Short segment of ? undersized gas pipe cost and performance

henry27

Hi

Im having a tankless water heater installed with two varying recommendations/bids.

I have a difficult to access black iron reducing T 1" x 3/4" x 3/4" 35' from the 8"wc source.

The 190 btu tankless is the longest run at 45'

One installer wants to upsize from the t to 1" black iron for the additional 10ft to the tankless. In essence i would have 35' at 1" then 4" at 3/4" then 10' at 1 in

The other installer want to change the T to 1" x 3/4" x 1". Their bid is $1200 more than the other intstaller and says it is necessary while the first stays it is not.

So would a 4" segment likely impact performance

Thanks for any help

H

Zman

It sounds like your installation is not a very good fit for the "longest run" formula.
Can you post a sketch with pipe sizes, lengths and all attached loads?.

henry27

The last Tee is the one in question and would have 4 inches or less of 3/4" before upsizing to 1"

Thanks. Water is leaking and need to decide

EBEBRATT-Ed

Have whomever does the job change the tee. Changing the tee is not $$$$$$$$ worth of work, but reducing and then upsizing is never done.

Changing that tee can probably be done in 45 min easily even if they cut the main, cut 1 thread and install a union or take the branch piping apart

Are you sure you want a tankless?? Some like them ,some don't

j a_2

The inside fit is of upmost importance when it comes to appliance performance, have the installer do a gas pipe sizing, as well as a static and dynamic test on the existing system.....Stay away from any of the flexible gas pipe out there...Why are you going tankless, just curious....take a pic of your gas meter and post it here

Zman

It doesn't look like you have accounted for fittings. I did a quick calculation of the drop of each section using engineer toolbox. I added some equivalent length, figuring you had some fitting loss. It looks like you are over the code required 0.5" wc in either case. Not changing that tee adds about .0.085" to the problem.

If you had oversized pipes, changing the tee would be a matter of quality workmanship. Being you are a bit undersized on the pipes, I would replace the Tee.

Do you have a picture of the Tee? I am curious how inaccessible it is.

henry27

Difficult to access because a new wall was framed in just beneath it, furnace venting, water line etc blocking wrench access from beneath even if cutting board spanning engineered trusses.

Why get a tankless? I guess the idea of repeatedly boiling a 60 gallon tank of water didn't make sense to me. Especially when i use hot water once every 2-3 days(yes i shower but often at work or the gym). Last tank lasted 7 1/2 years before leaked, the pan leaked and caused damage more than the cost difference the two systems.

Dont need the space, dont need endless hot water, do think i can do the maintenance flushing of the unit, do think it will last longer, do think i will save some money which may eventually make up for the difference.

henry27

One of the installers checked the pressure at my current tanked heater was 8"wc (? before meter upgrade was 7" ) and with both furnaces and gas range fully firing looked to be 7 something

j a_2

You most definitely need to size the gas according to manufacture specs...performance will suffer on the high load side, should You need service one of the first questions asked is about gas pipe sizing,just saying...Question is that pvc venting a gas furnace...secondly are you currently in the remodel stage, perforated strapping to hang pipe with is not professional looking,as well as the unlevel cpvc and glue drippings.....jmo

Zman

As for the question on the gas line. Yup that Tee could be a pain to remove and replace.
Do you know what the pressure drop was with everything running?
If you went from 8" to 7.9", I would say no problem. If it was 8" to 7.1" that is different. The pressure drop is going to go up when you add 130,000 btu.

As to the question of why do a tankless, I sure would not.
You are not boiling water only to waste it. You are heating water and storing it in an insulated tank. A newer higher efficiency gas water heater with flow checks, electronic ignition and a flue damper is pretty close in efficiency to a tankless. It just depends on your usage habits.

The short life span of your previous heater makes me suspect water quality issues. If you go the tankless route, be sure to do some research on how the brand you are selecting performs in your area.
Tankless heaters are less forgiving than tanks when it comes to scaling and other water issues.

henry27

Im assuming noth installers did the math and felt 1" to the tankless was adequate. The main question about delivery was theshort segment of downsizing before upsizing back to 1".

That is venting from one of the gas furnaces from the original builder. Basement finished 3 yrs ago wall seperates finished from unfinished hvac storage room.

ScottSecor

Not sure where you located, but here in NJ they typically supply 6" wc, 1PSI and 2 psi. The towns normally demand we use the most conservative pressure drop with 6" wc (I think it's .5" drop, but I don't have my charts handy).

Also, here in NJ many of the older mains are low pressure (mostly older neighborhoods around here). As such on bitter cold days the mains often drop to 5" wc, that can be a real problem with some systems. Luckily, they are replacing many of the old mains in my area with high pressure.

Hopefully, your area supplies 8" as you stated and the local utility pretty much guarantees it.

JUGHNE

Is it all possible to just run a new separate gas pipe from meter to tankless heater?

henry27

Sorry Zman. I did not see your post with before posting my last reply on my phone. Had a friend from the gas company check my pressures again. Pressure was approx 7.8 dropped to 7.5 with everything running.

I did have my water quality checked and it was within range for the tankless.

Early failure of the original likely due to a non-functioning thermal expansion tank, hard water 7-8grains and i doubt the tank was ever flushed.

Running a new pipe would be seriously cost prohibitive.

Have to admit the comments do have me wavering and considering tanks again.

henry27

Zman said:

As for the question on the gas line. Yup that Tee could be a pain to remove and replace.
Do you know what the pressure drop was with everything running?
If you went from 8" to 7.9", I would say no problem. If it was 8" to 7.1" that is different. The pressure drop is going to go up when you add 130,000 btu

Sorry i am remedial on this but if the new tankless requires a minimum of 4.5 " and with the increase in btu it dropped to say 6.5 instead of the less than 1/2" drop to 7.5 I'm currently seeing with everything running on the current set-up ......would there be an issue with gas delivery, unit functionetc

Zman

It looks like your actual drop is less that the calculated drop.
My guess is that your new tankless will work based on the info provided. It will probably not meet the 0.5" code but will most likely run just fine.

EBEBRATT-Ed

What @JUGHNE said may be the best answer

4Johnpipe

According to your drawing you have 7.56" water column at the new tankless. If you add for extra fittings you still have 7.22" water column at the new tankless.

j a_2

It may work just fine....but again always go by manf specs....If you have an issue and need to call tech for advice the first guestion will be is it piped correctly....as far as ur local code goes that's the installers call....can't go wrong going by the book

cnmdesign

Just a guide line, not in stone. Check to see if Ph is above 8.0 or below 6.0, and chloride concentrations not greater than 100 parts per million (ppm). Should help things last a little longer.