NG supply line undersized?

[Danno77]

I was looking at adding a 10,000BTU heater to my third floor where it's currently heated with Electrical because the NG Furnace isn't ducted up there. I won't get into the backstory of why I'm where I am on that decision, but I'm just planning still...

Anyway, i go into the basement to look at where I might hook into the current black pipe system and check stuff out. I've never messed with it, but everything was ran new about 4 years ago when they put in a new 93% efficient NG stove and I had a gas cook stove put in the kitchen.

the main is a 3/4" line that runs about 15 total. About halfway down that there is a T to a 1/2" for the furnace, which runs about another 10 feet (total including bends). Then at the end of the 3/4 there is a T which is the line that runs about 15' to the cook stove.

I've never seemed to have major problems with the furnace, other than it is undersized for the house. the cook stove runs well, too. I'm just curious, because the 1/2" line to the Furnace seems small to me.

Does 1/2" supply to a 100,000BTU furnace seem small to anyone else?

I don't know the BTU specs on the cook-stove, but I can dig them up if it's needed to calc the proper line size for the furnace...

Thanks in advance, guys, this NG stuff is new to me, so I'm kinda learning as I go.

 

[jtp10181]

According to two different charts, you are OK
http://www.gastite.com/popup/cht_pd1_2.php

Using the longest run, its a total of less than 20ft to the furnace, 1/2" pipe at that total run length will supply 120k BTU. Thats at a pressure drop of only 0.5", and with normal house pressures a pressure drop of 2.0" WC would still be enough.

If you have never used the longest run method before it seems confusing, but trust me, its OK like that.

Whats the max BTU on the range? Because as it stands with a total run length of 30', the 3/4" line can only supply 200k BTU. The last range / oven I looked at with all burners and the oven on it was close to 100k BTU.

IMO 3/4" for a main line coming in is not very smart, I see this very rarely and usually its only if the meter is right outside of where the DHW and furnace are located, and those are the only gas appliances in the house. It does not leave much for adding on.

Do you have a gas hot water heater?

 

[Danno77]

According to two different charts, you are OK
http://www.gastite.com/popup/cht_pd1_2.php

Using the longest run, its a total of less than 20ft to the furnace, 1/2" pipe at that total run length will supply 120k BTU. Thats at a pressure drop of only 0.5", and with normal house pressures a pressure drop of 2.0" WC would still be enough.

If you have never used the longest run method before it seems confusing, but trust me, its OK like that.

Whats the max BTU on the range? Because as it stands with a total run length of 30', the 3/4" line can only supply 200k BTU. The last range / oven I looked at with all burners and the oven on it was close to 100k BTU.

IMO 3/4" for a main line coming in is not very smart, I see this very rarely and usually its only if the meter is right outside of where the DHW and furnace are located, and those are the only gas appliances in the house. It does not leave much for adding on.

Do you have a gas hot water heater?

Electric HW. and the meter is just outside the house. inches away from the foundation. I'll have to check the oven/range.

I had looked at this total length run chart and it looked ok, too. I just wanted to hear from someone who knows more than I do on the matter. Now, if I send a run up to the attic, that will throw my longest run over, i think. then i'd have to replumb the furnace, right?

edit: 42,000(ish) for all burners + 18,000 for oven =60,000BTUs.

 

[jtp10181]

If you have a scanner and can draw the system out and scan in the picture that would be most helpful.

Adding a line off the 3/4" main will not change the longest run for the furnace, but it will change the longest run for the section of the main up to where you tee off for the attic run. From there back to the meter you might need to up the line to a 1" size, in case all appliances are running at the same time.

 

[Danno77]

If you have a scanner and can draw the system out and scan in the picture that would be most helpful.

Adding a line off the 3/4" main will not change the longest run for the furnace, but it will change the longest run for the section of the main up to where you tee off for the attic run. From there back to the meter you might need to up the line to a 1" size, in case all appliances are running at the same time.

I should draw it out, anyway, and add actual measurements instead of my guessing... When I get a chance I'll do it up real quick in MS Paint.

 

[Danno77]

here's a pretty close drawing. not to scale.

edit: Darnit, mislabeled that purple colored line should be 1/2"OD, not 3/4"...

 

[PJF1313]

Danno-

IF you need the gas co. out there to change your meter/supply lines, I would also suggest that you tell them that you are planning to add a hot water heater and a dryer to the service. That way, IF they have to dig/change anything, it'll be ready for you, just encase you do decide to do it at a later (or never?).

Did this at my parents house when they where the to "sleeve" the line; it would have been an internal "fix" - essentially making the 1" to a 5/8" or so supply from the street. They told them that they where going to get a gas furnace, hot water heater and a cloths dryer (the furnace and H H2o didn't happen [dino fluid], but the dryer did). They re-installed the service to 1-1/4 (1-1/2?) and located the meter outside; was inside. So who ever has the house now, has a large enough line to do it all, if they decide to.

EDIT - My parents only had a gas cook-top at the time; the oven was electric?!

 

[jtp10181]

Ok, so that's the furnace and range? Where would you add on the line for the heater and how long would it be?

Also, regulators??? You should not have regulators unless you have a meter pressure over 14" WC (most common would be 2 psi).

If you have a higher meter pressure then you have plenty of pressure.

 

[Danno77]

Ok, so that's the furnace and range? Where would you add on the line for the heater and how long would it be?

I dunno, off that 3/4 just after the Furnace line. UNLESS I could pull off the furnace line and go straight up. It would be a fairly long run to the attic, 8ft over then 25ft(ish) up...

Also, regulators??? You should not have regulators unless you have a meter pressure over 14" WC (most common would be 2 psi).

If you have a higher meter pressure then you have plenty of pressure.

I thought they were regulators, but I wasn't sure, so i googled it before I posted. that's definitely what they look like. As far as I know they have fairly low pressure service here. The Gas company's website says:

Most residences do not require pressure above ¼#, our standard pressure at residential meters. If you are having new appliances installed, please ask your installer if the appliance requires more pressure than 7" of water column (pressure requirement ranges are usually notated as X"–Y" w. c.) Residential appliances that may require higher pressure are usually older, on-demand hot water heaters and generators. Most pool heaters do not require an increase in pressure. If you are unsure if you have more than ¼# of pressure at the meter, please ask your Service Representative.

 

[Danno77]

for kicks, I just went out and read a bunch of meaningless specs and numbers on the meter, one place on it says something about 5psi. maybe that makes a difference... I really hate being uninformed about this sort of thing, sorry for sounding like a complete idiot.

 

[jtp10181]

Take a pic of the supposed regulators and post, or get some info off them for me. Most common would be a maxitrol model 325. It might also say something to the effect of 2psi to 7" WC, or 8" WC regulator.

http://images.drillspot.com/pimages/449/44998_300.jpg

The 5psi on the meter might be the maximum inlet pressure of the regulator out there, I have never heard of 5psi service into the house.

 

[North of 60]

2 Psi is MAX for residential. And that is what it looks like he has got. So, after the regs you have shown on your drawings, there will also be an appliance reg at the device to go from 1/2lb/14"wc to 1/4lb/4"wc. The ones in the field on your drawings would be 2lbs to 1/2lb/14"wc.

 

[Danno77]

ok, these are crappy pics, but it's hard because I can't get a clear shot without a flash and it's really too close with it. If you can't blow it up, it says this on the inlet:

0545 81
6.0

and on the side it says:

325-3
Maximum Inlet
Pressure
10 PSIG

 

[North of 60]

OK, that reg has a limiting orfice on the Vent. Looks like you have 2psi in your home. A whole new ball game with a maximum available more than you will ever need.

 

[k0wtz]

i had an a/c condendenser added one time in my business. the electrician said we were a tad undersized on the main wiring but the chances of them all coming on at the same time were nil. so he went ahead and hooked it up. it has been up there with 5 others for 25 years and no problems.

it probably will never happen that all these gas applances will ever be on at the same time and all using max gas.

just my 2 cents

bob

 

[Danno77]

ok, sounds good to me. The keypoint here, to me, though is that I now also know that if I draw off of that main 3/4 I'll need to make sure there is another regulator thrown in before the next appliance.

I can do that run to the attic off of that 1/2" pipe, then, preferably before the regulator that is there, right? That would be optimal for me in terms of access and shortest new run. Heck, according to the chart I'm looking at for 2psi, I can run 3/8 for an insane distance and still not have any problems for a 10,000BTU heater. When I was pricing black pipe I was looking at 1/2" stuff. is the 3/8 gonna be significantly cheaper or easier/harder to work with?

 

[North of 60]

i had an a/c condendenser added one time in my business. the electrician said we were a tad undersized on the main wiring but the chances of them all coming on at the same time were nil. so he went ahead and hooked it up. it has been up there with 5 others for 25 years and no problems.

it probably will never happen that all these gas applances will ever be on at the same time and all using max gas.

just my 2 cents

bob

Ifs and maybes are not acceptable or tabled in electrical or gas codes.
The authority of having jurisdiction will not let that hang on his/her head either.
My 3 cents

 

[Danno77]

Ifs and maybes are not acceptable or tabled in electrical or gas codes.
The authority of having jurisdiction will not let that hang on his/her head either.
My 3 cents

The chances of me running all the gas appliances at my house in the middle of winter are extremely high. At this point all i have to do is prepare Christmas dinner when it's cold.

 

[jtp10181]

Am I good or what? Guessed the brand and model number of the regulators.

Anyway, I have seen regulators installed in a normal 7-8" WC system for no apparent reason. Now your next task is to call your utility and verify your meter pressure. If its 2psi you could probably tap off right after the regulator for the stove, or you can run the line off the main to the attic and put the regulator up there for the best pressure (not 100% sure if thats legit to have in the attic?).

 

[Danno77]

Am I good or what? Guessed the brand and model number of the regulators.

Anyway, I have seen regulators installed in a normal 7-8" WC system for no apparent reason. Now your next task is to call your utility and verify your meter pressure. If its 2psi you could probably tap off right after the regulator for the stove, or you can run the line off the main to the attic and put the regulator up there for the best pressure (not 100% sure if thats legit to have in the attic?).

i'm already a step ahead of you. I put a call into the gas company today and was sent to a voicemail of someone who can answer my question when they come in tomorrow.