I live alone now and I can take a 10 minute shower with my 40 gallon electric before the amount of hot water is depleted. I would not have survived with two teenagers and my wife and I with the 40 Gallon electric that was installed under the steps when we moved in to that house in NJ in 1984. Today that is the home that my son lives in and the Crown MegaStor is the only indirect that has ever been in there. (I had a oil fired Bock 32E for some time but that failed at some point) It must be about 25 years old by now. Still plugging away.

And to clarify this point. I have a water heater, not a hot water heater. I did not pay the extra for the "Hot Features"

It heats the same water, It's just a little hotter.

yellowdog

@hot_rod I've been around for a long time and just came across my first blown out Boilermate the other day.

mattmia2

So does that dump like 30 gallons of water wherever it is or does it just make a noise?

yellowdog

This particular one dumped a lot more than 30 gallons before it was discovered.