# Gas line purge from new goodman 115,000 80%



## brandonmcginnis (Feb 14, 2010)

It's the gas line leading to the furnace you need to purge. You can either crack open a union or flare fitting near the furnace, open the pressure test port on the valve, (close it off as soon as you smell gas) or just go ahead and fire the furnace. It may take it a few times (you may have to interrupt power to the furnace if it goes into a lockout) but it will light eventually.


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## ben's plumbing (Oct 6, 2011)

did you also read to set manifold pressure...check heat rise for proper air flow over heat exchanger.....?????


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## brandonmcginnis (Feb 14, 2010)

Yeah, while you have that test port plug out would be a great time to check your gas pressure. Your new furnace will live a much longer happier life if it is properly commissioned.:thumbsup:


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## REP (Jul 24, 2011)

ben's plumbing said:


> did you also read to set manifold pressure...check heat rise for proper air flow over heat exchanger.....?????


You know what happens when someone that don't know exactly what they are doing checks gas pressure and temp rise don't ya.Thats right they think they can control it by dropping the pressure and also once they've done that they think they don't have to check the amps on the blower.If they didn't know about temp rise before there is no chance they will know that their duct and/or their return is too small.But hey look at all the money they saved.
It goes hand in hand with sizing the fornace to start with.The utilities love that because they get an extra $30 or so a month for the 10 years that the furnace will last.


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## ben's plumbing (Oct 6, 2011)

REP said:


> You know what happens when someone that don't know exactly what they are doing checks gas pressure and temp rise don't ya.Thats right they think they can control it by dropping the pressure and also once they've done that they think they don't have to check the amps on the blower.If they didn't know about temp rise before there is no chance they will know that their duct and/or their return is too small.But hey look at all the money they saved.


 had to ask because thats exactly what i was thinking ..looked at one the other day...homeowner installed 3 yrs old 100,000 btu...35'3"flue linner...8x14" main duct...14x 20 filter boot...with 2-6" runs off top.....heat exchanger look like swiss cheese....he saved money too...


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## Carlton (Jan 3, 2012)

*Thanks*



ben's plumbing said:


> had to ask because thats exactly what i was thinking ..looked at one the other day...homeowner installed 3 yrs old 100,000 btu...35'3"flue linner...8x14" main duct...14x 20 filter boot...with 2-6" runs off top.....heat exchanger look like swiss cheese....he saved money too...


I replaced th old 130,000 input 104,000 output with the 115,000 input 96,000 output w/ 20' flue and a 32"x 9" main duct a 30 x 8 return duct and a 16" x 25" filter boot.
I have not checked the gas pressure and temp. rise or manifold pressure.I started the unit and let it bring thermostat up 2 deg. to make sure the unit was cycling on and off,burners firing and blower coming on.I just didn't have the money for the installation (broke) i have read a whole encyclopedia on installation, gas and manifold pressures and temp rise.Is there a way to check gas pressure without a manometer.I have been a maintenance engineer (just got laid off due to closing of company.I have worked with boilers,chillers,Hvac,water heaters,electrical,ect.just never installed a gas furnace.I have the unit in and running,cycling properly in conjuction with thermostat.I am just looking for a little insight.
Thanks,
Carl


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## Carlton (Jan 3, 2012)

Please read my last post.
Thanks,
Carl


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## how (Feb 26, 2011)

At the risk of getting trashed here, over 50% of the installers I've watched never checked the gas pressure on a re & re unless I pointed it out to them. That doesn't make it right, just common.
Hey Carlton
If you've read as much as you say you have then you could clock your gas meter and see if it matched your furnace Btu's. Do this with all other gas appliances off. This would let you know if there is a problem that a pro needs to look at and it's manometer free.
And
*Do measure the temp rise through the furnace.*


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## Carlton (Jan 3, 2012)

how said:


> At the risk of getting trashed here, over 50% of the installers I've watched never checked the gas pressure on a re & re unless I pointed it out to them. That doesn't make it right, just common.
> Hey Carlton
> If you've read as much as you say you have then you could clock your gas meter and see if it matched your furnace Btu's. Do this with all other gas appliances off. This would let you know if there is a problem that a pro needs to look at and it's manometer free.
> And
> *Do measure the temp rise through the furnace.*


 I already read up on that but haven't done it yet Isn't that where you time the smallest dial in seconds and multiply.


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## how (Feb 26, 2011)

Yup
3600 (seconds in an hour) 
*x* calorific value of the gas in your area (you will need to find that) 
*x* the size of the smallest dial on your meter (.25 for 1/4 or .5 for 1/2) ,
*divided* by the seconds it takes for one complete rotation of that dial. 
= furnace Btu's being used.

Test it when the main burner start up, again after 5 minutes of a continuous burn and then again after 10 full minutes. 

Let me know if you have a metric meter for an adjusted formula..


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## REP (Jul 24, 2011)

Now why would anyone "trash " you for telling the truth.I've talked to guys in the business "for ever" that have never done a temp rise and who don't own a manometer.
All I can do is think how wonderfull life must have been when fuel was cheap.


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