3/4 gas line needs to be bigger

[raymond_anthony]

I had a new furnace put in today. Its a frigidaire 80,000 BTU force hot air unit. I was told by the installer that my gas line (3/4") is not big enough and that the line needs to open up to 1 1/2" after the main. I guess I am confused because main gas line coming up through the ground is only 3/4" so how would opening up to a 1 1/2" pipe increase flow. The main has a T connector on it with one (3/4")line going to another thermopride unit which works fine and the other 3/4" line going to my hot water heater and new furnace. The hot water heater works fine. I have no other appliances using the gas. The gas man said I had 8 something or other coming from the main which is more than enough. Anyone know what is going on here.

[BaldLoonie]

How far is it from the meter to the furnace/water heater area? And the only thing on this 3/4" line are those 2 units? How many BTUs is the WH?

Coming in from the street, the gas is at a higher pressure so the pipe can be small. At the meter it is reduced and yours apparently is 8" water column in pressure. That's fine. Allowing for .5" drop, 30' still gives you capability of 200,000 BTU. Even at 60' you are still barely OK if you haven't got a big BTU WH.

Tell him 1 1/2" gas line at house pressure allows OVER A MILLION BTUs of capacity at 30' and you don't need that unless you are heating 1/2 the neighborhood :)

[gas1]

8 inches Water colume is it nat gas or lp? 3/4" should be big enough if it is less than 50'. did your old furnace work on that same line?

[raymond_anthony]

its natural gas...The water heater is 40,000btu. Just to calrify my gas main has a T connector on it. ONe line goes to a 100,000 BTU thermopride heater. The line is about 25' and is 3/4". This unit runs fine. The other line coming out of the t is a 3/4" line as well and runs approximatly 35' supplying gas to my 40,000 btu water heater and my new frigidaire 80,000 btu gas furnace. But I feel like someone isnt telling me something.

[tinknocker service tech]

i could see him wanting to change the line to 1 inch to hold more volume and less chance of the pressure pulling down. 1/12 is totaly over kill for 120,000 btu

[raymond_anthony]

hes saying now that he cant get the furnace to work because the line isnt big enough.

[comfortdoc]

What size is the main off the meter. Depending on the length any pipe common to all appliances may need to be larger than 3/4 (between meter and T), but each 3/4 off the T sound like they are large enough for their connected loads. 1" is likely large enough for the common pipe.

Did he measure the gas pressure? What are inlet and outlet pressures?

Ask the gas company to evaluate the distribution system in the house. Some utilities are very easy to work with and will do this for you.

[hankmcneil]

Was this install done on a quote? I think proper size gas line to feed a furnace is part of installing it unless there was some reason he could't know ahead of time.

[raymond_anthony]

the main going into the meter is 3/4" and the line coming out of the meter is 3/4" the T is Right at the meter.

[raymond_anthony]

hankmcneil
he qouted me 2800 for everything. This is the system and electrical. But he SAW the old furnace AND 3/4" line going into it. He shoulda said something then. I inly gave him half and its all installed (just not running)

[hankmcneil]

Other Pro's:
I'm a service tech, am I off base here???

[comfortdoc]

I don't have capacity charts in front of me. Someone please correct me if I'm wrong here.

The common between the meter and T should be 1". This pipe has to carry 220 mbh. Then when it T's 3/4 will carry the appliances on each connected branch (100 mbh @ 25' and 120 mbh @ 35').

To clarify - the common pipe size should only be a problem when both furnaces are running. Otherwise the 3/4 is fine for either one.

If I missed this I would just fix it and bite the bullet. If it was alot of material needed I might ask the customer to help out with material cost. Depends on the entire situation though. Mistakes do happen.

[Edited by comfortdoc on 10-16-2006 at 09:45 PM]

[comfortdoc]

I will also add that pressure readings with the appliances running will verify the need to increase pipe size.

[t527ed]

3/4" for the short distance from the meter to the t should carry WAY more than what is needed. guy needs to check gas pressure at heater. tell him to shut off water heater and get furnace working. then see if firing water heater causes any problems. sounds like he is looking for excuses or more work.

[raymond_anthony]

after he couldnt get it to work he turned off my water heater AND other furnace....still couldnt get it to work. This is the point where he told me I would need to increase my pipe size from 3/4" to AT LEAST 1 1/4".

[raymond_anthony]

this is what was written on his paperwork

"Upon startup of new furnace found system not receiving enough gas pressure to hot water heater and furnace section. (my hot water heater has always worked fine) There is a 3/4" gas line that comes from the gas main that feeds a stove area (capped off) hot weater heater and forced hot air system. There is another 3/4" gas line that feeds the addition unit. Baystate gas arrived and checked meter pressure 8 'wc' . But only 4 'wc' at the new furnace. The baystate gas tech stated that the gas Main should be at least 1 1/4" to carry the pressure. Unable to perform startup until gas line is increased."

this is really pissing me off...I cant afford to have my lines redone.!!

[comfortdoc]

Originally posted by raymond_anthony
this is what was written on his paperwork

"Upon startup of new furnace found system not receiving enough gas pressure to hot water heater and furnace section. (my hot water heater has always worked fine) There is a 3/4" gas line that comes from the gas main that feeds a stove area (capped off) hot weater heater and forced hot air system. There is another 3/4" gas line that feeds the addition unit. Baystate gas arrived and checked meter pressure 8 'wc' . But only 4 'wc' at the new furnace. The baystate gas tech stated that the gas Main should be at least 1 1/4" to carry the pressure. Unable to perform startup until gas line is increased."

this is really pissing me off...I cant afford to have my lines redone.!!

Call Baystate Gas and ask for a supervisor. I think your installer is putting words in his mouth to help his case. There might be something we cannot see. Are there alot of fittings in the gas run (elbows etc)? Can you take a picture of the gas pipes for us or draw it out with dimensions and scan it?

[t527ed]

if you had a 75,000 btu there before AND he shut other stuff down it is a furnace problem not a gas problem.

[gasguy]

t527ed is correct. The 3/4" branch lines to each unit are big enough at the lenghts you have given. The line from the meter to the T should be 1". However, if the HWT and other furnace are shut off and the unit still won't work, it is the furnace and not the gas supply. The only thing that I can think of that may cause a problem is if there is some blockage or restriction in the line to that furnace. I'm assuming you have black iron pipe correct? Are there drip legs on the lines to the appliances? I once found a piping system that had no drip legs anywhere, and enough oil/sediment built up in a section that made a U going under a beam to restrict gas flow enough to cause problems.

[seatonheating]

Originally posted by raymond_anthony
this is what was written on his paperwork

"Upon startup of new furnace found system not receiving enough gas pressure to hot water heater and furnace section. (my hot water heater has always worked fine) There is a 3/4" gas line that comes from the gas main that feeds a stove area (capped off) hot weater heater and forced hot air system. There is another 3/4" gas line that feeds the addition unit. Baystate gas arrived and checked meter pressure 8 'wc' . But only 4 'wc' at the new furnace. The baystate gas tech stated that the gas Main should be at least 1 1/4" to carry the pressure. Unable to perform startup until gas line is increased."

this is really pissing me off...I cant afford to have my lines redone.!!

He's not out of line. You already have 140,000 btu on your 3/4" line. At 50' you will get 151 K btu, enough for 2 but not for 3.

Sounds to me like another cheapskate who is trying to find a reason not to pay to have it done right. ALL GAS LINES SHOULD BE SIZED PER MAXIMUM DEMAND....PERIOD!!!

[Black Adder]

Seaton: Quit calling names, you must work for a bunch of aholes that don't like to pay. Bottom line the gasfitter is retarded, you have a problem with the furnace and he can't fix it. The common pipe coming from the meter will be just fine at 3/4" if it is around 24" or less before it tees off. I cannot believe that the gas pressure with nothing running would have a pressure drop of 4" on that size pipe and those lengths. Call the gas company and have them come out and verify the readings in your presence. You are doing nothing wrong by withholding some of the payment from this clown. I would not expect to be payed if I installed a new furnace and it did not work. I am sure the unit he removed was at least as big as 80,000 btu's. Worked before, why not now? I know new equipment is more sensitive than the older stuff, but in a pinch I have seen furnaces that size running on 100' of 1/2" od copper with no problems. Granted this was not permanetly installed that way but for emergency heat in a flood situation.

[raymond_anthony]

its ok seaton. There is no question I am frugle with my money. The question now is, if there really is only 4" WT at the furnace maybe that is why the old one didnt work. The Installed said everything was corroded and qouted me 1600 to fix. I should have got a second opinion.

[duxinaroe]

Restriction. I've seen gas lines so full of pipe dope the furnace had 2 1/2 inches.

[duxinaroe]

You really won't know if its too small until everything is running and the restriction is found. If the old one didn't work I would trace it back to the "t". The part everyone missed in when you said "addition". Which means the home originally had one furnace and one waterheater that explains the 3/4.

[raymond_anthony]

Last year I had the 2 furnaces working with the water heater all at the same time. Then when I went to start up this year it didnt work.

[raymond_anthony]

I just got a call from baystate gas and they said they just got a call from the Installer and he has determined that I need a bigger gas meter to feed all my appliances. What the hell is going on?

[tatted1979]

hahah call a new tech in!

[raymond_anthony]

another install tech or a tech from baystate...Im sorry to sound stupid on here...I am a wedding photographer and know NOTHING about plumbing.

[gasguy]

OK, got out my gas sizing tables. Total BTU load you gave is 220,000. You said your longer run is 35'. I'm assuming that's from the T fitting. Add 5' from meter to T gives LMR of 40'. With a supply pressure from the meter of 7-14" wc, and allowable pressure drop of 1"wc, 3/4" black iron pipe has a capacity of 224,ooo btu's. This is enough to handle all your appliances running at the same time.

I can only think of 3 possible problems. One, obstruction in gas lines ipeding flow under load. Two, Faulty supply regulator at meter not delivering full pressure under load. Three, faulty gas valve on new furnace or inlet screen blocked with debris from the changeout.

OK, I just thought of a fourth: your installer is an idiot and is getting the gas supplier to cover for his dumb @ss!

[cn]

My furnaces are fed by a single trunk of 1" that splits into two (2) lines each 1/2" and they work fine the last 15 years:

Furnace A: 120,000 BTU
Furnace B: 80,000 BTU

My furncaes are about 30 feet from the gas entrance.

[Black Adder]

Has this new furnace ever worked correctly? Has your gas guy tried shutting down the other furnace and water heater and running this new unit all by itself? I would think the last thing you need is a bigger gas meter. The smallest meter we have in our area is good for a minimum of 400,000 btu's. This installer needs a serious lesson in how to diagnose and repair gas appliances. Provide his phone number and I will give him a call to see what the situation is. I am serious, email it to me (check my profile for address) and I will call this clown to see what the story is. This is not a situation that is going to be rectified by a bigger meter, bigger gasline or any of his solutions he has mentioned.

[raymond_anthony]

My hot weater heater work perfect which is RIGHT next to the furnace they are installing. we have shut down all apliance and nothing.

[tatted1979]

sounds like u gotta rookie tech working on your new install!

[gasguy]

Originally posted by raymond_anthony
My hot weater heater work perfect which is RIGHT next to the furnace they are installing. we have shut down all apliance and nothing.

Seems to be problem #3 I posted above. He needs to pull the line going into the valve and check for trash in the inlet screen. This is obviously a problem with the new furnace, NOT with the gas supply lines!

[raymond_anthony]

so they are now saying that my furnace is only getting 3.5 and the my hot water heat...even though its working is barely getting enough gas. My gas company wont come out and fix it because they measured it and said it was up to code

[tatted1979]

sounds like problem with the new furnace

[raymond_anthony]

my furnace installer just called
he said the gas inlet on the furnace is fine but the furnace needs 7 to start up and only has 3.5. He measured this at the furnace. and when my furnace TRIES to kick on the hot water heater flame goes way down. He said the main meter has a safety check valve or something that isnt working.

[t527ed]

Originally posted by raymond_anthony
my furnace installer just called
he said the gas inlet on the furnace is fine but the furnace needs 7 to start up and only has 3.5. He measured this at the furnace. and when my furnace TRIES to kick on the hot water heater flame goes way down. He said the main meter has a safety check valve or something that isnt working.


sounds like a bad regulator at gas meter. did they check pressure at meter end of line when unit tries to fire??

[raymond_anthony]

I believe they checked the pressure AT the meter and from what the install guy said no appliances were running/

[t527ed]

need to check pressure at meter when unit tries to fire. bad regulator would not open fast enough when unit fires, pressure drops unit don't work.

[raymond_anthony]

my thermopride units turns on fine but its a 2 stage unit. The installer thinks that there may only be enough gas for the first stage. The frigidaire unit need 7 WC to startup. Its only getting 3.5

[tinknocker service tech]

can not properly check the flo of gas with the units off
the pressure will show normal till there is demand then if the diaphram is defective the pressure will drop off with demand and volume

have him pull the gas piping he did just to make sure he didnt get a glob of pipe dope in the pipe or valve

have the meter checked with all the appliances operating and see what the pressure does
if it is holdong within 2in wc of the standing pressure then your problem is pipe related. if it drops off a lot then it is meter related


it is not uncommon for the diapham to be damaged if the gas was turned off at the meter then when turned back on the problem shows

[raymond_anthony]

are you guys ready for the answer
...................
In my town, 30 years ago, the town wanted some fire shutoff coming into the hour. So behind my finished basement walls was a elbow with a safety shutoff. It had vibrated shut and was not allowing gas to my furnace

[t527ed]

dat esplains it. knew it could not be a size problem.

[beenthere]

Good thing you stood your ground, and didn't just say go ahead and run a new gas line.

Bad thing, is that valve probaly what caused the corrosion in your old furnace.